a geochemical perspective and assessment of leakage potential for a mature carbon dioxide enhanced oil recovery project and as a prototype for carbon dioxide sequestration rangely field colorado measurements of co2 and ch4 soil gas concentrations and gas exchange with the atmosphere at a large scale co2 enhanced oil recovery eor operation at rangely colorado united states allowed assessment of the microseepage potential shallow and deep soil gas concentrations and direct transport of co2 and ch4 complemented by carbon isotopes have demonstrated an estimated microseepage rate to the atmosphere of approximately 400 t ch4 yr from the 78 km2 area of the rangely field preliminary estimates of deep sourced co2 losses are in the range of 170 to less than 3800 t yr several holes as much as 9 m deep for nested sampling of gas composition stable carbon isotopic ratios for co2 and ch4 and carbon 14 measurements on co2 indicate that deep sourced co2 microseepage loss was detected methanotrophic oxidation of microseeping ch4 to co2 in soils demonstrates significant contribution to soil gas co2 in high ch4 flux areas necessitating a revision of the estimated direct co2 microseepage rate to less than 170 t yr over the rangely field an evaluation of produced water quality from pre co2 eor to 1999 demonstrates an increase in some parameters particularly of ca2 and hco3 indicating dissolution of ferroan calcite and ferroan dolomite in the weber formation inverse computer modeling suggested carbonate mineral sequestration was possible within the constraints of evolution of produced water quality x ray analyses of well scales however do not support the presence of significant mineral sequestration instead modeling indicates that the bulk of the co2 that has been injected since 1986 is sequestered as dissolved co2

carbonate source rock with low total organic carbon content and high maturity as effective source rock in china a review abstract carbonate rocks with high maturity and low total organic carbon content are widely distributed in china whether they can be effective source rocks remains controversial but they have great significance for the evaluation of hydrocarbon generation potential and exploration prospects of carbonate rocks dataset reveals that as the depth or maturity increases total organic carbon toc content atomic h c ratio and hydrocarbon generation potential of carbonate source rocks with low total organic carbon csrltoc all decrease because of hydrocarbon expulsion moreover some pyrolysis experiments also indicate that the csrltoc are able to generate and expel a quantity of hydrocarbons the above studies indicate that csrltoc can be effective source rocks for oil gas pools the unique features of carbonate rocks and csrltoc demonstrate that they are easier to expel hydrocarbons and contribute to oil gas reservoirs than shale and thus the lower limit of toc lltoc of effective carbonate source rocks could be smaller than shale 0 5 the lltocs of effective carbonate source rocks with type i ii1 kerogen mainly sapropelic group at the levels of immaturity and low maturity maturity high maturity and over maturity are toc 0 5 0 5 0 3 0 3 0 2 and 0 2 0 1 respectively if the carbonate source rocks are at the high over mature stage we could take 0 2 as the lltoc the present organic poor source rocks with high maturity are possibly moderate or good source rocks at the low mature level in the geological periods especially carbonate source rocks if type i ii1 kerogen some typical oil and gas fields in china derive partly or mostly from the csrltoc proving that csrltoc could be effective source rock in china

a geochemical study of oil migration at source rock reservoir contacts stable isotopes abstract whereas organic geochemical analyses of oils and potential source rocks have enabled correlations to be drawn and have been utilized to suggest modes of migration only limited data has been published relating a known source rock in contact with an oil filled reservoir this paper presents initial results from the examination of an approximately 100 m continuous core through the kimmeridge shale of the north sea the variability in extractable source rock hydrocarbon contents kerogen toc asphaltene and their carbon isotopic contents are documented nitrogen isotopic content of kerogens and asphaltenes as well as kerogen and asphaltene ton are relatively constant carbon isotopic compositions of kerogen extractable hydrocarbons and asphaltenes covaried significantly as did nitrogen isotopic compositions of kerogen and asphaltenes average isotopic compositions of the asphaltene free extracts and asphaltenes were nearly identical to the oil in the primary reservoir small chemical differences are noted among extracts

hydrocarbon generation and expulsion characteristics of the source rocks in the third member of the upper triassic xujiahe formation and its effect on conventional and unconventional hydrocarbon resource potential in the sichuan basin abstract the third member of the upper triassic xujiahe formation t3x3 is a typical source reservoir cap unit for natural gas exploration in the sichuan basin however most previous studies mainly focused on the t3x3 as a source rock ignoring its role as a reservoir as a result the evaluation of hydrocarbon resource potential was not accurate this study established a hydrocarbon generation and expulsion model through analyzing the geological and geochemical characteristics of the t3x3 source rocks and calculated the resource potential of conventional gas tight gas and shale gas systematically with combining the lower boundary of buoyancy dominated accumulation lbba the results indicated that the thickness of the source rocks dominated by mudstone was distributed widely with an average value of more than 45 m the sedimentary environment was salty lacustrine deposits they have a high content of total organic carbon toc with an average value of 4 80 wt the kerogen is mainly type iii with minor type ii and the thermal evolution has entered the high to over mature stage the hydrocarbon generation threshold was determined to be 0 5 ro while the hydrocarbon expulsion threshold and the lbba were determined to be 0 83 ro and 1 12 ro respectively the efficiency of hydrocarbon expulsion was relatively high with an average of about 56 also the maximum hydrocarbon generation and expulsion intensity reached to 110 108 m3 km2 and 53 108 m3 km2 the amounts of hydrocarbon generation expulsion and residual associated with the t3x3 source rocks were 125 68 1012m3 70 38 1012m3 and 55 30 1012m3 respectively under the criterion condition of the lbba the conventional gas resource was 7 21 1010m3 the tight gas resource was 294 34 1010m3 and the shale gas resource was 2488 50 1010m3 it indicated good prospects for exploration

hydrocarbon generation and expulsion characteristics of eocene source rocks in the huilu area northern pearl river mouth basin south china sea implications for tight oil potential abstract in recent years new oil reservoirs have been discovered in the eocene tight sandstone of the huilu area northern part of the pearl river mouth basin south china sea indicating good prospects for tight oil exploration in the area exploration has shown that the huilu area contains two main sets of source rocks the eocene wenchang e2w and enping e2e formations to satisfy the requirements for further exploration in the huilu area particularly for tight oil in eocene sand reservoirs it is necessary to re examine and analyze the hydrocarbon generation and expulsion characteristics based on mass balance this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion the results show that the threshold and peak expulsion of the e2w source rocks are at 0 6 vitrinite reflectance and 0 9 vitrinite reflectance respectively there were five hydrocarbon expulsion centers located in the western eastern and northern huizhou sag and the southern and northern lufeng sag the hydrocarbon yields attributed to e2w source rocks are 2 4 1011 tons and 1 6 1011 tons respectively with an expulsion efficiency of 65 the e2e source rock threshold and peak expulsion are at 0 65 vitrinite reflectance and 0 93 vitrinite reflectance respectively with hydrocarbon expulsion centers located in the centers of the huizhou and lufeng sags the yields attributed to e2e source rocks are 1 1 1011 tons and 0 2 1011 tons respectively with an expulsion efficiency of 20 using an accumulation coefficient of 7 13 the eocene tight reservoirs could contain approximately 1 3 1010 tons to 2 3 1010 tons with an average of 1 8 1010 tons of in place tight oil resources highest recoverable coefficient can reach 17 18 indicating that there is significant tight oil potential in the eocene strata of the huilu area

experimental study on water rock interactions during co2 flooding in the tensleep formation wyoming usa abstract the conditions for mineral alteration and formation damage during co2 treatment of tensleep sandstone reservoirs in northern wyoming usa were examined through core flooding laboratory experiments carried out under simulated reservoir conditions 80 c and 166 bars subsurface cores from the tensleep sandstone which were cemented by dolomite and anhydrite and synthetic brines were used the brines used were ca mg na so4 nacl solution 9 69 g l total dissolved solids for run 1 and a 0 25 mol l nacl solution for run 2 the solution used in run 1 was saturated with respect to anhydrite at run conditions which is characteristic of tensleep formation waters three major reactions took place during flooding including 1 dissolution of dolomite 2 alteration of k feldspar to form kaolinite and 3 precipitation in run 1 or dissolution in run 2 of anhydrite all sample solutions remained undersaturated with respect to carbonates the permeability of all the cores except one used in run 2 decreased during the experiments despite the dissolution of authigenic cement kaolinite crystal growth occurring in pore throats likely reduced the permeability application of the experimental results to reservoirs in the tensleep formation indicates that an injection solution will obtain saturation with respect to dolomite and anhydrite in the immediate vicinity of the injection well the injection of nacl type water which can be obtained from other formations causes a greater increase in porosity than the injection of tensleep formation waters because of the dissolution of both dolomite and anhydrite cements

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

late gas generation potential for different types of shale source rocks implications from pyrolysis experiments abstract gas generation from shale source rocks typically occurs via cracking of both kerogen and retained oils such that it is difficult to predict and compare gas generation potentials of different shales because they are related not only to the kerogen type but also to the oil expulsion efficiency in this study five different shale kerogen samples were pyrolyzed in sealed gold tubes to investigate how kerogen type and oil expulsion efficiency affect their gas generation after oil window maturity the results illustrate that the maximum extractable organic matter eom and gas generation potentials of different original shale kerogens o kerogen in a closed system vary widely in the range of 229 790 mg g tocok and 308 594 ml g tocok respectively however the gas yields of different residual shale kerogens r kerogen with a starting equivalent vitrinite reflectance eqvro value of approximately 1 22 are quite similar and vary between 131 and 145 ml g tocrk pyrolysis experiments also reveal that the late gas generation potential eqvro 1 22 of shale is mainly controlled by the amount of retained eoms rather than kerogen type when the shale source rocks containing types i and ii kerogens have the same amount of retained eoms their gas generation potentials are quite similar under most geological conditions the late gas generation potentials of shale source rocks normalized to the toc of matured shale at 1 22 eqvro tocshale vary approximately in the range of 180 300 ml g tocshale to reach a gas content of 3 m3 ton shale for the present day overmature shale gas exploration in the lower palaeozoic shales of south china a conservative present day toc tocpd value of 2 0 is proposed as a screening parameter that can eliminate the risk of insufficient gas generation potential as much as possible

the impact of diagenetic fluid rock reactions on rotliegend sandstone composition and petrophysical properties altmark area central germany in the framework of the german r d joint project clean co2 large scale enhanced gas recovery in the altmark natural gas field rotliegend reservoir sandstones of the altensalzwedel block in the altmark area saxony anhalt central germany have been studied to characterise litho and diagenetic facies mineral content geochemical composition and petrophysical properties these sands have been deposited in a playa environment dominated by aeolian dunes dry to wet sand flats and fluvial channel fills the sediments exhibit distinct mineralogical geochemical and petrophysical features related to litho and diagenetic facies types in sandstones of the damp to wet sandflats their pristine red colours are preserved and porosity and permeability are only low rocks of the aeolian environment and most of the channel fill deposits are preferentially bleached and exhibit moderate to high porosity and permeability although geochemical element whole rock content in these rocks is very similar element correlations are different variations in porosity and permeability are mainly due to calcite and anhydrite dissolution and differences in clay coatings with fe bearing illitic chloritic composition exposed to the pore space moreover mineral dissolution patterns as well as compositions of clays and carbonate and morphotypes of authigenic minerals chlorite illite are different in red and bleached rocks comparison of the geochemical composition and mineralogical features of diagenetically altered sandstones and samples exposed to co2 bearing fluids in laboratory batch experiments exhibit similar character experiments prove an increase in wettability and water binding capacity during co2 impact

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

assessment of mesozoic and upper paleozoic source rocks in the south yellow sea basin based on the continuous borehole csdp 2 abstract being lack of core data and measured data although the marine oil gas exploration in the south yellow sea basin has been going on for 57 years no commercial hydrocarbon reservoirs have been found so far the quantitative source rocks evaluation based on geochemical data and fluid inclusions containing hydrocarbon benefits from the completion of borehole csdp 2 in 2016 a continuous coring well of the chinese continental shelf drilling program csdp which indicates that the marine origin oil gas exploration in the south yellow sea basin enters into a new stage as revealed by the well csdp 2 three sets of effective hydrocarbon source rocks in the mesozoic and upper paleozoic have been identified which are distributed in the lower triassic qinglong formation t1q upper permian longtan dalong formation p3l d and middle permian gufeng qixia formation p2g q respectively among them organic rich source rocks mainly concentrate in the lower part of the p3l d and the middle upper part of the p2g q and the p3d mudstone also works as good source rock the p3l d mudstone with high organic abundance is the chief source rock in the south yellow sea basin whose maximum hydrocarbon generating intensity may reaches up to 795 09 104 t km2 and hydrocarbon expulsing intensity remains at the level of 165 03 104 t km2 a noteworthy feature of the p2g q source rocks is the strong vertical heterogeneity with the hydrocarbon expulsing intensity of the upper part being 34 14 104 t km2 while that of the lower part being 18 07 104 t km2 in contrast the organic abundance of argillaceous limestone in the t1q is mainly poor to medium and its hydrocarbon expulsing intensity is the weakest one in the three sets of hydrocarbon source rocks only about 12 7 104 t km2 taking into consideration the joint influence of depositional environment organic matter parent source and biological productivity the overall quality of source rocks in the south yellow sea basin is at the similar level to the lower yangtze subei basin but lower than that of the upper yangtze sichuan basin the most significant oil gas information is that multiple direct oil indications and high value abnormalities of gas logging have been discovered in the well csdp 2 moreover the mesozoic and upper paleozoic marine strata in the south yellow sea basin have experienced three hydrocarbon charging stages indicating a broad prospect of marine oil gas exploration

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea ii molecular composition of alkylated naphthalenes phenanthrenes benzo and dibenzothiophenes abstract variations with depth in the quantitative distributions of di and tricyclic alkylaromatic hydrocarbons and sulfur heterocycles determined for a total of thirty two core samples from two thick shale intervals and thirteen thin interbedded shale layers of the upper jurassic age kimmeridge clay formation brae field area north sea reveal in part the effects of depletion with hydrocarbon expulsion trends of increasing depletion with approach to the nearest shale sandstone contacts as documented by a decrease in carbon normalized yields are more distinctive for the alkylnaphthalenes as compared to the alkylphenanthrenes and alkyldibenzothiophenes but less drastic than previously observed for long chain alkanes cf part i leythaeuser et al 1988 lowest yields consistently were encountered at the outermost 1 2 metres of the thick shale intervals and for the thin shale layers where the relative expulsion efficiencies were much higher for c15 to c30n alkanes 80 95 than for c2 and c3 alkylnaphthalenes 30 40 in contrast c2 and c3 alkylbenzothiophene yields were higher in these shale portions than further inside the thick shale which is interpreted to result from a post expulsion selective replenishment from the adjacent oil accumulation expulsion was not associated with any detectable fractionation among c1 and c3 alkylnaphthalenes or c1 and c2 alkylphenanthrenes as evidenced by a mass balance approach and concentration ratios of individual alkylaromatic isomers commonly used as maturity indicators based on a reconstruction of the quantitative distributions of aromatic hydrocarbons and sulfur aromatics expelled from thin shale layers from early mature through to mature stages of thermal evolution it was verified that the methylphenanthrene index mpi 1 and methyldibenzothiophene ratio mdr of the expelled oil reflects the average of the maturity levels during which the source rock has expelled petroleum

the influence of hydrocarbon expulsion on carbon isotopic compositions of individual n alkanes in pyrolysates of selected terrestrial kerogens expulsion of petroleum from source rock is a complex part of the entire migration process there exist fractional effects on chemical compositions in hydrocarbon expulsion does the carbon isotopic fractionation occur during expulsion and to what extent here the influence of hydrocarbon expulsion on carbon isotopic compositions of individual n alkanes from pyrolysates of selected terrestrial kerogens from tuha basin and fushun liaoning province of china has been experimentally studied the pyrogeneration expulsion experiments were carried out under semi closed system the carbon isotopic compositions of individual n alkanes were measured by gc irms the main conclusions are as follows first there is carbon isotopic fractionation associated with hydrocarbon expulsion from type iii kerogens in tuha basin there exist differences of carbon isotopic compositions between the unexpelled n alkanes and expelled n alkanes from tuha desmocollinite and tuha mudstone second there is almost no carbon isotopic fractionation associated with hydrocarbon expulsion from type ii kerogens in fushun and liaohe basin third carbon isotopic fractionation in hydrocarbon expulsion should be considered in making oil source correlation of type iii kerogens at least in the tuha basin further studies need to be carried out to determine whether this is true in other basins fourth oil and source at different maturity levels cannot be correlated directly for type iii kerogens since the carbon isotopic compositions of expelled hydrocarbons at different temperatures are different the expelled hydrocarbons are usually lighter depleted in 13 c than the hydrocarbons remaining in the source rock at the same maturity

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

expulsion of petroleum hydrocarbons from shale source rocks there is compelling evidence that movement of petroleum from organic rich shales into sandstones and limestones occurs in the subsurface1 this expulsion of material must occur if crude oil accumulations are to form and it is termed primary migration2 earlier studies3 4 suggested that this movement occurs with chemical fractionation some components are more mobile than others one of the agents of expulsion at early maturity stages is compaction which is not only capable of forcing water but also organic components out of the pore network of a source rock2 5 6 because the fractionation effects associated with expulsion provide clues to the transport mechanisms involved we have made detailed quantitative comparisons of the hydrocarbons of shales of different thicknesses the centre and edges of thick shales and sandstones adjacent to shales from two cored interbedded shale and sandstone sequences from spitsbergen island svalbard norway these observations confirm considerable movement of hydrocarbons in the subsurface with lower molecular weight components being more mobile up to 90 the original amount of n pentadecane may be lost from very thin shales sandwiched between sandstone horizons and from shales close to a lithological boundary with sandstone

carbon dioxide injection and resultant alteration of the weber sandstone rangely field colorado 1 geologic interpretations made during the current enhanced oil recovery project at rangely field rio blanco county colorado have shown the relationships between alteration of reservoir mineralogy and texture changes in produced water composition and increased problems with oil production the bottom hole ph of weber brine has decreased from approximately 7 5 to 4 5 since the initiation of co 2 injection into the pennsylvania permian weber sandstone in the central portion of the field much of the weber is partially cemented with carbonate minerals including ferroan calcite and ferroan dolomite with authigenic clay minerals predominately illite and mixed layer smectite illite also present these minerals are affected by the lowered ph of the co 2 flood changes in the chemistry of produced water are associated with alteration of reservoir mineralogy the co 2 flood has caused substantial increases in the concentrations of iron calcium and magnesium in the produced brine from the dissolution of carbonate cements and perhaps authigenic clays and detrital feldspars produced water from some wells has experienced large changes in barium and sulfate concentrations an increase in bromide concentration indicates that previously segregated portions of the reservoir which contained very saline original formation brine have been accessed by the carbonated water hypotheses based on the water chemistry changes were confirmed in core flood experiments these experiments also indicated that there was no net change in permeability following co 2 injection

relationship between the fluorescence color of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 1 fluorescence evolution of oil in the context of hydrous pyrolysis experiments with increasing maturity abstract the fluorescence evolution of oils has been measured by simulation of petroleum generation and expulsion in a half closed system using hydrous pyrolysis based on four oil prone source rocks type i and ii kerogens from the dongying depression bohai bay basin china the results suggest that the fluorescence characteristics of expelled oil are independent of oil prone kerogen types but are strongly related to oil generation and expulsion processes which are controlled by thermal maturity of source rocks the fluorescence spectral parameters max q650 500 and qf 535 of expelled oils show no obvious variation or even show gradual redshifts when the highest max occurs at peak bitumen generation depending on the expulsion process a blueshift of fluorescence color occurs only during the main oil generation and expulsion stage which immediately follows the peak bitumen generation stage however the expelled oil mainly exhibits green to yellow fluorescence colors 500 nm

pore scale oil distribution in shales of the qingshankou formation in the changling sag songliao basin ne china abstract a total of 19 representative lacustrine shale core samples from the upper cretaceous qingshankou formation in the changling sag songliao basin northeast china have been characterized to determine the types of shale oil reservoir lithofacies and investigate pore structures and pore scale oil distribution using an integrated petrographic geochemical and petrophysical approach based on the sedimentary structures and mineral compositions four lithofacies types have been recognized foliaceous argillaceous mudstone fam laminated diamictic mudstone ldm laminated felsic mudstone lfm and interbedded felsic mudstone ifm sequential extraction experiments via a soxhlet extractor were performed using different solvents to recover oils of varying polarities weak polar oil wpo was extracted with n hexane under room temperature while strong polar oil spo was extracted with a mix of dichloromethane and methanol 9 1 v v extraction low pressure n2 sorption data acquired from the original and solvent extracted samples indicates that the pore volumes occupied by wpo vwpo decrease progressively in lfm averaging 68 32 10 4 cm3 g ldm averaging 50 41 10 4 cm3 g fam averaging 48 86 10 4 cm3 g and ifm averaging 39 39 10 4 cm3 g while pore volumes occupied by spo vspo increase progressively in ifm averaging 8 00 10 4 cm3 g lfm averaging 12 62 10 4 cm3 g ldm averaging 38 85 10 4 cm3 g and fam averaging 65 08 10 4 cm3 g major factors controlling pore scale oil distribution in the shale reservoirs include pore structures toc and clay mineral contents pore structures can affect the distribution of wpo and spo to a great extent wpo is mainly distributed in the mesopores while spo is present in all pores in the four lithofacies spo is mainly distributed in mesopores in fam and ldm and in macropores in lfm and ifm toc and clay mineral contents have strong impacts on the distribution of spo carbonate minerals in ldm and ifm are dominated by ostracoda shells and authigenic calcite cement respectively the carbonate mineral content shows a positive correlation with wpo in ldm in which the carbonate minerals are dominated by ostracoda shells with well developed pores due to organic acid dissolution toc shows a positive correlation with wpo for toc less than 1 2 wt while shows a negative correlation for toc greater than 1 2 wt in the study area ldm and lfm are identified as favorable lithofacies or sweet spots for shale oil exploration because they have relatively high toc 0 7 2 wt high percentages of in situ wpo and a high mineral brittleness index

fractionation of azaarenes during oil migration abstract a comparative study of alkylbenzoquinolines in crude oils and rock extracts bitumens from japan and sumatra shows that the ratios of nitrogen masked isomers nmis to nitrogen exposed isomers neis and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens also a regular increase in the ratios of nmis to neis with increasing migration distance is observed for a series of crude oils from the sarukawa oil field northeastern japan these results are attributed to the preferential migration of nmis caused by their weak adsorption on clay minerals and or their low solubility in interstitial water and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration which are regarded as geochromatographic phenomena it is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration

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

evolution of alkanes and carboxylic acids in ancient sediments from the maracaibo basin abstract aliphatic hydrocarbons and carboxylic acids were analysed quantitatively in rock samples of different degrees of maturity from the icotea borehole eocene misoa formation maracaibo basin venezuela in order to compare their geochemical evolution in ancient sediments previously a double generation process for the carboxylic acids has been reported in which immature distributions of acids were generated at the highest maturities it was suggested that the generation of the organic acids was dependent on the nature of the binding in the kerogen and on steric factors by comparison the alkanes show different behaviour whilst a similar generation profile is observed for hopanes when compared to hopanoic acids no inversion of isomeric maturation parameters was observed in this case hopanes may be generated first by a release of hydrocarbons from the kerogen at low levels of thermal maturity r o 0 46 and secondly by cracking at higher temperatures the second generation being less significant than the first higher plant derived triterpanes behave similarly pristane phytane and n alkanes are generated at relatively high levels of thermal maturity r o 0 7 the generation profiles for the n alkanes are complicated by expulsion and cracking phenomena however these components are generated after the major release of n acids

quantitative modeling of organic matter connectivity in source rocks using fractal geostatistical analysis abstract numerical modeling of hydrocarbon expulsion requires accurate assessment of the 3 d geometry and connectivity of hydrocarbon pathways such as pore systems organic matter networks fractures and stylolites in source rocks in this paper a method combining scanning electron microscopy sem digital image analysis fractal geostatistical analysis and a renormalization algorithm is developed to determine the 3 d geometrical properties defined as organic matter connectivity factor ocf of these pathways in source rocks the method is applied to derive fractal geostatistical models and the ocfs of organic matter networks omn of fourteen source rocks with wide variation in total organic carbon toc content and texture the results show that the connectivity of the omns is affected by both the amount and distribution of organic matter in source rocks uniformly distributed omns lose 3 d connectivity when the toc content is below approx 6 whereas omns with preferred orientation may maintain lateral connectivity at 4 and perhaps lower toc content thus in shales such as the bakken in which vertical omn connectivity may not exist the fracture systems may provide not only primary migration pathway but hydrocarbon reservoirs that are recharged through the laterally connected omns the method developed in this paper can be used to quantify geological models and average geological properties over a wide range of scales and thereby provide reliable geometric parameters for basin modeling using a numerical technique

simple kinetic models of petroleum formation part ii oil gas cracking kinetic schemes describing oil gas cracking are a required component of models which predict the masses compositions and phases of petroleum expelled from source rocks an additional application is in predicting the temperature zone over which reservoired oil deposits will be degraded to gas this simple first order kinetic model calibrated on closed system laboratory pyrolysis of 16 different source rock samples describes the bulk conversion of oil c6 molecular range to gas c1 5 molecular range cracking rates vary markedly between samples depending on the saturate to aromatic ratio of the generated oil the initial hydrogen index hl0 of the sample taken as an indirect measure of the saturate to aromatic ratio of the oil it generates correlates strongly with optimized rate constants for oil cracking in individual samples thus cracking rates are predictable using a simple routinely performed geochemical screening measurement source rocks with high hl0 tend to generate saturate rich oils with a high mean activation energy and a tight distribution of bond energies which crack relatively slowly over a high but relatively narrow temperature range source rocks with low hl0 generate aromatic rich oils with a low mean activation energy and a broad distribution of bond energies which crack relatively rapidly over a lower but relatively wide temperature range this is an important contributing factor in the observed gas proneness of type iii source rocks with low hl0 the projected cracking window defined limits at 10 90 of initial oil degraded reference heating rate 2 c ma 1 varies from 155 to 205 c in very high quality source rocks hl0 600 mg g c 1 to 115 205 c in very poor quality source rocks hl0 50 mg g c 1 an order of magnitude increase decrease in heating rate elevates depresses these temperature windows by ca 15 c the extrapolations to the geological subsurface are subject to a confidence limit no better than 7 c extrapolation to the reservoir environment requires caution because kerogen an important potential catalyst and hydrogen donor allowing 100 cracking efficiency in the source rock is absent furthermore fractionation during expulsion causes saturate enrichment of expelled ultimately reservoired oils thus in reservoir cracking should be at least as slow as cracking in good quality source rocks and coke or pyrobitumen formation is needed to conserve the hydrogen balance a case history based on deep petroleum pools of the uk central north sea confirms these projections demonstrating no positive evidence of significant in reservoir cracking at temperatures as least as high as 174 c and perhaps even 195 c previous studies have overestimated the importance of in reservoir cracking future studies aiming to predict petroleum composition in traps should concentrate on understanding the charge composition expelled from the kitchen

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

influence of retained bitumen in oil prone shales on the chemical and carbon isotopic compositions of natural gases implications from pyrolysis experiments abstract retained bitumen in oil prone source rocks has a significant impact on late gas generation but such influence is still poorly quantified because it is quite difficult to restore the bitumen content retained in a mature source rock in this study a suite of artificially matured samples were prepared from a moderate maturity shale sample to represent shales with different amount of retained bitumen these samples were then pyrolyzed in sealed gold tubes to investigate how the amount of retained bitumen affects the changes in chemical and carbon isotopic compositions of generated gases and the uncertainty of the evaluation of gas maturity and source identification the results indicate that the decrease in yields of hydrocarbon gases is proportional to the reduction of retained bitumen content however a progressive enrichment in heavier carbon isotope 13c of gaseous hydrocarbons occurs while less amount of bitumen is retained in shales this experimental observation partly explains the heterogeneity of methane carbon isotopes for shale gases that have identical thermal maturity levels although the amount of retained bitumen can significantly change the carbon isotopic ratios of individual gas 13c1 13c2 and 13c3 the difference in carbon isotopic composition between gaseous components such as ethane and methane 13c2 13c1 or propane and ethane 13c3 13c2 are not significantly affected and therefore these differential values can be potentially used as maturity indicators for overmature natural gases exhibiting no carbon isotopic reversals geochemical and carbon isotopic diagrams that are widely used for the identification of oil and kerogen cracking gases are also found to be affected by the retained bitumen content these results illustrate that it is necessary to take into account the retained bitumen content of shales when thermal maturity and genetic origin of natural gases derived from oil prone source rocks are being evaluated

petroleum generation and migration in coal seams of the carboniferous ruhr basin northwest germany a series of 64 coal and clastic rock samples of westphalian age was taken from five narrow 3 m depth intervals between 1200 and 1530 m depth and studied by geochemical and petrological methods maturity increases regularly with increasing depth as indicated by several maturity parameters the influence of organic facies is evident in the uppermost coal seam 0 70 rr where a hand picked vitrinite contains less total extract and less saturated long chain hydrocarbons than a directly adjacent sporinite rich coal extracts from deeper and more mature coals are less affected by facies changes probably due to enhanced petroleum redistribution in the seams total yield and gross composition of extracts in the deepest seam 0 92 rr which is directly overlain by sandstone seem to be influenced by the preferential expulsion of saturated hydrocarbons

the effect of interbedding on shale reservoir properties north sea oil is overwhelmingly generated in shales of the upper jurassic basal cretaceous kimmeridge clay formation once generated the oil is expelled and ultimately migrates to accumulate in sandstone or carbonate reservoirs the source rock shales however still contain the portion of the oil that was not expelled as a consequence such shales and juxtaposed non source lithofacies can form the targets for the exploration of unconventional oil in this paper we examine part of the kimmeridge clay formation as a hybrid shale resource system within which hot shale and organic lean sandstone and siltstone intervals are intimately interbedded this hybrid system can contain a greater volume of oil because of the increased storage capacity due to larger matrix porosities of the sand silt interbeds together with a lower adsorptive affinity in the interbedded sandstone the relationship between the estimated volume percentages of sand and mudstone and free oil determined from rock eval s1 yields is used to place limits on the drainage of oil from source mudstone to reservoir sand at the decimeter scale these data are used to determine oil saturations in interbedded sand mudstone sequences at peak oil maturity higher values of free hydrocarbon as evidenced by the s1 value in mudstone suggest that more oil is being retained in the mudstone while higher s1 values in the interbedded sands suggest the oil is being drained to saturate the larger pore spaces high silica content in the interbeds confirms the brittleness in this mudstone sandstone lithofacies an important factor to be considered for fracture stimulation to successfully work in a hybrid system the key points of this hybrid unconventional system are the thickness storage capacity and the possibility to capture a portion of the expelled as well as retained oil

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

oil retention and intrasource migration in the organic rich lacustrine chang 7 shale of the upper triassic yanchang formation ordos basin central china the zhang 22 well was drilled in the ordos basin penetrating the chang 7 member of the triassic yanchang formation which cumulatively has more than 80 m 260 ft of black organic rich shale of oil window maturity using 76 samples collected every 1 m 3 ft from the well the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the chang 7 shale were qualitatively and quantitatively documented the organic rich intervals 1 2 and 5 having an average total organic carbon toc of 6 79 wt and pyrolyzable hydrocarbon potential of 9 40 mg g rock i e the amount of hydrocarbons generated by pyrolysis between 300 c and 650 c s2 are defined as generative units in the chang 7 shale system compared to the in source reservoirs or sweet spots i e the third and fourth intervals which contain a lower average toc of 4 19 wt and an average s2 value of 7 17 mg g rock but the highest amount of free oil average total oil of 7 35 mg g rock geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings for example bitumens from the generative units proportionally possess lower saturated hydrocarbons 56 66 than those from the in source reservoirs up to 81 the proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart the individual molecular weight distribution of sample extracts displays more light end moieties being enriched in the generative units by applying the compositional mass balance calculation the overall and compound specific expulsion efficiencies in the in source reservoirs are abnormally negative compared to the positive values in the generative intervals this finding in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in source reservoirs indicates a short distance intrasource migration of generated petroleum into the sweet spot intervals intervals 3 and 4 from the overlying units intervals 1 and 2 and the underlying interval 5 furthermore when quantifying the total amount of retained petroleum in the shale system an amended assessment has been introduced to overcome the systematic misestimations if only unextracted values for the amount of thermally extractable hydrocarbons volatilized at 300 c mg hc g rock were considered thus the oil crossover effect temperature at which the rate of s2 generation is at maximum shift phenomenon and the hydrogen index being shifted to higher values after extraction all account for identifying intervals 3 and 4 as the in source reservoirs in this study we have not only identified a set of promising in source targets for shale oil exploration and production but we also presented the chemical and molecular composition for these shale oils we have additionally speculated for the intrasource migration model and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation as well as the stratigraphic fractionation on differentiating the chemical compositions during migration the improved oil quality by fractionation the extra storage potential derived from microfossil quartz the weak adsorptive affinity of oil to organic matter and the good shale susceptibility to hydraulic fracturing all give a promising prospective for exploring and producing shale oil from the chang 7 shale system in the ordos basin

intraformational migration of petroleum insights into the development of sweet spot in the cretaceous niobrara shale oil system denver basin abstract the cretaceous niobrara formation is one of the latest unconventional exploration targets in north america in this paper an overall type ii marine organofacies with some variability is present within a core which consists of alternating marls and chalks covering a maturity range of 0 8 1 0 rc calculated vitrinite reflectance enhanced oil saturation index osi values have previously been reported for the chalk and here a positive trend r2 0 92 between the osi and the percentage of saturates in gross fractions is present thus the saturate fraction gradually increases from 40 to above 60 as the osi increases from 40 to 550 mg hc g toc total organic carbon extremely high osi values 300 mg hc g toc are characteristic of niobrara chalks therefore the chalk intervals represent primary sweet spots using a combined analytical approach petroleum has been shown to migrate from the organic rich marls into juxtaposed chalks and that this has fractionated oils into higher quality liquids extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons while the nso containing polar compounds are preferentially retained in the shale and marl units compared with the significant fractionation effects between these gross fractions fractionation within a given compound class is nevertheless indistinct

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

resource potential and core area prediction of lacustrine tight oil the triassic yanchang formation in ordos basin china unlike liquid rich hydrocarbons in marine shale systems in north america the triassic yanchang oil is preserved in tight sandstone reservoirs deposited in a lacustrine setting the tight reservoir covers an area of 30 000 km2 11 600 mi2 and is characterized by ultralow permeability 0 001 1 00 md 0 001 10 3 1 00 10 3 m2 a low subsurface pressure coefficient 0 6 0 8 and low single well yield several tons 10 40 bbl to 10 tons 70 bbl per day the reservoir also features a high content of quartz feldspar and carbonate averaging 70 80 and low crude oil density of 0 84 g cm3 36 5 api with an oil saturation of approximately 60 80 for the first time this study employs the assessment of petroleum in place resources based on the genesis and statistics predicting method gspm and estimated ultimate recovery method for the tight oil in the ordos basin the advantage of gspm over previously reported methodologies is the suitable combination of genetic and statistical methods to estimate proximally sourced tight oil the results show that the total in place resource potential of the investigated tight oil is approximately 42 26 108 t 295 82 108 bbl with an average abundance of 15 104 t km2 99 104 bbl mi2 the recoverable resources for the 50 probability of the chang 7 tight oil accumulation is 3 11 108 t 21 77 108 bbl in the ordos basin the top two grades of the chang 7 tight oil core area cover the total area of three layers comprising 12 745 km2 4921 mi2 with 22 51 108 t 157 57 108 bbl of in situ resources furthermore the four most promising zones have been identified

a revised method for organic porosity estimation in shale reservoirs using rock eval data example from duvernay formation in the western canada sedimentary basin studies suggest that nanometer scale pores exist in organic matter as a result of thermal decomposition of kerogen depending on the host rock lithology organic pores could be the primary storage for hydrocarbon accumulation in unconventional petroleum plays although various methods are publicly available estimation of organic porosity remains a challenge because the procedures involve certain simplification or some implicit assumptions on the calculation of initial total organic carbon toc in this study we propose a revised method to address some of these issues a model of estimating hydrocarbon expulsion efficiency is developed and incorporated into the calculation of initial toc thus producing an estimate of organic porosity with an improved mass balance the method has been tested and compared with estimates using other methods based on a rock eval data set in the literature an application of the method to a large data set from the upper devonian duvernay formation petroleum system in the western canada sedimentary basin reveals that the modification has a significant effect on the estimated organic porosity this study also indicates that organic porosity in the duvernay formation ranges greatly from none in immature intervals to 6 in highly mature and organic rich shale intervals scanning electron microscope images of immature and mature organic rich shale samples of the duvernay formation show a progressive increase in organic porosity with increasing thermal maturity supporting the proposed model calculation the presence of a large volume of organic porosity in mature shale intervals suggests a significant amount of hydrocarbon may be stored in the organic nanopores in the duvernay formation

efficiency of petroleum expulsion from shale source rocks the limited data available on the mechanism and the efficiency of the processes by which petroleum is expelled in the subsurface from source rocks into adjacent reservoir rocks are mostly qualitative1 2 we present here material balance type comparisons of sample series extending from the centre portions of two adjacent hydrocarbon source rock units towards their outer edges3 which enable expulsion efficiencies to be determined in certain parts of the shale the expulsion efficiencies for total extract and its saturated and aromatic hydrocarbon fractions have much higher values than previously thought reaching up to 80 for the total extract which increase towards possible secondary migration avenues the expulsion is associated with fractionation effects such as those based on polarity differences also expulsion efficiencies were found to be related to the degree of hydrocarbon saturation of the pore system they are higher for a rich oil prone source rock unit compared with a poorer quality one which had generated less hydrocarbons

experimental simulation of plagioclase diagenesis at p t conditions of 3 5 km burial depth dissolution of plagioclase under the physical conditions at shallow to intermediate burial depths is a prime candidate for secondary porosity generation in feldspathic siliciclastic sediments the diagenetic behavior of granular aggregates of plagioclase feldspar and quartz has been investigated by experimentation performed in a bridgeman type pressure vessel the experiments each of two weeks duration simulated pressure temperature conditions approximating 3 5 km burial depth by using a double acting pore fluid reservoir solutions of various chemistries were cycled through samples composed of oligoclase or labradorite feldspar and quartz 90 10 wt respectively

petroleum retention in the mandal formation central graben norway abstract upper jurassic organic matter rich marine shales of the mandal formation have charged major petroleum accumulations in the north sea central graben including the giant ekofisk field which straddles the graben axis recent exploration of marginal basin positions such as the mandal high area or the sogne basin has been less successful raising the question as to whether charging is an issue possibly related to high thermal stability of the source organic matter or delayed expulsion from source to carrier the mandal formation is in part a very prolific source rock containing mainly type ii organic matter with

subducted lithospheric boundary tomographically imaged beneath arc continent collision in eastern indonesia this work was funded by the national science foundation nsf grant ear 1250214 as well as dikti grant 127 sp2h ptnbh drpm 2018

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

an experimental study of co2 brine rock interaction at in situ pressure temperature reservoir conditions abstract a detailed investigation of co 2 brine rock interactions through a core flooding laboratory experiment was carried out under simulated reservoir conditions 100 c and 24 mpa changes in the ionic chemistry of the outlet solution combined with core scanning electron microscopy sem and bulk rock x ray diffraction xrd analysis of the core pre and post experiment reveal new insights into co 2 brine rock interactions minerals such as potassium k feldspar albite calcite and ankerite are variably dissolved after the experiments calcite is the mineral most affected by dissolution followed by ankerite whereas dissolution of feldspar minerals is minimal small amounts of kaolinite and solid phases were generated as a result of the experiment the solid phases are mainly comprised of c o na cl al and si and are presumed to be the transitional products in the formation of carbonate minerals the very low fluid penetration rate in the experiment resulted in significantly reduced contact area between the acidic co 2 fluid and minerals in the cores resulting in low rates of feldspar dissolution core permeability decreased substantially throughout the experiment although core porosity remained unchanged the permeability reduction is the result of precipitation of new mineral phases e g kaolinite and solid phases and potentially also the presence of clay particles released by the dissolution of carbonate cement which have then been transported in the fluid flow path and accumulated at pore throats the results provide new insights into co 2 trapping mechanisms in depleted oil and gas reservoirs and into the potential formation damage that may result from massive injections of co 2 into reservoirs during enhanced oil recovery programs

aspects of generation and migration of hydrocarbons from coal bearing strata of the hitra formation haltenbanken area offshore norway abstract the haltenbanken area situated 150 200 km offshore mid norway is a proven gas condensate and oil producing province with continuing exploration potential in this structurally and stratigraphically complex area with multiple source rock possibilities we have examined the upper triassic lower jurassic hitra formation to determine its possible contribution to the hydrocarbon pools in the area the 400 m thick hitra formation consists of interbedded shales siltstones sandstones and coal seams in this study conventional cores of the hitra formation from depths varying from 2 4 and 4 6 km have been examined with the objective to obtain a better understanding of hydrocarbon generation migration and expulsion processes in these coals as function of variation in facies and maturity in addition to basic geochemical measurements toc rock eval and gc analysis of c15 saturated hydrocarbons microscopic studies normal and uv reflected light were carried out to determine the abundance and initial distribution of hydrogen rich macerals including fluorescent mobile phases such as exsudatinities geochemical and microscopal evidence was obtained suggesting that some of the interbedded sandstones show indications of impregnation by migrated hydrocarbons some bitumen filled micro fractures were observed extending from the coals towards the adjacent sands a preliminary interpretation of these data is that these fractures represent conduits carrying hydrocarbons from the coal seams towards the sandstones the role of the kerogen type variations on the amount of hydrocarbons generated and the mechanism and efficiency of hydrocarbon expulsion from the coals is discussed

the pristane n heptadecane ratio as an indicator for recognition of hydrocarbon migration effects a simple scheme is proposed for type iii kerogen source rocks which uses pristane n heptadecane concentration ratios for recognition of hydrocarbon expulsion effects within the maturity interval 0 82 1 03 rm this scheme can be applied from gas chromatography data routinely obtained by most petroleum geochemistry studies in exploration exploration of this scheme to oil prone type ii source rocks appears very promising

rapid porosity and permeability changes of calcareous sandstone due to co2 enriched brine injection reservoir injectivity and storage capacity are the main constraints for geologic co2 sequestration subject to safety and economic considerations brine acidification following co2 dissolution leads to fluid rock interactions that alter porosity and permeability thereby affecting reservoir storage capacity and injectivity thus we determined how efficiently co2 enriched brines could dissolve calcite in sandstone cores and how this affects the petrophysical properties during computerized tomography monitored flow through reactor experiments calcite dissolved at a rate largely determined by the rate of acid supply even at high flow velocities which would be typical near an injection well the porosity increase was accompanied by a significant increase in rock permeability larger than that predicted using classical porosity permeability models this chemically driven petrophysical change might be optimized using injection parameters to maximize injectivity and storage