analysis of vadose zone inhomogeneity toward distinguishing recharge rates solving the nonlinear interface problem with newton method citation steward d r 2016 analysis of vadose zone inhomogeneity toward distinguishing recharge rates solving the nonlinear interface problem with newton method water resources research 52 11 8756 8774 doi 10 1002 2016wr019222

magnetic properties of hydrothermally synthesized greigite fe3s4 i rock magnetic parameters at room temperature summary greigite of variable purity has been synthesized hydrothermally at 140 c by injecting a mohr s salt solution into a sodium sulphide solution containing dissolved zerovalent sulphur ageing for 30 960 min and rapidly quenching oxygen was rigorously excluded during the synthesis scanning electron microscope sem observations yield a grainsize range up to 400nm the variable purity was deduced from a varying specific saturation magnetization 3 29 am2 kg i the mjm or ors os ratio varies between 0 3 and 0 4 which is indicative of fine grained greigite concurring with sem observations hysteresis measurements at low temperatures indicate the presence of grains that are superparamagnetic at room temperature coercivity parameters b 13 43 mt bo cr 37 73 mt are the highest obtained to date for synthetic greigite and compare well with those measured for natural greigite ranges for other rock magnetic parameters are discussed greigite hysteresis parameters overlap those of magnetite to a large degree a diagnostic interparametric ratio for greigite is its high o xin ratio the range of the present greigite is 40 75 kam

geochemical comparison of reservoir solid bitumens with diverse origins abstract geochemical and petrologic comparison of solid bitumens with various origins from reservoirs in zaire canada and kazakhstan were studied to provide insight into their formation processes and their physical and chemical properties results of this study can help develop methods for treatment and removal of solid bitumen and evaluating producibility of associated hydrocarbon fluids characterization of these solid bitumens reveals a wide range in quantity and composition of extractables soluble material and in solid bitumen reflectance which indicate significant differences in formation processes hydrocarbon source and thermal maturity the zaire and kazakhstan samples represent end members of the spectrum of solid bitumens studied solid bitumens from the motoba field zaire are highly extractable and low in thermal maturity 0 2 0 3 bitumen reflectance reservoir mixing of a cretaceous lacustrine sourced oil and a tertiary marine sourced oil of different thermal maturities appears to be responsible for their formation in contrast solid bitumens from the tengiz field kazakhstan are characterized by their extremely low extractables high bitumen reflectance 1 and low atomic h c ratios

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

nannofacies analysis as a tool to reconstruct paleoenvironmental changes during the early toarcian anoxic event the black shales of lower toarcian schistes carton in france jet rock in england posidonia shale in germany are sediments formed by fine alternations of millimetric to sub millimetric clear and dark laminae a study of polished core surfaces dotternhausen core sw germany was carried out in sem in order to characterize the micro fabrics of different laminae and their content in nannofossils two main intervals were recognized where fabrics and nannofossil content are significantly different in the clay rich interval characterized by high wt toc and a large negative carbon isotope excursion both in carbonates and organic matter the dominant micro fabrics are well foliated or lumpy giving evidence of the absence or reduction of benthic life nannofossils are scarce and only concentrated in discrete laminae separated by large abiotic intervals assemblages are indicative of a deep nutricline but sporadic nutrient inputs occurred as demonstrated by fluctuation in abundance of specimens of the biscutaceae nutrients were probably delivered to the german basin via riverine influx different sized framboids of pyrite were recognized in this interval the smallest ones 2 m being probably precipitated in an anoxic and sulphidic water column the clay rich interval was likely deposited during low sea level in a restricted basin these conditions were followed by a sea level rise and better water mass circulation within the german basin sedimentation records an increase in carbonate deposition organic matter content decreased and carbon isotopes came back to pre excursion values micro fabrics became less markedly laminated pyrite framboids nearly disappeared and rich and diversified nannofossil assemblages are recorded sea water conditions were probably highly fluctuating as indicated by alternation of intervals dominated in turn by schizosphaerella spp flourishing under generally oligotrophic conditions where nutrients were temporarily available in surface waters due to storms and by crepidolithus spp a deep dweller the results of this work fit well with a silled basin model

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

molecular measurements of maturity for lias δ shales in n w germany abstract the extractable aliphatic and aromatic hydrocarbons of twenty four lias shales from n w germany have been analysed by gas chromatography mass spectrometry particular attention has been paid to seven molecular measurements of thermal maturation which are based on appropriate ratios of the concentrations and products of certain reactions a sequence of increasing maturity towards the area of the bramscher massiv was determined because the reactions involved occur at different rates they reach completion at different levels of maturity and at variable distance from the centre of the bramscher massiv as defined by iso vitrinite reflectance contours reported previously for rhaetic lias and malm shales this has allowed the designation of zones of increasing maturity the molecular measurements appear more reliable assessors of maturity than vitrinite reflectance for samples less mature than the zone of oil generation but are not applicable to samples from within this zone because the reactions concerned have normally reached completion a mathematical model suggests that the maturity of samples less mature than a vitrinite reflectance of 1 can adequately be explained by substantial subsidence during early and middle cretaceous followed by major uplift and inversion in late cretaceous time without recourse to further heating from a deep seated igneous intrusion

cement distribution in a carbonate reservoir recognition of a palaeo oil water contact and its relationship to reservoir quality in the humbly grove field onshore uk abstract the distribution of mineral cements total porosity microporosity and permeability have been determined for the humbly grove oolitic carbonate reservoir middle jurassic great oolite formation weald basin onshore uk using a combination of optical petrography electron microscopy fluid inclusion analysis quantitative xrd wireline data analysis and core analysis data grainstone reservoir facies have porosities ranging between 5 and 24 but are mostly between 11 and 24 permeabilities vary from

pore types and pore size distributions across thermal maturity eagle ford formation southern texas pore types pore size and pore abundance vary systematically across thermal maturity in the eagle ford formation maverick basin southern texas scanning electron imaging of 20 samples from four wells is used to assess the complex response of pores to chemical and mechanical processes entailing both destruction of primary porosity and generation of secondary pores primary mineral associated pores are destroyed by compaction cementation and infill of secondary organic matter whereas secondary pores are generated within organic matter om destruction of primary pores during early burial to 0 5 occurs by compaction of ductile detrital om and clays and to a lesser degree as a result of cementation and infill of secondary om larger pores are associated with coccolith debris the dominant om is spatially isolated detrital om stringers porosity is volumetrically dominated average 6 2 by relatively large mostly interparticle mineral associated pores median size 51 6 nm 0 000002 in detection limit near 3 4 nm 0 00000012 0 00000015 in at low maturity porosity and pore size correlate directly with calcite abundance and inversely with om volumes at higher maturity further destruction of primary pores occurs through cementation secondary om infill and greater compaction mineral associated pores are present at high maturity 1 2 1 3 but are smaller median size 30 2 nm 0 0000011 in and less abundant average of 2 5 than at low maturity a large portion of om within high maturity samples is diagenetic in origin and has pervaded into primary pore space coating cement crystals and filling intraparticle pores substantial mineral associated porosity is locally present in samples where incursion of primary pore space by secondary om has not occurred abundant secondary porosity is generated as om matures into the wet gas window porosity in most high maturity samples is volumetrically dominated average of 1 3 by smaller om hosted pores median size 13 2 nm 0 00000051 in

haynesville and bossier mudrocks a facies and sequence stratigraphic investigation east texas and louisiana usa abstract upper jurassic haynesville and bossier shale gas plays of the northwestern gulf of mexico gom basin produce from organic rich marine transgressive to highstand mudrocks within mixed carbonate clastic depositional systems modern wireline log suites from 200 deep wells were used for detailed correlations and 10 cores throughout the upper kimmeridgian to lower tithonian basin were incorporated into detailed facies stratigraphic and lithologic analyses the haynesville shale lies within a 2nd order transgressive systems tract tst that encompasses back stepping ramp carbonates proximal and marine shales distal below a maximum flooding surface mfs this shale onlaps retrogradational carbonates and basement highs and is capped by the 2nd order mfs bossier shales and local sandstones prograde basinward above the haynesville shale and downlap the 2nd order mfs they grade upward and updip into the thick highstand systems tract hst fluvio deltaic sandstones of the cotton valley group distally organic rich facies developed in restricted bossier environments creating another productive gas shale opportunity several preexisting basement highs in the south and carbonate platforms in the northwest and west restrict and partition the basin thus influencing deposition of highly organic versus nonorganic and siliciclastic dominated versus carbonate dominated lithologies haynesville and bossier shales each compose three upward coarsening cycles that probably represent 3rd order sequences within the larger 2nd order tst and early hst respectively most of the three bossier 3rd order cycles are dominated by varying amounts of siliciclastics deposition of the haynesville mudrocks occurred below storm wave base under mostly dysoxic conditionsm allowing settlement of benthic bivalve communities and bioturbating organisms and oscillating periodically to more anoxic conditions on the seafloor however most of the sparse faunae found in these mudrocks are of planktonic origin bossier mudrocks exhibited more oxygenated and clastic rich lithologies related to progradation of the clastic shoreline and sea level highstand knowledge of lithologic stratigraphic geochemical and faunal variations across mudrock basins needs to be detailed so that shale gas basins might be successfully explored

source rock evaluation by well log analysis lower toarcian hils syncline abstract the feasibility of conducting petroleum source rock evaluations from well log data was examined using three continuously cored sections immature mature and postmature stages of the lower toarcian posidonia shale northern germany logs depicting natural gamma emission k u th bulk density sonic travel time and resistivity were utilised as was the borehole televiewer for fracture control selected data from these logs were correlated with parameters of source richness hydrocarbon content and maturity the resulting three dimensional cross plot shows at a glance well by well comparison of facies maturity and hydrocarbon content a simple correlation between organic geochemical and petrophysical parameters is of course not perfect since log response is complex and affected by mineralogical and pore fluid properties of the rock as well as by organics however source rock characterization by wireline logging is still a fast and therefore economical method relative quick look comparisons from well to well are possible without calibration to core data and can easily be performed at once at the drill site the present application is limited to clastic source rocks in basins with simple geologic histories

shale characteristics in the southeastern ordos basin china implications for hydrocarbon accumulation conditions and the potential of continental shales abstract continental shales in china are generally characterised by low thermal maturity and high clay content characteristics that are significantly different from those of marine shales documented in the usa and elsewhere whether such continental shales have commercial hydrocarbon potential as marine shale in the usa is a question for the china petroleum industry recently vertical drills in the lacustrine shales in the yanchang formation produced an average of two to five tons of oil and 1000 3000 m3 of gas per day by reservoir hydraulic fracturing which demonstrates that the continental shales can also achieve viable hydrocarbon production shale and gas samples collected from the chang 7 c7 and chang 9 c9 members yanchang formation in the southeastern ordos basin were examined for geochemical petrologic and gas content analysis the results show that the c7 and c9 members developed a huge volume of organic rich shales with 2 4 wt toc in the deep or semideep lacustrine characterised primarily by type ii kerogen with a relatively low thermal maturity and a vitrinite reflectance ranging from 0 5 to 1 5 ro which decreases from west to east the hydrocarbon product varies with the thermal maturity in the southwestern corner the gas content measured by canister desorption equals 1 15 3 49 m3 t rock and the gas absorption capacity ranges from 3 to 5 m3 t rock whereas in the eastern part the gas content is low and oil production is 1 4 m3 day on average nanometre scale pores and micro fractures are well developed all of this indicates that the continental shales in the southeastern ordos basin might have huge shale hydrocarbon resources however the clay content of the continental shales of c7 and c9 ranging from 40 to 60 of the bulk mineral content are much higher than for gas produced in marine shales which might lead to significant challenges for successful development

geochemical effects of petroleum migration and expulsion from toarcian source rocks in the hils syncline area nw germany for mature oil prone source rocks of toarcian age in the hils syncline area nw germany the geochemical effects of primary migration of petroleum are shown expulsion has occurred at high efficiencies primarily via a network of macro and micro fractures the effects of this fracture controlled expulsion with respect to gross and molecular composition of c15 soluble organic matter are documented samples from fractured intervals have expelled total c15 soluble organic matter more efficiently than adjacent unfractured intervals a systematic comparison of samples taken at cm intervals away from macro fractures reveals compositional gradients which are interpreted to reflect preferential depletion of saturated and aromatic hydrocarbons from the source rock shale into the fractures extracts of shale samples directly at fracture walls are enriched in nso compounds and highly polar asphaltene like fractions the composition of residual petroleum fluids extracted from the fracture fill materials is variable in some cases there is a close match with that of the shale at some distance away from the fractures in other cases there is geochemical evidence to suggest that petroleum fluids were chemically altered during lateral flow along the fractures based on available geological and geochemical evidence a conceptual model is proposed to explain fracture development and fluid flow processes rapid heating by a nearby intrusive body at shallow depths when the toarcian sediments still contained about 15 20 pore water has played an important role overpressuring of aqueous pore fluids with abundant dissolved carbonate caused intense fracturing of the rich intervals in the mature toarcian sections finally the closely interdependent relationships between petroleum generation and petroleum migration processes are documented especially the evolution of these relationships with maturity progress from immature 0 48 rm to mature 0 68 and 0 88 rm and overmature 1 45 rm stages is shown for example in the maturity interval from 0 68 to 0 88 rm most of the measured shale compaction and porosity decrease is achieved by expulsion of petroleum for some samples there is an inverse relationship between kerogen quality and extractable hydrocarbon yields suggesting that expulsion efficiencies were higher from the better quality intervals because the petroleum achieved higher saturations and hence higher relative permeabilities

the influence of solid reservoir bitumen on reservoir quality 1 reservoir bitumen precipitates in pore systems from the alteration of trapped or migrating oil in carbonate and siliciclastic reservoirs reservoir bitumen is not readily identified on typical log suites where it is read as open porosity which has hampered its broad recognition as a reservoir altering cement when present as a solid it can be as influential on reservoir quality as carbonate silica or authigenic clay cements and should therefore be evaluated as part of the diagenetic evolution of any pore system whenever encountered five morphotypes of reservoir bitumen have been identified and named droplets carpets peanut brittle vesicular and digitate data from east texas gulf coast and west african examples indicate that reservoir bitumen can significantly reduce total effective porosity permeability can be significantly reduced by restricted or closed pore throats and by fines migration even when bitumen occurs in only moderate amounts the occurrence and distribution of bitumen on well field and regional scales can range from uniform and predictable to irregular and unpredictable but mappable through examination of core and cuttings within a trap bitumen can cause heterogeneity and form permeability barriers not related to depositional facies or pre bitumen diagenesis and reservoir quality it economic importance must be recognized when reservoir parameters are adversely affected impacting reserves calculations recovery factors and secondary recovery programs on a regional scale predictive models can be developed to determine the areas of a trend or portions of a stratigraphic section that are most likely to be affected and these models can be incorporated with other data for evaluating expected reservoir quality in regional play assessments

maturity related compositional changes in the low molecular weight hydrocarbon fraction of toarcian shales abstract compositional changes in the light hydrocarbon content of sedimentary rocks and petroleum are known to reflect their maturation history the present contribution comprises the study of the low molecular weight hydrocarbon fraction in core samples of lower toarcian age posidonia shale lias the samples series collected by shallow borehole drilling in the hils syncline lower saxony basin northern germany represents an excellent petroleum source rock type ii kerogen of a wide maturity range mean vitrinite reflectance rm between about 0 5 and 1 5 about 30 compounds in the c2 c7 molecular range were determined quantitatively using a combined thermovapourization capillary gas chromatography method both quantity and composition particularly of the c7 hydrocarbon fraction are discussed in relation to vitrinite reflectance values measured at five locations rm 0 48 0 66 0 68 0 88 and 1 45 correlations between rm and paraffin naphthene concentration ratios are described also the isomer concentration ratios of 2 methylhexane 3 methylhexane and of trans to cis 1 2 dimethylcyclopentane are clearly related to the maturity of the organic matter

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

pressure solution and hydrothermal recrystallization of carbonate sediments an experimental study reply abstract the extent of calcite recrystallization was determined in pressure solution and hydrothermal experiments which were conducted on deep sea carbonates of low mg calcite iceland spar and reagent grade calcite powder in the pressure solution experiments wet sediments were subjected to confining pressures of 500 1500 bars and pore pressures of 150 500 bars at temperatures between 22 and 180 c for 21 240 h the hydrothermal experiments were performed in sealed teflon coated bombs at 200 c zero effective stress in sulfate free sea water for two weeks the hydrothermal system was solution dominated the extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment scanning electron microscope observations porosity and specific surface area measurements were performed in fine grained carbonate samples subjected to high effective stresses the mechanism for recrystallization apparently involves both relief of strain energy at grain to grain contacts and decrease in surface free energy by decreasing the surface area while in coarse grained carbonates relief of strain energy appears to be the most important control of recrystallization in the hydrothermal experiments however decrease in surface free energy is the only driving force for recrystallization effective stress increased the rate of calcite recrystallization in both pressure solution and hydrothermal experiments clay minerals retarded the reaction the effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments both admixed non carbonate materials retarded the reaction diatomite being the most effective inhibitor surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in nacl solutions of five different ionic strengths

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

metagenetic methane generation in gas shales i screening protocols using immature samples abstract the gas generative potential of organic matter is one key parameter for the calculation of total gas in place gip when evaluating thermogenic shale gas plays having first demonstrated that late gas forming structures are present in coals of anthracite rank 2 r0 we go on to examine other rocks at the immature stage of maturity and report on how to recognise which might generate significant amounts of late dry gas at geologic temperatures well in excess of 200 c in the zone of metagenesis r0 2 0 i e subsequent to primary and secondary gas generation by thermal cracking of kerogen or retained oil such a distinction could clearly be of major value when assessing risks and pinning down sweet spots a large selection 51 samples of source rocks i e shales and coals stemming from different depositional environments and containing various types of organic matter which contribute to the formation of petroleum in putative gas shales were investigated using open and closed system pyrolysis methods for the characterisation of kerogen type molecular structure and late gas generative behaviour a novel rapid closed system pyrolysis method which consists of heating crushed whole rock samples in mssv tubes from 200 c to 2 different end temperatures 560 c 700 c at 2 c min provides the basis for a newly proposed approach to discriminate between source rocks with low high or intermediate late gas potential it is noteworthy that late gas potential goes largely unnoticed when only open system pyrolysis screening methods are used high late gas potentials seem to be mainly associated with heterogeneous admixtures or structures in terrestrially influenced in some cases marine type iii and type ii iii coals and shales aromatic and or phenolic signatures are therefore indicative of the possible presence of elevated late gas potential at high maturities high temperature methane was calculated to potentially contribute an additional 10 40 mg g toc which would equal up to 30 of the total initial primary petroleum potential in many cases low late gas potentials are associated with homogeneous paraffinic organic matter of aquatic lacustrine and marine origin source rocks exhibiting intermediate late gas potentials might generate up to 20 mg g toc late dry gas and seem to be associated with heterogeneous marine source rocks containing algal or bacterial derived precursor structures of high aromaticity or with aquatic organic matter containing only minor amounts of aromatic phenolic higher land plant material

comment on formation of nanoporous pyrobitumen residues during maturation of the barnett shale fort worth basin by bernard et al 2012 abstract in their 2012 paper discussing the character of pores and organic matter in the mississippian barnett shale bernard et al 2012 identified only nonporous kerogen and nonporous solid bitumen in oil window maturity samples but nanoporous pyrobitumen in gas window maturity samples our examination of samples from the same wells shows that pores are also present in organic matter from oil window maturity samples we also argue that some of the pores we identified in gas window maturity samples are developed in organic matter that is unlikely to be pyrobitumen