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

the effects of depositional environment on vitrinite fluorescence intensity abstract the effects of depositional environment on vitrinite secondary fluorescence properties were investigated using a quantitative fluorescence microscopical technique fluorescence intensities relative to a uranyl glass standard were obtained on vitrinites formed under varying degrees of marine influence interpretations of the coals depositional environment used in this study were based on paleoenvironmental studies of the overlying strata some possible paleoenvironmental mechanisms responsible for diversity within this petrographic property are discussed

biological marker distribution in coexisting kerogen bitumen and asphaltenes in monterey formation diatomite california organic rich 18 2 monterey formation diatomite from california was studied the organic matter consist of 94 bitumen and 6 kerogen biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter while 17 alpha h 18 alpha h 21 alpha h 28 30 bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes it was not detected in the pyrolysates of the kerogen a c40 isoprenoid with head to head linkage however was present in pyrolysates of both kerogen and asphaltenes but not in the bitumen from the diatomite the maturation level of the bitumen based on the extent of isomerization of steranes and hopanes was that of a mature oil whereas the pyrolysate from the kerogen showed a considerably lower maturation level these relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock we consider the possibility however that some of the 28 30 bisnorhopane rich monterey formation oils have not been generated through thermal degradation of kerogen but have been expelled from the source rock at an early stage of diagenesis

geochemical attributes pore structures and fractal characteristics of barakar shale deposits of mand raigarh basin india abstract pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance twenty organic rich shale samples at different depths were collected from barakar formation of mand raigarh basin to examine the pore structure and their fractal characteristic fractal dimension was calculated by following fhh theory to investigate the complexity of pore surfaces storage mechanism and the pore network system the complex pore system influenced by thermal cracking of organic matter pore dissolution during geochemical weathering and tectonics of the basins having surface area 5 56 23 94 m2 g avg 14 21 m2 g whereas the pore volume determined using the bjh model varying from 0 035 to 0 076 cc g avg 0 053 cc g ftir spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume it is summarized that pores and matrix of shale are built by complex mixtures of organic and inorganic content further the pores are categorized into organic pores evolved during thermal cracking inter granular intra granular and inter crystalline due to the large content of altered clays and minerals showing fissile nature the sem edx derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment the d1 and d2 values obtained through fhh model range from 1 17 to 2 45 and 2 54 2 70 the fractal values particularly d2 are 3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous this study helps to enhance the exploration and advancement in the shale gas resources from ib river of mand raigarh basin india

paleoproterozoic late orogenic and anorogenic alkaline granitic magmatism from northeast brazil abstract during the transamazonian cycle 2 0 0 2 ga two silica saturated alkaline granite suites were intruded along the border of the sao francisco craton northeastern brazil the couro de onca intrusive suite cois is late tectonic relative to major deformational events and the serra do meio suite sms postdates this event being interpreted as anorogenic type deformed during the brasiliano cycle 0 65 0 52 ga the cois encompasses alkali feldspar granites syenogranites monzogranites with dykes of similar composition and age 2 157 5 ma they are metaluminous rocks of alkaline affinity whose evolution was probably controlled by mineral fractionation processes involving mainly plagioclase amphibole and fe ti oxide the sms whose probable age is 2 01 ga is composed of metaluminous and peralkaline granites with associated quartz syenites with ti aegirine transformed during the brasiliano deformation to riebeckite titanite aenigmatite the temperatures of two stages of metamorphic transformation overprinted during the brasiliano event are estimated at about 550 and 400 450 c both magmatic suites are derived from enriched mantle sources the metaluminous and peralkaline trends observed in the sms characterized by high concentrations of hfs and re elements controlled mainly by f activity reflect the evolution of different primary magmas produced by successive melting of the same mantle sources in an anorogenic setting

the barnett shale compositional fractionation associated with intraformational petroleum migration retention and expulsion abstract the marathon 1 mesquite well was drilled in hamilton county texas targeting the barnett shale with late oil window maturity combining a large suite of petrologic and high resolution organic geochemical analyses on 120 core samples we have been able to document qualitatively and quantitatively the effects of petroleum retention within and expulsion from five intervals within the barnett shale lithological heterogeneities control the composition and amount of retained fluids the sorption of oil by solid organic matter is important in all intervals applying empirical formulas we have been able to demonstrate not only that retention is primarily controlled by total organic carbon toc but also that the live or labile component rather than dead or inert carbon constitutes the most active sorptive sites additional retention in the micropores provided by biogenic microcrystalline quartz sponge spicules accounts for the sweet spot defined by an oil crossover in the 9 14 m 30 ft thick second interval the fluorescing oil occurring in the axial chamber of the sponge spicules and that sorbed on organic particles are together enriched in saturated hydrocarbons whereas the dispersed oil from the adjacent interval 3 is depleted in this compound class mass balance calculations reveal that short distance migration of petroleum into this reservoir interval second fractionates the generated oil into a higher quality oil by preferential retention in the order polar compounds aromatic hydrocarbons saturated hydrocarbons within the underlying organic matter and clay rich third interval source unit furthermore molecular fractionation i e a preferential expulsion of lower molecular weight hydrocarbons n alkanes could be calculated an additional practical result for source rock assessment is that corrected s2 petroleum generated by pyrolysis and toc values should be calculated by combining rock eval pyrolysis data on whole rocks and rocks following soxhlet extraction using parameters based on unextracted rock only the expulsion of petroleum is systematically overestimated and the degree of kerogen conversion is therefore concomitantly underestimated

mechanical and chemical compaction in fine grained shallow water limestones abstract artificial compaction of in situ cores of modern sediments from differing sedimentary environments resulted in 1 reduction of sediment thickness by 50 percent and more 2 reduction of initial porosities of 65 to 75 percent to 35 to 45 percent 3 creation of megascopic textures almost identical to many ancient lime mud and wackestones 4 creation of organic wispy stylolite like layers that in nature probably would initiate dissolution and stylolite development given burial and time 5 chemical compaction evidenced by thin sections showing quartz grains piercing mollusc shells without causing fractures and sem evidence of solutional interfitting of 1 to 4 m size aragonitic carbonate grains 6 obliteration of pellets and birdseye or fenestral voids in those sediments here early cementation was lacking pellets were preserved in slightly cemented bahama bank muds compacted to half the original thickness 7 obliteration of identifiable marine grasses and vertical root tube voids 8 mashing of sediment filled circular burrows to produce ellipsoidal structures significant mechanical compaction resulted from pressures simulating less than 1 000 ft 305 m of burial increasing loads to an equivalent of more than 10 000 ft 3 400 m did not significantly increase compaction or reduce sediment core length chemical compaction pressure dissolution was detected only in sediment cores compacted to pressures greater than 10 000 ft 3 400 m of burial these short term experiments suggest that chemical compaction would begin at much shallower depths given geologic time compaction experiments that caused chemical compaction lend support to the well established hypothesis that cement required to produce a low porosity low permeability fine grained limestone is derived internally dissolution ion diffusion and reprecipitation are considered the m st likely processes for creating significant thicknesses of dense limestones in the geologic record continuation of chemical compaction after significant porosity reduction necessitates expulsion of connate fluids possibly including hydrocarbons

aluminous granulites from the pulur complex ne turkey a case of partial melting efficient melt extraction and crystallisation abstract in the pulur complex ne turkey a heterogeneous rock sequence ranging from quartz rich mesocratic gneisses to silica and alkali deficient fe mg and al rich melanocratic rocks is characterized by granulite facies assemblages involving garnet cordierite sillimanite ilmenite spinel plagioclase quartz biotite corundum rutile and monazite textural evidence for partial melting in the aluminous granulites particularly leucosomes is largely absent or strongly obliterated by a late stage hydrothermal overprint however inclusion relations high peak p t conditions the refractory modes bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting the melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica rich bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with sio2 peak conditions are estimated to be 800 c and 0 7 0 8 gpa subsequent near isothermal decompression to 0 4 0 5 gpa at 800 730 c is suggested by the formation of cordierite coronas and cordierite spinel symplectites around garnet and in the matrix sm nd rb sr and 40ar 39ar isotope data indicate peak conditions at 330 ma and cooling below 300 c at 310 ma

an investigation of the in reservoir conversion of oil to gas compositional and kinetic findings from closed system programmed temperature pyrolysis abstract the thermal alteration of reservoired petroleum upon burial was simulated by closed system non isothermal pyrolysis samples of a medium gravity oil from the norwegian north sea central graben were pyrolysed in microscale sealed glass or quartz vessels at heating rates of 0 1 0 7 and 5 0 k min 1 up to temperatures varying from 300 to 650 c the composition of the oil and gas in each vessel was determined by a single step on line gas chromatographic analysis with increasing rate of heating the onset of all oil degradation reactions was shifted to higher temperatures the same successive compositional changes occurred in each case increase in the total yield of gc detectable compounds significant gas c1 c4 generation accompanied by a decrease in yield of heavy components aromatisation and attainment of maximum gas yield and finally a cracking of the c2 gas components the stable final mixture consisted of methane aromatic hydrocarbons pyrobitumen and possibly hydrogen kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal mol assigning 35 of the total gas potential 460 mg per g of oil to an energy of 66 kcal mol and 29 to 67 kcal mol pre exponential factor 1 1 1016 s 1 by extrapolation to natural maturation conditions the onset of gas generation is predicted to occur between 160 and 190 c for geological heating rates between 0 53 and 5 3 k ma 1 predictions from the model are in accordance with the observed preservation of liquid hydrocarbons in a deep hot 165 c petroleum reservoir from the saga 2 4 14 well norwegian continental shelf

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

the role of minerals in the thermal alteration of organic matter iii generation of bitumen in laboratory experiments abstract a series of pyrolysis experiments utilizing two different immature kerogens from the monterey and green river formations mixed with common sedimentary minerals calcite illite or namontmorillonite was conducted to study the impact of the mineral matrix on the bitumen that was generated calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate in contrast montmorillonite and illite to a lesser extent alter bitumen during dry pyrolysis montmorillonite and illite also display strong adsorption capacities for the polar constituents of bitumen by this process hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices the effects of the clay minerals are significantly reduced during hydrous pyrolysis the strong adsorption capacities of montmorillonite and illite as well as their thermocatalytic properties may in part explain why light oils and gases are generated from certain argillaceous source rock assemblages whereas heavy immature oils are often derived from carbonate source rocks

oil retention and porosity evolution in organic rich shales petroleum is retained in shales either in a sorbed state or in a free form within pores and fractures in shales with oil resource potential organic matter properties i e richness quality and thermal maturity control oil retention in general in gas shales organic pores govern gas occurrence although some pores may originate via secondary cracking reactions it is still largely unclear as to how these pores originate here we present case histories mainly for two classic shales the mississippian barnett shale texas and the toarcian posidonia shale lower saxony germany in both cases shale intervals enriched in free oil or bitumen are not necessarily associated with the layers richest in organic matter but are instead associated with porous biogenic matrices however for the vast bulk of the shale hydrocarbon retention and porosity evolution are strongly related to changes in kerogen density brought about by swelling and shrinkage as a function of thermal maturation secondary organic pores can form only after the maximum kerogen retention swelling ability is exceeded at tmax the temperature at maximum rate of petroleum generation by rock eval pyrolysis around 445 c 833 f approximately 0 8 vitrinite reflectance shrinkage of kerogen itself leads to the formation of organic nanopores and associated porosity increase in the gas window

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

mineral equilibrium modelling and calculated chemical potential relations of reaction textures in the ultrahigh temperature in ouzzal terrane in hihaou area western hoggar algeria

facies development and porosity relationships in the dundee limestone of gladwin county michigan the devonian of the michigan basin was a time of transgressive seas and extensive carbonate deposition including coral and stromatoporoid buildups deposited during the middle devonian the dundee limestone represents deposition in subtidal intertidal and restricted environments the buckeye oil field located in south central gladwin county is a combined stratigraphic and structural carbonate trap that produces from a series of intertonguing patch reefs fringing sand bodies and intertidal island fenestral zones the major reef building organisms include stromatoporoids corals calcareous algae brachiopods and crinoids with the stromatoporoids providing the major framework the patch reef facies is composed of massive stromatoporoid boundstones that contain primary intraparticle porosity the fringing grainstone sands are composed of coarse crinoid and brachiopod skeletal debris that have interparticle porosity the intertidal island zone found in the north buckeye field is represented by a pelletal packstone that has abundant fenestral porosity

petrogenesis of a type granitoids from the alto moxoto and alto pajeu terranes of the borborema province ne brazil constraints from geochemistry and isotopic composition abstract a type granitoids 512 ma either intruded into paleoproterozoic gneiss of the alto moxoto terrane prata complex and serra da engabelada pluton or into early neoproterozoic metavolcanic metasedimentary sequence of the alto pajeu terrane serrote santo antonio pluton constitute a small proportion of brasiliano pan african granitoids in the central tectonic domain of the borborema province northeastern brazil the prata complex consists of syenogranites monzogranites mafic enclaves of diorites and norites the felsic and mafic members are not genetically related through fractionation mingling and mixing were extensive processes within the prata complex the granites evolution appears to have involved fractionation of alkali feldspar biotite apatite and sphene without significant wall rock assimilation the serra da engabelada and serrote santo antonio plutons consist of biotite syenogranites with rare mafic enclaves the studied granitoids are dominantly metaluminous characterized by fe rich biotite and fe hornblende high total alkalis y nb and ree and low cao mgo and sr abundances and high feo feo mgo ratios characterize these granitoids chondrite normalized ree patterns show enriched lree moderate to strong negative eu anomalies and more or less flat heavy ree the studied granitoids and diabase from dykes and enclaves show negative end 512ma values 14 to 10 high incompatible elements such as lile hfse and ree suggesting important contribution of paleoproterozoic crust the origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust such isotopic signature of the diabase from the dykes also reflects a paleoproterozoic enriched lithospheric mantle in the area the intrusion of the studied granitoids contemporary with sub volcanic bimodal magmatism and deposition of many cambrian pull apart basins in the north and central tectonic domain of the borborema province suggest intrusion during post tectonic relaxation of the brasiliano orogeny following the assembly of west gondwana

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

differential evolution and the influencing factors of low maturity terrestrial shale with different types of kerogen a case study of a jurassic shale from the northern margin of qaidam basin china abstract the jurassic terrestrial shale on the northern margin of qaidam basin is characterized by high contents of organic matter but low maturity resulting in a lack of further research on shale gas in this area to better understanding the shale gas potential of organic matter with different types we conducted thermal maturity experiment of hydrocarbon generation from different kerogen types of low mature shales under closed conditions the results show that type ii and type iii kerogen have experienced similar hydrocarbon generation stages but they differ in the hydrocarbon generation interval and evolution process between liquid hydrocarbon and gaseous hydrocarbon compared with type iii kerogen type ii kerogen is characterized by a low initial temperature at each evolutionary stage and wide temperature range which caused the overall evolution of type iii kerogen lagged behind that of type ii kerogen the differential evolutions mainly result from the differences in hydrocarbon generation mechanism hydrocarbon generation activation energy and kerogen macerals among different kerogen types we summarized the evolution model of type ii and type iii kerogen based on the characteristics of kerogen in hydrocarbon generation carbon isotope change pore development and other aspects this work can provide theoretical and data support for reconstructing the hydrocarbon generation process of terrestrial shale gas investigating the hydrocarbon generation mechanism and predicting the hydrocarbon resources of terrestrial shale oil and gas on the northern margin of qaidam basin and even china

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

organic geochemistry of the 9 6 km bertha rogers no 1 well oklahoma abstract organic geochemical analyses of fine grained rocks from the 9 590 km bertha rogers no 1 well have been carried out total organic carbon soxhlet extraction and silica gel chromatography c15 saturated and aromatic hydrocarbon gas chromatography and mass spectrometry pyrolysis kerogen analysis x ray diffraction and visual kerogen analysis rocks ranged in age from permian to ordovician the well has an estimated bottom hole temperature of 225 c some data from this study are inconsistent with conventional theories concerning the generation and thermal destruction of hydrocarbons for example appreciable amounts of c15 gas condensate like hydrocarbons are present in very old rocks currently at temperatures where current theory predicts that only methane and graphite should remain also substantial amounts of pyrolyzable c15 hydrocarbons remain on the kerogen in these deeply buried paleozoic rocks this suggests at least in somes cases that temperatures much higher than those predicted by current theory are required for generation and thermal destruction of hydrocarbons the data from this well also suggest that original composition of organic matter and environment of deposition may have a much stronger influence on the organic geochemical characteristics of fine grained sediments than has previously been ascribed to them the results from this well from other deep hot wells in which temperatures exceed 200 c and from laboratory experiments suggest that some of the basic concepts of the generation and maturation of petroleum hydrocarbons may be in error and perhaps should be reexamined

the role of minerals in the thermal alteration of organic matter iv generation of n alkanes acyclic isoprenoids and alkenes in laboratory experiments a series of pyrolysis experiments utilizing two different immature oil prone kerogens type i green river formation kerogen type ii monterey formation kerogen mixed with common sedimentary minerals calcite illite or na montmorillonite was conducted to study the effects of minerals on the generation of n alkanes acyclic isoprenoids and alkenes during laboratory simulated catagenesis of kerogen the influence of clay minerals on the aliphatic hydrocarbons is critically dependent on the water concentration during laboratory thermal maturation under extremely low contents of water i e dry pyrolysis where only pyrolysate water is present c12 range n alkanes and acyclic isoprenoids are mostly destroyed by montmorillonite but undergo only minor alteration with illite both clay minerals significantly reduce alkene formation during dry pyrolysis under hydrous conditions mineralwater 2 1 the effects of the clay minerals are substantially reduced in addition the dry pyrolysis experiments show that illite and montmorillonite preferentially retain large amounts of the polar constituents of bitumen but not n alkanes or acyclic isoprenoids therefore bitumen fractionation according to polarity differences occurs in the presence of these clay minerals by this process n alkanes and acyclic isoprenoids are concentrated in the bitumen fraction that is not strongly adsorbed on the clay matrices the extent of these concentration effects is greatly diminished during hydrous pyrolysis in contrast calcite has no significant influence on the thermal evolution of the hydrocarbons in addition calcite is incapable of retaining bitumen therefore the fractionation of n alkanes or acyclic isoprenoids relative to the polar constituents of bitumen is insignificant in the presence of calcite

compositional variability of terrestrial mantle apatites thermodynamic modeling of apatite volatile contents and the halogen and water budgets of planetary mantles abstract apatites in ultramafic xenoliths from hawaii kamchatka nunivak island lunar crater volcanic field and the navajo volcanic field have variable volatile f cl oh compositions that correlate with their petrogenesis apatites in metasomatized lherzolite harzburgite xenoliths are relatively cl rich whereas apatites in igneous pyroxenite and amphibolite xenoliths are relatively f rich our results support the generalization of o reilly and griffin 2000 that metasomatic apatites tend to be cl rich and magmatic apatites tend to be f rich mantle metasomatism may largely be the consequence of devolatilization of cl rich fluids from subducted lithosphere however the occurrence of metasomatic xenoliths far removed from subduction zones e g bullenmerri as well as the geochemistry of cl in some plume basalts and diamonds indicates that not all metasomatism is subduction triggered thermodynamic modeling of the influence on apatite compositions of variable f cl h2o and p abundances as well as temperature is consistent with the idea that terrestrial mantle fluids are h2o rich and that halogen enrichment in terrestrial apatites need not represent large absolute halogen abundances in the fluids the models indicate that the occurrence of volatile poor calcium phosphate merrillite whitlockite in the martian and terrestrial mantles is facilitated by halogen and phosphorus rich and water poor environments the rarity of this assemblage in the terrestrial mantle compared to mars is consistent with the relatively wet and halogen and phosphorus poor nature of the terrestrial mantle compared to that of mars

interaction of coal and oil in confined pyrolysis experiments insight from the yields and carbon isotopes of gas and liquid hydrocarbons abstract isothermal confined gold capsule pyrolysis experiments were performed for coal alone oil alone and coal plus oil with oil coal ratios ranging from 0 006 to 0 171 at 315 c 345 c and 375 c respectively and 50 mpa for 72 h in the experiment for coal plus oil the amounts and compositions of hydrocarbon gases are substantially different from those predicted from the results in the experiments for oil alone and coal alone the results of these experiments demonstrate that kerogen and oil do not crack separately in the experiments of coal plus oil the interaction between kerogen and oil components leads to the generation of hydrocarbon gases with oil coal ratio increasing the amounts of individual and total hydrocarbon gases decrease at first and then increase rapidly up to several times those calculated from the yields of these components in the experiments for oil alone and coal alone the c1 c1 5 ratios of hydrocarbon gases decrease and are increasingly lower than those calculated from the yields of hydrocarbon gases in the experiments for oil alone and coal alone the amount and carbon isotopes of individual n alkane demonstrate that the free liquid n alkanes were incorporated into kerogen and replaced the bound liquid n alkanes covalently bonded alkyl groups in kerogen carbon isotopes of hydrocarbon gases further suggest that the bound liquid n alkanes in kerogen preferentially crack into hydrocarbon gases

reversed experiments on biotite quartz feldspar melting in the system kmash implications for crustal anatexis melting temperatures of biotite quartz and biotite quartz feldspar assemblages in the system k 2 o mgo al 2 o 3 sio 2 h 2 o have been determined in the pressure range 0 5 18 kbar the subsolidus dehydration of biotite quartz also has been investigated from 300 to 500 bars the melting equilibria studied are phlogopite quartz sanidine vapor liquid o phlogopite quartz vapor enstatite liquid k phlogopite quartz enstatite liquid k v and phlogopite quartz sanidine enstatite liquid v at 10 kbar the o reaction occurs at 700 720 c the k reaction at 780 790 c the k v reaction at 815 850 c and the v reaction at 800 850 c vapor saturated reactions were reversed isobarically in two stage experiments in which the starting assemblage was held at a temperature 10 above the temperature of previously observed melting for a duration equivalent to an initial melting experiment followed by lowering of the temperature below the temperature of initial mel

anorogenic alkaline granites from northeastern brazil major trace and rare earth elements in magmatic and metamorphic biotite and na mafic minerals abstract the anorogenic alkaline silica oversaturated serra do meio suite is located within the riacho do pontal fold belt northeast brazil this suite assumed to be paleoproterozoic in age encompasses metaluminous and peralkaline granites which have been deformed during the neoproterozoic collisional event preserved late magmatic to subsolidus amphiboles belong to the riebeckite arfvedsonite and riebeckite winchite solid solutions riebeckite winchite is frequently rimmed by ti aegirine ti aegirine cores are strongly enriched in nb y hf and ree which significantly decrease in concentrations towards the rims ree patterns of ti aegirine are strikingly similar to ti pyroxenes from the ilimaussaq peralkaline intrusion recrystallisation of mineral assemblages was associated with deformation although some original grains are still preserved magmatic annite was converted into magnetite and biotite with lower fe fe mg ratios recrystallised amphibole is pure riebeckite magmatic ti na bearing pyroxene was converted to low ti aegirine titanite astrophyllite aenigmatite the reaction riebeckite quartz aegirine magnetite quartz fluid is also observed biotite and na mafic minerals recrystallised under metamorphic oxidising conditions corresponding to temperatures of 600 c between the ninio and hm buffers

in situ high temperature esr measurements for kerogen maturation abstract kerogen samples from middle miocene mudstone cores in two japanese exploratory wells have been investigated by an in situ high temperature esr technique anhydrous pyrolysis of the kerogens results in four distinctstemperature stages in spin concentration ns ns increasessin the first and third at end of catagenesis is characterized only by two stages third and fourth these data are based on the formation and recombination of free radicals and have been used to derive parameters related to kerogen maturation and hydrocarbon generation

dehydration melting phenomena in leptynitic gneisses and the generation of leucogranites a case study from the kerala khondalite belt southern india

geology of the devonian dundee reservoir west branch field michigan 1 west branch field located near the center of the michigan basin is a low relief asymmetric northwest southeast trending anticline since 1934 the dundee reservoir middle devonian dundee and rogers city limestones has produced more than 12 million bbl 2 million m 3 of oil from this field dundee sediments were deposited on a carbonate ramp that dipped gently to the northwest core studies and log correlations show that the reservoir is dominated by normal marine somewhat lenticular beds of skeletal peloidal grainstones and packstones crinoids are very abundant comprising nearly 100 of the grains in some intervals the uppermost dundee consists of micritic carbonates with a restricted faunal assemblage the dundee rogers city contact is a disconformity that ppears to be a pyritized extensively bioeroded hardground the overlying rogers city limestone is a dark nodular wackestone with rare packstone interbeds trace amounts of dolomite are common throughout the field however pervasive dolomite is common only in the top 10 15 ft 3 4 5 m of the dundee this dolomite generally has high porosity 5 15 but very low permeability 0 1 0 md primary interparticle porosity in limestones accounts for most of the reservoir porosity although previous workers have concluded that fracture controlled dolomites are responsible for porosity and permeability in this field we conclude that such dolomites are not important we also conclude that at west branch field there is no evidence for reefal growth over a pre existing fold as has been reported in other dundee rogers city reservoirs

fluid absent melting of f rich phlogopite rutile quartz fluid absent melting is believed to be an important process in the generation of melts m the lower crust and upper mantle breakdown of phlogopite makes h 0 available and thus controls the conditions at which fluid absent melting occurs both f2andti in biotite ha e been shown to affect strongly the thermal stability of biotite to model better the fluid absenti eltmg of a ssemblagescontaining phlogopite the reaction f phlogopite quartz rutile enstatite melt has been studied experimentally experiments were pe o med at 7 10 and 15 kbar using a natural f rich phlogopite with a starting com os tion off f oh 0 43 and mg mg fe in molar proportions 0 94 results mdlcate that the therma l stability of f rich phlogopite quartz rutile is extended by as much as 450 c relative to the kmash system and by 300 c relative to the ti free f kmash system approach to equilibrium in the experiments was assessed by convergence of results of melting and crystallization experiments phlogopite compositions from e penmental products show that although f rich phlogopite incorporates relatively little ti 3 wt i02 the combination of f and ti increases the stability of phlogopite to considerably higher temperatures 300 0c than that of either component alone melts formed by the fluid absent melting off rich phlogopite quartz rutile at temperatures 1000 care anitic and stro g1yperaluminous the compositions of these melts suggest that the formationofmetalummous to peralkaline a type granites by fluid absent melting of halogen enriched sources is unlikely

archaean ttgs as sources of younger granitic magmas melting of sodic metatonalites at 0 6 1 2 gpa two natural low k2o na2o ttg tonalitic gneisses one hornblende bearing and the other biotite bearing were partially melted at 0 8 1 2 gpa fluid absent the chief melting reactions involve the breakdown of the biotite and hornblende the hornblende tonalite is slightly less fertile than the biotite tonalite but melt volumes reach around 30 at 1 000 c this contrasts with results of most previous work on more potassic ttgs which generally showed much lower fertility though commonly producing more potassic melts garnet is formed in biotite bearing tonalitic protoliths at p 0 8 gpa and at 1 0 gpa in hornblende bearing tonalitic protoliths all fluid absent experiments produced peraluminous granitic to granodioritic melts typically with sio2 70 wt for the biotite tonalite increasing t formed progressively more melt with progressively lower k2o na2o however the compositions of melts from the hornblende tonalite do not vary significantly with t with increasing p melts from the biotite tonalite become less potassic due to the increasing thermal stability of biotite for the hornblende tonalite again there is no consistent trend fluid absent melting of sodic ttgs produces melts with insufficient k2o to model the magmas that formed the voluminous late potassic granites that are common in archaean terranes reconnaissance fluid present experiments at 0 6 gpa imply that h2o saturated partial melting of ttgs is also not a viable process for producing magmas that formed these granites the protoliths for these must have been more potassic and less silicic nevertheless at granulite facies conditions sodic ttgs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths upward abstraction of this melt would result in some lile depletion of the terrane younger k rich magmatism is unlikely to represent recycling of ttg crust on its own and it seems most likely that evolved crustal rocks and or highly enriched mantle must be involved

fluorine end member micas and amphiboles the near end member minerals fluorphlogopite xf 0 96 and fluortremolite xf 0 82 have been found in grenville marbles near balmat new york these micas and amphiboles like other fluorine rich minerals reported in the literature are extremely low in iron the substitution of f for oh is partly responsible for stabilizing these minerals in the granulite facies marbles of the adirondacks fluorine rich amphiboles and micas are more common than generally recognized a literature review shows that many amphiboles and micas have more than fifty percent of the interlayer site occupied by fluorine this degree of solid solution qualifies these phases as independent minerals but they are not currently recognized by the i m a we propose that fluorbiotite fluorphlogopite fluoractinolite fluorarfvedsonite fluoredenite fluorhastingsite fluorpargasite fluorrichterite fluorriebeckite fluortremolite fluoredenitic hornblende fluorhastingsitic hornblende fluorpargasitic hornblende fluortremolitic hornblende fluorferro edenite and fluormagnesio arfvedsonite be formally applied as mineral names for these phases identification of the mineralogically and petrologically important solid solution of fluorine for hydroxyl is currently obscured by use of names that imply hydroxyl end members

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

modeling hydrocarbon generation from the paleogene source rocks in liaodong bay bohai sea a study on gas potential of oil prone source rocks abstract the exploration history of bohai sea reveals that liaodong bay is relatively rich in natural gas which is mainly gas condensate however the source rocks in liaodong bay share a medium maturity level with values of ro being generally three immature paleogene source rocks were selected to complete gold tube pyrolysis experiments the experiment results reveal that the secondary gas from oil cracking can be neglected until the cumulative yields of c6 c14 compounds reach the maximum corresponding to ro 1 3 above ro 1 3 oil starts to crack to wet gases substantially based on comparative analysis of pyrolysis results and source rock geochemical parameters we constructed a hydrocarbon generation model especially for hydrocarbon gas and validated the calculated ro values for pyrolysis conditions the c1 c5 yields for source rocks at 1 3 ro in gold tube pyrolysis approximate the maximum gas yield for source rock in open system pyrolysis indicating the majority of primary gas from kerogen cracking has been generated at 1 3 ro with its yields being 156 ml g toc 100 ml g toc and 117 ml g toc for ed3 es1 and es3 source rocks respectively this suggests that source rocks with ro

epr study of kerogens from three alaskan north slope wells abstract whole rock and isolated kerogens from the seabee inigok and ikpikpuk wells of the alaskan north slope have been analyzed by electron paramagnetic resonance epr spectroscopy the sample suite includes representatives of the torok kingak lisburne sadlerochit and endicott formations power saturation studies show a definite correlation with the downhole maturation the extent of aromaticity of the sample as defined by 13 c nmr and with the beginning of the oil window for the kingak formation strong correlations within formations across the depositional basin are seen abrupt changes in epr parameters indicate a change in the nature of the organic matter present and may reflect a facies change peak widths and spin densities correlate with maturity as indicated by vitrinite reflectance and sample aromaticity as measured in solid state 13 c nmr spectra

f rich phlogopite stability in ultra high temperature metapelites from the napier complex east antarctica fluorine rich phlogopite f content up to 8 wt f f oh 0 9 in ultra high temperature metapelitic granulites from the napier complex east antarctica is associated with aluminous orthopyroxene osumilite sapphirine garnet and quartz textural relationships imply that some of the phlogopite is of primary origin and stable under ultra high temperature conditions this is in accord with recent experimental evidence on the stability of f rich phlogopite because the f rich phlogopite also occurs as rounded inclusions in aluminous orthopyroxene al 2 o 3 up to 12 8 wt sapphirine osumilite and garnet it is inferred that the ultra high temperature mineral assemblages which includes these minerals formed during prograde partial melting reactions at the expense of phlogopite at a depth of less than 30 km thus the coarse grained peak metamorphic assemblages formed below 9 kbar and there is no evidence the rocks underwent any significant degree of decompression during or soon after peak metamorphic conditions the phlogopite breakdown reactions we suggest on the basis of textural arguments differ from those postulated from experiments on f free systems

burial diagenesis and specific catalytic activity of illite smectite clays from vienna basin austria a sequence of tertiary shales from the vienna basin austria contains a series of illite smectite i s clays that are the source of catalytic activity as measured by the method developed by goldstein in 1983 the source of this activity is bronsted acidity resulting from the dissociation of water molecules bonded to exchangeable cations in the interlayers of the smectite and on the external basal surfaces of illite platelets this specific catalytic activity sca is exchangeable cation dependent and correlates directly with increasing interlayer charge and tetrahedral substitution accompanying the diagenetic formation of thin interlayer illite particles with high charge external surfaces as a result diagenetic transformation of smectite to illite in this series resul s in increased catalytic activity from consideration of cation exchange capacity and interlayer charge of end member components of this i s series we show that a cation site resulting from tetrahedral substitution of al3 for si4 has an activity about 40 times greater than a site of octahedral origin the end member illite particles of this i s series have calculated mean thicknesses of about 80a eight 2 1 mica layers the linear relationship between sca values and estimated platelet thickness for three different micas and illites confirms the role of cation sites on external basal surfaces as sources of catalytic activity the possibility of direct involvement of catalytically active diagenetic illite in natural kerogen pyrolysis acting simultaneously with a fluid release mechanism and its geopressure development may provide optimum conditions for hydrocarbon generation and migration during i s diagenesis the presence of high surface area illite in diagenetically altered reservoir sandstones suggests the possibility for modifying the hydrocarbon constitution of crude oils within buried reservoirs the effects of exchange cation composition on catalytic properties of i s clays show that formation water chemistry must be considered in evaluating the effectiveness of clay catalysts in hydrocarbon forming reactions

natural gas composition in a geological environment and the implications for the processes of generation and preservation gases recovered from their location of formation for example gas recovered from drill cuttings are enriched in c2 components relative to gases recovered from reservoir production or testing streams because reservoir gases have been derived through a series of processes including generation from a source with a specific chemical character primary and secondary migration accumulation and selective preservation the compound distribution within these reservoir gases is less likely to be representative of the generation process than in situ gases such as cuttings gas thus rather than comparing compound distributions within reservoir or pipeline gas data to test whether laboratory catalysis experiments for the generation of gas are consistent with geological systems it is better to compare laboratory results of the distribution of gas compounds with gas data for which the opportunity for a wide range of different processes can be precluded the mismatch between compound distributions within cuttings gas recovered from fine grained rocks and those recovered from laboratory experiments disproves the hypothesis of gas generation catalysis in geological systems whereas the distribution of compounds within cuttings gas is consistent with simple non catalytic cracking the generation of natural gas in geological systems has been inferred in some publications to be a universally catalytic process on the basis of observations made during laboratory experiments however this extrapolation has been predicated on the premise that the distribution of compounds within natural gas methane in c1 c4 in reservoirs is different from that observed from non catalytic or simple cracking experiments and that reservoir gas precisely represents natural gas composition as it is generated within source rocks the extrapolation of the inferred kinetic stability of low molecular weight hydrocarbons such as propane determined during high temperature 530 c low pressure 600 mm hg water free experiments to geological time scales yields lower reaction rates than those actually observed for geological systems the inferred catalytically mediated kinetics yield reaction rates that are too high these observations coupled with the proof that transition metal catalysis is not operating in geological environments suggest that the overall kinetic controls under geological conditions are different from those in the dry quartz laboratory experiments

esr assessment of kerogen maturation and its relation with petroleum genesis abstract petroleum hydrocarbons are formed by breakdown of kerogen preserved in source rocks throughout the process of catagenesis this process is accompanied by free radical generation in kerogen the availability of measuring free radicals in kerogen using esr to deduce a maturation estimation of potential source rocks has been hindered due to the presence of the solvent extractable organic molecules seom trapped within the kerogen matrix spin concentration ns of the kerogen treated with pyridine k py represents the paramagnetic centers of the kerogen matrix itself and provides a potential parameter to evaluate kerogen maturation

regional scale grenvillian age uht metamorphism in the mollendo camana block basement of the peruvian andes the mollendo camana block mcb is a 50 150 km precambrian inlier of the andean belt that outcrops along the pacific coast of southern peru it consists of stromatic migmatites of paleoproter ozoic heritage intensely metamorphosed during the grenville event c 1 ga u pb and u th pb ages on zircon and monazite in the migmatites aluminous mesosomes fmas and quartzofeldspathic leucosomes kfmash contain various amounts of k feldspar kfs orthopyroxene xmg opx 0 86 plagioclase pl sillimanite sil exceptionally kyanite ky ilmenite ilm magnetite mag quartz qtz and minor amounts of garnet xmg grt 0 60 sapphirine xmg spr 0 87 cordierite xmg crd 0 92 and biotite xmg bt 0 83 the ubiquitous peak mineral assemblage is opx sil kfs qtz grt in most of the mcb which together with the high al content of orthopyroxene 10 al2o3 and the local coexistence of sapphirine quartz attest to regional uht metamorphism 900 c at pressures in excess of 1 0 gpa fluid absent melting of biotite is responsible for the massive production of orthopyroxene that proceeded until exhaustion of biotite and most of the garnet in the southern part of the mcb mollendo cocachacra areas in this area a first stage of decompression from 1 1 1 2 to 0 8 0 9 gpa at temperatures in excess of 950 c is marked by the breakdown of sil opx to spr opx crd assemblages according to several bivariant fmas reactions high t decompression is also shown by mg rich garnet being replaced by crd spr and crd opx bearing symplectites and reacting with quartz to produce low al opx sil symplectites in quartz rich migmatites neither osumilite nor spinel quartz assemblages being formed isobaric cooling at about 0 9 gpa probably followed the initial decompression and proceeded with massive precipitation of melts towards the os invariant point as demonstrated by bt qtz pl symplectites in quartz rich migmatites melt opx sil bt grt kfs qtz finally opx rims around secondary biotite attest to late fluid absent melting compatible with a second stage of decompression below 900 c the two stages of decompression are interpreted as due to rapid tectonic denudation whereas the regional extent of uht metamorphism in the area probably results from large scale penetration of hot asthenospheric mantle at the base of an over thickened crust

titanium substitution in biotite an empirical model with applications to thermometry o2 and h2o barometries and consequences for biotite stability abstract an empirical model for solution of ti in biotite is developed and calibrated on the basis of various equilibria among biotite and ti saturating assemblages sources of data used for the calibration include both experimental products and published analyses of natural assemblages ti solution in biotite can be satisfactorily modelled by means of the exchange component tife 2 whose non ideal behavior can be approximated empirically by means of a linear function of the relative concentrations of ti and octahedral al in biotite within assemblages which fix the chemical potential of the exchange component tife 2 the concentration of this component in biotite is very sensitive to temperature and oxygen fugacity making it possible to use biotite oxide assemblages to obtain reliable t and f o 2 estimates in igneous and metamorphic rocks in assemblages which also contain alkali feldspar it is possible to use breakdown equilibria of ti additive components in biotite to estimate h 2 o fugacity such uses are likely to find important applications in rocks in which other assemblages sensitive to temperature f o 2 and or f h 2 o are absent in general rocks containing a single oxide phase plus biotite as the only mafic silicate phase alkali feldspar the empirical model for solution of ti in biotite also allows to calculate the loci of various terminal reactions for the assemblage titanian biotite quartz which by comparison with equivalent equilibria in ti free systems provide insight into the effect of ti on the stability of biotite solubility of ti in biotite increases with temperature in a strongly non linear fashion as a consequence calculations predict that the effect of ti on the stability of biotite is very small up to conditions typical of the beginning of the granulite facies of metamorphism but beyond those conditions ti concentration increases markedly and biotite is rendered very refractory at mid to deep crustal pressures 10 kbar the vapor absent solidus of biotite quartz in rocks containing ti saturating phases is likely to exceed 900 c even in bulk compositions with subequal concentrations of fe and mg

pressure solution features in a shallow buried limestone abstract three distinct types of pressure solution features are found in the alpena limestone devonian michigan stylolites solution seams and fitted fabric texture the style of pressure solution is different in grainstones packstones and wackestones the difference is interpreted to be the result of preferential cementation of the grainstones well cemented grainstones typically have stylolites whereas solution seams and fitted fabric texture are more common in poorly cemented grainstones packstones and wackestones pressure solution occurs at e80 percent of the lithologic transitions this is probably due to competency contrasts between adjacent units that material dissolved at pressure solution surfaces is not locally reprecipitated is indicated by porous allochems which abut against stylolites and units of abundant intergranular pressure solution fitted fabric texture which lack cement the style of pressure solution in the alpena limestone and its relationship to cementation is also observed in the tuscarora quartz arenite silurian appalachian basin

impact of maturity on producible shale oil volumes in the silurian llandovery hot shales of the northern arabian plate southeastern turkey the silurian llandovery hot shales in southeastern turkey have excellent source rock potential with an average total organic carbon toc of 5 9 wt and generation potential values of 14 9 mg hc g toc the hot shales contain type ii organic matter and demonstrate oil and secondary gas generation potential hydrogen indices range from 36 to 510 mg hc g toc depending on maturity the hot shales in the gulf kevan 1 and turkish petroleum tp dogan 1 wells are immature early mature with a vitrinite reflectance equivalent requ of 0 58 0 76 the hot shales in the tp soguktepe 1 and tp k migo 2 wells are mature and in the oil window at 0 78 0 92 requ the hot shales are interpreted to be in the wet gas condensate maturity window with 1 08 1 30 requ in the tp g hazro 2 and tp arco abdulaziz 1 wells corrected evaporation loss restored using oil api gravity values oil saturation index values osic within the gulf kevan 1 tp dogan 1 and tp arco abdulaziz 1 wells are less than 100 mg hc g toc which indicates that unconventional commercial oil production is not probable the osic values of the mature hot shales at the tp soguktepe 1 tp k migo 2 and tp g hazro 2 wells all exceed 100 mg hc g toc indicating potentially producible oil and wet gas condensate thus producible oil and wet gas condensate in the hot shale play appear present in areas that have been assessed as having between 0 8 and 1 1 requ

titanium aluminum and interlayer cation substitutions in biotite from high grade gneisses west greenland detailed electron microprobe study pelitic to mafic metamorphic rocks from two localities higher ti k k na and possible k na similar al iv and lower al vi in granulite vs amphibolite grade samples modified journal abstract

cause of shale gas geochemical anomalies and mechanisms for gas enrichment and depletion in high maturity shales abstract this article reviews the abnormal characteristics of shale gases natural gases produced from organic rich shales and discusses the cause of the anomalies and mechanisms for gas enrichment and depletion in high maturity organic rich shales the reported shale gas geochemical anomalies include rollover of iso alkane normal alkane ratios rollover of ethane and propane isotopic compositions abnormally light ethane and propane 13 c values as well as isotope reversals among methane ethane and propane these anomalies reflect the complex histories of gas generation and associated isotopic fractionation as well as in situ mixing and accumulation of gases generated from different precursors at different thermal maturities a model was proposed to explain the observed geochemical anomalies gas generation from kerogen cracking at relatively low thermal maturity accounted for the increase of iso alkane normal alkane ratios and ethane and propane 13 c values normal trend simultaneous cracking of kerogen retained oil and wet gas and associated isotopic fractionation at higher maturity caused decreasing iso alkane normal alkane ratios lighter ethane and propane 13 c and corresponding conversion of carbon isotopic distribution patterns from normal through partial reversal to complete reversal relatively low oil expulsion efficiency at peak oil generation low expulsion efficiency at peak gas generation and little gas loss during post generation evolution are necessary for organic rich shales to display the observed geochemical anomalies high organic matter richness high thermal maturity high degrees of kerogen gas and oil gas conversions and late stage the stage of peak gas generation and post generation evolution closed system accounted for gas enrichment in shales loss of free gases during post generation evolution may result in gas depletion or even undersaturation total gas content lower than the gas sorption capacity in high maturity organic rich shales

nb and zr behavior in rutile during high grade metamorphism and retrogression an example from the ivrea verbano zone abstract detailed textural observations and in situ analyses emp sims and la icp ms are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile the ivrea verbano zone is a classic granulite area and rocks from the strona and d ossola valleys are an example of the amphibolite to granulite facies transition although different rock types occur in the area detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses these rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth but also for the effect of post peak processes on rutile chemistry nb concentrations in rutile from lower grade samples show a larger spread from 500 to 5000 ppm within one sample when compared to those from higher grades this pattern can be modeled using prograde rutile growth formed from biotite breakdown zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution maximum zr concentrations increase according to the general metamorphic gradient known for this area temperatures from zr in rutile thermometry although feasible are considerably higher than previous calculations increasing from ca 850 to 930 c a second cluster of zr concentrations in rutile occurs at rather constant concentrations ca 1000 ppm for all localities and is interpreted to be related to intense fluid influx at high temperature and or to post peak diffusional resetting favored by slow cooling rates alteration textures characterized by a complex network of micro veins are evidence for the late fluid influx the fluid strongly affected the rutiles which is evidenced by corrosion of older rutile grains and formation of rutile veinlets

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

calculated volume and pressure changes during the thermal cracking of oil to gas in reservoirs 1 the rising temperature that accompanies increasing burial depth converts oil in a reservoir into thermal gas a consideration of hydrogen balance during this cracking shows that approximately 3000 cubic ft 85 cubic meters of gas at standard temperature and pressure is generated from each barrel of oil in addition a graphitic residue is precipitated if the volume relationships among oil thermal gas and the graphitic residue are combined with data for gas solubility in pore water and gas nonideality z factor then pressure can be calculated for any degree of thermal cracking these calculations show that in an effectively isolated system pressures would become very high and could considerably exceed the rock load so that fracturing must occur causing pressure b eed off and loss of gas the lithostatic gradient 1 0 psi ft or 22 6 kpa m is reached after only about 1 0 of the oil is cracked if the reservoir system remains open i e at hydrostatic pressure and is initially filled with oil that is subsequently cracked to gas then roughly 75 of the gas will be lost or the reservoir volume must effectively increase in size for example by moving the gas water contact downward

radical concentration of kerogen as a maturation parameter a good correlation was found between spin concentration and burial depth for kerogen extracted with benzene methanol followed by pyridine or dioxane differences in slopes of the regression lines of spin concentration vs burial depth are dependent upon the geothermal gradient of the studied areas free radical concentration might be a good maturation parameter for kerogens of the same type

a dual porosity model for evaluating petroleum resource potential in unconventional tight shale plays with application to utica shale quebec canada unconventional tight to shale reservoirs vary from tight sandstone siltstone to organic rich mudstone shale commonly with mixed lithologies in such reservoir systems matrix pores and organic pores with different origins and distinct physical and chemical properties co exist for hydrocarbon storage traditional resource assessment methods designed for conventional reservoirs cannot handle the two pore systems properly this study proposes a dual porosity model to respond to the need for a new method in assessing hydrocarbon resource potential in such reservoir systems the dual porosity model treats the two types of pores separately and derives the resource estimates from different sources of data thus better characterizing unconventional reservoirs with complicated pore systems the new method also has the flexibility of assessing resource potential for the entire spectrum of mixed lithologies ranging from a complete tight to a pure source rock organic rich shale mudstone reservoir the proposed method is illustrated through the assessment of the in place petroleum resource potential in the upper ordovician utica shale of southern quebec canada the results of the application suggest that the proposed approach effectively handles the two pore systems in tight shale reservoirs effectively and provides a useful tool for estimating resource potential in unconventional plays

high temperature metamorphism and the role of magmatic heat sources at the rogaland anorthosite complex in southwestern norway the rogaland complex covers 1000 km in southwestern norway and consists mainly of anorthosite massifs and the layered bjerkreim sokndal lopolith bsl these rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites high temperature mineral isograds pigeonite osumilite and orthopyroxene in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex p t estimates from the country rocks show a roughly linear increase in temperature towards the bsl consistent with the distribution of isograds the peak p t conditions at 20 and 2 5 km from the contact at 5 kbar range from 700 to 41000 c field relations and age determinations link the high t metamorphism and the magmatism the two dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures two magmatic episodes separated by 3myr however can account for the high temperature metamorphism in this model the emplacement and crystallization of the anorthosite produces a regional thermal gradient from 750 to 600 c after a brief hiatus a second smaller body bsl provides an additional thermal input that results in an array of high temperature isograds and country rock temperatures 41000 c

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

birdseyes fenestrae shrinkage pores and loferites a reevaluation abstract birdseyes birdseye limestone fenestrae fenestral fabric shrinkage pores and loferites are considered similar if not synonymous when occurring in lime mudstone or syndepositional dolomite especially in association with mudcracks and stromatolites compaction experiments indicate however that in the absence of early cementation these rugs can be completely obliterated whereas mudcracks and stromatolites remain relatively unchanged lumping of burrows and root tubes under the general terms birdseyes or fenestrae such as for example tubular fenestrae burrow fenestrae or root tube fenestrae is discouraged they should be called burrows or root tubes because the birdseyes fenestrae and shrinkage pores are so intimately associated with tidal flats in the minds of most geologists submarine cementation of pelletal and oolitic botryoidal grainstone under 5 to 6 m of water on the bahama banks has resulted in rugs provocatively similar to many birdseyes and fenestrae generally attributed to peritidal conditions in the literature birdseyes and fenestrae in ancient grainstones cannot therefore be reliably identified without consideration of the sedimentary sequence and assoc ated sedimentary structures

characterization of methane adsorption on overmature lower silurian upper ordovician shales in sichuan basin southwest china experimental results and geological implications abstract a series of methane adsorption isotherms were measured at 35 4 c 50 6 c and 65 4 c at pressures up to 15 0 mpa for eight dried overmature lower silurian upper ordovician shale samples collected from the sichuan basin with toc values in the range of 1 87 5 74 the measured maxima of excess adsorption capacity of methane range from 1 25 to 2 50 cm 3 g rock at 65 4 c the maxima are slightly enhanced at 35 4 c but all are positively correlated with total organic carbon toc both the supercritical dubinin radushkevich sdr and langmuir based excess adsorption models were found to represent the experimental excess adsorption isotherms equally well within the experimental range the temperature dependent densities of adsorbed methane resulting from the parameter fit of the sdr based excess adsorption model are in the range of 297 415 mg cm 3 for the langmuir based excess adsorption model the adjusted densities range from 386 mg cm 3 to 1027 mg cm 3 and most of them are much larger than the liquid density of methane at its boiling point 424 mg cm 3 nevertheless the maxima of absolute methane adsorption capacity fitted by both models are not significantly different and are linearly correlated one of the contributors to the uncertainty of the gas in place estimation in geological conditions is the inconsistent utilization of experimental excess sorption data as absolute sorption values particularly at high pressures however the choice of adsorption model itself langmuir or sdr based and the fitting procedure assuming either constant or temperature dependent adsorbed phase density and maximum sorption capacity do not significantly affect the estimated gips for the geological system studied here with depths of less than 4000 m

source and seal coupling mechanism for shale gas enrichment in upper ordovician wufeng formation lower silurian longmaxi formation in sichuan basin and its periphery abstract in recent years theoretical geologic research has made important progress in shale gas exploration and development and new discoveries such as the jiaoshiba weiyuan and changning shale gas fields provide geological cases to define key controls on shale gas accumulation in wufeng formation longmaxi formation marine shale strata a mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source seal dynamic evolution great thickness wide distribution and high total organic carbon content toc of sources are key controls on the shale gas content and storage capacity in organic matter hosted pores micro cracks and bedding fissures is intensively developed the wufeng formation and the lower part of the first member of the longmaxi formation wf2 lm4 graptolitic zone are favorable sources that feature a slow deposition rate well graptolitic zone favorable organic organism type and high toc the organic matter type is benefit to the development of organic matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic matter pores both high biogenic quartz and high toc ensure development of abundant organic matter hosted pores and result in a three dimensional network of interconnected organic matter pores that allows shale gas storage and flow the seal can be divided into direct and indirect seals the direct seal refers to the middle and upper parts of the first member of the longmaxi formation lm5 and higher graptolitic zone that are characterized by low toc and low porosity the indirect seal refers to the regionally distributed lower middle triassic gypsum layer s and mudstone that maintain regional geopressure systems the shale gas fields of jiaoshiba fushun yongchuan and changning have high geopressure coefficient factors 1 5 2 0 and 1 5 respectively in the absence of the lower middle triassic gypsum layer s and mudstone regional seals the high pressure system was destroyed and resulted in low normal geopressure shale gas reservoirs for instance the pengshui and zhaotong wells the static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment the model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas this model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach in the sichuan basin and its peripheral areas the promising areas for shale gas accumulation are those with favorable sources in the wf2 lm4 graptolitic zone and the presence of the lower middle triassic gypsum layer s and mudstone regional seal

the use of free radicals of organic matter to determine paleogeothermal gradient abstract free radicals in 60 kerogen samples from 5 wells in the qiongdongnan tarim and liaohe basins in china were analyzed by electron spin resonance esr for use in geothermometry based on esr data for 44 kerogen samples from the tertiary qiongdongnan basin a regression curve was shown to fit free radical densities n g with burial depth of samples for use in geothermal gradient estimation using this curve the highest geothermal gradients experienced by carboniferous permian strata well tmc1 in the tarim basin and oligocene eocene strata well lr16 in the liaohe basin were estimated concurrently five samples from liaohe basin were examined by apatite fission track analysis to assess the reliability of the esr kerogen method for geothermal gradient determination results of esr analyses match those of vitrinite reflectance and apatite fission track analysis indicating that maximum geothermal gradients obtained from the esr curve are reliable this paper presents a useful esr kerogen method for estimating paleogeothermal gradients which is especially useful where vitrinite and apatite are not present

experimental investigation of oil generation retention and expulsion within type ii kerogen dominated marine shales insights from gold tube nonhydrous pyrolysis of barnett and woodford shales using miniature core plugs abstract although oil retention has recently emerged as a key topic of unconventional shale resource assessment oil retention and expulsion controls in organic rich shales during thermal maturation remain poorly constrained this study presents an experimental comparison of oil generation retention and expulsion in two immature type ii kerogen dominated marine shales the mississippian barnett shale and the upper devonian lower mississippian woodford shale mainly with respect to the combined effects of the organic macerals and rock fabric involved in both cases miniature core plugs drilled from the given samples were isothermally pyrolyzed at 130 to 425 c for 72 h under a confining pressure of 68 mpa during gold tube nonhydrous pyrolysis corresponding to the thermally immature early stage of the oil window the main stage of the oil window the late stage of the oil window the main stage of oil cracking to wet gas and the late stage of oil cracking yields of generated oil retained oil and expelled oil for the two studied samples were systematically quantified on the basis of mass balance calculation of measured oil and gas yields as well as rock eval analyses on pyrolyzed subsamples through the six stages of petroleum formation investigated the principal difference in oil generation was observed in the two studied samples with approximately 38 to 68 greater yields of generated oil equivalent to 130 mg oil g toco for the woodford shale when it evolved into the main and late stages of the oil window these elevated yields of generated oil for the woodford shale were compensated for by additional oil generation resulting from conversion of abundant type i kerogen like algae such as tasmanites and leiosphaeridia which lag in onset and have a shorter period of petroleum generation upon maturation as a response to the difference in oil generation oil retention was found to be significantly enhanced for the woodford shale at equivalent stages with 0 2 to 1 7 times more free oil equivalent to 24 105 mg oil g toco and 0 7 to 3 9 times more sorbed oil equivalent to 58 76 mg oil g toco being retained than that of the barnett shale although this effect was not pronounced for oil expulsion in contrast to the barnett shale relatively low expelled oil yields and expulsion efficiencies both indicate highly limited oil expulsion in the woodford shale implying that the woodford shale whose mineral composition and lithofacies are similar to those of the barnett shale may have a relatively low permeability rock fabric to prevent oil from being expelled furthermore not only significantly higher oil saturation index osi values but also a wider range of maturity at which the oil crossover effect osi 100 mg g toc occurs is expected for the woodford shale when extrapolation to a geological setting occurs these data suggest that the presence of abundant type i kerogen like algae and relatively low permeability rock fabric in the woodford shale are critical to significant oil retention during oil generation and expulsion which jointly raise the possibility of potential commercial shale oil within type ii kerogen dominated marine shales

mechanism of shale gas occurrence insights from comparative study on pore structures of marine and lacustrine shales abstract the exploration practices of marine and lacustrine shale gas in the upper yangtze platform south china show that there is a huge difference in gas content which is mainly related to the difference of pore structure this study is focused on marine longmaxi and lacustrine da anzhai shales in the upper yangtze platform and their pore structure characteristics were compared and the mechanism of shale gas occurrence were discussed first the pore structures of marine and lacustrine shales were characterized and the effects of organic matter abundance maturity and inorganic minerals on porosity were investigated then the contributions of different components to porosity were evaluated and the occurrence mode of methane in the pores of marine and lacustrine shales was established the results show that 1 three pore types can be observed in both marine and lacustrine shales organic matter hosted pores om pores framework minerals associated pores fm pores and clay minerals associated pores cm pores om pores are more developed in marine shale and cm pores are more developed in lacustrine shale 2 low pressure gas adsorption lpga results show that the micropores of marine shale are dominated by pores of 0 4 0 7 nm and the micropores of lacustrine shale are dominated by pores of 0 5 0 9 nm while the mesopores of marine shale are dominated by pores of 2 10 nm and the mesopores of lacustrine shale are dominated by pores of 3 30 nm which are consistent with mip results 3 organic matter has an impact on porosity of marine and continental shales but is not the most important controlling factor and the contribution of organic matter to porosity in marine shale is greater than the contribution of organic matter to porosity in lacustrine shale shale porosity increases first and then decreases with the increase of maturity which may be related to the carbonization of organic matter 4 om pores and cm pores tend to be preserved due to the presence of rigid grains that form rigid frameworks preventing these pores from collapsing fm pores are mainly related to the dissolution of framework minerals by organic acids and these dissolution pores can greatly improve the porosity and permeability of shale 5 quantification of porosity as related to mineralogy shows that om pores contribute approximately 37 to total porosity of marine shale and 24 to total porosity of lacustrine shale and cm pores contribute approximately 53 to total porosity of marine shale and 67 to total porosity of lacustrine shale 6 shale gas occurrence is mainly controlled by the distribution mode of pore systems which are composed of om pores fm pores and cm pores it is due to higher percentage on om pores and lower percentage on cm pores that gas content of marine shale is generally higher than that of lacustrine shale

characterization and origin of a compositionally zoned aluminous a type granite from south india the pan african ambalavayal granite intrudes the high grade metamorphic terrain of northern kerala south india and is spatially associated with the moyar and calicut lineaments the pluton was aligned nearly parallel to the northeast southwest and east west faults in the basement consistent with magma ascent along pre existing deep crustal lineaments in an extensional tectonic regime the pluton is characterized by the presence of iron rich hydrous mafic minerals primary magnetite f o2 above the ni nio buffer and high initial emplacement temperatures near 1000 c modal and textural analyses reveal two probable compositional zones within the pluton outer and inner major element variations support this zoning and point to a peralkaline to metaluminous outer zone and a metaluminous to slightly peraluminous inner zone both zones exhibit major and trace element characteristics of the a type granites with the outer zone belonging to the a1 subtype and the inner zone to the a2 subtype of eby the trace element trends observed from outer zone to the inner zone suggests that crystal fractionation may have been the dominant process in the generation of high levels of the incompatible elements in the case of inner zone samples the high initial 87sr 86sr ratio 0 7135 and high y nb ratios y nb 1 2 are in the range expected for rocks derived from crustal protoliths a petrogenetic model involving partial melting of a charnockitic mafic to intermediate lower crust followed by limited fractional crystallization of the magma in a high level magma chamber is proposed the enrichment of hfse and ree except eu in the inner zone is considered the ultimate product of crystal melt and volatile activity during the final stage of crystallization in a highly silicic sio2 74 magma chamber

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

melt producing and melt consuming reactions in the achankovil cordierite gneisses south india migmatitic cordierite gneisses within the achankovil zone az of southern pan african india record melt producing and subsequent melt consuming mineral reactions early mineral assemblages bt sil qtz and bt sil spl deduced from inclusion textures in garnet prophyroblasts break down via successive dehydration melting reactions to high t phase assemblages e g grt crd liq opx liq spl crd liq later back reactions between the restite and the in situ crystallizing melt resulted in thin cordierite coronas separating garnet from the leucosome and partial resorption of garnet to opx crd or crd bt qtz symplectites leucosomes generally display a moderate low strain gneisses to strong high strain gneisses depletion of alkali feldspar attributed to mineral melt back reactions partly controlled by the degree of melt segregation using a kfmash partial petrogenetic grid that includes a melt phase and qualitative pseudosections for microdomains of high and low al si ratios the successive phase assemblages and reaction textures are interpreted in terms of a clockwise p t path culminating at about 6 7 kbar and 900 950 c this p t path is consistent with but more detailed than published results which suggests that taking a melt phase into account is not only a valid but also a useful approach comparing p t data and lithological and isotopic data for the az with adjacent east gondwana fragments suggests the presence of a coherent metasedimentary unit exposed from southern madagascar via south india az and sri lanka wanni complex to the lutzow holm bay in eastern antarctica

free radical transformations in the irati oil shale due to diabase intrusion abstract electron spin resonance esr spectroscopy was used to evaluate the effect of a diabase intrusion on the production and decomposition of free radicals in the irati oil shale parana basin brazil free radical concentration measurements on the stratigraphic column ceri 2 indicated that the ratio between the extent of thermal alteration on sedimentary organic matter and the intrusive thickness was 1 14 kinetics of free radical transformation obtained from laboratory pyrolysis of irati oil shale can be described by first order production and decomposition reactions of distinct species although these species present different kinetic parameters they are not resolved and lie inside the envelope of the single line esr spectrum the activation energies for parallel first order production reactions of two main species of free radicals in the temperature range of 360 420 c were found to be 54 2 kcal mol 1 and 36 9 kcal mol 1

epr study of kerogens from middle valley northern juan de fuca ridge odp leg 139 abstract isolated kerogens from four sites in the middle valley hydrothermal region of the juan de fuca ridge ocean drilling project odp leg 139 were analysed by electron paramagnetic resonance epr spectroscopy measurements of peak width spin density and power saturation for site 857 kerogens which increased regularly in maturity downhole show correlation with vitrinite reflectance values from 0 61 to 2 5 indicating the start of the oil window at depths from 200 to 400 m spin density increases to 1 56 10 17 spins per gram and peak width decreases to 3 45 g gauss with increasing depth the tendency to power saturate also decreases with increasing maturity and increasing vitrinite reflectance within the oil window these trends are consistent with a model in which exchange processes are occurring and cause changes in the epr behavior of samples from this site sediments from other middle valley sites 855 856 and 858 contain large quantities of pyrite with mn 2 impurities which interact with the carbon radical to distort the epr measurements

modeling of gas generation from the barnett shale fort worth basin texas the generative gas potential of the mississippian barnett shale in the fort worth basin texas was quantitatively evaluated by sealed gold tube pyrolysis kinetic parameters for gas generation and vitrinite reflectance ro changes were calculated from pyrolysis data and the results used to estimate the amount of gas generated from the barnett shale at geologic heating rates using derived kinetics for ro evolution and gas generation quantities of hydrocarbon gas generated at ro 1 1 are about 230 l t 7 4 scf t and increase to more that 5800 l t 186 scf t at ro 2 0 for a sample with an initial total organic carbon content of 5 5 and ro 0 44 the volume of shale gas generated will depend on the organic richness thickness and thermal maturity of the shale and also the amount of petroleum that is retained in the shale during migration gas that is reservoired in shales appears to be generated from the cracking of kerogen and petroleum that is retained in shales and that cracking of the retained petroleum starts by ro 1 1 this result suggests that the cracking of petroleum retained in source rocks occurs at rates that are faster than what is predicted for conventional siliciclastic and carbonate reservoirs and that contact of retained petroleum with kerogen and shale mineralogy may be a critical factor in shale gas generation shale gas systems together with overburden can be considered complete petroleum systems although the processes of petroleum migration accumulation and trap formation are different from what is defined for conventional petroleum systems

experimental study on the gas generation processes of lacustrine and marine shales in north china source implications for shale gas abstract using a high pressure semi closed thermal simulation system two organic rich lacustrine and marine immature shales from north china were investigated to probe the dynamic processes and potential for the gas generation throughout the oil gas window the results identified at least two processes during gas generation as revealed by changes of the gas dry coefficient c1 c1 5 and carbon isotopic composition of methane 13cmethane the first process is associated with kerogen thermal degradation and occurs during the main phase of oil generation showing an increasing trend of the dry coefficient and 13cmethane the second process begins during the late phase of oil generation accompanied by increasing yields of wet gas components and 13c depleted methane due to the lack of aliphatic carbon in kerogen in the highly to over mature stage as demonstrated by ftir analyses the second process is mainly related to the cracking of kerogen generated bitumen which is retained in the shale the hydrogen content a key parameter for petroleum generation is then used to quantitatively evaluate the gas generation potential from kerogen thermal degradation and retained bitumen cracking mass balance calculations show that kerogen generated bitumen that is retained in lacustrine and marine shales is estimated to contribute 30 of the total gas yields at the stage of 1 5 2 0 ro this result is consistent with the theoretical calculations from xia et al 2013 and has important implications for the shale gas sources and further the shale gas resource assessments before exploration in shale gas petroleum systems

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

bulk and position specific isotope geochemistry of natural gases from the late cretaceous eagle ford shale south texas abstract a dataset of bulk and position specific isotope compositions of shale gases from the late cretaceous eagle ford shale south texas is reported the chemical and bulk isotopic compositions of the seven samples in this study and those available from the literature show that across the play produced natural gas from the eagle ford shale preserves a wide range of gas compositions wetness 5 to 90 and 13c values of c1 c3 the depth profiles of the isotopic compositions suggest that the western region of the eagle ford shale deposit had experienced as much as 700 800 m of uplift erosion or gas migration the timing of and lost gas fractions by gas expulsion events very likely affected their gas compositions and bulk isotope compositions some deep 3000 3500 m matured ro 1 5 gases with heavy 13c c1 c3 values indicate significant loss 50 of the early stage gases for the position specific isotope deviations of propane the c2 1 values of the five samples show small decrease with well depths while the h2 1 values have a general increasing trend although some samples fall very close to the equilibrium model trajectories with reasonable calculated temperatures 138 148 c the position specific isotope compositions of propane from the eagle ford shale gases are likely results of thermal cracking of various organic molecules within the source rocks which have different activation energy for cracking and non statistical distributions of c h isotope within them

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

petrology and geochemistry of paleoproterozoic a type granite at kanigiri in the nellore khammam schist belt andhra pradesh india abstract the kanigiri pluton 6 2 2 1 km 2 995 ma occurs close to a major fault and is intrusive into the meta volcanics in the western margin of the nellore khammam schist belt in andhra pradesh india the dominantly metaluminous pluton displays geochemical characteristics of a type granites including high abundances of nb zr y ta and ree except eu and low concentrations of sc ba sr and eu displaying distinct variation trends with increasing silica content it has less fractionated ree patterns and large negative eu anomalies the cluster analyses of major and trace elements indicate three main associations a a primary magmatic association characterized by the presence of la ce fe ti mn k ba and sr b ore related association consisting of zr hf nb y and c a volatile association with rb ta li and cs systematic variation in sr rb sr rb ba ratios along with and low k rb ratios reflects fractionation of feldspars variations in sc and ta result from fractionation of ferromagnesian silicates removal of zircon and allanite affected the hf ta and ce yb ratios limited variation in source sensitive y nb and yb ta ratios is consistent with the results of melting experiments and indicates that metaluminous granitoids of this pluton were probably derived through melting of lower crustal sources geochemical field and petrological data for the kanigiri granite suggest that the granite is a partial melting product of mafic rocks like gabbros that are also present in the study region

fluorine and chlorine behaviour during progressive dehydration melting consequences for granite geochemistry and metallogeny dehydration melting of biotite is the main control on crustal differentiation in the mid to lower continental crust because this reaction produces the most voluminous and most mobile granitic melts biotite breaks down over a broad temperature interval so the partitioning behaviour of elements between biotite and melt is likely to vary it has been hypothesized that fluorine may stabilize biotite to higher melting temperatures because biotite is typically f rich in ultra high temperature uht metamorphic rocks if true f would be an important influence on crustal differentiation because not only would it broaden the temperature range of melting but also elevated f concentration decreases melt viscosity furthermore ligand partitioning between biotite and melt may be an important influence on the metallogeny of magmas this study used electron microprobe analysis of biotite in rocks from the ballachulish and rogaland metamorphic aureoles to investigate the concentration of f and cl in biotite heated to 600 1 000 c results show a broad increase in biotite f content up to 5 04 f with temperature until 850 920 c beyond which f content decreases 2 5 f chlorine concentrations in biotite are consistently lower 1 cl and show a progressive decrease after the onset of partial melting it was found that mg content and the processes that control mg distribution are most strongly correlated with f and cl concentration in biotite calculations based on these results indicate that f enriched biotite could be a significant source of f for continental crust derived melts generation of a hot f rich melt at uht conditions could be important for transporting lower crustal metals to the upper crust