3d nanopores modeling using tem tomography dolostones upper triassic abstract transmission electron microscopy tomography temt stands as a novel and alternative tool to tridimensionally model the nano scale pores of rocks in this study it is flanked with traditional mercury capillary injection porosimetry micp nitrogen adsorption porosimetry np and scanning electron microscopy sem analysis to test a sample belonging to an upper triassic dolostone cropping out in northern calabria micp revealed low values of porosity and permeability 2 3 and the 0 11 md respectively nanopores account for the 94 of the pore volume whereas the remaining 6 is represented by micropores the integrated micp and np pore size distribution psd shows the presence of a dominant pore diameter population coincident with 50 nm with minor peaks at diameters of 12 m 850 25 13 6 2 nm however since the psd peaks of the two techniques do not match a comparison of the two curves is necessary to better characterized the overlapping area sem imaging analysis showed the presence of nano scale intercrystalline and intracrystalline pores the first corresponds with the spaces among dolomite crystals and as suggested by the np analysis shows a wedge slit morphology the second appears with a prevailing polygonal section or as tight microfractures since sem provides exclusively two dimensional images the morphology and development of these pores was obtained through temt 3d reconstruction the 3d model showed the presence of open cavities fractures and blind isolated pores cavities cross the entire dolomite crystals and can present a constant sub prismatic pores or variable channel section funnel shaped pores that can reduce its aperture as observed of also more than a ten factor e g from 300 nm to 20 nm fractures commonly developing on the existing cleavage surfaces cut the crystal faces for 300 350 nm reducing its aperture maximum of 20 30 nm from the edge towards the inner part of the crystal lastly blind isolated pores can assume diameters and thickness of 250 nm they show a sub cubic morphology and can be filled by solid liquid or gaseous inclusions

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

petrography and reservoir physics ii relating thin section porosity to capillary pressure the association between pore types and throat size porosity in reservoir rocks is configured into a few types of pores whose size and shape are controlled by depositional fabric and postdepositional processes the size shape and abundance of each pore type can be objectively determined from thin section using image analysis and pattern recognition procedures each pore type tends to be associated with a limited range of throat sizes the association between pore type and throat size can be determined using regression procedures linking pore type data obtained from thin section with capillary pressure data to do so a set of samples is required wherein the association between pore type and throat size is fixed but where pore type proportions vary between samples this condition is met by a sample suite representing res rvoir facies from a single core or in many cases from a single field the relationship between pore type and throat size is an effective means to relate reservoirs in terms of the efficiency of the porous microstructure to multiphase flow parameters derived from the relationship can be used to construct accurate physical models that subdivide physical response in terms of the contributions of each pore type

neotectonic deformation of the central chile margin deepwater forearc basin formation in response to hot spot ridge and seamount subduction 1 underlying the midslope valparaiso terrace the valparaiso basin constitutes a unique and prominent deepwater forearc basin on the central chile margin the basin contains a 3 3 5 km thick sediment fill of late cenozoic age the seismic stratigraphic architecture of the valparaiso basin fill shows that margin wide subsidence above the underthrusting juan fernandez ridge an aseismic volcanic swell crested with seamounts on the nazca plate characterized the basin evolution contemporaneously with margin subsidence and seaward rotation of the upper slope and shelf the outer part of the forearc was deformed by thrust faulting above the leading flank of underthrusting seamounts that rotated the middle slope to a more horizontal attitude and formed seaward vergent outer forearc highs subsidence of the margin above the underthrusting juan fernandez ridge is ascribed to processes of subduction erosion enhanced by factors related to subduction of the ridge that caused dismemberment of upper plate material along the shallow aseismic part of the plate interface and transfer of material to the downgoing nazca plate accelerated midslope subsidence 55 75 km landward of the trench coincides with the seaward limit of interplate seismicity suggesting that enhanced basal erosion is related to the transition from aseismic to stick slip subduction behavior since subduction of the juan fernandez ridge began near 33 s 10 ma ago the chile trench north of 33 s is inferred to have retreated 3 km myr and the midslope valparaiso basin subsided 0 3 0 5 km myr approximating analogous neogene rates for the peruvian margin

characterization of microscopic pore structures in lower silurian black shale s1l southeastern chongqing china abstract due to the large thickness and richness of organic matter in longmaxi shale southeastern chongqing is considered as the most promising area for shale gas exploration and development and was a focus of numerous research interests in china characterization on the pore system of organic rich shale is significant for the reserve estimation and better understanding the production mechanism of shale gas plays shale composition detected by x ray diffraction indicates that brittle minerals especially quartz was the most prevalent component with average contents of 41 72 wt pore types was classified by using a combination of argon iron milling and field emission scanning electron microscopy fesem and six types of pores were observed in rock images high pressure mercury intrusion and low pressure n 2 adsorption were performed to extract the pore size distribution of longmaxi shale the results show that the nanopore was the major pore type in shale samples which accounts for 95 6 of the pore volume in the nanopore system pore with diameters between 2 nm and 10 nm is the major component that contributes 76 of the total pore volume and 78 of the whole inner surface area furthermore the dominant pore shape was interpreted from the adsorption desorption hysteresis loop shape and the typical slit shaped pores were identified in the examined shale samples based on single factor analysis method organic matter richness is the main controlling factor for the volume of nanopore and the specific surface area no direct correlation between brittle minerals and nanopores but high quartz and calcite content makes it much easier for the formation to generate natural fractures and to be hydraulically fractured the study can inspire and guide shale gas exploration and exploitation southeastern chongqing to some extent

on geoid heights and flexure of the lithosphere at seamounts the sea surface height has now been mapped to an accuracy of better than 1 m by using radar altimeters on board orbiting satellites the major influence on the mean sea surface height is the marine geoid which is an equipotential surface we have carried out preliminary studies of how oceanic volcanoes which rise above the ocean floor as isolated seamounts and oceanic islands or linear ridges contribute to the marine geoid simple one and two dimensional models have been constructed in which it is assumed that the oceanic lithosphere responds to volcanic loads as a thin elastic plate overlying a weak fluid substratum previous studies based on gravity and bathymetry data and uplift subsidence patterns show that the effective flexural rigidity of oceanic lithosphere and the equivalent elastic thickness te increase with the age of the lithosphere at the time of loading the models predict that isolated seamounts emplaced on relatively young lithosphere on or near a mid ocean ridge crest will be associated with relatively low amplitude geoid anomalies about 0 4 0 5 m km of height while seamounts formed on relatively old lithosphere on ridge flanks will be associated with much higher amplitude anomalies 1 4 1 5 m km studies of the seasat altimetric geoid prepared by nasa s jet propulsion laboratory support these model predictions geoid amplitudes are relatively low over the mid pacific mountains and line islands which formed on or near a mid ocean ridge crest and relatively high over the magellan seamounts and wake guyots which formed off ridge direct modeling of the altimetric geoid over these features is complicated however by the wide spacing of the satellite tracks which can exceed 100 km and poor bathymetric control beneath individual satellite tracks in regions where multibeam bathymetric surveys are available models can be constructed that fit the altimetric geoid to better than 1 m studies of geoid anomalies over the emperor seamount chain for example suggest that these seamounts formed on 20 30 ma old oceanic lithosphere while anomalies over the louisville ridge and the hawaiian ridge suggest that these seamounts formed on lithosphere older than about 80 ma this indicates that geoid anomalies over bathymetrie features depend not only on the crustal structure prior to loading and the overall shape and density of the features but also on their tectonic setting we examine the implications of these results to studies which attempt 1 to separate temporal variations of the sea surface due to oceanographic effects 2 to predict seamounts directly from satellite derived gravity and geoid data and 3 to isolate the geoid effects of deep processes occurring beneath the lithosphere such as those due to mantle convection

seismic investigation of the continental margin off and onshore valparaiso chile abstract at the latitude of valparaiso chile a fundamental change in the configuration of the benioff zone volcanic activity and the structure of the continental margin occurs opposite the subducting juan fernandez ridge three legs of the german r v sonne cruises so101 so103 and so104 surveyed the continental margin and oceanic plate offshore valparaiso aiming at studying the crustal structure and investigating possible causes for the change in slab configuration sonne cruise so101 investigated the tectonic setting with swath mapping bathymetry magnetics and high resolution seismics following these investigations cruise so103 collected land sea wide angle seismic data and coincident deep seismic reflection data were acquired during cruise so104 coincident near vertical and wide angle seismic measurements were made along two profiles profile 1 located at the south of the study area away from the influence of the subducting ridge crosses the margin where thick trench sediment and an accretionary wedge near the trench is observed profile 2 located in the north runs from the juan fernandez ridge to the chilean coast the crustal velocity models obtained for the two profiles show that the continental crust extends to the middle lower slope boundary which is also reflected in morphology in addition they show that the crustal structure of the oceanic plate is rather similar but the plate seems to be slightly more inclined along the northern profile 13 versus 10 in the south the two profiles are only about 70 km apart but their structures differ significantly no straightforward correlation exists between the two profiles that can be attributed to ridge collision the data support that the 1985 central chile earthquake ruptured the plate boundary in the area that includes the segment boundary and mainly where continental crust forms the upper plate

organic matter clay mineral intergranular pores in the lower cambrian lujiaping shale in the north eastern part of the upper yangtze area china a possible microscopic mechanism for gas preservation abstract gas shales with a high gas content were encountered in the lower cambrian lujiaping formation in the northeast part of the upper yangtze area china in this area the tectonic condition is complex and the organic matter is over matured so conventional oil and gas exploration have not previously been considered during a recent shale gas exploration canister desorbed gas contents of more than 1 m 3 t were detected from 490 to 825 m depth with a maximum value of 3 18 m 3 t at 762 m hence to understand the mechanism of preservation of the gas is important the gas shales have a total organic carbon toc content of between 0 44 and 6 91 and vitrinite like macerals reflectance r o between 3 3 and 4 3 with type ii kerogen the porosity of 22 gas shale samples ranges between 0 4 and 2 29 and their permeability is between 6 9 10 5 and 3 8 10 1 md to investigate the shale s pore structure and its relation to gas storage behavior we studied the microscopic mechanism of gas preservation using a combination of pore characterization techniques including focused ion beam scanning electron microscope fib sem imaging and comparison of gas sorption and free gas storage capacity folding thrusting and subsequent rapid uplifting movements occurred after most of the dry gas had been originally generated and the present gas is a mixture originated from the cracking of liquid hydrocarbons at high maturity and kerogen pyrolysis in the early hydrocarbon generation phase sem observations combined with low temperature gas adsorption and mercury injection capillary pressure analyses show that pores within the organic matter or the mineral particles in the lujiaping shale are rare while the nanometer sized pores 1 4 nm between organic matter and clay mineral particles especially in cleavage domains are greatly developed thus the gas in these shales is mainly adsorbed gas due to the limited free gas storage space this is unlike most other shale gas reservoirs pores within the organic matter and pores between or within mineral particles are dominant moreover the desorbed gas content correlates well with toc content and the microporous and mesoporous specific surface area determined by low temperature co 2 and n 2 respectively suggesting that the nanometer sized pores associated with the organic matter make up the fundamental storage space for this shale the calculations based on fib sem observation showed that the nanometer sized intergranular pores have large specific surface areas with their small pore throat diameters resulting in high capillary pressure these characteristics have contributed to the preservation of shale gas in this complex tectonic area

composition effects on pore structure of transitional shale a case study of the upper carboniferous taiyuan formation in the eastern uplift of the liaohe depression china abstract transitional shale is very different from marine shale with respect to mineral composition and pore structure insights into the effects of rock composition on pore structure can aid understanding of the storage and migration mechanisms of shale gas in a reservoir to investigate the compositional effects on pore structure a combination of geochemical and petrophysical experiments were conducted on four bulk shale samples and their corresponding extracted organic matter om and clay mineral samples the experimental results show that the removal of om using h2o2 during clay mineral extraction oxidizes and removes pyrite and siderite from the samples while other inorganic phases remain unaffected om hosted more abundant micropores compared with clay minerals while mesopores and fine macropores are dominant in clay minerals effects of the om and clay minerals on pore volume and surface area are quantitatively evaluated on the basis of weight normalized pore size distribution psd curves of extracted om and clay mineral samples in terms of the co2 adsorption contribution from om and clay minerals to micropore volume miv are 19 43 32 92 and 18 75 39 05 respectively and to micropore surface area mis are 19 30 32 28 and 16 42 35 72 other minerals other than organic matter and clay minerals account for 34 29 48 93 of the miv and 39 75 52 98 of the mis n2 adsorption results reveal that the pore volume and surface area are mainly attributable to the clay minerals providing 54 37 80 75 of the bjh pore volume bjhv average 65 83 and 70 68 87 04 of the bet surface area bets average 78 71 the primary medium for pore development in marine shale is om whereas pores in the transitional shale are mostly found in the clay and other inorganic minerals therefore the hydraulic fracturing design and drilling related operations involved in the exploitation of transitional shale gas should be appropriately adjusted and improved in order to accommodate intrinsic characteristics of the transitional shale gas reservoir

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

microstructural characterization of pores in marine shales of the lower silurian longmaxi formation southeastern sichuan basin china abstract understanding the complexities of sedimentary pore systems is the key to understanding the mechanisms that lead to shale gas accumulation in this study the microstructures networks and connectivity of pores in marine shales of the longmaxi formation in the southeastern sichuan basin are investigated using a combination of qualitative and quantitative methods 2d and 3d characterizations of the formation provide an opportunity to describe the types of pores pore networks and pore connectivity in these shales the study s results show that nearly all pores are nanosized and that organic matter om pores are the most common but also include interparticle interp pores intraparticle intrap pores and micro fracture pores reconstructed 3d models show that there is limited connectivity of pores gas adsorption analysis and statistical results indicate that nearly 95 of the pores are micro to meso scale and account for approximately 23 and 73 of the pore space respectively a combination of image processing and calculations also shows that om pores account for approximately 87 of all pores and as such the pore networks are dominated by om pores om pores are associated with discontinuous occurrences of organic matter which results in relatively poor connectivity

the mw 5 4 reggio emilia 1996 earthquake active compressional tectonics in the po plain italy summary we have analysed the seismic sequence that occurred in october 1996 near the town of reggio emilia on the southern edge of the po plain the onset of the sequence was marked by a 5 4 moment magnitude main shock located at 15 km depth the main shock focal mechanism is a reverse solution with a strike slip component and the scalar moment is 1 46 1017 n m we used broad band digital recordings from a borehole station located at about 70 km from the epicentre for a spectral analysis in order to estimate attenuation and source parameters for the main shock in addition the empirical green s function method has been applied to evaluate the source time function in terms of both moment rate and stress rate we infer an asperity like rupture process for the main shock as suggested by the short duration of the stress release with respect to the overall duration of the moment rate function this analysis also allows us to estimate the average dynamic stress drop of the main shock 600 bar we analysed the digital recordings of the temporary local seismic network deployed after the main shock and of a permanent local network maintained by the italian petroleum agency agip during 15 days of field experiments we recorded more than 800 aftershocks which delineate a 9 km long ne elongated distribution confined between 12 and 15 km depth suggesting that the basement is involved in the deformation processes 102 focal mechanism of aftershocks have been computed from p wave polarities showing mainly pure reverse solutions we calculate the principal stress axes from a selected population of earthquakes providing a constraint on the stress regime of this part of the po plain the focal mechanisms are consistent with a n s subhorizontal 1 all the seismological data we have analysed confirm that this region is undergoing active compressional tectonics as already inferred from recent earthquakes geomorphological data and other stress indicators moreover the elongation of the reggio emilia aftershock sequence is consistent with the regional direction of the thrust fronts cropping out in the area suggesting that they are still active

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

seismic imaging of hotspot related crustal underplating beneath the marquesas islands volcanism in active continental rift zones1 2or on rifted continental margins3is frequently associated with unusually high lower crustal seismic velocities indicating the presence of large igneous intrusions at the base of the crust the only comprehensive investigation of crustal underplating at an oceanic hotspot beneath hawaii4 6 has yielded controversial results7 here we report the results of seismic refraction experiments across the marquesas islands hotspot trace which show that the island chain is underlain by crust 15 17 km thick and that a large lower crustal region 275 km wide and 2 8 km thick has seismic velocities 7 3 7 75 km s 1 indicative of crustal underplating wide angle reflections occur near the base of the normal lower crustal velocities and at the base of the underplating complex we interpret these reflectors as the relict pre hotspot moho and the current post hotspot moho respectively the high velocity material may be purely intrusive or may consist of a mixture of intrusive and preexisting rocks the volume of the high velocity body is impressive amounting to nearly twice the volume of volcanics erupted at the surface

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

fossil hot spot ridge interaction in the musicians seamount province geophysical investigations of hot spot volcanism at volcanic elongated ridges the musicians seamount province is a group of volcanic elongated ridges vers and single seamounts located north of the hawaiian chain a 327 trending seamount chain defines the western part of the province and has been interpreted as the expression of a cretaceous hot spot beneath the northward moving pacific plate to the east elongated e w striking ridges dominate the morphology in 1999 wide angle seismic data were collected across two 400 km long vers we present tomographic images of the volcanic edifices which indicate that crustal thickening occurs in oceanic layer 2 rather than in layer 3 this extrusive style of volcanism appears to strongly contrast with the formation processes of aseismic ridges where crustal thickening is mostly accommodated by intrusive underplating high resolution bathymetry was also collected which yields a detailed image of the morphology of the vers from the occurrence of flat top guyots and from the unique geomorphologic setting two independent age constraints for the pacific crust during the cretaceous quiet zone are obtained allowing a tectonic reconstruction for the formation of the musicians vers hot spot ridge interaction leads to asthenosphere channeling from the plume to the nearby spreading center over a maximum distance of 400 km the musicians vers were formed by mainly extrusive volcanism on top of this melt generating channel the proposed formation model may be applicable to a number of observed volcanic ridges in the pacific including the tuamotu isles the eastern portion of the foundation chain and the western termination of the salas y gomez seamount chain

geological and geochemical characteristics of marine continental transitional shale from the lower permian taiyuan formation taikang uplift southern north china basin abstract in recent years extensive studies have been conducted on conventional shale gas resources but little work has been performed on the resource potential of marine continental shales this paper takes the lower permian taiyuan shale in the taikang uplift of the southern north china basin as an example to characterize a transitional shale reservoir the results indicate that the taiyuan shale has high toc values averaging 2 67 and contains type iii gas prone organic matter the shale has high ro values averaging 3 44 and tmax ranges from 424 c to 601 c with respect to fracability or brittleness the content of brittle minerals in the taiyuan shale ranges from 21 to 71 averaging 45 55 and the average content of clay minerals is 44 1 based on sem and sem with ar ion milling observation interparticle pores intraparticle pores and microfractures are developed in the taiyuan shale which can provide reservoir space for the accumulation of shale gas organic matter pores rarely appear due to the organic type and high maturity the results of this study can guide the shale gas exploration of taiyuan formation in the taikang uplift of the southern north china basin

geochemistry of dissolved gases from the eastern carpathians transylvanian basin boundary abstract we show the results of a study on the volatiles dissolved in mineral waters discharged over a 200 km long transect along the rodna b rg u area and c limani gurghiu harghita volcanic chain eastern carpathians romania all of the collected mineral water samples carry dissolved gas with carbon dioxide content up to 1 99 cm 3 stp gh 2 o and helium content up to 2 3 10 5 cm 3 stp gh 2 o carbon 13 c tdic total dissolved inorganic carbon ranging from 15 6 to 5 32 vs vpdb he systematics he isotopes in the range of 0 38 0 99 ra ra air normalized 3 he 4 he ratio and co 2 3 he ratio spanning over four orders of magnitude from morb like values of 2 92 10 9 to crustal type values of 3 02 10 13 coherently indicate the presence of fluids from different crustal sources e g sediments hydrocarbon reservoirs besides minor but detectable contributions of mantle magmatic derived fluids up to 16 45 our investigations show that the wide range of chemical and isotopic composition can be explained in terms of mixings among different gas sources feeding the groundwater and the contemporary occurrence of gas water interactions like degassing and deposition of carbonates affecting the circulating waters after their infiltration

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

qualitative and quantitative characterization of a transitional shale reservoir a case study from the upper carboniferous taiyuan shale in the eastern uplift of liaohe depression china abstract the paper takes the upper carboniferous taiyuan shale in eastern uplift of liaohe depression as an example to qualitatively and quantitatively characterize the transitional coal associated coastal swamp shale reservoir focused ion beam scanning electron microscope fib sem nano ct helium pycnometry high pressure mercury intrusion and low pressure gas n 2 co 2 adsorption for eight shale samples were taken to investigate the pore structures four types of pores i e organic matter om pores interparticle interp pores intraparticle intrap pores and micro fractures are identified in the shale reservoir among them intrap pores and micro fractures are the major pore types slit shaped pores are the major shape in the pore system and the connectivity of the pore throat system is interpreted to be moderate which is subordinate to marine shale the porosity from three dimension 3d reconstruction of sem images is lower than the porosity of helium pycnometry while the porosity trend of the above two methods is the same combination of mercury intrusion and gas absorption reveals that nanometer scale pores provide the main storage space accounting for 87 16 of the pore volume and 99 85 of the surface area micropores contribute 34 74 of the total pore volume and 74 92 of the total pore surface area and mesopores account for 48 27 of the total pore volume and 24 93 of the total pore surface area and macropores contribute 16 99 of the total pore volume and 0 15 of the total pore surface area pores with a diameter of less than 10 nm contribute the most to the pore volume and the surface area accounting for 70 29 and 97 70 respectively based on single factor analysis clay minerals are positively related to the volume and surface area of micropores mesopores and macropores which finally control the free gas in pores and adsorbed gas content on surface area unlike marine shale toc contributes little to the development of micropores brittle minerals inhibit pore development of taiyuan shale which proves the influence of clay minerals in the pore system

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

evidence for diffuse extension of the pacific plate from pukapuka ridges and cross grain gravity lineations satellite altimeter measurements of marine gravity reveal 100 to 200 km wavelength lineations over a wide area of the pacific plate oriented roughly in the direction of absolute plate motion at least three mechanisms have been proposed for their origin small scale convective rolls aligned in the direction of absolute plate motion by shear in the asthenosphere diffuse n s extension of the lithosphere resulting in lineated zones of extension boudins and minihotspots that move slowly with respect to major hotspots and produce intermittent volcanism recently several chains of linear volcanic ridges have been found to be associated with the gravity lineations following ridgelike gravity signatures apparent in high resolution geosat gravity measurements we surveyed a series of volcanic ridges that extend northwest from the east pacific rise flank for 2600 km onto 40 ma seafloor our survey data as well as radiometric dates on samples we collected from the ridges provide tight constraints on their origin 1 individual ridge segments and sets of ridges are highly elongate in the direction of present absolute plate motion 2 the ridges formed along a band 50 to 70 km wide in the trough of one of the more prominent gravity lineations 3 radiometric dates of the largest ridges show no hotspot age progression moreover the directions predicted for minihotspot traces older than 24 ma do not match observed directions of either the gravity lineations or the ridges based on this last observation we reject the minihotspot model the occurrence of the ridges in the trough of the gravity lineation is incompatible with the small scale convection model which would predict increased volcanism above the convective upwelling we favor the diffuse extension model because it is consistent with the occurrence of ridges in the trough above the more highly extended lithosphere however the multibeam data show no evidence for widespread normal faulting of the crust as predicted by the model perhaps the fault scarps are buried under more than 30 m of sediments and or covered by the elongated ridges finally we note that if ridge push force is much smaller than trench pull force then near the ridge axis the direction of maximum tensile stress must be perpendicular to the direction of absolute plate motion

double seismic zone and dehydration embrittlement of the subducting slab 1 dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate depth earthquakes we explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast japan southwest japan northeast taiwan northern chile cape mendocino and eastern aleutians we calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions we then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams the depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age the dehydration loci of serpentine produce a double layered structure because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab we find that the lower plane seismicity is located at the lower dehydration loci of serpentine which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement

seismic investigations of the o higgins seamount group and juan fernandez ridge aseismic ridge emplacement and lithosphere hydration the o higgins seamount group is a cluster of volcanic domes located 120 km west of the central chilean trench on the crest of the juan fernandez ridge this aseismic hot spot track is subducting under south america triggering a belt of intraslab earthquake hypocenters extending about 700 km inland the juan fernandez ridge marks the southern boundary of a shallow subduction segment subduction of oceanic basement relief has been suggested as a cause for the flat slab segments characterizing the andean trench system the juan fernandez ridge however shows only moderate crustal thickening inadequate to cause significant buoyancy in 2001 wide angle seismic data were collected along two perpendicular profiles crossing the o higgins group we present tomographic images of the volcanic edifices and adjacent outer rise trench environment which indicate a magmatic origin of the seamounts dominated by extrusive processes high resolution bathymetric data yield a detailed image of a network of syngenetic structures reactivated in the outer rise setting a pervasive fault pattern restricted to the hot spot modified lithosphere coincides with anomalous low upper mantle velocities gained from a tomographic inversion of seismic mantle phases reduced uppermost mantle velocities are solely found underneath the juan fernandez ridge and may indicate mineral alterations enhanced buoyancy due to crustal and upper mantle hydration may contribute an additional mechanism for shallow subduction which prevails to the north after the southward migration of the juan fernandez ridge

geochemical characteristics of marine and terrestrial shale gas in china abstract although the annual production of shale gas in china was 13 10 8 m 3 in 2014 a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed in the present study almost all shale gas samples available in china including marine shale gas from the wufeng longmaxi formation in the sichuan basin o 3 w s 1 l and terrestrial shale gas from chang 7 member t 3 y 7 in the ordos basin were collected and analyzed for their geochemical and isotopic compositions the shale gas from the wufeng longmaxi shale is dry gas with an average methane content of 98 38 and records a highest content of ch 4 in the world 99 59 which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance eqvro values between 2 4 and 3 6 the 13 c 1 values are correspondingly heavy and record a heaviest 13 c 1 values 26 7 for the shale gases found in the world as well the average values of 13 c 1 13 c 2 and 13 c 3 for the wufeng longmaxi shale gas are 31 3 35 6 and 47 2 respectively displaying a complete carbon isotopic reversal i e 13 c 1 13 c 2 13 c 3 2 h ch4 and 2 h c2h6 has an average value of 148 and 173 respectively also yielding a hydrogen isotopic reversal i e 2 h ch4 2 h c2h6 the chang 7 shale has an average toc content of 13 81 with vitrinite reflectance vro values between 0 7 and 1 2 the chang 7 shale gas is wet gas with an average methane content of 84 90 and is rich in heavy gaseous hydrocarbons c 2 c 5 the respective values of 13 c 1 13 c 2 and 13 c 3 are 48 7 36 4 and 31 3 displaying a positive carbon isotopic distribution pattern i e 13 c 1 13 c 2 13 c 3 the average 2 h ch4 2 h c2h6 and 2 h c3h8 values are 256 244 and 188 respectively and are characterized by a positive distribution pattern i e 2 h ch4 2 h c2h6 2 h c3h8 the differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the wufeng longmaxi and chang 7 shale are attributed to variations in thermal maturity levels co 2 is present in low content in both the wufeng longmaxi and chang 7 shale gases mostly less than 1 13 c values for the co 2 in the wufeng longmaxi formation are between 8 9 and 9 2 indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures in contrast 13 c values of the co 2 in the chang 7 shale gas range from 8 2 to 22 7 indicating an organic origin from the thermal degradation of organic matter helium in both the wufeng longmaxi and chang 7 shale gases is dominantly of curst origin in terms of their r ra ratios that vary from 0 01 to 0 08 positive carbon isotopic distribution pattern is typical of primitive thermogenic gas however it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration the causes that yield carbon isotopic reversal include 1 mixing of gases with the same source but different thermal maturity levels 2 secondary cracking of oil or wet gas 3 formation water involved reactions 4 gas diffusion and 5 carbon isotope exchange between alkane gases at high temperature among them carbon isotopic exchange between alkane gases at high temperature is a key factor nine plots have been drawn based on the shale gases from china usa and canada among them the plot of 13 c 2 versus wetness demonstrates a lying s shape with two inflection points on the gas wetness axis the wetness value of 1 4 represents a critical point from pyrolytic gas primary cracking gas to cracking gas secondary cracking gas and whereas the wetness value of 6 marks the end of oil generation on the diagram of wetness versus 13 c shale gases with wetness values greater than 1 6 are characterized by positive carbon isotopic distribution pattern whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1 6

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

analysis of the developmental characteristics and major regulating factors of fractures in marine continental transitional shale gas reservoirs a case study of the carboniferous permian strata in the southeastern ordos basin central china abstract fractures play an important role in the formation of shale gas reservoirs because they can enlarge the transport channels and aggregation spaces and increase the specific surface area of the gas shale for artificial hydraulic fracturing of these reservoirs the natural fracture system must be fully integrated with the artificial fracture system to form an intact fracture system in this study we first comprehensively examined the fractures in 42 shale gas wells using several approaches including a systematic examination and description of the cores and the casting of thin sections a compilation of the statistics of fracture feature parameters and observation of various analytical and test data such as the mineral composition the organic carbon contents and the rock mechanics properties for specimens from the corresponding fractured intervals the data enabled us to thoroughly explore the developmental features and major factors affecting organic rich shale fractures in the upper paleozoic carboniferous permian marine continental transitional coal bearing formation which is located in the southeastern ordos basin our results reveal that in comparison with the paleozoic marine shale in the united states and southern china as well as the paleozoic basin transitional shale in northern china the upper paleozoic black shale in the ordos basin is primarily characterized by a relatively low content of brittle minerals and a high content of clay ingredients the total content of brittle minerals e g quartz feldspar and siderite was approximately 33 which included 27 quartz and 0 3 k feldspar but did not include carbonate the total content of clay minerals reached 64 and was dominated by mixed layer illite smectite i s which accounted for more than 41 of the total clay ingredients the shale accommodated the widespread development of various types of macro and microfractures in the core specimens medium angle slip fractures and horizontal bedding cracks were the most common types of fractures whereas vertical and high angle fractures and horizontal bedding cracks were underdeveloped in the thin sections microfractures arising in organic matter laminations or at their edges as well as those of tectonic origin were the predominant type of fractures and they were mainly short narrow and open overall the surface fracture ratios of the thin sections were concentrated in a range of approximately 0 1 0 3 the developmental level of the fracture was influenced by various factors including tectonism lithology rock mechanics and organic matter and mineral content thus increased developmental level of fractures was correlated with higher paleostructural elevation and increased sand content whereas the developmental level of microfractures was correlated with high lamellation development high level of organic carbon leading to more pronounced laminations and high contents of quartz mixed layer i s and illite leading to low levels of kaolinite these findings were corroborated by other data generated in this study including the rock mechanics results for the upper paleozoic black shale and silty shale the observation results from the cores and from the thin sections sampled from more than 40 shale gas wells and the anomalies of gas logging

nanoscale pore structure and fractal characteristics of a marine continental transitional shale a case study from the lower permian shanxi shale in the southeastern ordos basin china abstract shale samples collected from seven wells in the southeastern ordos basin were tested to investigate quantitatively the pore structure and fractal characteristics of the lower permian shanxi shale which was deposited in a marine continental transitional hereinafter referred to as the transitional environment low pressure nitrogen adsorption data show that the shanxi shale exhibits considerably much lower surface area sa and pore volume pv in the range of 0 6 1 3 m 2 g and 0 25 0 9 ml 100 g respectively type iii kerogen abundant in the transitional shanxi shale were observed to be poorly developed in the organic pores in spite of being highly mature which resulted in a small contribution of organic matter om to the sa and pv instead i s illite smectite mixed clay together with illite jointly contributed mostly to the sa and pv as a result of the large amount of inter layer pores associated with them which were evident in broad ion beam bib imaging and statistical analysis additionally the shanxi shale has fractal geometries of both pore surface and pore structure with the pore surface fractal dimension d1 ranging from 2 16 to 2 42 and the pore structure fractal dimension d2 ranging from 2 49 to 2 68 respectively the d1 values denote a pore surface irregularity increase with an increase in i s and illite content attributed to their more irregular pore surface compared with other mineralogical compositions and om the fractal dimension d2 characterizing the pore structure complexity is closely related to the pore arrangement and connectivity and i s and illite decrease the d2 when their contents increase due to the incremental ordering degree and connectivity of i s or illite hosted pores meanwhile other shale constituents including kaolinite chlorite and om that possess few pores can significantly increase the pore structure complexity by way of pore blocking

seismic body wave constraint on mechanisms of intermediate depth earthquakes 1 source parameters of six large earthquakes 7 1 mw 7 7 in the depth range between 112 and 277 km from five different subduction zones are derived from teleseismic body waves recorded by global seismic networks except for the 21 october 1995 mexican event which is consistent with the model of simple rupture on a planar surface the investigated earthquakes show complex rupture processes that can be explained by irregularities in the focal region as is the case of shallow events the inferred velocity of the moment release varies between 2 5 and 4 km s corresponding to 40 90 of the shear velocity at the focus four of the six earthquakes show stress drops in the range observed for shallow events 1 10 mpa ruptures extend mainly parallel to the strike of subducting slabs with dimensions reaching up to 50 km the extent of rupture perpendicular to slab dip of generally less than 15 km is comparatively small this suggests that the rupture during large intermediate depth earthquakes propagates predominantly parallel to the strike of the subducting plate and that the seismogenic zone perpendicular to the dip direction is limited to a narrow width the relatively small rupture size perpendicular to slab dip suggests that the rupture process does not extend into regions of significantly different temperatures the spatial extent of the investigated earthquakes is consistent with the orientation of trench parallel faults that are generally observed in near trench outer rise regions suggesting that these events may result from reactivation of such preexisting faults at intermediate depths through dehydration of hydrous minerals concentrated in these zones of weakness depths of most of the earthquakes are consistent with the dehydration embrittlement of serpentine the bolivian earthquake of 23 january 1997 seems to be too deep 277 km for such an explanation

characterizing the pore structure in the silurian and permian shales of the sichuan basin china abstract nitrogen sorption and mercury intrusion methods were applied to characterize the pore structure of the lower silurian shales of the long ma xi formation and upper permian shales of the da long formation in the sichuan basin the results indicate that the specific surface areas and porosities of the silurian shales are in the range of 17 83 29 49 m 2 g and 3 65 18 26 respectively the silurian shales show a bimodal pore size distribution and consist of both micropores and nanopores ranging from 30 to 60 m and 1 7 20 nm respectively a strong positive linear correlation between the surface areas and total organic carbon content toc suggests that the organic matter contributes mostly to the amount of specific surface area of the silurian shales whereas the contribution of clay minerals appears to be negligible the organic matter also accounts for 50 70 of the porosity in the silurian shales soluble organic matter in the form of bitumen however has a negative impact on the surface area and porosity of the silurian shales and reduce the amount of surface area and porosity in these shales for the permian shales their surface area and porosity are lower than those of the silurian shales and are in the ranges of 2 20 3 52 m 2 g and of 1 30 4 15 respectively the pore size distribution of the permian shales shows a unimodal pattern of micropores in a size range of 30 60 m their toc and clay mineral contents display poor correlation with the surface areas and suggest that both the organic matter and clay minerals have very low surface areas a clear negative correlation between the porosity and toc in the permian shales indicates that organic matter contributes little or insignificantly to the porosity due to poorly developed organic pores in kerogen because the permian shales are much lower in thermal maturity than the silurian shales furthermore there is a consistent negative linear correlations between the bitumen content and the porosity for both the permian shales and silurian shales and indicate that the bitumen may significantly reduce the porosity of the shales by occupying the pore spaces in the mineral and organic matrix finally it is clear that the lower silurian shales have a greater shale gas potential than the upper permian shales do based on their surface area and porosity

are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle in a number of subduction zones earthquakes at 50 200 km depth define two dipping planes separated by 20 40 km that appear to merge downdip upper plane earthquakes are inferred to occur within the subducting oceanic crust whereas lower plane earthquakes occur in the subducting oceanic mantle beneath northeast japan the results of a new finite element heat transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle lower plane earthquakes occur at 550 800 c at 100 km depth and at 350 600 c at 160 km depth these conditions coincide with the dehydration reaction antigorite serpentine forsterite enstatite h 2 o which suggests that lower plane earthquakes may be triggered by dehydration embrittlement which in turn suggests that the subducting oceanic mantle is partially hydrated serpentinization may occur in the trench outer rise region where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere if this hypothesis is correct current subduction zone h 2 o budgets may significantly underestimate the amount of bound h 2 o entering the subduction factory

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

do intermediate and deep focus earthquakes occur on preexisting weak zones an examination of the tonga subduction zone it has been proposed that intermediate and deep focus earthquakes occur on preexisting planes of weakness that were created at shallow depth the purpose of this study is to test this hypothesis we examined fault plane solutions for 360 events that occurred in the tonga subduction zone from january 1976 to february 1999 for events in the slab each fault plane solution is rotated by the slab dip angle so that the slab is in its original horizontal position we then compare fault plane solutions for events in the slab with those for events at the outer rise we find that an asymmetric fault system corresponding to that found for outer rise events persists down to about 450 km depth this suggests that earthquakes down to this depth are caused by the reactivation of preexisting faults created in the oceanic plate before subduction a similar pattern though less well constrained is found in the kurile subduction zone down to 200 km depth for earthquakes deeper than 450 km the fault plane solutions are much more scattered in some places the fault plane pattern suggests the creation of new fault planes along orientations of maximum shear with zero internal friction the pattern of fault plane solutions in particular localized volumes cannot be easily explained by the creation of new faults in the direction of maximum shear under a coherent regional tectonic stress field thus either a highly heterogeneous stress field exists or preexisting planes of weakness also account for some deep earthquakes

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

merging sequence stratigraphy and geomechanics for unconventional gas shales the recent revelation of vast global quantities of potentially gas and oil productive shales has paved the way for rapid advancements in understanding their geological properties many of which affect their geomechanical properties and ultimately reservoir operations and performance because of shale s unique and very intricate geological physical and mechanical properties at all scales from nano to macro scale abousleiman et al 2010 compared with sandstones and carbonates the ad jective unconventional has often been applied to their characterization although many shale characteristics are different than those of sandstones and carbonates and require new technologies to measure them other characteristics mentioned below are similar as such customized conventional methodologies and concepts can be applied to exploration and production of shale gas and oil

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

seismological evidence for the existence of serpentinized wedge mantle serpentinized peridotite is detected seismologically by mapping poisson s ratio beneath the kanto district central japan because serpentinite has a higher poisson s ratio than other rocks in the crust and upper mantle we determine three dimensional p and s wave velocity models using travel time tomography and then construct a three dimensional map of poisson s ratio the models show low velocity anomalies near the upper boundary of the slab in a depth range from 20 to 70 km in the low velocity region there is an area with poisson s ratio greater than 0 3 at depths of 20 45 km which we attribute to serpentinized peridotite the rest of the low velocity region is interpreted as descending oceanic crust with a poisson s ratio of about 0 25 the high poisson s ratio area is associated with low seismicity and weak interplate coupling which is consistent with the ductility of serpentinite

pore size distributions contributed by om clay and other minerals in over mature marine shale a case study of the longmaxi shale from southeast chongqing china abstract nano scale pores play an important role in determining the adsorption capacity of shale gas to quantitatively evaluate the pore size distributions contributed by organic matter om clay and other minerals in an over mature shale reservoir the lower silurian longmaxi shale from southeast chongqing was selected as a case study and was analyzed by the pore size distributions contributed by om clay and other minerals psdcoco method based on the results of total organic carbon toc carbon element content in om x ray diffraction xrd and low temperature nitrogen adsorption desorption ltna experiments the pore size distributions contributed by a unit mass of om clay and other minerals were calculated and the differences between the results of the ltna and psdcoco methods were determined for the four verified samples the average value of the difference between the experimental and calculated pore volumes is 0 154 10 3 cm3 g for the longmaxi shale from the py1 well the contributions of om and other minerals to the pore volume pore width

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

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

mantle wedge water contents estimated from seismic velocities in partially serpentinized peridotites 1 water carried into subduction zones with the down going plate and subsequently released by dehydration reactions at depth affects the composition of the mantle wedge triggers partial melting and affects subduction zone seismicity partially serpentinized peridotite may be a significant reservoir for water in the subducted plate the mantle wedge and the overriding plate here we develop a model that relates the degree of serpentinization and water content of partially serpentinized peridotites to their seismic p wave velocities in partially serpentinized ultramafic rocks a 1 decrease in p wave velocity corresponds to a 2 4 increase in serpentine content and a 0 3 0 18 moles m3 increase in h2o content up to a maximum of 13 where there is evidence of serpentinization mantle serpentine content is typically 15 corresponding to 4 5 wt h2o 6 10 moles m3

crustal structure of north atlantic fracture zones seismic studies have established that large offset transforms along the slow spreading mid atlantic ridge exhibit anomalous crustal structures that fall well outside the range typically associated with oceanic crust seismically fracture zone crust in the north atlantic is extremely heterogeneous in both thickness and internal structure it is frequently quite thin 1 2 km thick and is characterized by low compressional wave velocities and the absence of a normal seismic layer 3 a more gradual crustal thinning can extend up to several tens of kilometers from these fracture zones anomalously thin crust has also been inferred from both seismic and gravity studies at smaller ridge axis discontinuities along the mid atlantic ridge the geological nature of the seismically anomalous crust found within atlantic fracture zones and how this crust forms are still controversial one interpretation consistent with available seismic observations is that the crust within north atlantic fracture zones consists of a thin intensely fractured and hydrothermally altered basaltic section overlying ultramafics that are extensively serpentinized in places variations in apparent seismic crustal thickness along fracture zones may reflect different degrees of serpentinization of the upper mantle section or changes in the thickness of the igneous crust the existence of a thinner crustal section in fracture zones can be explained by a reduced magma supply within a broad region near ridge offsets due to the three dimensional nature of upwelling beneath a segmented spreading center and by tectonic dismemberment of the crust by large scale detachment faults that form preferentially in the cold brittle lithosphere near the ends of segments