geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 4 evidence for new exploration horizons in a maturely explored petroleum province abstract significant oil reserves have been discovered recently in the ek1 member of the paleocene eocene kongdian formation and the ordovician buried hill reservoirs in the basement of the niuzhuang south slope nss dongying depression bohai bay basin the physical properties and chemical compositions of these oils are different from those in the overlying eocene oligocene shahejie formation es displaying high wax 29 32 low sulfur 0 04 0 25 and high sterane isomerization ratios 0 46 0 52 for c29 sterane 20s 20s 20r in contrast the es reservoired oils have relatively low wax but high sulfur contents with the 20s 20s 20r ratio for c29 steranes in the range of 0 33 0 39 oil source correlation results show that the es reservoired oils were derived from source rocks in the es4 member of the shahejie formation within the conventional oil window whereas the dominance of c29 steranes observed in oils from the ek1 and ordovician reservoirs suggests a contribution from different source s for these oils within the deep es4 interval and the ek2 member of the kongdian formation the recent commercial oil discovery in the ek1 and older strata and the confirmation of the presence of organic rich dark mudstones in the ek2 member of the kongdian formation are significant for further petroleum exploration in the deep strata of the dongying depression and other parts of the bohai bay basin

practical estimation of compression behavior of clayey silty sands using equivalent void ratio concept abstractclayey silty sands are widespread as naturally sedimentary soils such as marine deposits in estuaries and offshore locations they belong to a unique class of gap graded soils featuring a d

practical approaches to identifying sealed and open fractures for one essential ingredient of permeable fracture networks degree of fracture pore space preservation in large fractures i show how the characterization challenge presented by sparse fracture sampling can be overcome by measuring a surrogate the abundance of rock mass cement that precipitated after fractures ceased opening sampling limitations are overcome because the surrogate is readily measured in small rock samples including sidewall cores and cuttings permitting site specific diagnosis of the capacity of fractures to transmit fluid over a wider range of sample depths than conventional methods allow a diverse core database shows that this surrogate correctly predicts where large fractures are sealed information on timing of fracture opening relative to cement sequence can be obtained in two ways first evidence of fracture movement history and cement sequences in sparse large fractures can be extrapolated to areas having only cement data alternately evidence of fracture timing can be acquired from sealed micrometer scale fractures distribution of porosity reducing cement is commonly heterogeneous from bed to bed and location to location in siliciclastic and carbonate rocks however because patterns of sealed or open fractures cannot be delineated using fracture observations alone surrogates have practical value for production fairway mapping and other applications in which identifying open fractures is essential this study highlights the vital interplay among structural and diagenetic processes for fracture porosity preservation or destruction

using natural maturation series to evaluate the utility of parallel reaction kinetics models an investigation of toarcian shales and carboniferous coals germany abstract open system pyrolysis is routinely performed on immature samples in order to determine the kinetic parameters of petroleum generation at both bulk and molecular levels this study tested such predictions for type ii and type iii organic matter by making calibrations with both artificial and natural maturity sequences of toarcian shales posidonia shale 0 48 1 44 rr and carboniferous vitrains 0 74 2 81 rr both natural series showed little or no compositional variability attributable to kerogen type artificially matured samples were prepared by non isothermal heating 0 7 k min of the least mature samples up to end temperatures between 375 and 470 c under either closed or open system conditions measured generation rate versus temperature curves were analyzed assuming a distributed system of activation energies and a single frequency factor in each case the resulting kinetic parameters were then used to assess bulk petroleum formation rates for geological heating conditions in the case of all artificially matured samples measured and predicted bulk petroleum formation rate vs temperature curves for each maturation stage remain within the original envelope defined by the least mature sample despite an upward shift of tmax temperatures this confirms that the reactions taking place during both the pyrolysis measurements and simulated maturation processes are the same involving mainly homolytic cracking a similar pattern of measured and predicted rate curves is reproduced by the natural maturation sequence of the toarcian shales in the maturity range of 0 53 to 1 44 rr suggesting that petroleum generation within these natural systems also results from cracking reactions and therefore that petroleum generation over geological time can be reliably extrapolated from open system pyrolysis of the appropriate immature sample by contrast significant deviations are observed for the natural coal series with measured and predicted rate curves extending beyond the immature envelopes in accordance with the pronounced increase of frequency factors and of protonated aromatic carbon concentrations this behavior is attributed to solid state aromatization reactions which compete with product generation during natural coalification but which are not reproducible to the same extent by experimental heating it is concluded that petroleum generation from vitrinitic coals over geological time cannot be reliably extrapolated from open system pyrolysis of low rank samples

mercia mudstone formation caprock to carbon capture and storage sites petrology and petrophysical characteristics porous rocks in the subsurface are now used for carbon capture and storage ccs to help ameliorate the effects of greenhouse gas emissions these porous reservoir rocks require a caprock to retain the co 2 it is important to characterize caprock quality and its stability in the presence of elevated partial pressures of co 2 lower triassic sandstones are common in the uk and nw europe and are being considered for future ccs projects the caprock to these sandstones is the middle and upper triassic mercia mudstone group we have studied the mercia mudstone using mineralogy petrology and mercury injection porosimetry to assess its caprock quality detrital minerals are dominated by quartz k feldspar illite and chlorite diagenetic pore filling minerals are dominated by calcite dolomite and gypsum in samples with abundant clay minerals there are only small quantities of pore filling diagenetic cements porosity is broadly uniform for both clay rich and clay poor samples the cleaner clay poor samples had their initial pore spaces filled with early diagenetic pore filling carbonates and gypsum despite the broadly uniform porosity mean pore throat diameter displays a strong inverse correlation with clay content whereas threshold capillary entry pressure shows a strong positive correlation with clay content the more clay rich samples represent much better caprock than the coarser grained samples that contain abundant pore filling cement the samples could support potential column heights of supercritical co 2 between 70 and 540 m and have calculated permeabilities between 10 20 and 10 19 m 2 leakage would occur only on geological time scales assuming that these samples are representative of the whole caprock because caprock quality correlates with illite content and illite will be relatively immune to elevated partial pressures of co 2 the mercia mudstone probably represents a durable caprock for future lower triassic sandstone ccs projects

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

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

kinetic modelling of petroleum formation and cracking implications from the high pressure high temperature elgin field uk north sea in this paper we use a case study to test the simulation of generation migration and cracking of petroleum fluids by a 2d compositional basin simulator using kinetic models based on chemical classes of compounds the selected area is the high pressure 1100 bar high temperature 190 c elgin field in the north sea this study is mainly focused on kinetic modelling of secondary cracking because in this zone paraffinic condensates with almost 50 c6 alkanes were recently discovered whereas only gas c5 was expected given the high temperature conditions the detailed hydrocarbon composition observed today in the fulmar sands reservoir of the elgin field is compared with the results of several simulations aimed at testing the influence of jurassic source rocks retention properties kinetic parameters and temperature variations on the predicted composition of fluids the influence of pressure was neglected in the modelling on the basis of results published in the literature results show that in this north sea area primary cracking of the kerogen into oil is completed whichever source rock is considered and that secondary cracking of accumulated petroleum compounds in the reservoir is presently in progress under these conditions source rock type and retention during primary and secondary migration have little influence on the present oil composition the occurrence of a monophasic paraffinic fluid in the elgin reservoir despite the high temperature is due to its very recent increase from 160 c to over 180 c in the last million years the fluid composition evolves rapidly and our compositional kinetic scheme accounts correctly for the presence of c6 hydrocarbons in these geological conditions first results using the compositional kinetic scheme of behar et al behar f kressman s rudkiewicz j l vandenbroucke m 1991 experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking organic geochemistry 19 1 3 173 189 for secondary cracking showed a reasonably good fit between calculated and observed detailed fluid composition except for methylated aromatics which are overestimated and methane which is underestimated a recent comparison of kinetic parameters obtained from pyrolysis experiments on model compounds showed that it is not realistic to assume as done previously the same frequency factor for all chemical classes of compounds the higher stability of methylated aromatics relative to saturates observed under laboratory conditions would be extended to geological conditions a second set of simulations using frequency factors and activation energies obtained on these model compounds gave a better fit for methylated aromatics however methane is still strongly underestimated and reasons which could explain this discrepancy are discussed

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

the complexity secondary geochemical process genetic mechanism and distribution prediction of deep marine oil and gas in the tarim basin china abstract most paleozoic marine craton basins in china are rich in natural gas except the tarim basin where both oil and gas are prolific various hydrocarbon types have been found in this basin including deep ultra heavy oil heavy oil normal oil volatile oil condensate and natural gas petroleums with diverse types even coexist within a single reservoir generally the ordovician and cambrian reservoirs are deeply buried 5500 8000 m and intensively altered after initial oil and gas accumulations bringing challenges to physical property prediction before drilling and evaluation of exploration targets based on recent exploration discoveries and experimental data we systematically analyzed the origin of oil and gas demonstrated the mechanisms and processes of secondary geochemical alteration e g biodegradation gas washing fractionation tsr and high temperature cracking moreover the preservation mechanism of ultra deep normal oil was also clarified and the distribution patterns of oil and gas were predicted tarim basin has been uplifted and shallowly buried in the early accumulation stage then rapidly and deeply buried in the late stage resulting in various geochemical alteration processes at different burial stages through the reconstruction of complex deep strata oil and gas accumulation histories the spatial distribution of deep petroleum types were predicted this review has provided detailed assessment with case studies in the tarim basin and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums in addition to massive gas accumulations liquid oils still have great exploration potential in strata deeper than 8000 m in the tarim basin

kinetic study of marine and lacustrine shale grains using rock eval pyrolysis implications to hydrocarbon generation retention and expulsion abstract the kinetic parameters of marine and lacustrine shale grains 4 mm were retrieved by using rock eval pyrolysis in comparison with finely ground powder

the effect of oil expulsion or retention on further thermal degradation of kerogen at the high maturity stage a pyrolysis study of type ii kerogen from pingliang shale china high maturity oil and gas are usually generated after primary oil expulsion from source rocks especially from oil prone type i ii kerogen however the detailed impacts of oil expulsion or retention in source rock on further thermal degradation of kerogen at the high maturity stage remain unknown in the present study we collected an ordovician pingliang shale sample containing type ii kerogen the kerogens which had previously generated and expelled oil and those which had not were prepared and pyrolyzed in a closed system to observe oil expulsion or oil retention effects on later oil and gas generation from kerogen the results show that oil expulsion and retention strongly impacts on further oil and gas generation in terms of both the amount and composition in the high maturity stage gas production will be reduced by 50 when the expulsion coefficient reaches 58 and gas from oil expelled kerogen less oil retained is much drier than that from fresh kerogen the oil expulsion also causes n alkanes and gas compounds to have heavier carbon isotopic compositions at high maturity stages the enrichment of 13c in n alkanes and gas hydrocarbons are 1 and 4 6 respectively compared to fresh kerogen oil expulsion may act as open system opposite to the oil retention that influences the data pattern in crossplots of 13c2 13c3 versus c2 c3 13c2 13c3 versus 13c1 and 13c1 13c2 versus ln c1 c2 which are widely used for identification of gas from kerogen cracking or oil cracking these results suggest that the reserve estimation and gas source correlation in deep burial basins should consider the proportion of oil retention to oil expulsion the source rocks have experienced

origin of satin spar veins in evaporite basins abstract satin spar fibrous gypsum veins occur in rocks overlying evaporites in the amadeus basin australia appalachian basin usa cheshire basin england elk point basin canada palo duro basin usa paradox basin usa and zechstein basin england these antitaxial veins which are characterized by central partings and near vertical fibers fill horizontal and inclined fractures most satin spar veins occur in highly fractured or brecciated clastic strata that overlie or are associated with bedded halite anhydrite and gypsum saline springs are commonly present indicating that halite dissolution is active the similarities in morphology and occurrences of these veins suggest a common genesis satin spar veins result from several simultaneously active processes recharge of low salinity surface water results in dissolution of shallow 200 m to 750 m deep halite development of cavernous porosity and formation of extensional fractures in the rock column overlying salt dissolution zones greater solubility of anhydrite than gypsum at low temperatures and at salinities below halite saturation causes hydration of anhydrite to gypsum which takes place without significant volume change once groundwater is saturated with respect to gypsum any further anhydrite hydration and solution must result in supersaturation and the excess caso4 carried by ground water flowin from dissolution zones precipitates as gypsum in open high permeability fractures

the interaction of propagating opening mode fractures with preexisting discontinuities in shale field observations show that hydraulic fracture growth in naturally fractured formations like shale is complex preexisting discontinuities in shale including natural fractures and bedding act as planes of weakness that divert fracture propagation to investigate the influence of weak planes on hydraulic fracture propagation we performed semicircular bend tests on marcellus shale core samples containing calcite filled natural fractures veins the approach angle of the induced fracture to the veins and the thickness of the veins have a strong influence on propagation as the approach angle becomes more oblique to the induced fracture plane and as the vein gets thicker the induced fracture is more likely to divert into the vein microstructural analysis of tested samples shows that the induced fracture propagates in the middle of the vein but not at the interface between the vein and the rock matrix cleavage planes and fluid inclusion trails in the vein cements exert some control on the fracture path combining the experimental results with theoretical fracture mechanics arguments the fracture toughness of the calcite veins was estimated to range from 0 24 mpa m1 2 to 0 83 mpa m1 2 depending on the value used for the young s modulus of the calcite vein material measured fracture toughness of unfractured marcellus shale was 0 47 mpa m1 2

trace elements and environmental significance of messinian gypsum deposits the nijar basin southeastern spain abstract the messinian evaporites in nijar basin southeastern spain are composed of coarse crystalline yesares selenites and feos laminated fine crystalline gypsum these primary yesares selenites feos gypsum and secondary vein gypsum were analyzed for trace elements na mg and sr in order to understand gypsum origin trace element concentrations from the three types of gypsum differ significantly the consistency of the yesares data with natural marine and modeled marine results suggests that yesares selenites were deposited from marine dominated environments within the entire yesares formation or within one single gypsum bed sr mg and na concentrations increase upward while crystal size decreases probably indicating an increase of brine concentration as yesares selenites were accumulating the sr na and mg concentrations from the feos gypsum are partially overlapped with but also significantly higher than those of the yesares selenites these feos data are inconsistent with natural marine and modeled marine data one interpretation for the inconsistency is that diagenetic alteration occurred to primary marine feos gypsum an alternative scenario is that the feos gypsum was deposited from mixed nonmarine fluids with marine brine during the late messinian the latter interpretation is consistent with the stratigraphic sedimentary and o s and sr isotopic data

basin inversion by distributed deformation the southern margin of the bristol channel basin england several models of basin inversion described in the literature are tested in a study of triassic and early jurassic strata exposed along the southern margin of the bristol channel basin in somerset england that has been exhumed by 95 of them are still in net extension despite widespread kinematic evidence for reverse reactivation when coupled with the general absence of thin skinned thrusts and the widespread occurrence of regional contractional folds it appears that none of three main inversion models the fault reactivation model the thin skinned model and the buttress model are by themselves applicable we erect a new model of basin inversion the distributed deformation model which consists of three stages of basin inversion stage one involved early partial reactivation of large displacement steep normal faults stage two was dominated by folding wherein fault blocks underwent oblique non coaxial shortening by map scale folding accompanied by formation of outer arc normal faults minor cleavage and neoformed thrusts stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike slip faults that partitioned deformation into compartments

source rocks in mesozoic cenozoic continental rift basins east china a case from dongying depression bohai bay basin abstract lake basin evolution microscopic and organic geochemistry characteristics are investigated for the paleocene hydrocarbon source rocks of dongying depression bohai bay basin the upper e 2 3 s 4 and the lower e 2 3 s 3 are balanced filled lake basin sediments which show strong climate driven rhythmicity source rocks of these two units have relatively high organic matter content and are dominated by type i kerogen sedimentary and geochemical characteristics indicate there exist persistent lake water stratification and bottom anoxicity during the deposition process by contrast the middle e 2 3 s 3 is an over filled lake deposit dominated by uniform mudstones lacking obvious transgressive regressive cycles it indicates that the lake water lacks stratification and the bottom water is ventilated source rocks of this unit have relatively low organic abundance and are dominated by types ii and iii kerogen thermal evolution studies show that the upper e 2 3 s 4 has a relatively early and multi stage of hydrocarbon generation process and can generate immature oils while the lower e 2 3 s 3 and the middle e 2 3 s 3 have a relatively late and simple hydrocarbon generation process and mainly generate mature oils in addition the persistent increase of eom toc and total hydrocarbons toc indicates that the expelled hydrocarbons from the middle e 2 3 s 3 are in relatively small amounts compared with the other two units the middle e 2 3 s 3 acts as regional caprocks instead of significant source rocks as previously thought the viewpoint will be of great significance in future exploration

comparison of petroleum generation kinetics by isothermal hydrous and nonisothermal open system pyrolysis this study compares kinetic parameters determined by open system pyrolysis and hydrous pyrolysis using aliquots of source rocks containing different kerogen types kinetic parameters derived from these two pyrolysis methods not only differ in the conditions employed and products generated but also in the derivation of the kinetic parameters i e isothermal linear regression and non isothermal nonlinear regression results of this comparative study show that there is no correlation between kinetic parameters derived from hydrous pyrolysis and open system pyrolysis hydrous pyrolysis kinetic parameters determine narrow oil windows that occur over a wide range of temperatures and depths depending in part on the organic sulfur content of the original kerogen conversely open system kinetic parameters determine broad oil windows that show no significant differences with kerogen types or their organic sulfur contents comparisons of the kinetic parameters in a hypothetical thermal burial history 2 5 c my show open system kinetic parameters significantly underestimate the extent and timing of oil generation for type iis kerogen and significantly overestimate the extent and timing of petroleum formation for type i kerogen compared to hydrous pyrolysis kinetic parameters these hypothetical differences determined by the kinetic parameters are supported by natural thermal burial histories for the naokelekan source rock type iis kerogen in the zagros basin of iraq and for the green river formation type i kerogen in the uinta basin of utah differences in extent and timing of oil generation determined by open system pyrolysis and hydrous pyrolysis can be attributed to the former not adequately simulating natural oil generation conditions products and mechanisms

influence of gravel on the compression characteristics of decomposed granite soil large scale one dimensional compression tests were performed in order to analyze the influence of gravel on the compression properties of gravel mixed decomposed granite soils after adjusting the gravel contents of the said soil specimens compacted at a certain level of compaction energy and water content were tested based on the test results it was observed that when gravel mixed decomposed granite soil was compacted at the same energy level there existed a specific gravel content at which the dry density was maximum and which also produced the minimum compression index furthermore an expression based on two phase mixture theory was proposed to quantitatively evaluate the effects of gravel content through a material parameter calculated using the theory and the estimated compression curves agreed very well with the results of the experiments

cyclic fluid flow through a regionally extensive fracture network within the kodiak accretionary prism two types of periodic textures observed in veins from the kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8 12 km depth 1 crack seal microstructures with bands of mica inclusions and 2 collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz the difference in texture reflects the closure of cracks crack seal microstructures record the complete chemical sealing of the crack after each fracture event whereas the collapse features record longer fluid filled periods followed by more rapid draining of fractures collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the kodiak formation reveal local depletion of silica adjacent to veins but no evidence for long distance silica transport within the system both crack seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry with thin closely spaced 0 5 3 cm near vertical crack seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced 500 mm southeast dipping en echelon sets the mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures as the fracture density increased arrays of fractures locally provided zones of weakness and southeast dipping brittle ductile shear zones nucleated these en echelon cracks remained open and provided small reservoirs of fluid textures show that en echelon fractures remain open but periodically grow by upward and downward propagation crack tips are then sealed with locally derived silica and fluid drains back into en echelon fracture arrays this local fluid movement is punctuated by less frequent events where the system links up over a greater distance fractured reservoirs become interconnected and the fluid within reservoirs is drained upward or laterally periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

are light dark coupled laminae in lacustrine shale seasonally controlled a case study using astronomical tuning from 42 2 to 45 4 ma in the dongying depression bohai bay basin eastern china abstract as a typical sedimentary structure in fine grained rocks laminae are widely distributed in shales and mudstones in sedimentary basins the shahejie formation 42 2 45 4 ma formed during the eocene of the paleogene in the dongying depression of china is recognized as a typical area to study lacustrine shale according to the composition of different lamina four types of couplets are identified including carbonate clay couplets carbonate organic couplets clay organic couplets and carbonate clay organic triplets all couplets are composed of light and dark layers a combination of core images microscopic observations mineral compositions geochemical data carbon and oxygen isotopes and strontium isotopes verifies that the laminae are primarily developed in a saline and anoxic or even euxinic environment with a high organic matter om flux through astronomical cycle analysis of the natural gamma ray gr curve from sample site well ny1 the data suggest that the lacustrine shale laminae are formed annually with an average duration of 1 34 yr the formation of laminae is affected by the season which is closely related to the seasonal growth and death of algae during the period of algae growth a large number of light colored carbonate laminae are deposited whereas when the algae dies organic matter accumulates at the bottom of lakes and forms dark organic rich laminae the interbedded and lenticular laminae which are subdivided by layering characteristics are primarily affected by diagenesis in postdepositional processes study of the laminae is helpful in understanding the formation process of lacustrine shale and it provides invaluable sources of information for paleoclimate reconstruction

basin modelling a new comprehensive method in petroleum geology abstract integrated basin modelling is used to understand and reconstruct the geological and thermal evolution of a sedimentary basin to quantify this information and hence to derive among other results the history of generation migration and accumulation of petroleum this new methodical approach is rapidly gaining world wide recognition throughout the geo scientific community because it offers two distinct advantages when addressing geological problems firstly it enables a logical quantitative treatment of very complex interrelated geological processes and secondly it permits these processes to be examined on the basis of an absolute geological time scale the prerequisites for basin modelling are 1 the translation of logical and consistent geological concepts into numerical form and then into suitable computer programs and 2 the application of these programs using high speed computers with large memories using such an approach is an important part of modern petroleum exploration because 1 1 provision is made for total coverage of the basin by allowing extrapolation to non drilled often deeper parts of the basin accessible only by using seismic data 2 2 a three dimensional view of the basin can be constructed and followed through geological time 3 3 an internal logic is utilised which is consistent with physical and chemical laws 4 4 geological geophysical and geochemical data are integrated and modelled iteratively and therefore control each other this paper shows the rapidly widening scope of basin modelling and points out some of the present day limitations and necessary research directions for the future it describes concepts for modelling of tectonic processes and for simulating expulsion of liquid petroleum

a stable isotope study of the mercia mudstones keuper marl and associated sulphate horizons in the english midlands abstract widespread evaporitic sulphate horizons occur in the frequently dolomitic mercia mudstones upper triassic of the english midlands the mudstones were deposited on an extensive peneplain which had areas of upstanding minor relief charnwood massif derbyshire pennines london platform horst and graben structures formed during the early and middle triassic controlled late triassic sedimentation rates and peneplain slope directions a stable isotope study s c o of the sulphates and dolomites of the trent formation indicates that during the deposition of the lower fauld member grabens such as the need wood basin in staffordshire and areas marginal to a graben such as newark in nottinghamshire had a marine brine regime with minor continental input using constraints applied by sulphate concentrations of modern waters in arid environments the ratio of volume of marine input to volume of continental input lay between 3 1 and 4 1 the horst area east leake nottinghamshire was strongly influenced by continental brines which derived sulphate from the exposed carboniferous hathern anhydrite series a predominantly continental brine regime existed across the whole area during deposition of the overlying hawton member periodic marine influxes gave rise to thin sulphate horizons whilst continental run off was occasionally sufficient to form temporary lakes the blue anchor formation rhaetian was deposited in a lacustrine environment with waters of mixed marine and continental origin salinities were lower than those of the preceding trent formation brines

lithological control on fracture cementation in the keuper marl triassic north somerset uk the spatial arrangement of gypsum veins as preserved natural hydraulic fractures have been characterized in the triassic keuper marl formation uk a caprock for hydrocarbon reservoirs and co 2 sequestration the marls cropping out are subdivided into five discrete fracture units based on the presence and abundance of gypsum veins the nodular gypsum in evaporite horizons provides excess gypsum for nodule rooted horizontal gypsum veins our petrographic observations demonstrate that the development of gypsum veins in beds lacking macroscopic evaporites is closely associated with disseminated gypsum cement in the marls we interpret that the gypsum veins in marl are sourced from disseminated gypsum cements in the host rocks based on stratigraphic correlations and much lower sr concentrations than gypsum nodules gypsum was transported to adjacent veins mainly through diffusion in the low permeability marls the localization of gypsum veins and varied sr concentrations of veins and nodules indicate that the diagenetic fluids are a mix of connate water with meteoric water rather than brines transported from evaporite beds along faults to non evaporite beds this results in the absence of gypsum fillings in fractures in rocks without primary gypsum cements the study implies that the cementation of natural fractures in low permeability rocks can highly depend on the presence of cement minerals in the host rock

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

modelling petroleum formation from heterogeneous source rocks the influence of frequency factors on activation energy distribution and geological prediction abstract the application of basin modelling programs permits the prediction of organic matter transformation to oil and gas under variable geological conditions simplified kinetic models are commonly applied with a distribution of activation energies and a single average frequency factor here it will be shown that such simplified kinetic models are not sufficient to correctly predict organic matter transformation in heterogeneous kerogens under geological conditions in the present paper individual pairs of frequency factors and activation energies were calculated from the temperature shift of nine different levels of organic matter transformation ranging from 0 1 to 0 9 tr at different heating rates 0 1 0 7 and 5 0 k min this type of extended kinetic evaluation has been applied on samples from the green river shale the toarcian shale the duvernay formation the draupne formation a type ii s source rock petroleum asphaltenes and a tertiary coal from the mackenzie delta respectively for terrestrial and heterogeneous marine source rocks the frequency factors systematically increase with increasing level of transformation while such an increase was insignificant or absent when homogeneous source rocks were studied by applying geological heating rates it was possible to illustrate the significance of the extended calculation of individual frequency factors the predicted onset temperature of petroleum formation was displaced to 60 70 c in case of lignites coals and type ii s source rocks which was up to 30 40 c lower than predicted by the use of a conventional single frequency factor model to a lesser extend such a shift was also documented for some marine shales e g draupne formation and the duvernay formation the reason for this phenomenon is that an average single frequency factor suppresses the initial formation of petroleum at geological heating rates because high activation energies are needed to maintain the kinetic equation at low generation temperatures in contrast correct activation energies derive from individual frequency factors which keep the activation energies low at low levels of organic matter transformation and result in a more reliable description of the low energy bonds in the heterogeneous organic matter types

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

minor and trace element analyses on gypsum an experimental study abstract minor and trace element na cl mg k sr abundances in gypsum and anhydrite can be used to help elucidate paleosalinity and depositional environments however sulfates may contain abundant fluid and solid inclusions which can contribute considerable amounts of elements to bulk analyses previously published element data in gypsum and anhydrite show highly variable values which may have been significantly influenced by inclusions this study developed procedures for grinding heating and rinsing with alcohol hno 3 and deionized water to fracture and remove fluid and solid inclusions from gypsum and anhydrite samples used for this study are petrographically unaltered miocene and holocene marine gypsum crystals ranging from 10 cm to gypsum na the previously published k gypsum na may need to be revised moreover the methods used in this study can be applied in other evaporative minerals e g halite and dolomite for minor and trace analyses

petrographic and geochemical characterization of microfacies in a lacustrine shale oil system in the dongying sag jiyang depression bohai bay basin eastern china abstract petrology and rock eval analyses have been conducted in the lower third and upper fourth members lower es3 and upper es4 of the shahejie fm source rock intervals in well fanye1 in the dongying sag jiyang depression bohai bay basin eastern china the organic matter in rocks intersected by this well is dominated by lamalginite and bituminite and most samples contain type i or ii kerogen microfacies a h has been identified according to their organic mineral composition and structure using polished thin sections under microscopy the form and location of hydrocarbon residue occurrences mainly as solid bitumen with fluorescence are different in those microfacies microfacies a which is dominant in well fanye 1 is calcareous mudstone without lamination and the hydrocarbon residue is dispersed through the rock with some being present in subtle microfractures microfacies b and f are mostly composed of shale with adsorbed hydrocarbon indicated by fluorescence along mineral grains microfacies c is laminated argillaceous carbonate with hydrocarbon residue mainly occurring in thin microfractures along the bedding plane microfacies d and e are mainly carbonate and microfacies d is laminated with micrite and sparite and hydrocarbon residue occurrence is not only in the microfractures along the bedding but also in the micropores among the grains in the sparite layers which is the main place for hydrocarbon residue occurrence in microfacies type e without lamination microfacies g and h are both micrite microfacies g shows bioturbation and hydrocarbon residue occurs within small irregular microfractures along the bedding planes and pores only a little solid bitumen without fluorescence has been observed in microfacies h the rock eval oil saturation index osi s1 100 toc value is variable because of the different characteristics of these hydrocarbon residue occurrences osi values in microfacies a are normally high 74 8 242 8 mg hc g toc average of 117 2 mg hc g toc and likely much higher if microfractures develop 200 mg hc g toc osi values averaging 43 7 mg hc g toc are lowest in microfacies f because of adsorption on the shales and osi values are the highest in microfacies d 371 3 mg hc g toc and e 199 9 mg hc g toc since the hydrocarbon residues are stored both in microfractures and pores between the grains both osi values are high in microfacies g and h because of low toc content the combination of petrographic and osi analysis appear to be a promising tool for characterizing shale oil systems

crystallization pressure versus crack seal as the mechanism for banded veins banded fibrous veins are often pointed to as evidence for episodic crack opening driven by oscillations in fluid pressure or bulk strain advances in understanding the geochemistry of precipitation data on veins and experiments suggest that pressure due to growing crystals may be an alternate explanation for many observations on these types of veins we propose that some veins originate at sites of precipitation and then propagate due to the pressure exerted by the crystal growth as materials precipitate the vein walls are pushed apart the resulting veins have shapes typical for mode i cracks except that mechanically crystallization pressure replaces the role of internal fluid pressure in their propagation a nonzero remote differential stress serves to align veins mechanical and geochemical considerations suggest that this process will be most important in fine grained rocks such as greenschist grade pelites where diffusion from sites of dissolution rather than advection is the dominant mass transport process veins may owe their orientation to tectonism but their initiation and growth are due to processes that supersaturate the pore fluid veins formed by this mechanism involve cracking to the extent that precipitation forces an original flaw to extend during precipitation cyclic quartz mica bands may indicate geochemical self organization at the vein wall driven by pressure solution enhanced supersaturation in the pore fluid and nonlinear precipitation kinetics at the vein wall

a biomarker study of immature crude oils from the shengli oilfield people s republic of china abstract a suite of crude oils from the shengli oilfield in northwestern china was subjected to detailed chemical analysis crude oils in this suite believed to be derived from source rocks deposited under fresh brackish and saline environments have chemical compositions and biological marker compounds indicative of immature source rocks in this respect the crude oils are unusual apparently having been formed and expelled from source rocks that have been subjected only to mild thermal stress prior to the main zone of petroleum generation

middle eocene paleohydrology of the dongying depression in eastern china from sedimentological and geochemical signatures of lacustrine mudstone previous understanding that stratigraphic variability in lacustrine sequences is primarily caused by depositional processes governed by regional tectonics and climatic change remains to be tested on microscopic scale here we study the upper fourth member es4u of the eocene shahejie formation the major source rock of the dongying depression eastern china in order to understand stratigraphic heterogeneity and tectonic and climate controls on depositional processes in lacustrine mudstone our study integrates core descriptions microscopic observations and studies of mineralogy toc and chemical weathering proxies of cia and ln al2o3 na2o from two full bore cores and correlation of gamma ray logs from six wells across the depression we identified four major lithofacies including the interbedded evaporite and mudstone deposited in a shallow salt lake the silt bearing clay rich mudstone deposited in a pro delta environment within a shallow open lake the laminated calcareous mudstone deposited in a deep stratified meromictic lake with frequent earthquake activities and the massive calcareous mudstone deposited in a shallow and oxygenated lake the es4u member changed from the interbedded evaporite and mudstone dominated lithofacies association to silt bearing clay rich mudstone dominated lithofacies association and then laminated calcareous mudstone dominated lithofacies association suggesting basin wide changes in depositional processes lake level lake water chemistry and paleohydrology we suggest that these changes reflect balance between sediment and water supply and potential accommodation of the lake basin which were governed by paleoclimate in the lake drainage and extensional tectonics we infer that during the deposition of the es4u member the lake basin evolved from an underfilled lake basin with salty lake water under arid climate to a shallow balanced fill lake basin when climate became humid then to a deep balanced fill basin with stratified bottom lake water when climate became more humid and the basin was deepened by tectonic activity this study demonstrates that climate and tectonics both control paleolimnological changes and depositional processes of lacustrine mudstone

the composition and origin of brines during the messinian desiccation event in the meditterranean basin as deduced from concentrations of ions coprecipitated with gypsum and anhydrite abstract gypsum and anhydrite from the upper miocene messinian evaporites of the mediterranean basin were analysed for their coprecipitated ion compositions the concentrations of mg na k sr and cl in gypsum and anhydrite samples from dsdp leg 42a sites 372 374 and 376 and from boreholes yafo 1 ashdod 2 talme yafe 3 and afiq 1 from the coastal plain of israel were used to calculate the composition of the brines from which these calcium sulfate minerals were deposited or in which they have undergone recrystallization or phase transformation results reveal basic differences between the eastern central and western mediterranean basins during the last stage of the messinian salinity event the western mediterranean and the ionian basin were characterized by marine brines during most of the second stage of the salinity event upper evaporite member during this period the eastern mediterranean basins were fed with brines of continental origin these brines are characterized by high ca concentrations relative to seawater brines one core from the eastern mediterranean yafo 1 indicated that anhydrite was deposited along the continental margin of the eastern mediterranean from brines of marine composition which evolved into carich continental brines following a marine regression

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

fibrous gypsum and fibrous anhydrite in veins fibrous calcium sulphate occurs in nature mainly as gypsum satinspar in extensional veins several mechanisms have been put forward to account for these veins and their fillings but a number of features remain unexplained or are not in accord with the interpretation s given this paper describes anhydrite as a fibrous vein precipitate which shows most features typical of satinspar subhorizontal attitude of the vein s vertical fibres a parting separating a lower from an upper seam and incorporated wall rock fragments new observations include the stacked nature of the fibres pressure shadows next to wall rock fragments and parabolic alignment of the latter these features suggest that the veins opened due to vertically oriented tensile stress the vein filling crystals grew centrifugally outwards from the initial plane of rupture which now forms the parting keeping pace with the dilation the mode of incorporation of wall rock fragments in the fibres requires repeated differential opening of the fissure thereby either wall rock fibre interface ruptured at a time and statistically the ruptures alternated so that trace element trends across the vein s are roughly symmetrical to the parting the source of the calcium and sulphate ions may have been adjacent evaporite beds but an external source is indicated where no evaporite beds are present in contrast to previous interpretations hydration of anhydrite to gypsum in the host rocks is not a prerequisite for the formation of satinspar veins the exact causes for the vertical dilation remain somewhat speculative and may have been different in various locations the vertically oriented tensile stress may have resulted from lateral tectonic compression or hydraulic overpressure or a combination of the two

a new method for predicting sweet spots of shale oil using conventional well logs abstract in this paper a new method called sweet spot index ssi is proposed by the combination of shale oil mobility and shale reservoir fracability to predict the vertical distribution of shale oil sweet spots using conventional logs in the ssi method logging evaluation models for toc s1 volatile petroleum and mineral content are initially established mobile oil content is obtained by subtracting the amount of adsorbed oil from the total oil content which is the s1 value after the recovery of light and heavy hydrocarbons the adsorbed oil content is calculated based on the oil adsorption model established by a stepwise pyrolysis experiment the formation fracability is estimated by a combination of estimates of brittle mineral content and young s modulus formations with higher brittleness and lower young s modulus are considered better simulation candidates the ssi value is the product of the normalized mobility and the fracability index which minimizes the section of just an organic matter sweet spot i e high oil content or an inorganic sweet spot i e easily fractured and has the advantage of accurately predicting its vertical distribution in the case study the new method is successfully implemented to predict sweet spots of the es3l lower sub member of the third member of the eocene shahejie formation in the bonan sag bohai bay basin china the lower limit value of ssi is set to 0 1 based on its relationship with shale oil production the effectiveness reliability and adaptability of the ssi method have been verified by three wells in the bonan sag

adsorption of mudstone source rock for shale oil experiments model and a case study abstract inorganic minerals were separated from mudstone and shale to investigate their oil adsorption potential a conceptual model was developed to reconstruct the oil adsorption capacity of underground mudrock shale by combining adsorption and organic matter swelling data the predictions for the free hydrocarbon oversaturation sorption zones in the well ny1 profile were taken as a case study the results suggest that the best depth for the shale oil prospect of the es4s member strata lies between 3400 and 3600 m in the dongying depression hydrocarbon starvation zones occur mainly at a depth of

geochemical and mineralogical variations in the upper mercia mudstone group late triassic southwest britain correlation of outcrop sequences with borehole geophysical logs the mercia mudstone group comprises up to 1200m of predominantly red mudstones and siltstones laid down in rift related basins during a period of regional subsidence the mudstones are commonly dolomitic and contain horizons of sulphate and halide salts up to 150m of undifferentiated red mudstones of norian and rhaetian age late triassic were examined in coastal outcrops in devon and somerset southwest britain and mineralogical and stable isotopic studies were carried out in order to identify any subtle changes in the succession gamma ray measurements were taken at outcrop to provide correlation with published borehole logs in which the mercia mudstone group has been subdivided on the basis of gamma ray and sonic response one of the borehole subdivisions was identified at outcrop within a sequence of otherwise undifferentiated red mudstones and was related to a transition in clay mineral assemblage and stable isotopic composition over 20 to 30 m of section the red mudstones below this transition have a higher proportion of magnesian clay minerals and enriched carbonate oxygen isotope compositions indicating deposition from mg 2 rich marine derived waters clay mineral assemblages in the succeeding red mudstones are dominated by illite and oxygen isotopic compositions are relatively depleted indicating a greater influence of k rich continental derived waters

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

pmod a flexible model of oil and gas generation cracking and expulsion a new computer program pmod is used to develop and test a wide variety of global models of varied complexity for the generation and destruction of hydrocarbons from petroleum source rocks chemical reaction models are constructed interactively by supplying the empirical formula of the reactants and products desired reactions and reaction constraints pmod calculates stoichiometric coefficients that conserve elemental balance the chemical reactions are integrated into two compaction and bulk flow expulsion models in order to predict the amounts and compositions of products expelled from the source rock under geological conditions a variety of published and unpublished experiments are used to show when various model types are required and to derive the parameters for the various models this exercise provides a good means to compare the strengths and weaknesses of the various models and provides guidance on the types of information needed to calibrate them chemical properties calculated by pmod for all models include apparent rock eval parameters and other common geochemical measurements

creep behavior of slip zone soil of the majiagou landslide in the three gorges area the creep properties of slip zone soil are critical to deformation prediction and slope stability analysis a series of triaxial drained creep tests were conducted on the slip band soil from a creeping landslide the results indicate that soil creep occurs in two stages with confining and deviatoric stresses being critical factors the long term strength of the soil was estimated to be 60 75 of the conventional strength according to the isochronous curves the soil creep characteristics were used to predict the creep strain using both the burgers and the singh mitchell model and large discrepancies were found between the predicted strain and test results accordingly a new empirical model based on the morgan mercer flodin growth model has been developed to describe the creep behavior of gravely clay in the slip zone four parameters of this model are estimated by nonlinear regression the deformations predicted by this model are in reasonable agreement with experimental data

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

kinetics of oil generation from brackish lacustrine source rocks in the southern bohai sea east china abstract oil generation c14 hydrocarbons of three type ii kerogen samples isolated from brackish lacustrine mudstones from palaeogene strata ed3 es1 es3 in the southern bohai sea was simulated by closed system gold tube experiments in addition a series of complementary analyses rock eval pyrolysis total organic carbon vitrinite reflectance trace element x ray diffraction and flash pyrolysis gas chromatography mass spectrometry were also performed to identify the bulk geochemistry palaeo environment and chemical composition of the kerogen the aim of this study was to achieve a better understanding of the kinetics of oil generation from lacustrine source rocks in the southern bohai sea the results show that the three samples are type ii source rocks deposited in similar palaeo environments hot and arid climates anoxic conditions and brackish water in shallow to semi deep lakes with consequent similarity in the chemical compositions of their kerogens the organic matter inputs are predominantly composed of lacustrine microalgae with a relatively small contribution from land plants the activation energies of oil generation from these samples show a range of 44 52 kcal mol with a frequency factor varying from 1 116 1014 to 1 274 1014 s 1 due to the similar palaeo environments and chemical composition samples in this study exhibit strong consistencies in kinetic parameters transformation ratio tr evolution curves of oil generation from the three samples calculated under a linear heating rate 3 k ma exhibit a slight difference which varies within 4 c at a given tr due to the great similarities of the three kinetic models an average kinetic model for the type ii brackish lacustrine source rocks in the southern bohai sea was established this model integrates the characteristics of the three kinetic models and is still dominated by activation energy of 52 kcal mol the geological temperature of the oil generation phase for the average model in the southern bohai sea is from 92 to 137 c

geochemical variations within a laminated evaporite deposit evidence for brine composition during formation of the permian castile formation texas and new mexico usa abstract the upper permian castile formation of the delaware basin in northwest texas and new mexico consists of up to 600 m of evaporites and is subdivided into units of anhydrite overlain by halite the castile formation has commonly been interpreted as a deep water deep basin deposit in which sediments were laid down in several hundred metres of water or brine recent textural observations within anhydrite units in which the thick bedded anhydrite horizons have been interpreted as being of shallow water origin have challenged this assumption this geochemical study of the oldest anhydrite unit in the castile formation the anhydrite 1 member attempts to resolve some of the problems regarding brine depth and evolution in the basin the anhydrite 1 member has been subdivided into five major cycles on the basis of the distribution of stratigraphic units of thick bedded anhydrite stable isotopic analyses of sulphur from anhydrite and oxygen and carbon from calcite show that the basin waters were chemically homogeneous during precipitation of anhydrite and do not indicate any significant input of meteoric continental derived waters throughout the section studied progressive enrichment of 18 o upwards within cored intervals indicates continuous evaporation of the water body carbon isotopes appear to indicate fluctuations in organic activity within the cycles trace elemental analyses of fe mg sr mn al ba zn pb and cu from the sulphate fraction of the samples show a very high variability there is a distinct increase in trace elemental abundances at the tops of cycles which may indicate variations in precipitation kinetics analyses of texturally defined cycles show that up core trends for many of the trace elements correlate with changes in 18 o indicating a progressive increase in the influence of evaporation in addition cyclical variations in trace elemental composition indicate changes in basin conditions with around a 350 year cyclicity these changes are independent of 18 o values the geochemical data do not provide conclusive proof of water depth during deposition of the castile formation the data are interpreted as reflecting small scale changes in conditions of deposition despite the fact that water input remained essentially constant in terms of chemical composition

fault fracture mesh petroleum plays in the jiyang superdepression of the bohai bay basin eastern china abstract based on the results of laboratory simulation experiments and field observations the concept of fault fracture mesh petroleum play is proposed to explain the secondary petroleum accumulations in the neogene reservoirs of the jiyang superdepression bohai bay basin eastern china a well defined fault fracture mesh petroleum play usually contains three basic elements an oil source network at the base a transient storage for migrating hydrocarbons in the middle and a petroleum accumulation network at the top the oil source network provides fairways for hydrocarbons generated in a deep source to migrate vertically upward to shallow strata often consisting of primary faults and fracture zones and or regional unconformities in direct contact with mature petroleum source beds and secondary faults intercepting lenticular fluvial sandstones the transient storages for migrating hydrocarbons include the thick porous mat or sheet like sandstones deposited under the fluvial braided stream setting and occurring over relatively large geographic areas these sandstones serve as temporary storage spaces through which deep sourced petroleum fluids migrate further either laterally or vertically into shallower reservoirs the upper petroleum accumulation network provides suitable habitats for oil and gas accumulation comprising structural lithologic stratigraphic and combination traps the jiyang superdepression of the bohai bay basin hosts several excellent examples of the fault fracture mesh petroleum play where hydrocarbons in the neogene reservoirs were derived either directly from eocene oligocene source rocks or from the redistribution of pre existing oil accumulations in the deeper reservoirs reactivation of basement involved faults and regional unconformities provided conduits for channeling the pre neogene hydrocarbons into the shallow strata the magnitudes and frequencies of the faulting activities and their relative timings to those of peak oil generation and expulsion were critical factors for controlling the quantities of hydrocarbons transmitted to the neogene strata the thick sandstones and conglomerates in the lower guantao formation acted as excellent transient storages for the deep sourced oils which were then trapped to form accumulations in the shallow structural lithologic stratigraphic and combination traps of the guantao ng minhuazhen nm formations with the recent discovery of several giant oilfields in the shallow neogene reservoirs both onshore and offshore bohai bay basin the proposed fault fracture mesh petroleum play concept helps the exploration geologists to modify and clarify long held traditional concepts of petroleum play types in this basin and expand upon the new exploration horizons of the shallow subtle petroleum traps

kinetic analysis of california petroleum source rocks by programmed temperature micropyrolysis three california shales were examined by micropyrolysis to determine laboratory pyrolysis kinetics samples from the modelo formation with 6 16 wt s in kerogen monterey formation with 13 58 wt s in kerogen and with 8 88 wt s and 13 16 wt o in kerogen exhibited shift in tmax and principal discrete distribution energies of 54 and 57 51 and 52 and 65 and 59 kcal mol respectively these results are evidence that laboratory decomposition kinetics of high sulfur kerogens and in particular monterey kerogens appear not to be governed by organic sulfur content alone particularly because the kinetic parameters for the 13 16 wt o monterey sample were well outside the range generally seen for type i ii and ii s kerogens and closer to type iii kerogens

kinetics of oil group type generation and expulsion an integrated application to dongying depression bohai bay basin china pyrolysis of two kerogens isolated from the e2 3s 3 3 and e2 3s 1 4 source rocks in the niuzhuang sag dongying depression bohai bay basin china was performed in a confined system the products were extracted with solvent and separated using micro column chromatography into group type fractions saturates aromatics resins and asphaltenes with the kerogen residue in each case undergoing swelling with a variety of solvents the kinetics for generation and retention of crude oil and its group type fractions from the kerogens were studied and the kinetic parameters applied to modeling generation and retention of crude oil and its fractions from the e2 3s 3 3 and e2 3s 1 4 source rocks on the basis of burial and thermal history of the niuzhuang sag the results show that the normal oil was generated at about 4 26 ma and 24 85 ma ago but expelled at about 3 96 ma and 17 46 ma ago respectively from e2 3s 3 3 and e2 3s 1 4 source rocks the current proportions of the expelled saturates aromatics and nsos are about 60 15 and 25 respectively