d shear velocity heterogeneity anisotropy and discontinuity structure beneath the caribbean and central america the d region in the lowermost mantle beneath the caribbean and central america is investigated using shear waves from south american earthquakes recorded by seismic stations in north america we present a large scale composite study of volumetric shear velocity heterogeneity anisotropy and the possible presence of a d discontinuity in the region our data set includes 328 s sdiff sks differential travel times 300 scs s differential travel times 125 s sdiff and 120 scs shear wave splitting measurements and 297 seismograms inspected for scd the seismic phase refracted from a high velocity d layer broadband digital data are augmented by high quality digitized analog wwssn data providing extensive path coverage in our study area in all data from 61 events are utilized in some cases a given seismogram can be used for velocity heterogeneity anisotropy and discontinuity analyses significant mid mantle structure possibly associated with the ancient subducted farallon slab affects shear wave travel times and must be corrected for to prevent erroneous mapping of

geologic framework of the mississippian barnett shale barnett paleozoic total petroleum system bend arch fort worth basin texas this article describes the primary geologic characteristics and criteria of the barnett shale and barnett paleozoic total petroleum system tps of the fort worth basin used to define two geographic areas of the barnett shale for petroleum resource assessment from these two areas referred to as assessment units the u s geological survey estimated a mean volume of about 26 tcf of undiscovered technically recoverable hydrocarbon gas in the barnett shale the mississippian barnett shale is the primary source rock for oil and gas produced from paleozoic reservoir rocks in the bend arch fort worth basin area and is also one of the most significant gas producing formations in texas subsurface mapping from well logs and commercial databases and petroleum geochemistry demonstrate that the barnett shale is organic rich and thermally mature for hydrocarbon generation over most of the bend arch fort worth basin area in the northeastern and structurally deepest part of the fort worth basin adjacent to the muenster arch the formation is more than 1000 ft 305 m thick and interbedded with thick limestone units westward it thins rapidly over the mississippian chappel shelf to only a few tens of feet the barnett paleozoic tps is identified where thermally mature barnett shale has generated large volumes of hydrocarbons and is 1 contained within the barnett shale unconventional continuous accumulation and 2 expelled and distributed among numerous conventional clastic and carbonate rock reservoirs of paleozoic age vitrinite reflectance ro measurements show little correlation with present day burial depth contours of equal ro values measured from barnett shale and typing of produced hydrocarbons indicate significant uplift and erosion furthermore the thermal history of the formation was enhanced by hydrothermal events along the ouachita thrust front and mineral wells newark east fault system stratigraphy and thermal maturity define two gas producing assessment units for the barnett shale 1 a greater newark east fracture barrier continuous barnett shale gas assessment unit encompassing an area of optimal gas production where dense impermeable limestones enclose thick 300 ft 91 m barnett shale that is within the gas generation window ro 1 1 and 2 an extended continuous barnett shale gas assessment unit covering an area where the barnett shale is within the gas generation window but is less than 300 ft 91 m thick and either one or both of the overlying and underlying limestone barriers are absent

microstructural investigation of different nanopore types in marine continental transitional shales examples from the longtan formation in southern sichuan basin south china abstract variations in pore types the complexity of pore structures and strong heterogeneity complicate the thorough characterization of pore networks in marine continental shales in this study a novel 2d image processing method was proposed expounded and verified to clarify the geometrical morphologies formation mechanisms the size distributions proportions and the fractal characteristics of different types of pores in marine continental shales six types of pores inter particle intra particle organic matter om inter crystalline dissolved pores and micro fractures were classified and morphologically characterized the different types of shale pores had distinct relatively restricted morphologies formation mechanisms and size ranges nano and micron sized pores were controlled by om pores and micro fractures with the size ranging of 6 80 nm and 200 350 nm and 6 10 m respectively furthermore the fractal dimension characteristics were investigated on the basis of the 2d binary images and the results were verified by the fractal findings obtained from the n2 adsorption data these fracture dimension results demonstrated that the longtan shale pore structures had strong complexity and heterogeneity which was strongly and positively controlled by micro fractures inter crystalline and om pores in addition the total organic carbon content strongly and positively influences the development and anisotropy of the nanoscopic pores which were dominated by om pores while the clay minerals content has a minor effect on the total pore development and heterogeneity of shales but a significant effect on the dissolved pore development of shales whereas brittle minerals inhibit total pore development and heterogeneity of shales but contribute greatly to the development of the inter crystalline pores

the uranium mineralization potential of the paleoproterozoic sioux basin and its relationship to other basins in the southern lake superior region abstract the paleoproterozoic sioux basin and the baraboo barron flambeau mccaslin and waterloo quartzites in northcentral usa are all supermature quartz arenites that are among the world s oldest redbeds these quartzites were deposited on a stable craton at ca 1750 ma following exhumation and uplift of penokean crust and major orogenic activity related to the amalgamation of archean microcontinents at ca 2 0 1 8 ga to form laurentia 40ar 39ar ages of 1615 1543 ma from diagenetic muscovite in the sioux basin provide the first geochronological evidence for mazatzal related deformation and low grade metamorphism of the quartzites during subsequent convergence on the southern margin of laurentia one muscovite sample from the sioux basin has a 40ar 39ar age of 1465 ma that likely corresponds with fluid and thermal resetting due to felsic magmatism in the region and is similar to 40ar 39ar ages for muscovite from the baraboo and waterloo quartzites thus the sioux basin and other quartzites in the region have experienced a similar tectonic and fluid history the sioux basin has similar sedimentologic characteristics as other paleoproterozoic basins in north america including the uranium rich athabasca basin canada that is host to some of the world s largest and highest grade unconformity type uranium deposits we compared key characteristics such as the stratigraphy character of diagenetic fluids paleoaquifer characteristics and composition of leachable pb in the sandstones from the sioux basin with the athabasca basin in order to evaluate the fluid history of the basin and the potential of the sioux basin to host unconformity type uranium mineralization based on the hydrogen and oxygen isotopic composition of muscovite m1 that formed during diagenesis at 150 200 c the pore fluids that were present during peak diagenesis in the sioux basin had 18o and d values of 0 5 to 5 2 and 32 to 46 respectively similar to those of the fluids associated with uranium mineralization and alteration in the athabasca basin however fluid flow in the sioux basin was likely restricted to relatively thin and discontinous proximal fluvial facies that could have been diagenetic paleoaquifers in contrast to the extensive paleoaquifers in the athabasca basin that promoted large scale diagenetic reactions and alteration that led to the formation of unconformity type uranium mineralization in addition the non radiogenic isotopic composition of leachable pb in the sioux basin sandstones indicates that the majority of the pb is from a normal crustal source inconsistent with mobilization of radiogenic pb from a uranium rich source such as a uranium deposit although the sioux basin shares similar general characteristics to the athabasca basin the results of this study suggest that it has a lower potential than the athabasca basin to host significant high grade unconformity type deposits

logging identification and characteristic analysis of marine continental transitional organic rich shale in the carboniferous permian strata bohai bay basin abstract currently global shale gas exploration and exploitation are focused on marine shale recently major shale gas oil breakthroughs have been made within continental and marine continental transitional shale in china this study will show how transitional shale is of great importance based on geological field surveys core observations thin section analysis organic geochemistry and x ray diffraction we systematically studied the basic geological characteristics including lithology mineral composition and organic geochemistry of this transitional shale by comparative analysis of well logging data from 260 wells in the taiyuan shanxi shale we will show that these methods are effective for identifying organic rich shale from conventional well logs and determining its thickness distribution in the carboniferous permian strata of the taiyuan shanxi transitional coal bearing formation the results indicate that the taiyuan shanxi shale has a high toc most 2 4 and that the lithology is primarily carbonaceous shale with type 2 kerogens the high thermal maturation ro 1 1 favors the generation of gas the mineral components primarily include clay minerals quartz and plagioclase with a moderate brittle mineral content 47 wt and high clay mineral content 51 wt dominated by kaolinite 43 and mixed layer illite smectite 31 the transitional organic rich shale on conventional log curves is generally characterized by higher gamma ray gr neutron porosity cnl acoustic travel time ac resistivity r t potassium k and uranium u readings and a lower density den photoelectric absorption index pe and thorium uranium ratio th u after analyzing the log response characteristics of the organic rich shale the most sensitive logging curves such as cnl ac den pe and u were optimized to conduct logging overlays and to construct cross plots to qualitatively identify organic rich shale the identified organic rich shale amalgamates in the middle upper member of the taiyuan formation and the lower member of the shanxi formation consistent with the results of the toc analysis and practical gas logging based on the qualitative evaluation methods of the modified logr and a multivariate linear regression model we calculated the toc of shale wells in the taiyuan shanxi formation from this we calculated the characteristic values of organic rich shale thickness the results indicate that organic rich shale in the taiyuan formation is thicker than that in the shanxi formation additionally the thickness of organic rich shale within lagoons and deep reed swamp facies are much thicker 25 35 m and 40 80 m than other structural profile types whereas their lateral distribution is less than that of marine shale the relatively small continuous thickness of the single shale layer and high clay content may have negative effects for developing the shale gas potential

remigration and leakage from continuous shale reservoirs insights from the sichuan basin and its periphery china shale gas in the sichuan basin and its periphery potentially plays an important role in the world shale gas industry an understanding of remigration and leakage from continuous shale reservoirs is very important for shale gas exploration especially in the sichuan basin and its periphery the shale gas accumulation models that relate to remigration and leakage were developed within the wufeng and longmaxi black shales in the jiaoshiba and the youyang blocks first a tectono sedimentary history of the wufeng and longmaxi black shales in the sichuan basin and its periphery was developed based on the published literature the history exhibits a continuous distribution of high quality wufeng and longmaxi black shale which is the foundation of the shale gas formation second the shale gas remigration accumulation model in the anticlines was clarified by using data collected from the shale gas fields in jiaoshiba block the shale gas model for the jiaoshiba block was developed on the basis of a continuous shale reservoir distribution differentiated structural deformation and a gas self sealed system third the shale gas fault failure leakage model in the fault blocks and the erosion model in the residual areas were revealed based on the shale reservoir and shale gas content heterogeneity in the youyang block these two models were validated by available data including 13 two dimensional seismic lines and 2 shale gas exploration vertical wells in the youyang block shale gas areas with high gas resource and gas production rates in the anticlines were defined by the remigration accumulation model the fault failure leakage model was used to find shale gas with limited commercial potential whereas commercial shale gas was largely lacking according to the erosion residual model the study on remigration and leakage from continuous shale reservoirs in the sichuan basin and its periphery can be used to better understand and improve the exploration efforts based on resource preservation

evolution and source of ore fluids in the stringer system hellyer vhms deposit tasmania australia evidence from fluid inclusion microthermometry and geochemistry the hellyer deposit is a classic large tonnage high grade mound style volcanic hosted massive sulphide vhms deposit in the cambrian mt read volcanic belt of western tasmania in the footwall directly underlying the deposit there is an extensively altered pipe which cootains a well developed and preserved stringer zone the vein paragenesis at hellyer indicates that premineralization stage i veins consist entirely of quartz and occur throughout the alteration pipe the synmineralization stage 2 veins are the most abundant veins in the stringer zone and consist of three sub stages stage 2a veins of crustiform quartz pyrite and carbonate with minor amounts of chalcopyrite sphalerite and galena stage 2b veins with abundant base metal sulphides minor quartz carbonate and barite gangue and stage 2c veins of coarsely crystalline barite with variable amounts of pyrite sphalerite galena and carbonate stages 3 6 veins are postmineralization veins and are related to the devonian tabberabberan orogeny textural petrographic and microthermometric investigations of fluid inclusions in the hellyer stringer system indicate that type i primary liquid vapour inclusions occur along growth planes of crustiform quartz crystals or within colour banding of zoned sphalerite these inclusions are 10 15 m in size and yielded homnogenisation temperatures of 170 220 c in early 2a veins 165 322 c in main stage 2b veins and 190 256 c io late stage 2c veins these data suggest a waxing and waning thermal history however the average salinity remained between 8 11 naci equiv wt in all stage 2 veins chalcopyrite bearing primary fluid inclusions have been recognised in the base metal rich stage 28 veins no evidence for presence of co2 e g formation of clathrates was recorded by rnicrothermometry however laser raman spectroscopic lrs analysis indicates the presence of co2 1 mole in the stage 2b veins and no detectable co2 in 2a and 2c vein stages semi quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer ore fluid was enriched in potassium and calcium but depleted in magnesium relative to seawater pixe microanalysis of fluid inclusions in quartz indicates that the stage 2b ore fluids have a significantly higher base metal concentration compared to the stage 2a veins the postmineralization stage 4 veins have a variable but lower base metal content in this study there was no fluid inclusion evidence of boiling cation composition higher salinities relative to seawater and the presence of co2 suggest that recycled seawater alone cannot be the sole source of the ore fluids this interpretation is in agreement with previous isotopic studies in the hellyer stringer system although direct input of bulk ore constituents from a magma chamber cannot be demonstrated from the present fluid inclusion data such a contribution of ore fluids from a magmatic source cannot be ruled out the possible input from the magmatic source may have occurred during the base metal rich stage 2b vein formation characterised by the intensifying temperature of deposition higher base metals and co2 contents

reevaluation of thermal maturity and stages of petroleum formation of the mississippian barnett shale fort worth basin texas new data including measured reflectance ro programmed open system pyrolysis data and kerogen elemental analyses obtained on the mississippian barnett shale in the fort worth basin texas indicate that secondary gas generation starts at 1 5 ro and not at the previously prescribed 1 1 ro oil cracking kinetic parameters derived from pyrolysis experiments in the presence and absence of water indicate that secondary gas generation will not occur at a thermal maturity as low as 1 1 ro and requires a minimum thermal maturity of 1 5 ro this difference is especially important in using the barnett shale as an analog for evaluating other possible shale gas plays the new reflectance measurements have a good relationship with hydrogen indices his and compare well with other published data sets however the relationship does not compare well with the previously published data used to prescribe 1 1 ro as the start of secondary gas generation in the barnett shale this discrepancy is attributed to differences in measured ro values and not attributed to differences in the hi values lack of publicly available information on the previously reported ro values makes it difficult to ascertain the reason for their lower values these lower ro values also have impact on the previously prescribed relationship for estimating ro from the temperature at maximum yield by programmed open system pyrolysis tmax as a result the new data do not agree with a previously described relationship and the considerable scatter makes the new relationship unreliable however the relationship between the hi and ro has less scatter which indicates that hi offers a better proxy in calculating ro than tmax for the barnett shale comparison of various programmed open system pyrolysis methods i e rock eval ii rock eval 6 source rock analyzer and hawk indicates that variations in hi are within 10 of one another an hi of at least 44 mg g total organic carbon is prescribed as a more certain limit for the start of secondary gas generation and prospective in situ gas shale accumulations

lateral variations in d below the caribbean broad band data from the canadian national seismograph network cnsn shows evidence for a laterally varying s wave discontinuity in the lowermost mantle beneath the caribbean the magnitude of the velocity contrast across this d discontinuity varies inversely with its distance from the core mantle boundary cmb clear evidence for a 2 75 increase in shear velocity 250 km above the cmb is observed in a region 10 n and 60 85 w a thicker d layer 290 km with a less pronounced topside discontinuity 2 45 is interpreted in the region 80 90 w and 20 n and there is no evidence for a d discontinuity in the region 65 80 w and 25 n considerable 3d structure within the d region is suggested by travel time scatter in scs arrivals and s arrivals which turn within d transverse component sks signals due to upper mantle anisotropy can be confused with d signals however we show that false interpretations of d structure can be mitigated through the careful analysis of travel time moveout and low pass filtering

clay alteration associated with proterozoic unconformity type uranium deposits in the east alligator rivers uranium field northern territory australia clay minerals associated with the unconformity type uranium deposits of the east alligator rivers uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of uranium deposition within the altered basement underlying the kombolgie unconformity alteration develops a similar pattern at regional and smaller scales with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity e g faults fractures breccias these discontinuities were mechanically active during the hydrothermal activity the hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks the time space alteration sequence established in this study can be summarized as follows 1 early crystallization of illite illite smectite i s mixed layer minerals lree sr bearing aluminum phosphate sulfates aps in sandstones above the unconformity illite i s mixed layer minerals sudoite aps on both sides of the unconformity and in fault gouges and illite i s mixed layer minerals chlorite apatite deeper in the basement and 2 late precipitation of chlorite in the open fracture network mainly centered below the unconformity the main stage of uranium deposition was associated with chloritization in the basement rocks smaller particle size lath shaped or flaky morphology common interstratification with expandable layers lower crystallinity and mg rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and or chlorite hydrothermal illite can be distinguished from diagenetic and metamorphic illite phengite by its poor crystallinity along the c axis interstratification with minor amounts of smectite layers and a 1m polytype in which trans vacant octahedral sites predominate 1 mt chemically the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher mg content the hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size spherulitic habit poor crystallinity along the c axis and common association with corrensite and or chlorite corrensite mixed layers most of the hydrothermal chlorite is mg rich and has a structural formula close to that of clinochlore xfe 0 20 near the uranium deposits the spherules of hydrothermal chlorite are chemically zoned from xfe 0 10 to xfe 0 40 which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization the space time alteration sequence established for clay minerals and the observed transition of aps to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub basinal brines in turn these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron bearing phyllosilicates fe chlorite and biotite and iron sulfides of metamorphic origin the ore deposits are surrounded by zones in which the degree of fluid rock interaction was very high and chloritization is most abundant the octahedral mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of uranium orebodies in the basement rocks tens to hundreds of meters below the crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30 to 50 c lower than those expected at the peak diagenesis of the kombolgie sandstones near the unconformity

comparison of diagenetic fluids in the proterozoic thelon and athabasca basins canada implications for protracted fluid histories in stable intracratonic basins the paleoproterozoic thelon basin located on the border between nunavut and the northwest territories of canada is a contemporaneous analog of the uranium rich paleoproterozoic athabasca basin in canada early diagenesis resulted in precipitation of extensive hematite on the surfaces of detrital quartz grains throughout the thelon formation and minor hydroxy phosphate in veins locally continued diagenesis then resulted in syntaxial quartz cementation of detrital quartz at 130 c from fluids having ca 17 wt equivalent nacl similar to the athabasca basin cementation of this type is most pronounced in fine grained sequences in the thelon basin a period of extensive desilicification during continued burial was followed by formation at ca 200 c of peak diagenetic illite having ar ar ages of ca 1400 1690 ma in the thelon formation this illite was associated with fluids with 18 oa nd d values of ca 6 and 50 respectively similar to those during peak diagenesis of the athabasca basin although the timing salinity and isotopic composition of the peak diagenetic fluids in the thelon and athabasca basins are similar the peak diagenetic mineral assemblage in the athabasca formation is dickite and illite with minor dravite and goyasite rather than simply illite consequently the fluids at peak diagenesis which in the athabasca basin are synchronous with formation of world class unconformity type uranium deposits had different compositions in each basin post peak diagenesis in the thelon basin was quite distinct from that in the athabasca basin in that illite was replaced in the central portion of the basin by k feld spar and then sudoite which crystallized from saline brines at ca 1000 ma and 100 c evidence for later infiltration of these brines is absent in the athabasca basin although uranium mobilization at ca 900 ma from fluids having the same characteristics as those at peak diagenesis was pronounced in the athabasca basin recent incursion of meteoric waters along reactivated structures into the athabasca basin has variably affected hydrous and uraniferous minerals but evidence for this is lacking in the thelon basin the thelon basin reflects less intensive fluid rock interaction in its early history than that recorded in the basal units of the athabasca basin 132

geological and geochemical characterization of the lower cretaceous pearsall formation maverick basin south texas a future shale gas resource as part of an assessment of undiscovered hydrocarbon resources in the northern gulf of mexico onshore mesozoic section the u s geological survey usgs evaluated the lower cretaceous pearsall formation of the maverick basin south texas as a potential shale gas resource wireline logs were used to determine the stratigraphic distribution of the pearsall formation and to select available core and cuttings samples for analytical investigation samples used for this study spanned updip to downdip environments in the maverick basin including several from the current shale gas producing area of the pearsall formation the term shale does not adequately describe any of the pearsall samples evaluated for this study which included argillaceous lime wackestones from more proximal marine depositional environments in maverick county and argillaceous lime mudstones from the distal lower cretaceous shelf edge in western bee county most facies in the pearsall formation were deposited in oxygenated environments as evidenced by the presence of biota preserved as shell fragments and the near absence of sediment laminae which is probably caused by bioturbation organic material is poorly preserved and primarily consists of type iii kerogen terrestrial and type iv kerogen inert solid bitumen with a minor contribution from type ii kerogen marine based on petrographic analysis and pyrolysis carbonate dominates the mineralogy followed by clays and quartz the low abundance and broad size distribution of pyrite are consistent with the presence of oxic conditions during sediment deposition the pearsall formation is in the dry gas window of hydrocarbon generation mean random vitrinite reflectance values ro 1 2 2 2 and contains moderate levels of total organic carbon average 0 86 wt which primarily resides in the inert solid bitumen solid bitumen is interpreted to result from in situ thermal cracking of liquid hydrocarbon generated from original type ii kerogen that was prevented from expulsion and migration by low permeability the temperature of maximum pyrolysis output tmax is a poor predictor of thermal maturity because the pyrolysis s2 peaks from rock eval analysis are ill defined vitrinite reflectance values are consistent with the dry gas window and are the preferred thermal maturity parameter a maverick basin pearsall shale gas assessment unit was defined using political and geologic boundaries to denote its spatial extent and was evaluated following established usgs hydrocarbon assessment methodology the assessment estimated a mean undiscovered technically recoverable natural gas resource of 8 8 tcf of gas and 3 4 and 17 8 tcf of gas at the f95 and f5 fractile confidence levels respectively significant engineering challenges will likely need to be met in determining the correct stimulation and completion combination for the successful future development of undiscovered natural gas resources in the pearsall formation

the calculated solubility of platinum and gold in oxygen saturated fluids and the genesis of platinum palladium and gold mineralization in the unconformity related uranium deposits thermodynamic calculations on the solubility of platinum and gold indicate that saline 1 m nacl fluids saturated with atmospheric oxygen can transport geologically realistic concentrations of platinum group elements pge gold and uranium as chloro complexes a number of calculations involving fluid rock interaction suggest that the oxygen saturated fluids flowing through rocks containing quartz muscovite kaolinite magnetite and hematite initially oxidize any magnetite to hematite allowing subsequent batches of ore fluids to retain their high oxidation state during their migration through the aquifer the oxidizing fluids would move the oxidation reduction interface deeper into the aquifer leaching and redepositing platinum and gold the redissolution of earlier precipitated platinum and gold depends on the fluid rock ratio and the associated increase in the oxidation state therefore lowering of fluid rock ratios and or mixing of the oxidized fluids with a large amount of reduced fluid will precipitate uranium pge and gold it is suggested that this model can explain the genesis of gold and pge mineralization in the unconformity related uranium deposits of the alligator rivers uranium field in the northern territory australia

small scatterers in the lower mantle observed at german broadband arrays seismograms of earthquakes from the south pacific recorded at a german broadband array and network show precursors to pkpdf these precursors mainly originate from off path scattering of pkpab or a nearby pkpbc to p for receiver side scattering or from scattering of p to pkpab or pkpbc on the pkpdf path for source side scattering standard array processing techniques based on plane wave approximations such as vespagram or frequency wavenumber analysis are inadequate for investigating these precursors since scattered waves cannot be approximated as plane waves for arrays and networks larger than 300 300 km for short period waves we therefore develop a migration method to estimate the location of scatterers in the mantle at the core mantle boundary and at the top of the outer core with our method we are able to find isolated scatterers at the source side and the receiver side although the depth of the scatterer is not well constrained however from looking at the first possible arrival time of precursors at different depth and the region where scattering can take place scattering volume we believe that the location of the scatterers is in the lowermost mantle since we have detected scatterers in regions where ultralow velocity zones have been discovered recently we think that the precursor energy possibly originates from scattering at partial melt at the base of the mantle comparing results from broadband and band pass filtered data the detection of small scale structure of the ultralow velocity zones becomes possible

topography on the 410 km seismic velocity discontinuity near subduction zones from stacking of ss sp and pp precursors we stack the teleseismic depth phases ss sp and pp produced by deep focus earthquakes to image precursory arrivals that result from near source underside reflections off the 410 km seismic velocity discontinuity hereinafter referred to as the 410 and use differential time measurements between these phases and their precursors to compute discontinuity depths near seven subduction zones around the pacific ocean margin we begin by selecting seismograms with high quality depth phase arrivals recorded by several long period networks between the years 1976 and 1996 filtering the waveforms and stacking them along theoretical travel time curves reveals clear precursors which vary in shape and timing we compute confidence levels to evaluate the reliability of the observed precursory features using a bootstrap method that randomly resamples the seismograms prior to stacking we measure the differential travel time between the reference pulse and the precursor using a cross correlation technique and convert this time to an apparent discontinuity depth using the isotropic preliminary reference earth model prem at 25 s period corrected to an oceanic crustal thickness the lateral resolution of our long period stacks for 410 topography is limited compared to that sometimes achieved in short period analyses but is much higher than that obtained from global ss precursor studies for most subduction zones the results indicate little change in the average depth to the 410 km discontinuity in the local areas sampled by the precursor bounce points compared to broad regional depths inferred from ss precursor results this implies that any large variations in depth to the 410 km discontinuity near subduction zones are limited to a narrow zone within the slab itself where they may be difficult to resolve with long period data coverage for the tonga and peru chile subduction zones is sufficiently dense that we can observe lateral variations in 410 depths in tonga the results suggest depth variations perpendicular to the slab of up to 33 km after correcting for probable lateral heterogeneity in velocity above 400 km depth and variations parallel to the slab orientation as large as 13 km the cross slab variation is consistent with the elevation of olivine phase transformations in cold regions the variation along strike suggests a more complex thermal heterogeneity that may be related to the subduction history of this region we see evidence for additional reflectors above the 410 in some of the waveform stacks but the inconsistency and weak amplitude of these features preclude definitive interpretations

resource assessment perspectives for unconventional gas systems concepts are described for assessing those unconventional gas sys tems that can also be defined as continuous accumulations contin uous gas accumulations exist more or less independently of the wa ter column and do not owe their existence directly to the buoyancy of gas in water they cannot be represented in terms of individual countable fields or pools delineated by downdip water contacts for these reasons traditional resource assessment methods based on es timating the sizes and numbers of undiscovered discrete fields can not be applied to continuous accumulations specialized assessment methods are required unconventional gas systems that are also continuous accumu lations include coalbed methane basin centered gas so called tight gas fractured shale and chalk gas and gas hydrates deep basin and bacterial gas systems may or may not be continuous accumu lations depending on their geologic setting two basic resource assessment approaches have been em ployed for continuous accumulations the first approach is based on estimates of gas in place a volumetric estimate of total gas in place is commonly coupled with an overall recovery factor to nar row the assessment scope from a treatment of gas volumes residing in sedimentary strata to a prediction of potential additions to re serves the second approach is based on the production perfor mance of continuous gas reservoirs as shown empirically by wells and reservoir simulation models in these methods production characteristics as opposed to gas in place are the foundation for forecasts of potential additions to reserves

preliminary study on the pore characterization of lacustrine shale reservoirs using low pressure nitrogen adsorption and field emission scanning electron microscopy methods a case study of the upper jurassic emuerhe formation mohe basin northeastern china in this study we investigate the pore systems in lacustrine shales from the upper jurassic emuerhe formation mohe basin northeastern china using organic geochemistry analysis x ray diffraction field emission scanning electron microscopy and low pressure nitrogen adsorption analysis because of the large amount of terrestrial input the organic matter in these lacustrine shales are dominated by type iii kerogen which have moderate total organic carbon contents ranging between 0 37 wt and 4 13 wt and thermal maturity ranging from 0 6 ro to 1 15 ro brittle minerals including quartz and feldspar in the emuerhe formation comprise 50 of the samples by weight and illite dominates the clay minerals with the relative content ranging from 45 to 95 the dominant pore types in the emuerhe formation shale reservoir are interparticle pores between clay mineral crystals and intraparticle pores within feldspar grains pores that are larger than 20 nm primarily contribute to the total pore volume whereas pores that are less than 10 nm primarily contribute to the specific surface area the major storage and flow space for hydrocarbon in these lacustrine shales largely resides in inorganic matter porosity and partially in microfacture porosity organic matter pores are rare in the lacustrine shales of the emuerhe formation attributed to the humic organic matter and the relatively low thermal maturity the negative correlation between the total organic carbon and nitrogen bet surface area also indicate that the organic fractions have no significant influence to the petroleum storage potential of these shales in this case the clay minerals specifically illite could be the major medium for gas adsorption

experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of chang 7 shale ordos basin abstract thermal maturity has a significant impact on hydrocarbon generation and the storage capacity within shales but explicit and quantitative characterization of that impact on continental shales is scarce to better understand how thermal maturation affects the organic and inorganic changes of the continental shale reservoirs hydrous pyrolysis was performed to simulate the maturation process toc rock eval and adsorption isotherms tests were used to obtain various geochemical parameters of the shale solid residues the results indicate that with pyrolysis temperature increasing from ambient temperature to 550 c the vitrinite reflectance increases from 0 5 to 2 5 ro and the toc total organic carbon loss weight reaches 25 regarding porosity the fraction of micro to meso pores in the shale increases with an increase in the pyrolysis temperature whereas the macro pores do not change significantly the total amount of gas adsorption does not necessarily increase as the toc is consumed but the gas adsorption capacity per unit of toc increases with increasing thermal maturity our finding provides theoretical modelling for identifying shale gas development prospective zones according to thermal maturity mapping and for predicting quantitatively the geochemical and inorganic changes that occur with thermal evolution

fluid inclusion evidence on the origin of some australian unconformity related uranium deposits fluid inclusions in altered and unaltered host rocks and hydrothermal quartz calcite and dolomite from the unconformity related uranium deposits of koongarra nabarlek and jabiluka northern territory australia were examined using standard microthermometry laser raman microprobe and scanning electron microscopy decrepitated gases were analyzed in a mass spectrometer the relationship of fluid inclusions to alteration and mineralization was established by occurrence restricted to the alteration zones around the deposits and the presence in fluid inclusions of solid phases which also occur as megascopic phases in the alteration secondary halite saturated fluid inclusions in altered host rock quartz and in early hydrothermal quartz veins are believed to relate to hydrothermal alteration associated with ore deposition these inclusions are identical to primary inclusions in silicified and boron metasomatized kombolgie formation sandstone above the jabiluka 2 deposit durak et al 1983 and hence sample post kombolgie fluids the trapped fluid is saline and calcium rich ca 23 equiv wt cacl 2 and sulfate poor so super 2 4 0 001 m no gases were detected in the vapor phase of such inclusions and the median vapor disappearance temperature is 140 degrees c primary inclusions in postore dolomite veins and secondary inclusions in host rock and hydrothermal quartz sample postore hydrothermal fluid this fluid is hypersaline and also calcium rich typically 35 equiv wt cacl 2 and is saturated with as many as 11 solid phases including dolomite and iron rich chlorite vapor bubbles in these inclusions contain methane and minor n 2 and the median vapor disappearance temperature is 127 degrees c aromatic hydrocarbons detected by mass spectrometry are possibly related to this population the calcic brines are thought to have been terrestrial in origin and derived from the oxidized red bed sediments overlying the deposits macarthur basin ore deposition was a response either to reduction of the ore bearing fluid by direct interaction with graphite and ferrous iron in the wall rocks or by mixing with a methane and higher hydrocarbon bearing brine represented by postore fluid inclusions ore deposition and related hydrothermal alteration occurred between 200 degrees and 300 degrees c under a depth of cover of ca 2 km this temperature is consistent with independent temperature constraints and suggests an anomalous thermal gradient during ore formation

lateral variations in lowermost mantle shear wave anisotropy beneath the north pacific and alaska s waves recorded by long period world wide standardized seismograph network and broadband stations in north america for deep northwest pacific subduction zone earthquakes provide evidence for anisotropy in the lowermost mantle shear velocity structure beneath the north pacific and alaska systematic delays of up to 4 s are observed between longitudinal components sv and transverse components sh of motion for core reflected scs waves as well as for core grazing and diffracted s waves the absence of significant splitting for s waves that have turning points more than a few hundred kilometers above the core mantle boundary indicates that anisotropy is localized within the d region the lowermost portion of the mantle sv sh differential arrival times for both scs and sdiff along with path length estimates assuming a 250 km thick d region indicate spatial variations in the strength of shear wave anisotropy the strongest anisotropy 1 1 5 is found in the eastern part of the study area with systematic reduction in magnitude toward the west a transverse isotropy model can explain the data with the velocity structure for horizontally polarized waves vsh having a 2 3 discontinuous shear velocity increase at the top of d as proposed in earlier studies of the region and a similar structure for s wave particle motion in the direction normal to the core mantle boundary vsv but with the velocity jump at the top of d and the velocity within d being reduced from that for vsh by 0 5 1 5 km s large uncertainties exist for velocity gradients above and below the velocity jump but the requirement of a reduced vsv relative to vsh in d is clear synthetic waveforms calculated by using separate isotropic structures for sh and sv match the observations well and constrain the basic anisotropic structure because the shear waves all traverse the region with near grazing geometries the study area exhibits strong lateral variations in lower mantle shear velocity structure and variable thickness of the d layer topography of the d layer is not well resolved because of trade off with volumetric heterogeneity

geometallurgy of australian uranium deposits abstract australian uranium ores are often composed of complex mineral assemblages differences in ore compositions and textures are seen between deposits as well as within a single deposit which can host a range of ore types such a wide variety of uranium ores make it impossible for a single extraction or treatment process to be developed that will accommodate all of the ores from a mineralogical perspective key issues confronting the australian uranium mining industry include the prevalence of low grade ores a lack of detailed chemical and mineralogical information uranium speciation texture grainsize for the various ore deposit types and the presence of refractory uranium bearing minerals and highly acid consuming gangue minerals this paper reviews some of the main controls on uranium geometallurgy by linking concepts relating to ore genesis and the resulting ore mineralogy with the processing behaviour of specific australian uranium ore types emphasis is placed on the value of detailed ore mineralogical analysis and the insight this provides into the factors of importance when considering uranium extraction

seismic detection of folded subducted lithosphere at the core mantle boundary seismic tomography of the d region beneath the caribbean reveals a 100 km vertical step in an otherwise flat d shear velocity discontinuity and localized low velocities at the edge of the slab material which may involve upwellings caused by the slab laterally displacing a thin hot thermal boundary layer seismic tomography has been used to infer that some descending slabs of oceanic lithosphere plunge deep into the earth s lower mantle1 2 the fate of these slabs has remained unresolved but it has been postulated that their ultimate destination is the lowermost few hundred kilometres of the mantle known as the d region relatively cold slab material may account for high seismic velocities imaged in d beneath areas of long lived plate subduction and for reflections from a seismic velocity discontinuity just above the anomalously high wave speed regions3 4 the d discontinuity itself is probably the result of a phase change in relatively low temperature magnesium silicate perovskite5 6 here we present images of the d region beneath the cocos plate using kirchhoff migration of horizontally polarized shear waves and find a 100 km vertical step occurring over less than 100 km laterally in an otherwise flat d shear velocity discontinuity folding and piling of a cold slab that has reached the core mantle boundary as observed in numerical and experimental models can account for the step by a 100 km elevation of the post perovskite phase boundary due to a 700 c lateral temperature reduction in the folded slab we detect localized low velocities at the edge of the slab material which may result from upwellings caused by the slab laterally displacing a thin hot thermal boundary layer

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

seismic ray path variations in a 3d global velocity model abstract a three dimensional 3d ray tracing technique is used to investigate ray path variations of p pcp pp and pp phases in a global tomographic model with p wave velocity changing in three dimensions and with lateral depth variations of the moho 410 and 660 km discontinuities the results show that ray paths in the 3d velocity model deviate considerably from those in the average 1d model for a pcp wave in western pacific to east asia where the high velocity 1 2 pacific slab is subducting beneath the eurasian continent the ray path change amounts to 27 km for a pcp ray in south pacific where very slow 2 velocity anomalies the pacific superplume exist in the whole mantle the maximum ray path deviation amounts to 77 km ray paths of other phases p pp pp are also displaced by tens of kilometers changes in travel time are as large as 3 9 s these results suggest that although the maximal velocity anomalies of the global tomographic model are only 1 2 rays passing through regions with strong lateral heterogeneity in velocity and or discontinuity topography can have significant deviations from those in a 1d model because rays have very long trajectories in the global case if the blocks or grid nodes adopted for inversion are relatively large 3 5 and only a low resolution 3d model is estimated 1d ray tracing may be feasible but if fine blocks or grid nodes are used to determine a high resolution model 3d ray tracing becomes necessary and important for the global tomography

uranium deposits of the mount isa region and their relationship to deformation metamorphism and copper deposition the mount isa region contains over 20 uranium deposits few of which contain economic concentrations of uranium they are thought to be significant in the exploration for new copper deposits based on the model that the uranium deposits are located in the pathways of oxidized hydrothermal fluids that formed the postmetamorphic mount isa copper orebodies there are two uranium deposit types both hosted in volcanosedimentary rocks we suggest that they represent one mineralization event but different metamorphic histories examples in the eastern low grade metamorphic zone are dominated by a brannerite anatase apatite assemblage and are low in uranium the examples in the western high grade metamorphic zone are characterized by uraninite and titanite with higher uranium concentrations the chemical association of u ti and ca is consistent for all deposits however phosphate is only important at low metamorphic grade the most likely mechanism of formation in the lower metamorphic grade anderson s lode example is the complete replacement of chlorite in the sedimentary host rock matrix by the mineralizing assemblage in this model chlorite acted as a reductant allowing the deposition of uranium from an oxidized fluid this mechanism of uranium deposition is similar to that proposed for unconformity type uranium deposits we conclude that these uranium deposits are metamorphosed equivalents of proterozoic unconformity type uranium deposits found elsewhere in northern australia at anderson s lode brannerite and apatite were concentrated in veinlets by pressure dissolution after the deposition of the original assemblage these pressure dissolution seams are cut by premetamorphic quartz chlorite veins examples at higher metamorphic grade have textures that suggest uranium deposition was pre to synmetamorphic at the latest this precludes any genetic or temporal connection between the uranium deposits and the postmetamorphic mount isa copper deposit

mapping proterozoic unconformity related uranium deposits in the rockhole area northern territory australia using landsat etm abstract the rockhole area northern territory australia hosts a number of proterozoic unconformity related uranium deposits the geology of the area features within paleoproterozoic rocks of the pine creek orogen near the unconformity with overlying platform cover sandstone of the paleo to mesoproterozoic mcarthur basin landsat enhanced thematic mapper plus etm data was used in the rockhole area to assist in mapping geological structures and lithology and to identify anomalous concentrations of ferrous minerals the product of alteration which can be indicators of buried uranium mineralization several image processing procedures were applied to the etm data to identify isolate and enhance mineralogical information as simple and complex false color composites etm 754 shown as red green and blue respectively was the best simple image overall complex images based on principal component analysis proved to be the most useful products sandstone shale and siltstone the target lithologies koolpin formation the target stratigraphic unit and bleaching pattern due to the removal of iron ii compounds the target alteration pattern were confidently mapped to provide information required by the mineral emplacement model which ultimately identified areas of likely uranium mineralization thus the contrasting behavior of the two principle oxidation states of uranium and iron can be utilized to map delineate bleached alteration zones associated with economic concentrations of uranium using multispectral sensors like landsat or better hyperspectral sensors

lateral variations in d thickness from long period shear wave data we explore global variations in d shear wave structure by examining 12 years of long period global digital seismograph network gdsn data to identify reflected phases from the d layer in the lowermost mantle we restrict our search to epicentral distances between 63 and 74 where a precritical d reflection will lie between the s and scs arrivals with gdsn long period records a d signal at these ranges is generally obscured by the stronger neighboring phases so to isolate the d reflections we develop a technique for stripping away the interfering s and scs waveforms we interpret travel time variations in the observed sds phases in terms of variations in d thickness and generate maps of inferred d thickness for areas of good seismic coverage the regions of observed d reflections are beneath australasia north central asia the arctic alaska and central america we find considerable variation in d structure in these regions a result consistent with previous studies which have found evidence for lateral heterogeneity in d on average the estimated d thickness is 260 km but there is a fairly uniform distribution of thicknesses between 150 km and 350 km a possible correlation is observed between d thickness and regions of predicted strong horizontal mantle flow

fluid p t x characteristics and evidence for boiling in the formation of the phoenix uranium deposit athabasca basin canada implications for unconformity related uranium mineralization mechanisms abstract the phoenix uranium deposit in the southeastern athabasca basin canada is a typical unconformity contact hosted uranium deposit characterized by an association with reactivated basement faults graphite rich rocks in the underlying basement and a pervasive clay alteration halo surrounding the mineralized zones petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events uraninite and clay size minerals tourmaline kaolinite illite and minor chlorite mainly precipitated in the desilicification periods whereas hydrothermal quartz mainly drusy quartz formed during the silicification periods primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore forming fluids even though quartz did not co precipitate with uraninite the coexistence of multiple types of fluid inclusions liquid dominated biphase vapor dominated biphase vapor only and halite bearing triphase within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping bulk fluid inclusion volatile analysis by mass spectrometry indicates h2o as the dominant species with less than 1 mol non aqueous volatiles that show a compositional trend typical of fluid boiling microthermometric and cryogenic raman spectroscopic analyses indicate that the mineralizing fluids are of h2o nacl cacl2 mgcl2 composition with salinities ranging mainly from 23 4 to 31 1 wt the liquid dominated biphase inclusions excluding those interpreted to have resulted from heterogeneous trapping have homogenization temperatures from 90 to 157 c these data are generally consistent with the classical diagenetic hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults and precipitated uraninite near the unconformity through reaction with reducing agents however the relatively low fluid inclusion homogenization temperatures documented in this paper together with fluid boiling inferred from fluid inclusion assemblages suggest that the deposit may have formed in a shallower environment 2 5 km than assumed in the conventional diagenetic hydrothermal model 5 km abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling flash vaporization changing the fluid ph and promoting uraninite precipitation with the alternating liquid vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively

total petroleum system assessment of undiscovered resources in the giant barnett shale continuous unconventional gas accumulation fort worth basin texas undiscovered natural gas having potential for additions to reserves in the mississippian barnett shale of the fort worth basin north central texas was assessed using the total petroleum system assessment unit concept and a cell based methodology for continuous type unconventional resources the barnett paleozoic total petroleum system is defined in the bend arch fort worth basin as encompassing the area in which the organic rich barnett is the primary source rock for oil and gas produced from paleozoic carbonate and clastic reservoirs exploration technology and drilling in the barnett shale play have rapidly evolved in recent years with about 3500 vertical and 1000 horizontal wells completed in the barnett through 2005 and more than 85 of the them completed since 1999 using framework geology and historical production data assessment of the barnett shale was performed by the u s geological survey using vertical wells at the peak of vertical well completions and before a transition to completions with horizontal wells the assessment was performed after 1 mapping critical geological and geochemical parameters to define assessment unit areas with future potential 2 defining distributions of drainage area cell size and estimating ultimate recovery per cell and 3 estimating future success rates two assessment units are defined and assessed for the barnett shale continuous gas accumulation resulting in a total mean undiscovered volume having potential for additions to reserves of 26 2 tcfg the greater newark east fracture barrier continuous barnett shale gas assessment unit represents a core producing area where thick organic rich siliceous barnett shale is within the thermal window for gas generation ro 1 1 and is overlain and underlain by impermeable limestone barriers pennsylvanian marble falls limestone and ordovician viola limestone respectively that serve to confine induced fractures during well completion to maximize gas recovery the extended continuous barnett shale gas assessment unit which had been less explored defines a geographic area where barnett shale is 1 within the thermal window for gas generation 2 greater than 100 ft 30 m thick and 3 where at least one impermeable limestone barrier is absent mean undiscovered gas having potential for additions to reserves in the greater newark east assessment unit is estimated at 14 6 tcf and in the less tested extended assessment unit a mean resource is estimated at 11 6 tcfg a third hypothetical basin arch barnett shale oil assessment unit was defined but not assessed because of a lack of production data

geology geochronology and emplacement structures associated with the jimbu microgranite mcarthur basin northern territory abstract the jimbu microgranite a series of high level microgranite plutons exposed in central arnhem land in northern australia was emplaced into flat lying sandstones and lesser mudstones carbonates and basalts of the katherine river group during the latter stages of deposition new shrimp u pb zircon results indicate a crystallization and emplacement age for the jimbu microgranite of 1720 7 ma intrusion took place in an essentially static tectonic setting and accommodation space was not created by regional extension or by consumption of the host package by the intrusion rather pluton emplacement was facilitated by three distinct mechanisms the thick basal sandstone package was updomed overlying lutite units were laterally shortened by outward gravity slide the uppermost sandstone unit was raised vertically above the pluton by way of a monoclinal margin and steep reverse detachment faults decollement at ductility transitions in the rock package is required for the coexistence of these three structural styles the three resulting structural elements include relatively steeply and radially outward dipping domes of lower katherine river group sandstones with granite cores irregular short wavelength fold patterns in the overlying incompetent lutites discrete flat lying blocks of the uppermost sandstone unit with steeply upturned or downturned margins plutonism is also suspected of being the cause of similar domes elsewhere in the mcarthur basin and in the adjacent mount isa inlier the model presented here may also be partly applicable to other basins with similar geometries and volcano sedimentary histories where tectonism is currently invoked to explain deformation

complexity of d in the presence of slab debris and phase changes 1 a lower mantle s wave triplication with a scd branch is easily observed beneath central american and its lateral variations has been studied extensively attempts to model scd depth variations with a phase boundary based on tomography predict smooth variations e g sidorin et al 1999a recently hutko et al 2005 presents evidence of a sharper feature with a vertical step like jump of over 50 km for paths sampling the western edge of a fast lower mantle structure beneath the cocos plate we present a similar type of very anomalous scd waveforms sampling the edge further to the east we are able to model these waveforms by adopting the phase boundary model but enhancing the existing tomographic anomaly just above the velocity jump which appears to be a folded slab

mississippian barnett shale fort worth basin north central texas gas shale play with multi trillion cubic foot potential the mississippian barnett shale serves as source seal and reservoir to a world class unconventional natural gas accumulation in the fort worth basin of north central texas the formation is a lithologically complex interval of low permeability that requires artificial stimulation to produce at present production is mainly confined to a limited portion of the northern basin where the barnett shale is relatively thick 300 ft 92 m organic rich presentday total organic carbon 3 0 thermally mature vitrinite reflectance 1 1 and enclosed by dense limestone units able to contain induced fractures the most actively drilled area is newark east field currently the largest gas field in texas newark east is 400 mi 2 1036 km 2 in extent with more than 2340 producing wells and about 2 7 tcf of booked gas reserves cumulative gas production from barnett shale wells through 2003 was about 0 8 tcf wells in newark east field typically produce from depths of 7500 ft 2285 m at rates ranging from 0 5 to more than 4 mmcf day estimated ultimate recoveries per well range from 0 75 to as high as 7 0 bcf efforts to extend the current barnett play beyond the field limits have encountered several challenges including westward and northward increases in oil saturation and the absence of lithologic barriers to induced fracture growth patterns of oil and gas occurrence in the barnett in conjunction with maturation and burial history data indicate a complex multiphased thermal evolution with episodic expulsion of hydrocarbons and secondary cracking of primary oils to gas

scale lengths of shear velocity heterogeneity at the base of the mantle from s wave differential travel times resolving the seismic velocity heterogeneity in the lowermost mantle is essential for understanding the chemical and dynamical processes operating in the boundary layer between the core and the mantle several regions of the lowermost mantle appear to have abrupt increases in shear velocity several hundred kilometers above the core mantle boundary at the top of the d sup prime prime layer this structure is revealed by seismic wave energy refracted by the velocity increase resulting in an extra arrival scd in teleseismic s wavetrains at distances from 65 to 95 degree anomalies in differential travel times of the extra arrival relative to direct s which turns at shallower depths in the midmantle or scs which reflects from the core mantle boundary below the velocity increase provide probes of the velocity heterogeneity in the lowermost mantle with better vertical resolution than provided by conventional scs s measurements we explore the spatial patterns in scd s scs scd and scs s differential time residuals for paths through the lower mantle beneath alaska eurasia and india all being regions with coherent scd phases to place constraints on the strength and scale lengths of shear velocity heterogeneity and or variable topography of the lower mantle discontinuity in these regions the observed patterns are poorlymore predicted by existing global tomographic models significant small scale heterogeneity with lateral length scales of 200 endash 500 km or less exists even within regions that display a relatively uniform d sup prime prime discontinuity structure over scale lengths of 1500 endash 2000 km the strongest travel time variations are associated with structure above the d sup prime prime region in contrast to common assumptions rapid lateral fluctuations in scs scd differential times suggest that the anomalies accumulate within a relatively thin zone less than the overall thickness of d sup prime prime abstract truncated less

on the primary and secondary petroleum generating characteristics of the bowland shale northern england the carboniferous bowland shale of northern england has drawn considerable attention because it has been estimated to have 1329 trillion cubic feet hydrocarbons in place gas and liquids resource potential andrews 2013 here we report on the oil and gas generation characteristics of three selected bowland shale whole rock samples taken from cores and their respective kerogen concentrates compositional kinetics and phase properties of the primary and secondary fluids were calculated through the phasekinetics and gor fit approaches and pvt modelling software the three bowland shale samples contain immature marine type ii kerogen pyrolysate compositions imply primary generation of paraffinic naphthenic aromatic pna oil with low contents of wax and sulphur bulk kinetic parameters have many similarities to those of productive american palaeozoic marine shale plays the secondary gas generation potential of bowland shale is greater than the primary gas potential although it requires a 10 kcal mol 1 higher activation energy to achieve peak production primary oil primary gas and secondary gas reach their maximum generation at 137 150 and 200 c respectively for a 3 c ma 1 heating rate different driving forces of expulsion including the generation of hydrocarbon and overpressure caused by phase separation during sequential periods of subsidence and uplift could be inferred

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

age and paragenesis of mineralisation at coronation hill uranium deposit northern territory australia coronation hill is a u au platinum group elements deposit in the south alligator valley sav field in northern australia south of the better known unconformity style u east alligator rivers ear field the sav field differs from the ear by having a more complex basin basement architecture a volcanically active fault trough jawoyn sub basin developed on older basement and then was disrupted by renewed faulting before being buried beneath regional mcarthur basin sandstones that are also the main hanging wall to the ear deposits primary mineralisation at coronation hill formed at 1607 26 ma rather than 600 900 ma as previously thought and so it is likely that the sav was part of a single west mcarthur basin dilational event most ore is hosted in sub vertical faults and breccias in the competent volcanic cover sequence this favoured fluid mixing acid buffering forming illite and oxidation of fe2 and reduced c rich assemblages as important uranium depositional mechanisms however reduction of u in fractured older pyrite pb model age of 1833 67 ma is an important trap in diorite some primary ore was remobilised at 675 21 ma to form coarse uraninite ni co pyrite networks containing radiogenic pb coronation hill is polymetallic and in this respect resembles the egress style u deposits in the athabascan basin canada however these are all cover hosted a hypothesis for further testing is that coronation hill is also egress style with ores formed by fluids rising through basement hosted fault networks u reduction by diorite pyrite and carbonaceous shale and into veins and breccias in the overlying jawoyn sub basin volcano sedimentary succession

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

geochemical and geological characterization of marine continental transitional shales from longtan formation in yangtze area south china abstract although previous research has provided useful insights into unconventional shale gas resources in recent years the geochemical and geological characteristics of marine continental transitional shale have not been studied systematically during the late permian longtan formation shales were widely deposited in the yangtze area of south china these shales clearly indicate the need to deepen our understanding of marine continental transitional shales this study describes the various characteristics of black shales from the longtan formation in this area on the basis of a field investigation and relevant laboratory analyses longtan shale reservoirs with a thickness and burial depth range of 20 650 and 800 2400 m respectively are usually interbedded with coal and compact sandstone reservoirs due to their special sedimentary environment geochemical analysis of the samples of longtan shales from seven wells in the yangtze area indicates the presence of high organic matters oms with a total organic carbon content in the range of 0 85 35 7 average of 7 33 but low hydrocarbon genetic potential s2 with a value below 3 mg hc g rock the analysis of carbon isotopes and organic macerals demonstrates that the investigated samples mainly contain type iii kerogen data from gas chromatography and gas chromatography mass spectrometry analyses illustrate a weakly oxidizing to a weakly reducing environment with most organic materials originating from algal bacterial organisms and terrestrial plants the terrestrial plants contribute significantly to the om the longtan shales are thermally over matured and they have entered the dry gas generation window according to ro production index data and biomarker maturity ratios x ray diffraction analyses show that the content of brittle minerals of the longtan shales is generally lower than that of marine shales in north america the longtan shales show a high clay content averaging 60 32 wt and low calcite mineral content averaging 3 73 wt field emission scanning electron microscopy shows that various types of nanometer to micrometer scale pores including interparticle and intraparticle pores om pores and microfractures are well developed in the shales generally high om abundance thermal evolution degree clay mineral content and pore space porosity of 0 56 10 6 positively influence shale gas content 1 0 3 8 however high clay content and variable reservoir thickness hinder the successful production of shale gas

oil and gas geochemistry and petroleum systems of the fort worth basin detailed biomarker and light hydrocarbon geochemistry confirm that the marine mississippian barnett shale is the primary source rock for petroleum in the fort worth basin north central texas although contributions from other sources are possible biomarker data indicate that the main oil generating barnett shale facies is marine and was deposited under dysoxic strong upwelling normal salinity conditions the analysis of two outcrop samples and cuttings from seven wells indicates variability in the barnett shale organic facies and a possibility of other oil subfamilies being present light hydrocarbon analyses reveal significant terrigenous sourced condensate input to some reservoirs resulting in terrigenous and mixed marine terrigenous light hydrocarbon signatures for many oils the light hydrocarbon data suggest a secondary condensate generating source facies containing terrigenous or mixed terrigenous marine organic matter this indication of a secondary source rock that is not revealed by biomarker analysis emphasizes the importance of integrating biomarker and light hydrocarbon data to define petroleum source rocks gases in the fort worth basin are thermogenic in origin and appear to be cogenerated with oil from the barnett shale although some gas may also originate by oil cracking isotope data indicate minor contribution of biogenic gas except for reservoirs in the pennsylvanian bend group which contain gases spanning the complete range of observed maturities the gases appear to be stratigraphically segregated younger reservoirs contain less mature gas and older reservoirs contain more mature gas we cannot rule out the possibility that other source units within the fort worth basin such as the smithwick shale are locally important petroleum sources

lateral variation of the d discontinuity beneath the cocos plate 1 broadband shear wave signals from 15 deep south american earthquakes reveal small scale variations of the d shear velocity discontinuity beneath the cocos plate deconvolution by average event source wavelets allows multiple event and california station combinations to be double array stacked in 4 geographically separate reflection point bins with lateral dimensions of about 200 km reflections from the top of d are apparent in all 4 bins with significant variations in timing and strength relative to scs the data are compatible with a discontinuous shear velocity increase 264 km above the core mantle boundary that varies laterally in strength from 0 9 to 2 6 with corresponding lateral velocity variations within d

aspherical structure of the core mantle boundary from pkp travel times maps of aspherical structure in the vicinity of the core mantle boundary have been constructed from a tomographic analysis of p df and p ab travel times in the distance range 150 180 these maps reveal long wavelength features not previously detected by mantle tomography the peak to peak amplitude of these features is on the order of 1 s in vertical travel time too large to be explained by conventional thermal boundary layer models or dynamically supported topography on the core mantle boundary we hypothesize the existence of one or more chemical boundary layers whose large scale accumulations on the surface of the core may in some ways be analogous to continents at the earth s surface

finite frequency tomography of d shear velocity heterogeneity beneath the caribbean 1 the shear velocity structure in the lowermost 500 km of the mantle beneath the caribbean and surrounding areas is determined by seismic tomography applied to a suite of sd sks scs s scd sbc s and scs scd sbc differential times where scd sbc is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the d region the inclusion of the triplication arrivals in the inversion a first for a deep mantle tomographic model is possible because of the widespread presence of a d velocity discontinuity in the region the improved ray path sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the d region the reference velocity model taken from a prior study of waveforms in the region has a 2 9 shear velocity discontinuity 250 km above the core mantle boundary cmb effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long wavelength shear velocity tomography models born frechet kernels are used to characterize how the finite frequency data sample the structure for all of the differential arrival time combinations inversions are performed with and without the kernels the use of three dimensional kernels stabilizes the tomographic inversion relative to a ray theory parameterization and a final model with 60 and 50 km correlation lengths in the lateral and radial dimensions respectively is retrieved the resolution of the model is higher than that of prior inversions with 3 4 velocity fluctuations being resolved within what is commonly described as a circum pacific ring of high velocities a broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the gulf of mexico with several percent lower shear velocities being found beneath northern south america concentrated low velocity regions extend through the d layer under the caribbean colombia and ecuador suggestive of small scale plumes in the boundary layer and possible lateral variations of the d discontinuity one scenario consistent with the imaged features involves subducted farallon plate ponding at the base of the mantle and laterally displacing hot boundary layer material that piles up and destabilizes on its margins

high resolution investigation of shear wave anisotropy in d beneath the cocos plate 1 broadband shear wave signals from 16 deep south american earthquakes are used in a high resolution analysis of lowermost mantle structure beneath the cocos plate shear wave splitting of 162 scs phases is generally compatible with vertical transverse isotropy vti in the d region with little path length or spatial dependence across the 200 800 km2 area sampled assuming a 250 km thick d layer the vti has an average value of 0 63 scs s differential travel time anomalies for the same data indicate a lateral gradient in positive d transverse component velocity perturbations increasing northward s wave triplication arrivals from a shear velocity discontinuity at the top of d show splitting similar to the scs phases but with smaller magnitude vertical resolution remains limited but the data are consistent with vti material being concentrated in just the upper portion or at the top and bottom of d

seismic evidence of partial melt within a possibly ubiquitous low velocity layer at the base of the mantle three source regions show evidence of a low velocity layer that is less than 15 kilometers thick on top of the core mantle boundary and require about a 3 1 ratio of shear to compressional velocity reduction which is consistent with partial melt layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity these observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core mantle boundary low viscosity accompanying partial melt can localize the upwelling of warmed mantle making the low velocity layer a plausible source of mantle plumes

significance of alteration assemblages for the origin and evolution of the proterozoic nabarlek unconformity related uranium deposit northern territory australia the proterozoic nabarlek unconformity related uranium deposit in the alligator rivers uranium field is hosted by paleoproterozoic amphibolite grade metamorphosed semipelitic sedimentary rocks and amphibolite schist high grade ore is confined to the nabarlek fault a reverse fault shear zone that crosscuts a series of interbedded muscovite quartz biotite schists and amphibolite petrographic studies on polished thin sections combined with electron microprobe analyses x ray diffraction fluid inclusion data o h and u pb isotope values as well as 40 ar 39 ar dating have identified up to eight significant fluid events beginning with the precipitation of early quartz veins during uplift of the myra falls metamorphics at 1830 ma and ending with limited uraninite recrystallization during reactivation of the nabarlek fault between 1380 and 750 ma quartz veins that likely formed toward the end of the top end orogeny represent the earliest recorded fluid event fluid inclusion data and 18 o and d values indicate that these veins formed from basement derived fluids that may have been heated by a cooling nabarlek granite during circulation through reverse faults shear zones the next fluid event represented by fine grained sericite and chlorite occurred when fluids passed into these faults and altered the metamorphic minerals following the exhumation of the basement and deposition of the kombolgie subgroup at ca 1760 ma the intrusion of the oenpelli dolerite at ca 1720 ma resulted in the local remobilization of silica and the precipitation of quartz associated with minor pyrite and dolomite around the reverse faults uranium mineralization is associated with an inner and outer alteration halo that extends as far as 1 km from the nabarlek fault alteration in the outer halo began as early as 1700 ma and is dominated by chlorite and sericite which formed when a 200 c fluid flowed into the nabarlek fault from the overlying kombolgie subgroup u pb and 207 pb 206 pb dating reveals that massive uraninite precipitated at ca 1640 ma and formed together with illite and hematite at ca 200 c chlorite was not coeval with uraninite precipitation stable isotope values indicate that the pre and synore alteration assemblage formed from basinal brines with 18 o fluid and d fluid values of 2 2 and 25 10 per mil respectively reactivation of the nabarlek fault at ca 1360 1100 and 900 ma is indicated by u pb and 207 pb 206 pb dating of uraninite these ages correlate with the intrusion of the maningkorrirr phonolitic dikes and the derim derim dolerite at ca 1316 40 and 1324 4 ma respectively the amalgamation of australia and laurentia during the grenville orogen at ca 1140 ma and the breakup of rodinia between 1000 and 750 ma fluid incursions associated with these events precipitated much of the chlorite that has previously been related to uraninite precipitation drusy quartz veins that host high salinity fluid inclusions and sulfides particularly galena also formed after the initial uraninite forming event finally erosion of the kombolgie subgroup and subsequent weathering of the deposit resulted in the recent formation of kaolinite and numerous secondary uranium minerals these data constrain individual events more precisely than previous studies and thus advance the current genetic model to a level that takes into account the multiple stages of fluid overprinting that occurred over a period of at least 800 m y

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

mapping global d p velocities from isc pcp p differential travel times abstract we analyze 78 793 differential pcp p travel times reported by stations world wide to the international seismological centre isc during 1963 1987 to examine the seismic structure of the base of the mantle data were selected for earthquake station pairs within a 30 85 distance range and corrected for ellipticity and mantle path heterogeneity using the tomographic p velocity model iasp3d p of vasco et al 1994 j geophys res 99 13727 13755 the pcp p paths sample a very small number of regions of the base of the mantle limiting the amount of the lowermost mantle d that could be examined we find that the pcp p differential times are on average 0 49s greater than the times predicted by the iasp91 model of kennett and engdahl 1991 geophys j int 105 429 465 suggesting that that the mean p velocity within a 300 km thick d may be 0 35 slower than iasp91 for the regions sampled by our data we have attempted to create an image of some of the higher wavelength d heterogeneity to form a p wave comparison for the scs s and sscs ss study of wysession et al 1995a j geophys res 100 8351 we have therefore used the similar technique of converting the travel time residuals into velocity anomalies in the lowermost 300 km of the mantle and then stacking and smoothing them to create a geographical coherency plot for d lateral heterogeneity there are five regions with data coverage good enough to allow inferences about d p velocity structure relative to iasp91 1 velocities at least 0 9 1 2 fast beneath alaska 2 velocities at least 0 5 1 0 slow beneath hawaii 3 velocities 0 65 fast beneath northern asia our region of greatest coverage 4 a broad slow velocity region up to 3 0 beneath the western pacific and eastern asia 5 a complicated region of fast velocity 0 7 surrounded by two slow velocity regions 1 8 and 0 8 within d beneath central america the transition from slow to fast d velocities moving from beneath the western pacific ocean toward asia occurs in a different location for p velocities than for the s velocities of wysession et al 1995a

pre ore hydrothermal alteration in an unconformity type uranium deposit hydrothermal alteration associated with the formation of unconformity type uranium deposits is manifested mainly by intense chloritic replacement of metamorphic mineral assemblages at the koongarra deposit northern australia three stages of pre ore alteration were identified in chloritized metamorphic muscovite using optical microscopy the electron microprobe and transmission and analytical electron microscopy tem and aem during the first stage metamorphic muscovite was altered to a mica with very low interlayer occupancy k content as low as 0 35 compared to 1 for ideal muscovite high octahedral cation content up to 2 3 whereas ideal muscovite has 2 and high si content high resolution tem images show that these changes in composition were accompanied by frequent layer terminations in contrast to the metamorphic muscovite whereas selected area electron diffraction patterns indicate that the altered muscovite remained a two layer polytype the alteration of muscovite appears more extensive in the outer alteration halo and has been almost completely eradicated in the ore zone where chloritization is more complete during the second stage of the pre ore alteration the altered muscovite was replaced by mg rich serpentine lizardite and clinochlore high resolution tem images show two 10 a mica layers coalescing to one 14 a chlorite layer this type of coalescence appears to involve transformation of one dioctahedral layer of the mica structure to one trioctahedral brucite layer in the chlorite structure through dissolution of the tetrahedral sheets and cation influx in the octahedral site the final stage of the pre ore alteration resulted in replacement of lizardite and clinochlore by fe rich chlorite comparison of the alteration observed in metamorphic muscovite with the alteration observed in metamorphic biotite and garnet shows clearly that chloritization of these phases was also a pre ore alteration event pre ore alteration was principally characterized by the evolution of chlorite from a mg rich phase to an ferich one

properties and shale oil potential of saline lacustrine shales in the qianjiang depression jianghan basin china abstract the geochemical and petrographic characteristics of saline lacustrine shales from the qianjiang formation jianghan basin were investigated by organic geochemical analysis x ray diffraction xrd scanning electron microscopy sem and low pressure nitrogen adsorption analysis the results indicate that the saline lacustrine shales of eq3 member with high oil content are characterized by type i and type ii oil prone kerogen variable toc contents 1 0 10 0 wt and an early maturity stage ro ranges between 0 41 and 0 76 the mineral compositions of eq3 saline shale show strong heterogeneity brittle intervals with high contents of quartz and carbonate are frequently alternated with ductile intervals with high glauberite and clay contents this combination might be beneficial for oil accumulation but may cause significant challenges for the hydraulic stimulation strategy and long term production of shale oil the interparticle pores and intraparticle pores dominate the pore system of eq3 shale and organic matter hosted pores are absent widely distributed fractures especially tectonic fractures might play a key role in hydrocarbon migration and accumulation the pore network is contributed to by both large size inorganic pores and abundant micro factures leading to a relatively high porosity 2 8 30 6 and permeability 0 045 6 27 md within the saline shale reservoir which could enhance the flow ability and storage capacity of oil the oil content s1 100 toc mg hc g toc and s1 mg hc g rock and brittleness data demonstrate that the eq33x section has both great potential for being a producible oil resource and hydraulic fracturing considering the hydrocarbon generation efficiency and properties of oil the mature shale of eq3 in the subsidence center of the qianjiang depression would be the most favorable zone for shale oil exploitation

wettability and connectivity of overmature shales in the fuling gas field sichuan basin china the fuling gas field in sichuan basin china has produced greater than 1 5 1010 m3 0 53 tcf of natural gas from overmature upper ordovician wufeng and lower silurian longmaxi shales to systemically investigate the characteristics of wettability and connectivity and to understand the underlying causes of production behavior we study five samples of wufeng and longmaxi shales with different total organic carbon contents and mineral compositions complementary approaches include mercury intrusion capillary pressure micp contact angle measurement spontaneous imbibition and saturated diffusion and tracer both nonsorbing and sorbing migration mapped via laser ablation inductively coupled plasma mass spectrometry according to measured contact angles and imbibition tests conducted on aqueous deionized water and brine and oleic n decane phases wufeng and longmaxi shales are strongly oil wet and moderately strong water wet the lower boundary of estimated permeability obtained from n decane imbibition can reach 137 nd which is higher than the geometric mean permeability derived from the micp method 5 5 68 8 nd effective diffusion coefficients of the wufeng and longmaxi shales are in the range of 10 13 m2 s 1 1 10 12 ft2 s tests of imbibition and saturated diffusion using tracer containing brine show that concentrations of nanometer sized tracers decrease rapidly a factor of 10 over a migration distance of a few millimeters from the sample edge suggesting the presence of poorly edge connected water wet pores sparsely connected hydrophilic pores mixed wettability and highly restricted pathways collectively contribute to the limited migration of nano sized tracers which probably results in the production behavior of initial steep decline and low overall recovery in the fuling gas field

uraniferous diagenetic xenotime in northern australia and its relationship to unconformity associated uranium mineralisation stratabound uraniferous diagenetic xenotime cements provide a minimum depositional age of 1 632 3 ma for the sedimentary birrindudu group in the killi killi hills tanami region in northern australia the age of xenotime formation is broadly coeval with that recently proposed 1 650 1 600 ma for uranium mineralisation in the unconformity associated deposits of the pine creek inlier northern australia and athabasca basin canada the geological setting and formation model for the uraniferous xenotime crystals are similar to those widely proposed for unconformity associated uranium deposits suggesting a genetic link between the two however xenotime formation in the birrindudu group occurred during an apparently earlier stage of diagenesis compared to late diagenetic formation of unconformity associated uranium deposits this could be explained by variations in the thickness of sediment cover and diachronous diagenesis across the basin at the time of the basin wide uranium mobilisation event herein dated at ca 1 630 ma in such a scenario stratabound uraniferous xenotime cements could represent the remote distal zones of a more deeply buried uranium mineralising system alternatively the xenotime layer represents a precursor to or a source for later unconformity associated ore deposition in this case the presence of diagenetic uraniferous xenotime in an area prospective for unconformity associated uranium mineralisation would be an indication of and still provide an approximate age for uranium mobilisation within the cover sequence xenotime is a far more robust mineral than uraninite for u pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent recrystallisation events if present in the immediate uranium ore environment

natural sealed fractures in mudrocks a case study tied to burial history from the barnett shale fort worth basin texas usa abstract the mississippian barnett shale texas usa consisting of organic rich shales and limestones hosts the largest gas fields of north america this study examines sealed fractures from core and outcrop samples of the barnett shale of the fort worth basin and aims to 1 characterize the phases occurring in the fractures from samples having experienced different burial histories 2 establish a paragenetic sequence to relate the timing of fracture origin and sealing with the burial history of the basin and 3 contribute to the understanding of the mechanisms of fracture formation in shales including overpressure origin four fracture generations were distinguished in the most deeply buried core samples by characterizing the sealing minerals petrographically and geochemically the generations were inserted into the framework of a reconstructed burial history for the fort worth basin which allowed a time sequence for fracture development to be established this in turn allowed inference of conditions of fracture development and consideration of fracture mechanisms as well as the origin of the parent fluids of sealing minerals type 1 fractures formed during early mechanical compaction at a few 10 s to 100 m of depth of still not fully cemented sediments type 2 fractures formed during moderate burial 2 km from slightly modified seawater their timing is consistent with overpressure generated during rapid deposition and differential compaction of pennsylvanian lithologies during the onset of the ouachita compressional event type 3 fractures formed during deep burial 3 km from silica rich basinal brines possibly derived from clay diagenesis type 4 fractures formed at very deep burial 4 km from hot and 18 o rich fluids carrying light oil 20 30 api and record the opening of the fluid system after hydrocarbon migration differences are highlighted between the timing and thermal regimes under which fractures formed in barnett lithologies from different areas of the basin this suggesting that extrapolation of outcrop observations to subsurface must be used with due care

2d and 3d nanopore characterization of gas shale in longmaxi formation based on fib sem abstract studying complex pore structures is the key to understanding the mechanism of shale gas accumulation fib sem focused ion beam scanning electron microscope is the mainstream and effective instrument for imaging nanopores in gas shales based on this technology 2d and 3d characteristics of shale samples from lower silurian longmaxi formation in southern sichuan basin were investigated 2d experimental results show that the pores in shale are nanometer sized and the structure of those nanopores can be classified into three types organic pores inorganic pores and micro fractures among the three types organic pores are dominantly developed in the om organic matter with three patterns such as continuous distributed om om between clay minerals and om between pyrite particles and the size of organic pores range from 5 nm to 200 nm inveresly inorganic pores and micro fractures are less developed in the longmaxi shales 3d digital rocks were reconstructed and segmented by 600 continuous images by fib cutting and sem imaging simultaneously the pore size distribution and porosity can be calculated by this 3d digital core showing that its average value is 32 nm and porosity is 3 62 the 3d digital porosity is higher than its helium porosity which can be regarded as one important parameter for evaluation of shale gas reserves the 2d and 3d characterized results suggest that the nanometer sized pores in organic matter take up the fundamental storage space for the longmaxi shale these characteristics have contributed to the preservation of shale gas in this complex tectonic area

nanoscale relationships between uranium and carbonaceous material in alteration halos around unconformity related uranium deposits of the kiggavik camp paleoproterozoic thelon basin nunavut canada concentrations of 7 u and 1 cu were identified in massive brecciated and amorphous carbonaceous materials cm characterized by strongly negative values of carbon stable isotopes 13c 39 1 relative to pdb the anomalies are restricted to clay alteration halos developed in neoarchean woodburn lake group metagreywacke that is the predominant host of unconformity related uranium u deposits in the kiggavik exploration camp petrographic and microstructural analyses by sem x ray diffraction hr tem and raman spectroscopy identified carbon veils best described as graphene like carbon upon which nano scale uraninite crystals are distributed cm are common in u systems such as the classic cretaceous roll front deposits and the world class paleoproterozoic unconformity related deposits however the unusual spatial and textural association of u minerals and cm described herein raises questions on mechanisms that may have been responsible for the precipitation of the cm followed by crystallization of u oxides on its surfaces based on the characteristics presented herein the cms at kiggavik are interpreted as hydrothermal in origin furthermore the nanoscale organization and properties of these graphene like layers that host u oxide crystallites clearly localized u oxide nucleation and growth

organic geochemistry of the woodford shale southeastern oklahoma how variable can shales be woodford shale samples obtained from a cored outcrop in southeastern oklahoma were geochemically analyzed to determine vertical variations of organic facies thermal maturity and an evaluation of their depositional environments total organic carbon values ranged from 5 01 to 14 81 indicating a good source rock potential in this area the woodford shale is marginally mature as indicated by vitrinite reflectance values rock eval data revealed that the samples are dominated by type ii kerogen biomarker ratios based on pristane phytane steranes and hopanes show a mix of marine and terrigenous organic matter high salinity conditions and water density stratification also prevailed during deposition of this formation as indicated by the presence of gammacerane the woodford shale was subdivided into lower middle and upper members based on the integration of geochemical and geologic data moreover the presence and extent of photic zone anoxia pza were determined by the presence of aryl isoprenoids the lower and upper woodford shale members were deposited under dysoxic to suboxic conditions and episodic periods of pza the middle member was deposited under anoxic conditions and persistent pza in addition aryl isoprenoids helped infer the position of the chemocline during deposition of the different members the relative hydrocarbon potential parameter was used in determining transgressive and regressive cycles within the woodford shale this study undoubtedly demonstrates the significant lithologic and chemical variability that occurs within shales the application of this workflow to regional studies can have a direct influence on exploration and production activities in shale gas systems

controlling factors on the formation and distribution of sweet spot areas of marine gas shales in south china and a preliminary discussion on unconventional petroleum sedimentology abstract shale gas resources in china are abundant with the marine shales accounting for the largest proportion i e 13 1012 m3 the wufeng longmaxi shale system deposited across the late ordovician and early silurian transition in south china is currently the target for shale gas exploration and development in china its annual output in 2018 reached 10 8 109 m3 making china the largest shale gas production region outside north america within this shale system the sweet spot intervals of shale gas formed vertically and sweet spot areas of shale gas formed regionally the sweet spot intervals occur mainly at the bottom of the wufeng longmaxi shale and are 10 40 m in thickness the sweet spot interval is characterized by high total organic carbon toc and gas contents relatively high porosity high brittle mineral content and abundant lamination fissures and fractures the formation of shale gas sweet spot intervals is mainly controlled by four factors in south china they are anoxic shelf environment abundant nano pores in organic matter sealed roof and floor strata and abundant lamination and high silica content in shale respectively as the regional extension of the sweet spot intervals the formation of the sweet spot area requires all the controlling factors for the sweet spot interval it was born in regional anoxic shelf with stable tectonics and preserved in relatively stable tectonic zones three sweet spot areas are identified for the wufeng longmaxi shale in south china i e fuling weiyuan fushun yongchuan and changning zhaotong areas the total area is about 2 104 km2 with technically recoverable resources of 3 3 1012 m3 in addition with the rapid progresses of exploration and development of unconventional petroleum resources such as shale gas the petroleum industry around the world extends to unconventional petroleum resources gradually accomplishing an important change of petroleum geology research focus from conventional to unconventional unconventional petroleum geology research focuses on continuously or semi continuously distributed sweet spot areas for which the formation would be the result of coupling sedimentology from several geological events such as global or regional tectonic activity volcanic eruption climate change anoxic water biotic mass extinction and radiation and gravity current it is necessary to innovatively construct new insights of unconventional petroleum sedimentology in order to enrich and improve the petroleum sedimentology research and its application therefore the concept of unconventional petroleum sedimentology is proposed and its research task method aim and importance are preliminarily discussed

the rožna uranium deposit bohemian massif czech republic shear zone hosted late variscan and post variscan hydrothermal mineralization three major mineralization events are recorded at the ro na uranium deposit total mine production of 23 000 t u average grade of 0 24 u 1 pre uranium quartz sulfide and carbonate sulfide mineralization 2 uranium and 3 post uranium quartz carbonate sulfide mineralization 1 k ar ages for white mica from wall rock alteration of the pre uranium mineralization style range from 304 5 5 8 to 307 6 6 0 ma coinciding with the post orogenic exhumation of the moldanubian orogenic root and retrograde metamorphic equilibration of the high grade metamorphic host rocks the fluid inclusion record consists of low salinity aqueous inclusions together with h2o co2 ch4 co2 ch4 and pure ch4 inclusions the fluid inclusion paragenetic and isotope data suggest that the pre uranium mineralization formed from a reduced low salinity aqueous fluid at temperatures close to 300 c 2 the uraniferous hydrothermal event is subdivided into the pre ore ore and post ore substages k ar ages of pre ore authigenic k feldspar range from 296 3 7 5 to 281 0 5 4 ma and coincide with the transcurrent reorganization of crustal blocks of the bohemian massif and with late stephanian to early permian rifting massive hematitization albitization and desilicification of the pre ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the moldanubian domain the wide range of salinities of fluid inclusions is interpreted as a result of the large scale mixing of basinal brines with meteoric water the cationic composition of these fluids indicates extensive interaction with crystalline rocks chlorite thermometry yielded temperatures of 260 c to 310 c during this substage uranium was probably leached from the moldanubian crystalline rocks the hydrothermal alteration of the ore substage followed or partly overlapped in time the pre ore substage alteration k ar ages of illite from ore substage alteration range from 277 2 5 5 to 264 0 4 3 ma and roughly correspond with the results of chemical u pb dating of authigenic monazite 268 50 ma the uranium ore deposition was accompanied by large scale decomposition of biotite and pre ore chlorite to fe rich illite and iron hydrooxides therefore it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore bearing fluid by interaction with ferrous iron bearing silicates biotite and pre ore chlorite the th data on primary mostly aqueous inclusions trapped in carbonates of the ore substage range between 152 c and 174 c and total salinity ranges over a relatively wide interval of 3 1 to 23 1 wt nacl eq gradual reduction of the fluid system during the post ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite chlorite thermometry yielded temperatures of 150 c to 170 c solid bitumens that post date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives the origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in upper stephanian and permian sediments 3 k ar ages on illite from post uranium quartz carbonate sulfide mineralization range from 233 7 4 7 to 227 5 4 6 ma and are consistent with the early tethys central atlantic rifting and tectonic reactivation of the variscan structures of the bohemian massif a minor part of the late variscan uranium mineralization was remobilized during this hydrothermal event

thermal maturity and organic composition of pennsylvanian coals and carbonaceous shales north central texas implications for coalbed gas potential thermal maturity was determined for about 120 core cuttings and outcrop samples to investigate the potential for coalbed gas resources in pennsylvanian strata of north central texas shallow 600 m 2000 ft coal and carbonaceous shale cuttings samples from the middle upper pennsylvanian strawn canyon and cisco groups in archer and young counties on the eastern shelf of the midland basin northwest and downdip from the outcrop yielded mean random vitrinite reflectance r o values between about 0 4 and 0 8 this range of r o values indicates rank from subbituminous c to high volatile a bituminous in the shallow subsurface which may be sufficient for early thermogenic gas generation near surface 100 m 300 ft core and outcrop samples of coal from areas of historical underground coal mining in the region yielded similar r o values of 0 5 to 0 8 carbonaceous shale core samples of lower pennsylvanian strata lower atoka group from two deeper wells samples from 1650 m 5400 ft in jack and western wise counties in the western part of the fort worth basin yielded higher r o values of about 1 0 pyrolysis and petrographic data for the lower atoka samples indicate mixed type ii type iii organic matter suggesting generated hydrocarbons may be both gas and oil prone in all other samples organic material is dominated by type iii organic matter vitrinite indicating that generated hydrocarbons should be gas prone individual coal beds are thin at outcrop 1 m 3 3 ft laterally discontinuous and moderately high in ash yield and sulfur content a possible analog for coalbed gas potential in the pennsylvanian section of north central texas occurs on the northeast oklahoma shelf and in the cherokee basin of southeastern kansas where contemporaneous gas producing coal beds are similar in thickness quality and rank

numerical study of multi period palaeotectonic stress fields in lower cambrian shale reservoirs and the prediction of fractures distribution a case study of the niutitang formation in feng gang no 3 block south china abstract fractures not only control the distribution of oil and gas reservoirs but also are key points in the research of oil and gas reservoir development programmes the tectonic fractures in the lower cambrian shale reservoirs in the feng gang no 3 block are effective reservoir spaces for hydrocarbon accumulation and these fractures are controlled by palaeotectonic stress fields therefore quantitatively predicting the development and distribution of tectonic fractures in the lower cambrian shale reservoir is important for the exploration and exploitation of shale gas in the feng gang no 3 block in the present study a reasonable geological mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data fracture characteristics from drilling data uniaxial and triaxial compression tests and experiments on the acoustic emissions ae of rocks then a three dimensional 3 d finite element method is applied to simulate the palaeotectonic stress field with the superposition of the yanshan and himalayan movements and used to predict the fracture distribution the simulation results indicate that the maximum principal stress value within the study area ranged from 269 97 mpa to 281 18 mpa the minimum principal stress ranged from 58 29 mpa to 79 64 mpa and the shear stress value ranged from 91 05 mpa to 106 21 mpa the palaeotectonic stress field is controlled by the fault zone locations the fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults at the end of the fault zones at the inflection point and at the intersection of the fault zones

anoxia controlled by relative sea level changes an example from the mississippian barnett shale formation abstract a continuous core drilled in the barnett shale formation fort worth basin texas united states a remarkable example of paleozoic organic rich sediments deposited in a narrow inland seaway was analysed by means of sedimentological geochemical and biostratigraphic data as the influence of sea level fluctuations on benthic anoxia in ancient seas is still poorly understood our work aims to shed light on the control exerted by relative sea level variations on the paleoceanographic processes that drove fine grained sediment deposition organic matter dispersal and preservation during the sedimentation of the barnett shale formation using spectral gamma ray log a large second order sequence modulated by a total of thirteen third order sequences was inferred third order relative sea level cycles modulated the level of restriction of the basin through time alternating pulses of bottom water oxygenation and relatively more efficient watermass circulation with times of sluggish bottom water and stagnation which controlled the facies stacking pattern and organic matter preservation in particular relatively increased stagnation occurred during lowstand phases while relatively reduced restriction was principally associated with transgressive and highstand systems tracts with more efficient bottom current circulation on a larger scale second order eustatic cycles played a crucial role in determining the paleoceanographic and depositional processes responsible for anoxia during the early phase of sea level rise the pre existing topography was flooded establishing the conditions for a shallow strongly restricted anoxic basin during the second order regression the basin experienced increased isolation with bottom water stagnation and deep water renewal of 6000 years anoxia terminated abruptly corresponding to the eustatic sea level rise associated with the beginning of a new second order sequence therefore the barnett shale formation represents a significant example of the complex interplay between sea level controlled basin physiography and local paleoceanographic conditions

formation of nanoporous pyrobitumen residues during maturation of the barnett shale fort worth basin abstract hydrocarbon generation reactions occur within organic rich shales as a response to thermal maturation here we report observations on samples from the organic rich mississippian barnett shale gas system fort worth basin texas usa at varying stages of thermal maturation a multiscale characterization was achieved using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm and transmission electron microscopy tem we document the chemical evolution of the macromolecular structure of barnett shale kerogen with increasing maturity from an immature kerogen containing a significant aliphatic component and an important concentration of oxygen and sulfur containing functional groups to an overmature kerogen dominated by poorly condensed aromatic structures in addition to the presence of bitumen in samples of oil window maturity very likely genetically derived from thermally degraded kerogen the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by secondary cracking of bitumen compounds

lower mantle structure from scs s differential travel times knowledge of the spectrum of structure in the lower mantle is crucial to our understanding of the dynamical evolution of the earth and in principle can be inferred from the analysis of global seismic data sets the long wavelength compressional velocity structure has usually been constrained through tomographic inver sion of the isc catalogue of p wave travel times1 3 whereas shear velocity has been inferred from waveform modelling of long period shear waves4 6 the models that have been produced are similar in only the largest scale features7 and explain little of the variance of the raw data used in their construction thus there is a legitimate concern that the current generation of global scale models give only a crude approximation to the largest scale structure and that there may be significant aliasing of short wavelength heterogeneity here we use scs s differential travel times to demonstrate that the three dimensional structure of the lower mantle is indeed dominated by continental scale features particularly convincing is the fact that the features are apparent in the raw data and are not the product of a complicated modelling procedure

determination of critical parameters for evaluating coal measure shale gas in china abstract coal measure shale is one of the most abundant types of marine continental shales in china two sets of typical coal measure shales in china are developed in the shanxi formation ordos basin and in the longtan formation guizhou province in this study thermal simulation rock pyrolysis and x ray diffraction experiments were used to analyze four coal measure shale samples collected from typical areas of china based on the study of hydrocarbon generation process of the samples the lower limits of thermal maturity ro of favorable and target areas for coal measure shale were 1 8 and 2 5 respectively the threshold ro value of oil generation in coal measure shale was preliminarily inferred to be 0 6 the gaseous hydrocarbon production per unit of s1 s2 after the gas generation threshold was linearly and positively correlated with ro the lower limits of total organic carbon toc corresponding to the favorable and target areas were 2 45 wt and 2 84 wt respectively combined with x ray diffraction experiments the diagenetic stage and the hydrocarbon generation model of coal measure shale were established and could be divided into four evolutionary stages the results of this study have direct scientific and practical significance for the evaluation of gas content and selection of areas in china for the extraction of coal measure shale

tomographic inversion of s sks times for shear velocity heterogeneity in d degree 12 and hybrid models differential travel times between s or diffracted s and sks were measured to study the global distribution of shear wave velocity heterogeneity in the lowermost 250 km of the mantle the d region commencing with 3000 s sks times with variable qualities we minimize uneven path coverage by thinning redundantly sampled regions e g the fiji tonga to north america corridor and collect additional data for sparsely sampled areas especially in the southern hemisphere about 1500 paths were retained distributed to reconcile both high density and homogeneous sampling we compare 1 spherical harmonic and 2 equal area block parameterizations of d shear velocity heterogeneity for identical minimum resolving lengths and mean model errors we show that the two parameterizations result in indistinguishable patterns of heterogeneity and power distribution for resolution down to a block size of 4 5 4 5 and maximum spherical harmonic degree of 40 we demonstrate synthetically that a high degree l inversion followed by a lower degree ls spherical harmonic synthesis effectively circumvents model contamination from expansion truncation effects tomographic inversion of this data set yields a global distribution of d heterogeneity robust up to degree 12 in our preferred model l 40 ls 12 rms 1 surface hotspots and estimated lower mantle plume roots are located in or at edges of low velocity regions vs 2 for both the atlantic indian low velocity corridor as well as the low velocities beneath the central pacific although the above parameterizations entail no intrinsic difference in resolvability higher resolution is regionally achieved by removing the derived degree 12 model from the data then inverting the corrected residuals using 4 5 4 5 blocks this hybrid method prevents power loss at intermediate to long wavelengths from otherwise severe damping and recovers smaller scale structure where constraints are better than the global average such as beneath the pacific and eurasia a synthetic recovery test yields resolvability maps that reflect both the path geometry and the quality of data which help to identify robust features in both the degree 12 and the hybrid d models

seismic imaging of the laterally varying d region beneath the cocos plate summary we use an axisymmetric spherical earth finite difference algorithm to model sh wave propagation through cross sections of laterally varying lower mantle models beneath the cocos plate derived from recent data analyses synthetic seismograms with dominant periods as short as 4 s are computed for several models 1 a d reflector 264 km above the core mantle boundary with laterally varying s wave velocity increases of 0 9 2 6 per cent based on localized structures from a 1 d double array stacking method 2 an undulating d reflector with large topography and uniform velocity increase obtained using a 3 d migration method and 3 cross sections through the 3 d mantle s wave velocity tomography model txbw we apply double array stacking to assess model predictions of data of the models explored the s wave tomography model txbw displays the best overall agreement with data the undulating reflector produces a double scd arrival that may be useful in future studies for distinguishing between d volumetric heterogeneity and d discontinuity topography synthetics for the laterally varying models show waveform variability not observed in 1 d model predictions it is challenging to predict 3 d structure based on localized 1 d models when lateral structural variations are on the order of a few wavelengths of the energy used particularly for the grazing geometry of our data iterative approaches of computing synthetic seismograms and adjusting model characteristics by considering path integral effects are necessary to accurately model fine scale d structure

2015 us geological survey assessment of undiscovered shale gas and shale oil resources of the mississippian barnett shale bend arch fort worth basin texas the mississippian barnett shale within the bend arch fort worth basin is a major continuous shale gas resource in the united states the barnett shale was last assessed by the u s geological survey in 2003 and only included vertical drilling the barnett shale was reassessed in 2015 for undiscovered technically recoverable gas and oil resources to include the impact of over 12 years of horizontal drilling development the 2015 usgs assessment delineated three continuous assessment units aus 1 barnett continuous gas au 2 barnett mixed continuous gas and oil au and 3 western barnett continuous oil au the au boundaries were defined by hydrogen index hi values as a proxy for thermal maturity in addition to shale thickness an hi value of 100 mg hc hydrocarbon g toc total organic carbon was used to define the barnett continuous gas au boundary the barnett mixed continuous gas and oil au was defined within the northeastern part of the basin where hi values are 100 mg hc g toc and the shale thickness exceeds 100 feet resulting undiscovered technically recoverable resource estimates for these two aus were 53 trillion cubic feet of natural gas tcfg 172 million barrels of oil mmbo and 176 million barrels of natural gas liquids the western portion of the barnett shale hi 100 comprises the western barnett continuous oil au and was not quantitatively assessed the recent usgs assessment is nearly double the 2003 mean resource estimate of 26 2 tcfg and is the first study to provide quantitative estimates for shale oil resources in the barnett shale

identification of source carbon for microbial methane in unconventional gas reservoirs a method is proposed for identifying the carbon source for methane generated by carbonate reduction microbial methanogenesis using the isotopic and compositional mass balance of carbon in cogenerated carbon dioxide co2 and methane microbial methanogenesis from bitumen or petroleum generates more methane than co2 so the carbon isotopic compositions of methane and co2 are relatively heavy and similar to the carbon isotopic composition of thermogenic methane microbial methanogenesis that uses kerogen or recent organic matter as a carbon source generates relatively more co2 than methane therefore methane and co2 have the light carbon typical of shallow microbial methane this concept was quantified and tested against three literature examples to determine if the relative amount of co2 generation could be estimated with sufficient resolution to predict source carbon type and generation temperature in gas shales and coalbed methane antrim shale michigan gases are demonstrated to be derived mainly from immature bitumen in the shale at modern reservoir temperatures and cooler temperatures fruitland coal gases in the western san juan basin are derived mainly from bitumen in oil window maturity coals at modern temperature southwest indiana coal gases are derived mainly from thermally immature kerogen at modern and warmer temperatures identification of the methane carbon source and temperature helps delineate microbial methane resource fairways where fairways are limited by microbial gas generation temperatures may help determine if microbial methane is actively generated today or a relict from earlier microbial generation

fluid evolution and uranium mo f mineralization at the maureen deposit queensland australia unconformity related hydrothermal ore formation with a source in the volcanic cover sequence maureen is the largest among several u mo f prospects occurring along a late devonian unconformity in the georgetown area northern queensland australia mineralization is structurally controlled by the intersection of steep east west fractures with an unconformity between a proterozoic basement and a paleozoic cover sequence of continental sedimentary rocks and abundant rhyolitic volcanic rocks the mineralogical composition of high grade ore pitchblende fe rich molybdenite arsenopyrite arsenian pyrite fluorite dickite chlorite goyazite graphite or hematite postlithification brecciation and quartz dissolution indicate a strong chemical gradient and disequilibrium during mineralization between the reduced basement and the largely oxidized cover sequence elemental and mineral zonation centered to faults and fractures cutting the unconformity indicates locally reducing and quartz dissolving conditions during the formation of tabular u mo orebodies which are surrounded by a halo rich in fluorite a detailed petrographic study microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of quartz and fluorite hosted fluid inclusions provide concentrations of ore forming components in fluids related to hydrothermal uranium mineralization three fluids were involved in the mineralizing process at maureen a likely oxidized saline l3 fluid an aqueous l1 fluid and a ch4 bearing carbonic vapor cv the oxidized saline l3 fluids trapped in fluorite and dickite bearing hydrothermal quartz veinlets crosscutting detrital quartz show the highest average concentrations of u 10 47 ppm mo 489 888 ppm and as 318 777 ppm with element ratios close to those of high grade mineralized rocks we suggest that aqueous l1 fluids mixed in the cover sequence with oxidized saline fluids l3 to precipitate fluorite as a distal halo surrounding the east west fractures their mixture an oxidized moderately saline fluid l2 reacted with methane bearing carbonic vapor cv to precipitate u and mo by reduction close to the intersection of the fractures with the unconformity geochemical analysis of coexisting vapor and liquid assemblages indicate mixing of oxidized saline fluids with reduced carbonic vapors to be the driving force for uranium precipitation the maureen deposit shares essential geologic characteristics and hydrothermal processes with proterozoic unconformity related u deposits but probably owes its unusual element association of u with equally redox sensitive mo and abundant f to a source region in the volcano sedimentary cover sequence that was enriched in these elements due to the presence of highly fractionated easily leachable and oxidizable felsic volcanics

petrography fluid inclusion analysis and geochronology of the end uranium deposit kiggavik nunavut canada the end deposit is one of several uranium deposits in the kiggavik area near the proterozoic thelon basin which is geologically similar to the athabasca basin known for its unconformity related uranium deposits the mineralization occurs as uraninite and coffinite in quartz veins and wall rocks psammopelitic gneisses in the sub thelon basement and is associated with clay and hematite altered fault zones fluid inclusions were studied in quartz cementing unmineralized breccias formed before mineralization q2 quartz veins that were formed before mineralization but spatially associated with uranite q4 and calcite veins that were formed after mineralization four types of fluid inclusions were recognized namely liquid dominated biphase liquid vapor vapor dominated biphase vapor liquid monophase vapor only and triphase liquid vapor halite inclusions the first three types were found in q2 whereas all four types were found in q4 and calcite the coexistence of these different types of inclusions within individual fluid inclusion assemblages is interpreted to indicate fluid immiscibility and heterogeneous trapping based on microthermometry the fluids associated with q2 are characterized by low salinities 0 4 to 6 6 wt and moderate temperatures from 148 to 261 c and the fluids associated with calcite show high salinities 26 8 to 29 3 wt and relatively low temperatures from 146 to 205 c whereas the fluids associated with q4 have a wide range of salinities from 0 7 to 38 8 wt and temperatures from 80 to 332 c microthermometric and cryogenic raman spectroscopic studies indicate that the high salinity fluids in q4 and calcite belong to the h2o nacl cacl2 mgcl2 system with some dominated by nacl and others by cacl2 the fluid inclusions in q2 are interpreted to be unrelated to mineralization whereas those in q4 and calcite reflect the mineralizing fluids the fluid inclusion data are consistent with a genetic link of mineralization with basinal brines derived from the thelon basin however unlike the conventional deep burial 5 km diagenetic hydrothermal model proposed for the unconformity related uranium deposits the uranium mineralization in the end deposit is inferred to have formed in a shallow environment probably 2 km based on fluid immiscibility and low fluid pressures obtained in this study the u pb age of uraninite 1295 12 ma is interpreted to reflect isotopic resetting after the primary mineralization

paleo ocean redox environments of the upper ordovician wufeng and the first member in lower silurian longmaxi formations in the jiaoshiba area sichuan basin a study of paleo ocean redox environments is important for understanding the deposition of black shale and has practical implications for shale gas exploration here we selected a total of 52 shal

a rock physics model for characterizing the total porosity and velocity of shale a case study in fuling area china abstract the total porosity in a shale gas reservoir is the key parameter to evaluate its potential production capability petroleum geologists have been pursuing an accurate way of predicting total porosity in shale gas reservoirs from logging curves in the fuling area near chongqing in china we use core test data and well logging data in order to establish a logging response model for porosity through the analysis of the data we found that the porosity and the p sonic p velocity have a strong correlation by combining our results with previous research i e physical rock data we establish a new model which better predicts the total porosity of a given a shale reservoir than the models established in previous research in addition to total porosity mineral composition pore pressure pore fluid type and confining pressure affect p velocity by taking a series of artificial cores as test objects and systematic analysis of total porosity mineral composition and content pore fluid type and pressure on the p velocity we establish response templates between every individual parameter and p velocity to this end we further establish a multi parameter rock physical characterization equation for the total porosity and p velocity and analyze its applicable conditions using the rich geological and geophysical data of the lower silurian series in the fuling area we gradually improve the model for the total porosity and verify the results using well logging data finally a set of accurate methods are established to predict the total porosity in shale gas reservoirs by using well logging data

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

pore characterization of organic rich lower cambrian shales in qiannan depression of guizhou province southwestern china abstract nine organic rich shale samples of lower cambrian black shales were collected from a recently drilled well in the qiannan depression guizhou province where they are widely distributed with shallower burial depth than in sichuan basin and their geochemistry and pore characterization were investigated the results show that the lower cambrian shales in qiannan depression are organic rich with toc content ranging from 2 81 to 12 9 thermally overmature with equivalent vitrinite reflectance values in the range of 2 92 3 25 and clay contents are high and range from 32 4 to 53 2 the samples have a total helium porosity ranging from 2 46 to 4 13 and total surface area in the range of 9 08 37 19 m2 g the estimated porosity in organic matters defined as the ratio of organic pores to the volume of total organic matters based on the plot of toc vs helium porosity is about 10 for the lower cambrian shales in qiannan depression and is far lower than that of the lower silurian shales 36 in and around sichan basin this indicates that either the organic pores in the lower cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the lower silurian shales our studies also reveal that the micropore volumes determined by dubinin radushkevich dr equation is usually overestimated and this overestimation is closely related to the non micropore surface area of shales i e the surface area of meso and macro pores however the modified bet equation can remove this overestimation and be conveniently used to evaluate the micropore volumes surface area and the non micropore surface areas of micropore rich shales

accurate and precise quantification of major and trace element compositions of calcic sodic fluid inclusions by combined microthermometry and la icpms analysis abstract determination of absolute trace element concentrations in fluid inclusions using laser ablation la icpms requires an internal standard i e the concentration of one element must be independently known from independent observation microthermometric determination of the last melting temperature of ice hydrohalite or halite is routinely used to calculate apparent salinities in wt nacl equivalent using phase relations in the binary h 2 o nacl system to estimate na concentration calculating the concentrations of all other elements requires an empirical correction if additional salt concentrations are of similar magnitude as that of nacl if cacl 2 is the main additional salt component as in many low temperature basin and basement brines absolute na concentrations wt nacl abs can be obtained by observing two melting temperatures hydrohalite and either ice or halite uniquely defining the major element composition of the fluid in the ternary model system h 2 o nacl cacl 2 and allowing na to be used as internal standard for quantifying all minor and trace elements test results for a range of compositions show that calcium concentration can be determined more precisely by microthermometry than by la icpms analysis but that both methods agree within error the combined approach of microthermometry and la icpms analysis described here permits reliable quantification of major ca na as well as trace element concentrations in sodic calcic brine inclusions even in ca rich host minerals such as fluorite or ca bearing carbonates

microstructure of graptolite periderm in silurian gas shales of northern poland abstract core samples of silurian graptolite shales from an exploration borehole within the baltic basin were examined by optical microscopy raman spectroscopy and high resolution transmission electron microscopy graptolite periderm is composed of poorly ordered carbonaceous material of mainly aromatic structures the dimension of the coherent domains is 1 2 nm they are composed of two to three stacked layers raman spectral parameters of graptolite periderm are correlated with the mean random rr and mean maximum rmax reflectance of graptolites the spectral id1 ig ratio predicts thermal maturity in a mean reflectance of graptolites rr range between 1 30 and 1 80 rmax 1 40 2 00 vitrinite reflectance equivalent vre 1 10 1 50 it is possible to calculate vreraman from the id1 ig ratio

modelling d structure beneath central america with broadband seismic data deep south american events recorded at distances between 70 and 96 are used to constrain the lower mantle structure beneath central america employing data from the terrascope bdsn iris and cnsn canadian national seismic network broadband arrays we obtain a 1 d shear model with a 200 km thick d layer with a 3 velocity jump at the top and a negative gradient within the layer from broadband waveform modelling of sh polarized s scs and scd the shear structure above d is similar to the preliminary reference earth model prem dziewonski and anderson 1981 preliminary reference earth model physics of earth planetary interiors 25 297 356 in terms of dt d and s sks differential times sv synthetics for this model assuming a prem core produce a satisfactory fit to the data except at the larger ranges to the north where the waveforms display rapid variation this feature is indicative of lateral variation of the type suggested by grand 1994 where the discontinuity becomes less well defined synthetics computed for a simplified 2 d cross section through this structure produce the scd phase and simple s at larger distances while scd is easily observed in the shear wave data there is little evidence of its counterpart in the p data by testing several models with different p velocity jumps at the same depth as the d jump in shear structure we conclude that the velocity jump must be less than 1 in fact prem provides an excellent fit both in timing and waveform shapes and therefore we conclude that lower mantle structure beneath central america shows clear evidence for a discontinuity in s velocity but not in p

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale