specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

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

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

effects of complicated 3 d rupture geometries on earthquake ground motion and their implications a numerical study summary we present a numerical study of the effects of geometrically complicated 3 d ruptures on near source ground motions in most of the kinematic and dynamic rupture modelling studies or seismic moment tensor and slip inversions the strong assumption of a perfectly planar fault is made however it is known from geological field studies that real fault traces are not planar but characterized by relatively strong deflections bends and other irregularities in this paper we investigate the effects of such non planar earthquake ruptures on ground motion modelling in comparison to their equivalent planar ones for this purpose we apply the highly accurate discontinuous galerkin method that is capable of incorporating the geometry of complicated non planar rupture surfaces by a set of double couple point sources that do not have to coincide with the mesh vertices we generate a set of kinematic rupture models characterized by random spatial deflections with various correlation lengths and root mean square values these deflections then determine the associated spatial strike and dip variations we find that the deflected rupture models have the same seismic moment tensor as the perfectly planar one however with a reduced scalar moment which we correct for after a sound validation of our modelling approach we present the effects of the deflections on synthetic velocity seismograms computed in the vicinity of the rupture we observe that these geometrical irregularities do not just lead to high frequency effects but can strongly affect the synthetics in the whole frequency band finally we discuss our observations in detail and conclude that the correct incorporation of the geometrical properties such as local strike and dip variations of the rupture surface is an important issue we also discuss possible implications for some seismological fields such as strong motion simulations or seismic moment tensor and slip inversions where these results might have significant consequences

gas potential of proterozoic and phanerozoic shales from the nw himalaya india inferences from pyrolysis abstract organic richness and kerogen properties of sixty seven shales obtained from the outcrops and underground mines of jammu kashmir and ladakh regions of northwest himalaya india have been studied to evaluate their gas generation potential using rock eval pyrolysis ranging in age from the proterozoic to tertiary organic matter content and characteristics of the carbonaceous and coaly shales vary widely indicating that sedimentary and burial history significantly affected the preservation and maturation of organic components in rocks the total organic carbon toc content ranges from 0 01 to 1 2 in the permian jurassic and paleozoic tertiary shales of ladakh to as high as 32 5 in the eocene shales coaly shales from jammu the thermo labile hydrocarbons s1 and those from cracking of kerogen s2 released from the pyrolysis of eocene subathu shales are observed to be high from 0 1 to 2 6 and from 0 5 to 15 5 mg hc g rock respectively rock eval thermal maturity parameters indicated by tmax temperature at highest yield of s2 490 c and calculated vitrinite reflectance 1 5 to 3 7 ro suggest a post mature dry gas stage for the hydrocarbon generation based on hydrogen index hi and tmax correlations organic matter in the subathu shales is characterized by a late metagenetic gas prone type iii kerogen and a fair to excellent gas potential is exhibited by these shales the interbedded shale units in the proterozoic sirban limestone formation occurring as an isolated inlier in jammu show toc values from 0 1 to 1 4 with quite low s1 s2 and hi values thermal maturity of shales within the stromatolitic sirban succession indicates a post mature and or already spent hydrocarbon stage the plio pleistocene carbonaceous clays lignites and mudstones from the lower karewa group of kashmir basin are organically rich with toc content ranging from 5 86 to 29 4 a thermally immature type ii type iii kerogen is indicated by the hi 109 to 278 mg hc g toc and tmax 399 to 427 c plots of the karewa samples the exposed lower triassic black shales from the permian triassic boundary sections in kashmir are comparatively lean in organic matter with toc values ranging from 0 18 to 0 93 whereas the permian jurassic and paleozoic tertiary shales from ladakh have a toc content ranging from 0 01 to 1 22 the pyrolyzable organic carbon is

net subsidence and number of cycles their interrelationship in different permian gondwana basins of peninsular india abstract seven data sets were structured from subsurface lithologs of permian gondwana coal measures comprising the karharbari barakar and raniganj formations of the koel damodar and mahanadi basins of peninsular india all three formations are fluvial in nature and composed largely of fining upward cycles of clastic sediments capped by coal carbonaceous shale simple linear regression lines and correlation coefficients were computed for total thickness of strata net subsidence and number of cycles in each data set the strong positive relationships between total thickness of strata and number of cycles in permian coal measures suggest that the fluvial cycles of karharbari barakar and raniganj are formed by intrabasinal mechanisms of channel migration sedimentation and subsidence rather than tectonic events in the source area the slopes of linear regression lines fitted to the data sets vary more than has hitherto been supposed and are classified into two categories three out of seven regression lines exhibit steeper slopes and they are closely similar in this respect to other permian and upper carboniferous coal measures of australia great britain and germany the other four have gentler slopes these dissimilarities in the slopes of regression lines are attributed to the differential rate of increase in the number of cycles with respect to the total thickness of the strata net subsidence as well as the differential subsidence of the permian gondwana supergroup through space and time

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

experimental investigation of matrix permeability of gas shales predicting long term production from gas shale reservoirs has been a major challenge for the petroleum industry to better understand how production profiles are likely to evolve with time we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability experiments were conducted on intact core samples from the barnett eagle ford marcellus and montney shale reservoirs the methodology used to measure permeability allows us to separate the reduction of permeability with depletion because of the resultant increase in effective confining stress and the increase in permeability associated with knudsen diffusion and molecular slippage also known as klinkenberg effects at very low pore pressure by separating these effects we are able to estimate the relative contribution of both darcy and diffusive fluxes to total flow in depleted reservoirs our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures because of the slippage effects we use the magnitude of the klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100 200 nm in a relatively high permeability eagle ford sample finally to gain insight on the scale dependence of permeability measurements the same core plugs were crushed and permeability was again measured at the particle scale using the so called gas research institute method the results show much lower permeability than the intact core samples with very little correlation to the measurements on the larger scale cores

fractal characteristics of upper cretaceous lacustrine shale from the songliao basin ne china abstract to improve our understanding of the characteristics of nanopores and their influence on liquid hydrocarbon occurrences in lacustrine shale we carried out fractal analysis on 21 lacustrine shale cores from the upper cretaceous qingshankou formation k2qn in the songliao basin ne northeast china using toc total organic carbon and rock eval analysis xrd x ray diffraction low pressure nitrogen adsorption experiments and the fhh frenkel halsey hill method the relationships between composition of lacustrine shale toc minerals oil content the pore structure parameters bet surface area pore volume pore average diameter and the fractal dimensions were investigated two fractal dimensions d1 and d2 at relative pressures of 0 5 1 and 0 0 5 respectively were obtained with d1 ranging from 2 5055 to 2 8888 and d2 between 2 1026 and 2 733 d1 is greater than d2 indicating that small pores are more homogeneous than larger pores both d1 and d2 increase with increasing bet surface areas and total pore volumes and increase with decreasing average pore diameters the fractal dimensions of lacustrine shale are negatively correlated with the clay content but show no obvious relationship with the quartz content the relationship between fractal dimensions both d1 and d2 and toc content is a u shaped curve with minimum d values at 2 5 3 wt toc fractal dimension d1 can be used to characterize the shale oil content and lacustrine shale samples with a lower fractal dimension have greater free oil therefore considering the influence of toc content on fractal dimension and the relationship between oil content and fractal dimension we conclude that lacustrine shale in the oil generation stage with 2 5 3 0 wt toc is probably the preferred shale oil exploration target in the songliao basin the results indicate that fractal analysis leads to a better understanding of the pore structure and oil storage capacity of lacustrine shale

architecture and facies pattern of a sublacustrine fan jharia basin india abstract a small sublacustrine fan deposit has been identified within a lacustrine succession belonging to the barren measure formation middle permian of the lower gondwana deposits of jharia basin india the stratigraphic position of the fan and its structural relationship with the associated sediments suggest that the east west aligned elongate trough formed in the central part of the basin experienced intrabasinal normal faulting of limited lateral extent and accumulation of clastic input within the associated hangingwall syncline led to formation of this deposit three major framework components can be identified within this deposit a sheet like sandstone aprons b channel fill sandbodies and c lensoid massive beds of pebbly sandstone the laterally extensive sheet like bodies of sandstone covering almost the whole of the older sediments appear to be the product of deposition from unconfined sediment laden flows during episodic flood events the proximal part of the deposit is dominated by the successive deposition of sandstone aprons with a few channel plug sandbodies produced through rapid sedimentation from channelised sediment laden turbulent flows the distal part on the other hand is mainly represented by the stacked channel fills with alternate sandstone aprons following the deposition of bedded sandstones as the slope of the depositional surface reduced turbulent flows with relatively less grain concentration extended towards the ambient waterbody through channels incised into the preexisting unconsolidated sediments during this process of incision the flows gradually became hyperconcentrated the channels were ultimately filled in by concordant bedsets in approximate conformity with the shape of the channel either through bedload deposition or suspension fall out from these submerged currents a few massive channel fills indicating emplacement of liquefied sandflows caused by slope instability during high flood event are also present isolated channel fills show lateral uniformity in facies pattern while confluent channels produced laterally variable composite facies association with a distinct zone of interference lensoid mass flow deposits with distinct upslope slide scarps represent the event of slope failure as a result of cannibalisation during low water stand these slide lenses are present in different levels in association with either the sandstone aprons or the channel fills showing high degree of randomness in their order of appearance the consistently developed round bottomed geometry of the channels and the nature of channel fills strongly advocate in favour of their subaqueous origin absence of any subaerial character within the sandstone aprons also suggests their emplacement under subaqueous condition the thick stacks of channel fill sandbodies were developed as a consequence of vertical channel aggradation under continued hangingwall subsidence and the upward declining trend in vertical aggradation suggests gradual fall in the rate of this subsidence subsequently the whole block subsided and went under deepwater condition due to lacustrine transgression and the fan was buried under deepwater carbonaceous shale

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

effect of grain scale alignment on seismic anisotropy and reflectivity of shales the elastic properties and anisotropy of shales are strongly influenced by the degree of alignment of the grain scale texture in general an orientation distribution function odf can be used to describe this alignment which in practice can be characterized by two legendre coefficients we discuss various statistical odfs that define the alignment by spreading from a mean value in particular the gaussian fisher and bingham distributions we compare the statistical models with an odf resulting from pure vertical compaction no shear strain of a sediment the compaction odf may be used to estimate how the elastic properties and anisotropy evolve due to burial of clayey sediments our study shows that the three statistical odfs produce almost identical correspondence between the two legendre coefficients as a function of the spreading parameter so that the spreading parameter of one odf can be converted to the spreading parameter of another odf in most cases it is then sufficient to apply the spreading parameter for the odf instead of the two legendre coefficients the effect of compaction on the odf gives a slightly different correspondence between the two legendre coefficients from that for the other models in principle this opens up the possibility of distinguishing anisotropy effects due to compaction from those due to other processes we also study reflection amplitudes versus angle of incidence ava for all wave modes where shales having various odfs overlie an isotropic medium the ava responses are modelled using both exact and approximation formulae and their intercepts and gradients are compared the modelling shows that the s wave velocity is sensitive to any perturbation in the spreading parameter while the p wave velocity becomes increasingly sensitive to a perturbation of a less ordered system similar observations are found for the ava of the p p and p sv waves modelling indicates that a combined use of the amplitude versus offset of p p and p sv reflected waves may reveal certain grain scale alignment properties of shale like rocks

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

the raniganj coal basin an example of an indian gondwana rift abstract rifting occurred in peninsular india during permian triassic gondwana sedimentation the rocks of the paleozoic mesozoic indian gondwana supergroup succeed the mesoproterozoic vindhyan sedimentary rocks and the indian precambrian shield unconformably and are renowned for their coal resources the rocks of the gondwana supergroup occur mainly in trough like depressions arranged in a more or less en echelon fashion along distinct shear fault zones which are parallel to ancient structural lineaments in the indian peninsular shield thus the gondwana group of basins occurs along the three major directions a son narmada and damodar koel valley running east west b son mahanadi valley with a nw se trend and c rewa pranhita godavari valley which trends in a nnw sse direction the important common structural imprints in most of the above basins are i a half graben basin geometry with a strong master boundary fault on one side and a homoclinal tilt of the basin towards it ii a network of intrabasinal faults one set oriented along the basin axis and which formed during the tensional stage and another iii transverse to it basin marginal oblique faults and slips coincide with both the tensional and compressional stages and have different manifestations syndepositional subsidence of the basin floor through loss of support from below due to the lateral transport of sub crustal mantle materials caused faulting at the axial zones of the basins sub basins to accommodate a thick pile of sediments volcanic activities in the region or in adjacent areas provide further support for these inferred processes and are confined within comparatively narrow and linear zones defined by the crustal weaknesses of considerable antiquity all these stages have their signatures imprinted in the sediments which have been studied in detail this paper presents relevant data on the raniganj coalfield of eastern india in order to examine whether these linear depressions are of rift origin the process of rifting was a prelude to the rafting of gondwana continents after the early cretaceous fragmentation of gondwanaland thus the gondwana rift valleys flanked the periphery of the peninsular indian stable blocks to collide ultimately with the sino eurasian plate in the north

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

geochemical and petrophysical characteristics of permian shale gas reservoirs of raniganj basin west bengal india abstract thick shale horizons of permian age emerged as the potential source of gas through primary investigation and resulted into the first indian pilot scale gas recovery demonstration project in the raniganj basin however the relation of geochemical properties with shale pore matrix porosity and permeability mechanism are yet to be evaluated for better dealing the phenomena of diffusion transport and gas recovery in this study the analyses like proximate rock eval toc vro low pressure n2 sorption porosity permeability sem edx and image processing have been carried out the values of s1 s2 toc and tmax indicated fair to excellent source rock potential of the shales having type iii iv kerogens prone to thermal gas genesis the low pressure n2 desorption curve of raniganj formation shales shows the type h3 hysteresis comprising slit shaped pores the barren measures shales have type h2 and h3 hysteresis patterns specifying to ink bottle shaped pores and slit shaped pores whereas the oldest barakar formation shales are having ink bottle shaped pores caused due to blocking effect the slit shaped pores favour the pore network and characteristically excellent for the flow of gas the results of sem edx are indicating alteration stability in the order of o the increasing tmax values with a centric decrease in porosity and permeability specifying the role of devolatilization disintegration and blocking of pore spaces openings is a function of the thermal gradient the linear evolution of multipoint bet surface area with increasing porosity suggests that the porosity values from 2 0 to 6 5 mainly corresponds to pore size of 3 0 11 0 nm similarly the inverse relationship between average pore size and porosity attributed to a greater contribution of smaller pores in total porosity the pore network model derived through the sem image processing has shown two types of connectivity i various pore sizes of diverse pore throats with dual opening directions and ii interlinked large and small pores obeying similar normal distributions the barren measures shales have shown higher pore connectivity than the raniganj and barakar formation shales

assessment of organic richness and hydrocarbon generation potential of raniganj basin shales west bengal india abstract high energy prices and severe energy shortage has led shale gas to become the focus of study and exploration in many countries india like many other countries around the world with shale gas potential recognizes the strategic importance of developing its shale gas resources for the purpose of shale gas assessment the authors have selected sixty six borehole shale samples of different formations from different parts of raniganj basin west bengal india rock eval pyrolysis and total organic carbon toc analysis and petrographic characterization of the shales were carried out shales from barakar lower permian barren measures upper permian and raniganj formation upper permian are marked by good to excellent toc content input of type iii organic matter and are capable of generating oil and thermogenic gas upon thermal cracking igneous intrusives dykes and sills in the formations occurring in and around the areas of sitarampur si and kulti ku in western part of the basin might have resulted in cooking of the shales increasing their maturities estimated vitrinite reflectance vro as indicated by the barren measures shales of shallow depths from the above mentioned areas majority of the samples are marked by low oxygen index oi values

native terranes of the central klamath mountains california the klamath mountains of northern california and southern oregon contain several good examples of terranes which have developed in situ the term native is proposed for five of these terranes and all terranes whose development can be tied to an adjacent cratonal area the klamath terranes discussed herein include disrupted stratigraphic and metamorphic types three disrupted terranes the rattlesnake creek eastern hayfork and north fork contain fossiliferous blocks derived from both north american and exotic sources the unique mixed faunal assemblage stratigraphic ties to north america in the source terranes of the blocks and paleomagnetic evidence indicate that the tectonic and sedimentary processes responsible for mixing these blocks occurred in proximity to north america not distant from the terranes present positions coeval blueschist metamorphism in a fourth inboard terrane the stuart fork suggests that all four terranes developed during a late triassic to early jurassic subduction event a fifth stratigraphic terrane the western hayfork was constructed upon the assembled disrupted and metamorphic terranes in the middle jurassic disrupted terranes with similar mixtures of north american and exotic faunas occur throughout the cordillera from central california possibly as far north as british columbia late triassic deformation has been documented in several of these terranes suggesting that 1 subduction operated along at least this portion of north america during the late triassic early jurassic and 2 many additional cordilleran terranes should also be considered native

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

geological controls on coalbed methane reservoir capacity and gas content the influence of coal composition and rank on coalbed methane reservoir capacity gas content and gas saturation have been investigated for a series of australian canadian and united states coals globally there is no or little correlation between coal rank and methane adsorption capacity as commonly assumed although in particular basins there are general trends with rank and composition micropore1 capacity and surface area determined from low pressure carbon dioxide adsorption isotherms 0 c decrease and then increase with rank passing through a minimum in the high volatile bituminous coal rank there is no consistent variation in modal micropore size or size distribution with rank for suites of isorank coals there is a poor permian bulli and wongawilli seams australia to good positive correlation gates formation coal seams lower cretaceous canada between vitrinite content and methane adsorption capacity dry ash free and as received bases for each isorank coal suite there is a good correlation between micropore capacity and abundance of vitrinite and high pressure methane adsorption capacity comparison of coals of similar composition but from different isorank suites indicates however that the coals with the highest methane adsorption capacity do not necessarily have the highest micropore capacity such results are counterintuitive most pore volume available for methane adsorption is generally assumed to be microporosity it is suspected that moisture prevents methane from accessing some microporosity or competes with methane for adsorption space carbon dioxide micropore capacity which is performed on a dry basis may thus not reflect the microporosity available for gas adsorption in moisture equilibrated coals alternatively because of differing physical and chemical properties of carbon dioxide and methane apparent microporosity available to carbon dioxide due to greater energy of adsorption may not be available to methane total desorbed gas from canister analyses of sydney basin australian coals suggests that most coals are under saturated for a small data set the degree of saturation is negatively correlated with permeability r 0 78 suggesting preferential gas leakage from the higher permeability coals which are vitrite rich some degree of under saturation is probably the result of increased reservoir capacity as a consequence of uplift of the coal seams and thus lower temperatures following gas generation rates of desorption are correlated with total gas content r 0 79 but do not correlate with rank or any compositional parameter

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

seismic anisotropy of shales shales are a major component of sedimentary basins and they play a decisive role in fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid lithology and pore pressure from seismic data and to understand time to depth conversion errors and non hyperbolic moveout a single anisotropy parameter thomsen s parameter is sufficient to explain the difference between the small offset normal moveout velocity and vertical velocity and to interpret the small offset avo response the sign of this parameter is poorly understood with both positive and negative values having been reported in the literature is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles if the ratio of the normal to shear compliance of the contact regions exceeds a critical value the presence of these regions acts to increase and a change in the sign of from the negative values characteristic of clay minerals to the positive values commonly reported for shales may occur misalignment of the clay particles can also lead to a positive value of for transverse isotropy the elastic anisotropy parameters can be written in terms of the coefficients w 200 and w 400 in an expansion of the clay particle orientation distribution function in generalized legendre functions for a given value of w 200 decreasing w 400 leads to an increase in while for fixed w 400 increases with increasing w 200 perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of w 200 and w 400 given by w max 200 10 8 2 and w max 400 3 2 8 2 a comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the w 200 w 400 plane defined by w 400 w 200 w max 400 w max 200