geochemistry reservoir characterization and hydrocarbon generation potential of lacustrine shales a case of yq 1 well in the yuqia coalfield northern qaidam basin nw china abstract ever since a breakthrough of marine shales in china lacustrine shales have been attracting by the policy makers and scientists organic rich shales of the middle jurassic strata are widely distributed in the yuqia coalfield of northern qaidam basin in this paper a total of 42 shale samples with a burial depth ranging from 475 5 m to 658 5 m were collected from the shimengou formation in the yq 1 shale gas borehole of the study area including 16 samples from the lower member and 26 samples from the upper member geochemistry reservoir characteristics and hydrocarbon generation potential of the lacustrine shales in yq 1 well were preliminarily investigated using the experiments of vitrinite reflectance measurement maceral identification mineralogical composition carbon stable isotope low temperature nitrogen adsorption methane isothermal adsorption and rock eval pyrolysis the results show that the shimengou shales have rich organic carbon averaged 3 83 which belong to a low thermal maturity stage with a mean vitrinite reflectance ro of 0 49 and an average pyrolytic temperature of the generated maximum remaining hydrocarbon tmax of 432 8 c relative to marine shales the lacustrine shales show low brittleness index averaged 34 9 but high clay contents averaged 55 1 high total porosities averaged 13 71 and great langmuir volumes averaged 4 73 cm 3 g unlike the marine and marine transitional shales the quartz contents and brittleness index bi values of the lacustrine shales first decrease then increase with the rising toc contents the kerogens from the upper member shales are dominant by the oil prone types whereas the kerogens from the lower member shales by the gas prone types the sedimentary environment of the shales influences the toc contents thus has a close connection with the hydrocarbon potential mineralogical composition kerogen types and pore structure additionally in terms of the hydrocarbon generation potential the upper member shales are regarded as very good and excellent rocks whereas the lower member shales mainly as poor and fair rocks in overall the shales in the top of the upper member can be explored for shale oil due to the higher free hydrocarbon amount s1 whereas the shales in the lower member and the upper member with the depths greater than 1000 m can be suggested to explore shale gas

stable chlorine isotopes in the palo duro basin texas evidence for preservation of permian evaporite brines experimental evaporation of seawater yields brines with 37cl from 0 0 initial to 0 9 in the palo duro basin brines with 37cl values overlapping the 0 1 to 0 4 range of halite evaporite can be generated by a set of processes including dissolution of halite in meteoric water such brines occur above and below an evaporite aquitard brines with 37cl values of 0 4 to 1 0 in the evaporite aquitard and in a deep brine aquifer cannot be generated by dissolution of halite considered with br and cl content d and noble gas content the 37cl data indicate that such brines originated as evapoconcentrated seawater high br evaporite brine formed directly from seawater on the eastern side of the basin whereas low br evaporite brines on the western side formed after an influx of meteoric water at the time of evaporite formation there has not been detectable vertical flow of meteoric water across the evaporite aquitard strata beneath the evaporite contain compartments that have been isolated geochemically since the permian

evidence of multiple halogen sources in scapolites from iron oxide copper gold iocg deposits and regional nacl metasomatic alteration norrbotten county sweden abstract scapolites from barren regional na cl metasomatic assemblages rm iron oxide copper gold deposits iocg scapolite altered metabasic rocks iocg m and from iocg proximal alteration na skarns iocg ps from norrbotten county in northern sweden have been analysed for halogen content and cl stable isotope composition the aim of the study was to constrain the source of halogens within alteration assemblages and to investigate the possible fractionation of cl isotopes between scapolite and the hydrothermal fluid scapolite separates were analysed for cl br and major oxide concentrations using electron probe micro analysis epma and micro x ray fluorescence xrfm spectrometry chlorine was extracted from the scapolite separates via pyrohydrolysis and then analysed for their stable cl isotope compositions by isotope ratio mass spectrometry irms all samples of scapolite investigated in this study are marialitic in composition one of the scapolites from the gruvberget deposit iocg ps had a cl br molar ratio of 2363 which is the highest amongst all scapolites reported in the literature to date cl br molar ratios lower than seawater 650 were identified in two iocg ps scapolite samples cl br 554 and 271 as well as in two iocg m scapolites cl br 393 and 565 three rm scapolites had cl br molar ratios very close to or slightly higher than seawater values 639 to 770 samples with cl br molar ratios less than seawater are inferred to have halogens derived from evaporative residual brines whereas samples with molar ratios higher than seawater may have halogens derived from fluids that have dissolved halite and or are from magmatic systems considering the wide variation of the cl br molar ratios in the iocg ps and iocg m scapolites compared to the restricted composition of the regional alteration rm it is proposed that the hydrothermal fluids interacted with several different protoliths to generate the iocg alteration rm alteration scapolites had 37 cl values from 0 1 to 0 3 two iocg m scapolites had values of 0 2 and iocg ps scapolites had 37 cl values from 0 1 to 1 0 using a previously published 37 cl value from fluid inclusion leachates 1 7 from the iocg m mineralisation at pahtohavare and the 37 cl value of co existing scapolite measured in this study 0 2 an empirical fluid scapolite fractionation factor was calculated to be 1 9 this large fractionation factor is not supported by previous predictions for monovalent chlorides and assuming equilibrium indicates that 37 cl was preferentially accommodated in the a site of the scapolite structure this indicates that either the stable cl isotope partitioning between the cacl 2 rich brine and the scapolite may differ from currently available estimates for nacl brines in equilibrium with silicate minerals or that the scapolite and brine are not in isotopic equilibrium overall the data in this study suggest that halogens in early scapolites were derived from residual brines and halite during metamorphism of evaporites linked to the rm alteration later in the history of the norrbotten district components of the rm alteration were recycled and mixed during magmatic and local metasomatic events to varying extents resulting in the brines associated with iocg alteration

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

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

origin and mixing history of brines palo duro basin texas u s a formation waters in the palo duro basin texas u s a fall into four major groups based on integrated chemical and isotopic characteristics 1 interbed brines within the major permian evaporite aquitard these are the most chemically concentrated and18o rich fluids in the basin and are interpreted as evaporatively concentrated sea water which has been hydrologically isolated since the permian 2 brines below the salt on the eastern side of the basin have clbr divalent cation and isotopic systematics indicating a mixture of evaporatively concentrated sea water and meteoric water of d 20 3 brines below the salt on the western side of the basin have chemical and isotopic systematics suggesting a mixture of two pulses of meteoric water one with d 20 and the other with d 55 and 4 waters above the salt have the isotopic composition of meteoric waters diagenetic alteration of the cation chemistry has occurred for brines within and below the salt aquifers below the salt on the eastern side are interpreted as having been charged with dense permian evaporite brines which subsequently mixed in various amounts with a basin wide pulse of triassic meteoric water on the western side the descending triassic meteoric waters became saline by dissolution of halite and are currently mixing with a tertiary pulse of meteoric water initiated by the laramide uplift to the west the hydrochemistry suggests flow on the western side of the basin and static conditions on the eastern side an unrecognized approximately n s permeability restriction or discontinuity in the potentiometric flow surface is inferred for major aquifers in the central area of the basin

influence of petrographical composition on coking behavior of inertinite rich coals abstract medium rank inertinite rich coal samples were collected for study from limnic and paralic facies in the upper silesian coal basin of poland the microlithotypes seem to control the content of the mosaic textures it also appears that carbominerites favor the formation of pyrolytic carbons the coke obtained from poorly pyrofusinitized homogeneous limnic coal has higher mechanical strength with larger and thicker cell walls and is less porous than those derived from highly pyrofusinitized heterogenous paralic ones the microstructure of the cokes appears to be controlled by different amounts of fibers and coarse mosaics

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

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

thermal maturity source rock potential and kinetics of hydrocarbon generation in permian shales from the damodar valley basin eastern india abstract this study investigates the source rock characteristics of permian shales from the jharia sub basin of damodar valley in eastern india borehole shales from the raniganj barren measure and barakar formations were subjected to bulk and quantitative pyrolysis carbon isotope measurements mineral identification and organic petrography the results obtained were used to predict the abundance source and maturity of kerogen along with kinetic parameters for its thermal breakdown into simpler hydrocarbons the shales are characterized by a high toc 3 4 mature to post mature heterogeneous type ii iii kerogen raniganj and barren measure shales are in mature late oil generation stage rr raniganj 0 99 1 22 rr barren measure 1 1 1 41 vitrinite is the dominant maceral in these shales barakar shows a post mature kerogen in gas generation stage rr barakar 1 11 2 0 and consist mainly of inertinite and vitrinite the 13corg value of kerogen concentrate from barren measure shale indicates a lacustrine marine origin 24 6 30 84 vs vpdb and that of raniganj and barakar 22 72 25 03 vs vpdb show the organic provenance to be continental the 13c ratio of thermo labile hydrocarbons c1 c3 in barren measure suggests a thermogenic source discrete bulk kinetic parameters indicate that raniganj has lower activation energies e 42 62 kcal mol compared to barren measure and barakar e 44 68 kcal mol temperature for onset 10 middle 50 and end 90 of kerogen transformation is least for raniganj followed by barren measure and barakar mineral content is dominated by quartz 42 63 siderite 9 15 and clay 14 29 permian shales in particular the barren measure as inferred from the results of our study demonstrate excellent properties of a potential shale gas system

geochemical evaluation of upper cretaceous fruitland formation coals san juan basin new mexico and colorado geochemical analyses of coal samples from the upper cretaceous fruitland formation in the san juan basin of new mexico and colorado were used to determine thermal maturity type of kerogen and hydrocarbon generation potential mean random vitrinite reflectance rm of the fruitland coal ranges from 0 42 to 1 54 rock eval pyrolysis data and saturated to aromatic hydrocarbon ratio indicate that the onset of thermal hydrocarbon generation begins at about 0 60 rm and peak generation occurs at about 0 85 rm several samples have hydrogen index values between 200 and 400 indicating some potential for liquid hydrocarbon generation and a mixed type iii and ii kerogen pentacyclic and tricyclic terpanes steranes aromatic steroids and methylphenanthrene maturity parameters were observed through the complete range of thermal maturity in the fruitland coals aromatic pentacyclic terpanes similar to those found in brown coals of australia were observed in low maturity samples but not found above 0 80 rm n alkane depleted coal samples which occur at a thermal maturity of approx 0 90 rm paralleling peak hydrocarbon generation are fairly widespread throughout the basin depletion of n alkanes in these samples may be due to gas solution stripping and migration fromthe coal seams coincident with the development of pressure induced fracturing due to hydrocarbon generation however biodegradation may also effect these samples

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

characterization of coal derived hydrocarbons and source rock potential of coal beds san juan basin new mexico and colorado u s a coal beds are considered to be a major source of nonassociated gas in the rocky mountain basins of the united states in the san juan basin of northwestern new mexico and southwestern colorado significant quantities of natural gas are being produced from coal beds of the upper cretaceous fruitland formation and from adjacent sandstone reservoirs analysis of gas samples from the various gas producing intervals provided a means of determining their origin and of evaluating coal beds as source rocks the rank of coal beds in the fruitland formation in the central part of the san juan basin where major gas production occurs increases to the northeast and ranges from high volatile b bituminous coal to medium volatile bituminous coal rm values range from 0 70 to 1 45 on the basis of chemical isotopic and coal rank data the gases are interpreted to be thermogenic gases from the coal beds show little isotopic variation 13c1 values range 43 6 to 40 5 ppt are chemically dry c1 c1 5 values are 0 99 and contain significant amounts of co2 as much as 6 these gases are interpreted to have resulted from devolatilization of the humic type bituminous coal that is composed mainly of vitrinite the primary products of this process are ch4 co2 and h2o the coal generated methane rich gas is usually contained in the coal beds of the fruitland formation and has not been expelled and has not migrated into the adjacent sandstone reservoirs in addition the coal bed reservoirs produce a distinctive bicarbonate type connate water and have higher reservoir pressures than adjacent sandstones the combination of these factors indicates that coal beds are a closed reservoir system created by the gases waters and associated pressures in the micropore coal structure in contrast gases produced from overlying sandstones in the fruitland formation and underlying pictured cliffs sandstone have a wider range of isotopic values 13c1 values range from 43 5 to 38 5 ppt are chemically wetter c1 c1 5 values range from 0 85 to 0 95 and contain less co2 2 these gases are interpreted to have been derived from type iii kerogen dispersed in marine shales of the underlying lewis shale and nonmarine shales of the fruitland formation in the underlying upper cretaceous dakota sandstone and tocito sandstone lentil of the mancos shale another gas type is produced this gas is associated with oil at intermediate stages of thermal maturity and is isotopically lighter and chemically wetter at the intermediate stage of thermal maturity as compared with gases derived from dispersed type iii kerogen and coal this gas type is interpreted to have been generated from type ii kerogen organic matter contained in coal beds and carbonaceous shales of the fruitland formation has hydrogen indexes from rock eval pyrolysis between 100 and 350 and atomic h c ratios between 0 8 and 1 2 oxygen indexes and atomic o c values are less than 24 and 0 3 respectively extractable hydrocarbon yields are as high as 7 000 ppm these values indicate that the coal beds and carbonaceous shales have good potential for the generation of liquid hydrocarbons voids in the coal filled with a fluorescent material that is probably bitumen is evidence that liquid hydrocarbon generation has taken place preliminary oil source rock correlations based on gas chromatography and stable carbon isotope ratios of c15 hydrocarbons indicate that the coals and or carbonaceous shales in the fruitland formation may be the source of minor amounts of condensate produced from the coal beds at relatively low levelsof thermal maturity rm 0 7

petrographic characteristics and methane sorption dynamics of coal and shaly coal samples from ib valley basin odisha india abstract hydrocarbon generation potential methane sorption capacity maturity and petrographic composition of ten borehole 2 shaly coals and 8 coals samples from ib valley india were determined rock eval pyrolysis and total organic carbon toc analysis indicate that all the samples have excellent toc content and hydrocarbon generation potential though tmax values indicate the samples are mostly immature in nature vitrinite reflectance analysis shows that the samples are within the vitrinite reflectance oil window moreover vt60 vitrinite grains having reflectance greater than 0 60 indicates that thermogenic gas generation is occurring to some degree in almost all sample intervals toc content of the samples 25 35 58 15 wt shows good positive relation with langmuir volume vl 0 481 0 551 mmol g rock and methane sorption capacity msc 0 317 0 379 mmol g rock indicating that organic matter abundance is the significant factor in gas sorption capacity of these samples while fourier transform infrared spectrometry ftir spectrum of coal samples shows the presence of aromatic h the same was not observed in the case of shaly coal samples which may be attributed to their lesser organic matter and greater content of clay

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

stable chlorine isotopes in hydrothermal processes abstract values of 37cl can now be routinely measured with an analytical precision of 0 2 as reported herein on fluid inclusion leachates from the elmwood gordonsville mississippi valley type deposit and formation waters from its host formation basin brines from the gulf coast and palo duro basins and fluid inclusion leachates and biotites from the bingham silver bell and panguna porphyry copper deposits isotopic measurements are not affected by reaction yield in the range 85 100 or by generation of free i2 during sample preparation in the elmwood gordonsville deposit five successive paragenetic stages of ore and gangue sphalerite fluorite calcite 2 barite and calcite 3 each yielded multiple 37cl measurements ranges of 37cl vary in alternating fashion between stages with more negative values sphalerite calcites 2 and 3 and those with more positive values fluorite barite an interface between two brine systems with 37 cl and 0 0 appears to have moved back and forth across the zone of mineralization brines from the gulf coast and palo duro basins are apparently bimodal in 37cl with modes near 0 9 and 0 0 consistent with the variation in 37cl observed in fluid inclusion leachates from elmwood gordonsville biotite in the bingham deposit has 37cl values up to 1 7 and chlorine isotopes that are fractionated with respect to salt rich hydrothermal fluid hydrothermal fluids in all three porphyry copper deposits studied have a 37cl range of 0 1 to 0 4 with the one exception of a 0 5 value at bingham loss of low 37 cl chloride in vapor may balance chloride with a net 37 cl 0 in the porphyry deposits

a review of the thermal maturity and hydrocarbon potential of the mancos and lewis shales in parts of new mexico usa abstract this study reviews specific public geochemical data mainly toc and rock eval pyrolysis parameters of the mancos shale and the lewis shale located in an area to the south of the san juan basin new mexico both shale formations are immature within the study area proper and surrounding acreage maturity increases in a southeastern direction within the study area and is the only location where the mancos shale has thermogenic gas generating potential the quality of the organic matter kerogen reported for the mancos and the lewis shales is mostly of type iii gas prone with type ii being less dominant the thicknesses of both the mancos and lewis shales are adequate to generate and store large volumes of natural gas in the thermally mature areas the study area is also faulted which may provide opportunities for natural fracturing to have formed furthermore silt and sand layers within the mancos shale could provide permeability pathways for the gas in a similar fashion to the lewis shale in the san juan basin the part of the study area that belongs to the albuquerque basin contains thick sections of the mancos shale but at great depths 13 000 ft or 4 km however it might be possible to find prospective areas near the margins of the basin particularly if there is an active hydrologic system that operates close to the shale that may be responsible for late stage biogenic gas generation

depositional palaeoenvironment and economic potential of khadsaliya lignite deposits saurashtra basin western india based on petrographic palynofacies and geochemical characteristics abstract the lignite and associated shale of the khadsaliya clays formation eocene of saurashtra basin india have been studied organic petrographic palynofacies and organic geochemical analyses have been carried out to deduce the depositional palaeoenvironment including the assessment of the hydrocarbon potential of this sequence petrographically the lignites constitute huminite macerals in dominance av 60 the organic facies as derived from maceral composition and biomarker data suggests that the peat biomass was formed from woody forest vegetation consists of angiosperms and pteridophytes microbial activity was also prominent over the peat biomass the peat biomass was deposited in tropical subtropical humid climatic conditions under deltaic control and brackish water influence further there are signatures of intermittent floods in the mire and is evident from the shift from mesotrophic to rheotrophic conditions the organic matter has been categorized into two palynofacies and is derived from degraded terrestrial biomass the extrapolation of tyson s app diagram and pr n c17 vs ph n c18 plot suggest that deposition took place in dysoxic to sub oxic conditions the huminite reflectance values 0 30 0 38 av 0 34 rr suggest that lignites are less mature and have reached up to lignitic stage low rank b of coalification the geochemical proximate ultimate analyses reveal that the lignites are characterized by high moisture content av 18 and relatively low ash yield av 27 the volatile matter yields and carbon contents are moderately high whereas fixed carbon sulphur and oxygen contents are average and hydrogen and nitrogen contents are relatively low rock eval pyrolysis data indicate that the hydrogen index values of the samples vary between 23 and 477 mg hc g toc av 188 mg hc g toc the tmax values of the lignites range between 377 and 433 c av 418 c along with the presence of hopanes suggesting the immature nature of the deposits hi vs tmax s2 vs toc hi vs oi and h c vs o c plots of the studied samples indicate that the organic matters are a mix of type ii iii kerogens the types of kerogen along with high toc contents av 33 wt indicate the ability of lignite bearing sequence of khadsaliya to generate mix of oil gaseous hydrocarbons upon maturation

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 effects of igneous dike intrusion on organic geochemistry of black shale and its implications late jurassic jhuran formation india abstract this study documents the effects of igneous dike intrusion on organic geochemical parameters of a shallow marine originated late jurassic black shale av toc 2 2 wt in the kutch rift basin in western india the dike intrusion forms extremely to mildly altered meter scale zones around them the primary wrinkled micro texture of the shale is lost completely and organic matter is charcoalized in the extremely altered zone recording a rock eval tmax 458 c immature type iii kerogen dominating the unaltered shale records abundant coniferal biomarkers such as retene ent beyerane phyllocladane ent kaurane abietane labdane and norisopimarane besides n alkanes hopanes and steranes the transition from the unaltered rock eval tmax

influence of geochemical organo petrographical and palynofacies assemblages on hydrocarbon generation a study from upper oligocene coal and shale of the makum coal basin assam india abstract the makum coal basin of northeast india comprises important coal and shale reserves of upper oligocene age a total of twenty samples were collected to evaluate the kerogen type hydrocarbon generation potential and thermal maturity through geochemically organo petrographically and palynofacies analyses the samples are characterized by high toc total organic carbon and large s2 remaining heavier hydrocarbons meet the required standards as good to excellent generation potential the coal and shale are marked by mixed type iii ii kerogen with minor occurrence of type i kerogen moderate to high hydrogen index hi values and are considered to generate thermogenic gas with some condensate oil the reflectance values indicate samples are mostly immature and close to the oil birth line the amount of vt60 grains also suggests that the samples can produce some condensate oil along with thermogenic gas the rock eval pyrolysis rep data stands with the interpretation through petrographic palynofacies and fourier transform infrared spectroscopy ftir in determining kerogen type and generation potential the generation potential is also controlled by the degree of organic matters reactivity the estimated reactivity indicates that besides vitrinite and liptinite up to 70 vol of the inertinite macerals have the potential to generate hydrocarbon the occurrence of a substantial amount of reactive macerals i e collotelinite vitrodetrinite collodetrinte corpogelinite alginite resinite and bituminite within the samples makes them more potential to generate hydrocarbons the diagram proposed based on our data of macerals and palynofacies assemblages may also be a convenient tool in detecting kerogen type s and nature of hydrocarbons

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

insights into the effects of matrix retention and inert carbon on the petroleum generation potential of indian gondwana shales abstract the rock eval pyrolysis and total organic carbon toc analysis technique is widely used for organic geochemistry screening of source rocks and potential unconventional petroleum reservoirs the rock eval derived parameters the hydrogen index hi which is the ratio between hydrocarbons released under the s2 curve hydrocarbon formed by thermal pyrolysis s2 is an indicator of petroleum generation potential and total organic carbon toc can be used to infer the type of organic matter present in a rock however hi is often under estimated due to retention of some hydrocarbons included under the s2 curve by the rock matrix and the presence of inert carbon within the rock here we describe and correct the matrix retention and inert carbon effects on hydrocarbon generation from a suite of shale samples from indian gondwana shale reservoirs removal of the petrographically identified inert carbon component from the samples tested leads to less scatter in the toc s2 relationship obtained the ratio of volume percentage of organic matter identified through optical microscopy to toc is calculated and that ratio was least in the one heat affected sample but higher in low toc shales 12 5 with decreasing toc content in the sample set analyzed the corrected hi values calculated using the s2 toc intercept increase significantly this correction can therefore lead to false indications about the type of organic matter present a key novel finding of this work is the need while correcting hi for matrix retention effects to consider samples with a specific range of toc contents and to match them to the kerogen types present e g types iii and iv in the samples analyzed filters should also be applied to adjust for the degree of thermal maturity and organic facies

organic geochemical and petrographic characteristics of tertiary coals in the northwest sarawak malaysia implications for palaeoenvironmental conditions and hydrocarbon generation potential abstract tertiary coals from mukah and balingian coalfields in the northwest sarawak malaysia were investigated to evaluate their regional rank variation petroleum generative potential and to reconstruct the palaeoenvironment conditions during peat accumulation the tertiary coals are characterized by high total organic carbon contents toc and yield of bitumen extraction ranging from 31 3 to 55 9 wt and 25 724 9 92 143 7 ppm respectively meet the standard as a good source rock potential the mukah and balingian coals were generally plotted in an area of type iii kerogen and mixed type ii iii kerogens with hi values between 90 and 289 mg hc g toc whereby the coals were derived from plant materials of terrigenous origin this shows that the balingian coals are dominated by type iii terrigenous kerogen while mukah coals are dominated by type ii iii kerogens and are thus considered to be generate mainly gas prone and limited oil prone this is also supported by macerals composition and open system pyrolysis gas chromatography py gc the mukah and balingian coals are thermally immature in rang from lignite to sub bituminous c rank possessing huminite reflectance in the range of 0 26 0 39 this immaturity has a considerable influence on the proximate analysis particularly on relatively high moisture and volatile matter contents and relatively low fixed carbon content petrographically it was observed that the mukah and balingian coals are dominated by huminite with low to high amounts of liptinite and relatively low amounts of inertinite pointing to predominantly anaerobic deposition conditions in the paleomires with limited thermal and oxidative tissue destruction the palaeoenvironment conditions of the coals are generally interpreted as a lower deltaic plain wet peat swamp depositional setting which are generally characterised by low tpi and high gi values and are plotted on the marsh field of the diessel s diagram this is usually consistent with generate relatively high ash yield as is the case of the mukah and balingian coals

multi proxy approach on the hydrocarbon generation perspective of barjora basin india abstract barjora basin in india is a small basin characterized by a high organic richness of early mature nature the present study aims to find the source of organic matter om and hydrocarbon generation potential of barjora basin systematically collected coal and shale samples from r ii seam of the basin were used for proximate and ultimate analyses rock eval pyrolysis along with total organic carbon toc content organo micropetrographic framework thermal maturity carbon isotopic signature biomarker composition functional group studies and estimation of relative aliphaticity and aromaticity through fourier transform infrared spectroscopy ftir the novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon 13c biomarker signatures thermal maturity parameters organo micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin a dominant terrestrial om input in barjora basin is indicated by the toc to total nitrogen ratio c n 13c and biomarker compositions high gelification index gi tissue preservation index tpi and carbon preference index cpi values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity in addition large liptinite content tpi and gi designate short transportation of the om before burial leading to organic richness of the barjora basin moreover high liptinite content type ii iii admixed kerogen input s2 s3 ratio tpi and index for hydrocarbon generation ihg signify higher potential of the basin for hydrocarbon generation

preferential diffusion of 35cl relative to 37cl in sediments of kau bay halmahera indonesia kau bay a 470 m deep basin is separated from the pacific ocean by a shallow 40 m deep sill during the last glaciation this sill was above sea level and the bay turned into a freshwater lake after glaciation the sea level rose and the bay turned saline again since then chloride from the newly formed saline sediments diffused into the freshwater sediments as the sedimentation rate was constant throughout the holocene it is relatively easy to model the chloride concentration in the sediment pore water the diffusion coefficient of 35cl is slightly higher than the diffusion coefficient of 37cl thus variations in 37cl were expected in the pore water because the pore water history of kau bay is well known it was possible to use 37cl variations to determine the diffusion coefficient ratio d35d37 for the two stable isotopes of chlorine it was found that this ratio is 1 0023 in the pore water from sediments in this bay

source potential and reservoir characterization of the cambay shale cambay basin india implications for tight gas and tight oil resource development new organic geochemical investigations of the eocene cambay shale cambay basin india from five wells and an open cast lignite mine reveal that the total organic carbon ranges from 0 37 to 10 68 wt with an average of 2 43 wt the pseudo van krevelen diagram hydrogen index versus the maximum pyrolysis yield temperature tmax crossplot and the visual kerogen assessment of the cambay shale indicate the dominance of type iii kerogen with some well samples showing mixed type iii and ii kerogen the vitrinite reflectance values range between 0 46 and 0 7 with tmax values ranging from 387 c to 441 c and are consistent with an immature to early oil generation stage the dominance of vitrinite macerals and high pristane phytane pr ph ratios 6 of the well samples indicate an oxic to dysoxic depositional environment whereas the presence of botryococcus braunii and low pr ph ratios 1 in the lignite mine samples suggesting a more reducing brackish water environment the estimation of hydrocarbons generation expulsion and retention data suggest a low retention of 10 12 of generated hydrocarbons within the cambay shale the mineralogical data show an abundance of clay minerals average 62 9 implying poor to moderate mineral brittleness index the kerogen type and maturity level along with the high clay content and poor to moderate brittleness indicate low fracability thereby restricting the production potential of the cambay shale for tight gas or tight oil exploration

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

investigation on the lignite deposits of surkha mine saurashtra basin gujarat western india their depositional history and hydrocarbon generation potential abstract an integrated approach is adopted to study the lignite deposits of surkha mine associated with the khadsaliya clays formation eocene of saurashtra basin western india the compilation of detailed investigation includes organic petrographical palynofacies and geochemical analyses the type and amount of organic matter and its relation to palaeoenvironmental conditions have been determined and discussed along with its significance as hydrocarbon source the macerals of huminite group show dominance av 61 over the liptinite and inertinite groups the petrographical indices gi tpi gwi vi indicate wood dominated precursors of peat were deposited in limno telmatic to telmatic regime under mesotrophic hydrological conditions in palynofacies analysis it is observed that the particulate organic matter is dominated by the phytoclasts group av 69 followed by the amorphous organic matter aom and palynomorphs the biomarker signatures show angiosperm and gymnosperm source vegetation the presence of sesquiterpenoids indicate the occurrence of dipterocarpaceae flora suggesting the existence of rain forest vegetation in the vicinity of depositional site the kaurane type of diterpenoids suggest the presence of conifers among the source flora the extrapolation of organic matter data on tyson s app diagram along with the pr n c 17 vs ph n c 18 plot indicate that the deposition took place in dysoxic suboxic conditions with intermittent shifting of the environment in proximal settings the huminite reflectance values av 0 31 r r show a good correlation with gross calorific values av 3917 cal g and average t max value 416 c of the lignites furthermore the abundance of thermally unstable hop 17 21 ene and hopane indicate immature stage of lignites these lignites contain high toc av 35 wt and low ash yields the volatile matter carbon and oxygen contents are relatively high whereas sulphur content is moderate and hydrogen and nitrogen contents are comparatively low in all the lignite samples the hydrogen index values vary between 53 and 538 mg hc g toc the atomic values of h c range from 0 47 to 1 04 and of o c from 0 20 to 0 29 overall the lignite bearing sequence is characterized by type ii iii admixed kerogens organic matters and has potential to generate hydrocarbons upon maturation

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

influence of saline groundwater discharge on river water chemistry in the athabasca oil sands region a chloride stable isotope and mass balance approach abstract a chloride mass and stable isotope 37 cl balance approach was employed to calculate the effect of saline groundwater discharge into the athabasca and clearwater rivers in the athabasca oil sands region aosr in north eastern alberta canada saline groundwater affected by halite carbonate and anhydrite dissolution discharges na cl type water with total dissolved solids tds up to 51 700 mg l from exposed devonian and cretaceous units in the river valleys in this area in this study nine springs discharging groundwater with a median cl concentration of 9800 mg l were sampled and chloride stable isotope ratios were determined with 37 cl values ranging from 0 2 to 1 0 in contrast river waters had historical monthly median cl concentrations between 5 9 and 49 5 mg l and 37 cl values between 2 2 and 1 4 the discharge rate of saline groundwater was calculated to be 100 20 l s into the clearwater river and 134 68 l s into the athabasca river the chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions metals and pahs in the athabasca and clearwater rivers overall saline groundwater contributed less than 0 2 of river discharge but 0 04 39 of major ion concentrations in the rivers with highest contributions under winter low flow conditions in the clearwater river saline groundwater contributed 23 39 of average monthly cl flux and 18 32 of average monthly na flux for the same major ion fluxes in the athabasca river saline groundwater contributed 12 18 and 6 12 respectively the influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible contributing less than 1 of river fluxes of cu ni pb and zn similarly the influence on mass flux of pahs in the rivers was found to be negligible

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

coalbed methane characteristics of gates formation coals northeastern british columbia effect of maceral composition the majority of research reported on methane adsorption characteristics of coal seams has focused on vitrinite rich coals however western canadian coals are more inertinite rich than those of the western united states and are shown to differ in gas adsorption characteristics the influence of maceral composition upon gas adsorption characteristics of medium volatile coal samples from the middle cretaceous gates formation of northeastern british columbia was investigated lithotype coal facies samples were analyzed for surface area maceral and mineral composition and methane adsorption standard coal analyses were also performed proximate low temperature ash and equilibrium moisture the vitrinite content of the samples analyzed ranges from 18 to 95 vol min ral matter free the ash yield varies from 4 4 to 33 7 wt both maceral composition and mineral matter content have an important influence on adsorption characteristics as indicated by carbon dioxide surface areas and methane adsorption isotherms on a mineral matter free basis the amount of methane adsorbed generally increases with vitrinite enrichment the lowest methane adsorption occurs in the sample with the highest inertinite content carbon dioxide surface areas of the lithotypes range from 87 to 176 m2 g on a raw coal basis and from 99 to 184 m2 g on a mineral matter free basis surface area generally decreases with increased mineral matter content and increases with increased vitrinite content the increase in adsorption of both methane and carbon dioxide with increased vitrinite concentration is interpreted a resulting from differences in the pore size distribution of vitrinite and inertinite vitrinite is predominantly microporous whereas inertinite is meso to macroporous the monolayer volumes of carbon dioxide as calculated from the dubininradushkevich equation are higher than those of methane as determined from the langmuir equation but are correlated the methane adsorption isotherms and surface area data indicate that the maceral compositional variations in coal are at least as significant as coal rank in determining the potential volume of adsorbed methane and thus the coalbed methane potential of a deposit

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

the beginning development and termination of the middle miocene badenian salinity crisis in central paratethys abstract middle miocene badenian evaporites of the carpathian region are underlain and overlain by deep water deposits the onset of evaporite deposition was sudden but not synchronous in all facies zones and the deposition of evaporites was controlled by the evolution of carpathian orogen in the carpathian foredeep and most probably in other basins the badenian evaporites represent the lower part of the nn6 zone halite and associated deposits in the central part of the badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins characteristic marker beds made it possible to correlate various facies zones of the marginal ca sulfate platform these marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry which in turn imply major changes in basin hydrology the onset of the evaporitic deposition in the carpathian foredeep was clearly diachronous and the evaporites deposited in the basin centre preceded the beginning of evaporite sedimentation in the marginal basin however depositional history in the marginal basin and the basin centre was the same a general transgressive sequence of evaporites found in the carpathian foredeep resulted from the migration of facies zones induced by the nappe movement isotopic studies of badenian foraminifers occurring below evaporites suggest that the interrupted communication of the paratethys with the ocean was a consequence of eustatic sea level fall possibly related to climatic cooling and it was coupled with a tectonic closure of connection with the tethys thus both tectonics and eustacy have contributed to the origin of salinity crisis sedimentological and geochemical data indicate recycling of evaporites throughout most of the evaporite deposition the recycling at the end of gypsum deposition in the marginal sulfate platform was accompanied by a change in the hydrology of the central paratethys that was tectonically driven and possibly related to the block tectonic phase manifested in the marginal part of the carpathian foredeep basin the change in hydrology implied the dilution of brines by inflowing marine water and this terminated the middle miocene badenian salinity crisis the onset of the badenian salinity crisis shows great similarities to the onset of the messinian salinity crisis and the terminations of both crises were different

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

geochemical and petrographic characterization of organic matter in the upper jurassic madbi shale succession masila basin yemen origin type and preservation the upper jurassic madbi formation located in the masila basin eastern yemen represents the major source rock in this basin organic rich shales from two oilfields kharir and wadi taribah were analysed to evaluate the type and origin of the organic matter and to determine the factors controlling its deposition this study is based on geochemical analyses of whole rock total organic carbon content rock eval pyrolysis and carbon isotope data and petrographic analyses on organic matter kerogen maceral composition and palynofacies by optical and scanning electron microscopy organic petrographic composition of kerogen shows that the madbi shale is characterized by high amounts of organic matter consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin terrigenous organic materials such as vitrinite spores and pollen are present in low quantities the predominance of marine plankton as indicated by visual kerogen analysis is consistent with reported carbon isotopic values it appears that the high amounts of organic matter in the madbi shale succession might be mainly due to good preservation under suboxic anoxic conditions consequently the madbi shales possess very good petroleum generative potential owing to high content of hydrogen rich type ii and i oil prone kerogen

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

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

nacacl saline formation waters frio formation oligocene south texas usa products of diagenesis abstract saline formation waters from reservoirs in oligocene deltaic clastic sedimentary rocks frio formation south texas are derived from three sources mixtures characterize most samples accounting for the wide range in chemistry low salinity water is derived from cenozoic shales in contrast saline water having variable br cl ratios is allochthonous and is derived from at least two sources in mesozoic strata which underly the cenozoic units saline water in this area regardless of br cl ratio contains variable high concentrations of ca calcium is derived primarily from dissolution of plagioclase as demonstrated by petrography 87 sr 86 sr analyses and chemical modelling the mccl 2 or carpenter function of saline formation waters in this area thus can be derived from water rock interaction and cannot be used to identify the ultimate source of solutes reverse osmosis is an unimportant processes in this area and 18 o and d values converge on rock buffered values of approximately 8 o and 30 o respectively

assessment of hydrocarbon source rock potential of polish bituminous coals and carbonaceous shales abstract we analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity vitrinite reflectance 0 59 to 4 28 from the upper carboniferous coal bearing strata of the upper silesian lower silesian and lublin basins poland to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons we evaluated source rock potential based on rock eval pyrolysis yield elemental composition atomic h c and o c and solvent extraction yields of bitumen an attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors a few carbonaceous shale samples contain sufficient generation potential pyrolysis assay and elemental composition to be considered potential source rocks although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective type iii source rocks most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion primary migration to occur in view of these findings it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential but could not be clearly delimited with the number of samples analysed in our study because of their high heteroatomic content and high amount of asphaltenes the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

rates and geochemical processes of soil and salt crust formation in salars of the atacama desert chile abstract the hyperarid atacama desert contains numerous local basins with surficial salt crusts known as salars where evaporation of shallow groundwater drives the major soil processes we examine chemical and isotopic profiles in two soils of differing ages from the salar llamara to determine the geochemical processes involved in their formation evaporation which provides salts to the soils through mineral precipitation decreases with increasing salt crust thickness and average 0 03 mm m 2 d 1 over geological time frames salt distribution varies predictably with depth and soil age with the most soluble compounds concentrated nearest to the land surface indicating the direction of fluid flow 34s values of mineral sulfate tend to decrease with decreasing soil depth following a pattern indicative of rayleigh like fractionation as solute rich waters migrate toward the land surface 13c and 18o values of carbonate suggest that the uppermost halite layers which contain very small amounts of carbonate have a strong biological signature in contrast carbonate rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions the continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules the crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions and we found that the halite nodules on the surface of the salar llamara are nearly always at or above deliquescence relative humidity the interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment radiocarbon measurements of occluded organic c in the surface crusts indicate that c cycling occurs at differing rates depending on local micrometeorological conditions and that a given salt crust feature may persist for thousands of years once formed

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

the stable isotope composition of halite and sulfate of hyperarid soils and its relation to aqueous transport halite nacl and gypsum or anhydrite caso4 are water soluble minerals found in soils of the driest regions of earth and only modest attention has been given to the hydrological processes that distribute these salts vertically in soil profiles the two most notable chloride and sulfate rich deserts on earth are the dry valleys of antarctica and the atacama desert of chile while each is hyperarid they possess very different hydrological regimes we first show using previously published s and o isotope data for sulfate minerals that downward migration of water and sulfate is the primary mechanism responsible for depth profiles of sulfate concentration and s and o isotopes in both deserts in contrast we found quite different soluble cl concentration and cl isotope profiles between the two deserts for antarctic soils with an ice layer near the soil surface the cl concentrations increase with decreasing soil depth whereas the ratio of 37 cl 35 cl increases based on previous field observations by others we found that thermally driven upward movement of brine during the winter described by an advection diffusion model qualitatively mimics the observed profiles in contrast in the atacama desert where rare but relatively large rains drive cl downward through the profiles cl concentrations and 37 cl 35 cl ratios increased with depth the depth trends in cl isotopes are more closely explained by a rayleigh like model of downward fluid flow the isotope profiles and our modeling reveal the similarities and differences between these two very arid regions on earth and are relevant for constraining models of fluid flow in arid zone soil and vadose zone hydrology 2012 elsevier ltd all rights reserved