the thickness of faults from laboratory experiments to field scale observations to assess the role of the fault thickness on its mechanical behavior we first present the results of an experimental modeling of a thick fault core our laboratory setup consists in an annular simple shear apparatus in which we can apply very large shear displacements 50 m to 100 particle thick granular samples thanks to a window in the apparatus pictures of the microstructures can be continuously taken during shear we observe from a correlation image velocimetry technique that a significant strain field exists outside of the observable shear band this strain field though of small magnitude compared to that existing inside the shear band is very structured and extends in a region much wider than expected from individual static observations i e wider than the directly observable shear band moreover this strain field controls most of the evolution of the shear strength of the fault we then propose plausible comparisons of our experimental results to geological observations of fault cores in the region of aigion corinth gulf greece the studied faults indeed display spectacular indurated fault planes lying on weakly cohesive material signatures of cementation clay mineral distribution and porosity profile of one of the studied fault cores are included and discussed in the light of the experimental results our observations suggest that the maximum shear strain during earthquakes might occur not in the center but on the border of the fault cores it is presumably localized in a transition zone which exhibits a significant cementation owing to a process of mechanical smearing by fine particles this zone may also act as a very low permeability layer responsible for a channeling of the fluid flow such a scheme of progressive multi sub localizations is different from classical descriptions of faults and consistent with a layering of the core consisting of separated zones of high strains or large cataclastic flows

fracture characterization of chalk in uniaxial and triaxial tests by rock mechanics fractographic and electromagnetic radiation methods abstract this study relates to fracture characterization of chalk in uniaxial and triaxial tests by combined application of rock mechanic fractographic and electromagnetic radiation emr methods we found high strength results 1 3 that ranged from 37 7 to 52 6 mpa we identified several key surface morphologies that were distinct from each other and expanded on their characterization according to tensile and shear categories tensile features include plumes or striae and stairs shear features include a sugary texture ridges and grooves and steps fracture surfaces induced by tension and shear show distinct morphologies longitudinal splitting domains can occur continuously on an axial tensile plane or adjacent parallel planes on the other hand shear failure into meso fractures up to about 10 cm in length is a process that combines a series of distinct domains on separate surfaces that slightly differ in curvature and orientation and are inclined to the sample axis four fracture sequences that initiated either in tensile or in shear surfaces were distinguished in the failed samples results obtained by rock mechanics and by emr methods are well correlated for microcracks and for meso fractures and may vary over five orders of magnitude in size and this correlation is partially supported by fractography in particular a very good linear relationship was obtained between the ratio of the time interval to reach emr pulse envelope maximum and the pulse frequency t and the largest fractures formed extrapolating this result enabled us to calculate fracture sizes when the value of t was known

palaeostress superimposition deduced from mesoscale structures in limestone the matelles exposure languedoc france abstract this study investigates the reasons for the superimposition of several maximum principal stress directions 1 in the same area and examines the contrast between unperturbed areas stable direction of 1 and perturbed areas changing 1 direction we studied mesoscale structures on a 1000 m2 continuous limestone exposure near a regional scale strike slip fault local 1 directions were deduced from a high concentration of minor strike slip faults extension fractures and stylolites formed during the pyrenean shortening in languedoc france most of the stylolites were formed in a stress field which was homogeneous on the exposure scale this was followed by the reactivation of pre existing extension fractures as strike slip faults whose activity determined stress perturbations a very heterogeneous stress field was produced leading to the formation of new localized stylolites and extension fractures especially at fault terminations and at oversteps thus the final pattern shows the superimposition of all these structures reactivation of structures was caused by slight temporal changes in the orientation and intensity of the stress field produced by the nearby regional strike slip faults our study suggests that the origin of stress deviations or superimpositions cannot be explained by random measurements of 1 it is essential to be able to synthesize the fault pattern and the stress trajectories which it determines and to do this a very high density or a selection of data from mesoscale structures is needed

geomagnetic reversal spurts and episodes of extraterrestrial catastrophism the possibility that the observed 26 32 myr periodicity in the records of extinction events1 and astrobleme ages2 was caused by periodic episodes of physical bombardment of the planetary surface has raised the likelihood that such an astronomical clock also affects geomagnetic reversals3 4 however the detection5 of a comparable 30 myr harmonic in the geomagnetic reversal record has now been found6 to be an accident of data length while the earlier reported7 32 34 myr harmonic of the reversal record may well be an artefact of the data base here we examine the temporal relation between geomagnetic reversals and those catastrophic episodes which occurred during periods of frequent reversals as geomagnetic history comprises long intervals of frequent reversals alternating with intervals of fixed polarity our rationale is that the geomagnetic field should be most susceptible to catastrophism during its relatively unstable periods of frequent reversals we find spurts in the frequency of geomagnetic reversals at approximately 30 myr intervals correlated with catastrophic episodes these spurts can be seen as the geomagnetic signatures of terrestrial catastrophism and we tentatively ascribe them to enhanced core turbulence during episodes of bombardment the absence of reversal spurts during long intervals of fixed polarity is attributed to the failure during these intervals of the geomagnetic dynamo s bi stable oscillations

hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

organic petrography of leonardian wolfcamp a mudrocks and carbonates midland basin texas the fate of oil prone sedimentary organic matter in the oil window abstract to better understand evolution of oil prone sedimentary organic matter to petroleum and expulsion from source rock we evaluated organic petrographic features of leonardian wolfcamp a repetitive siliceous and calcareous mudrock and fine grained carbonate lithofacies cycles occurring in the r ricker 1 core from reagan county midland basin texas the objectives of the petrographic investigation were to estimate thermal maturity identify organic matter types and abundances and identify the presence or absence of migrated hydrocarbons in organic lean carbonate layers an integrated analytical program included geochemical screening total organic carbon toc content by leco programmed pyrolysis by hydrocarbon analyzer with kinetics hawk including analysis of solvent extracted samples x ray diffraction mineralogy organic petrography scanning electron microscopy with energy dispersive spectroscopy sem eds including correlative light and electron microscopy clem and micro fourier transform infrared spectroscopy ftir analyses of solid bitumen the data indicate all samples are early to middle oil window thermal maturity with solid bitumen reflectance bro values of 0 55 0 86 and tmax of 440 455 c organic matter is predominantly solid bitumen as identified by optical microscopy in all lithofacies with minor contributions from inertinite solid bitumen abundance decreases from siliceous mudrock toc 3 0 wt to calcareous mudrock toc 1 0 to 3 0 wt to fine grained carbonate toc

petroleum origin and accumulation in basin evolution a quantitative model basin data geologic geophysical geochemical hydrodynamic and thermodynamic can be combined for quantified hydrocarbon prediction a three dimensional deterministic dynamic basin model can be constructed to calculate all the measurable values with the help of mass and energy transport equations and equations describing the physical and or physicochemical changes in organic matter as a function of temperature input data consist of heat flux initial physical and thermal properties of sediments paleobathymetric estimates sedimentation rate and amount and type of organic matter subsequently the model computes pressure temperature physical and thermal properties of sediments maturity of organic matter and the hydrocarbon potential of any source rock as a func ion of space and time thus the complex dynamic processes of petroleum formation and occurrence in a given sedimentary basin can be quantified for example hydrocarbon potential maps for any given source rock and any geologic time slice of the basin evolution can be provided as computer printouts the computer model can be applied to any stage of an exploration campaign and updated as more information becomes available

the isotopic composition of uranium and lead in allende inclusions and meteoritic phosphates we measured the isotopic compositions of u and pb in eight ca al rich inclusions from the allende chondrite in whitlockite from the st severin chondrite and in a whitlockite and a whole rock sample from the angra dos reis achondrite ador the total range in 235 u 238 u in the acid soluble phases of the allende inclusions and meteoritic whitlockites is from 1 137 6 to 1 138 3 and to within the error limits 3 20 indistinguishable from normal terrestrial u the 235 u 238 u ratios for whitlockites from st severin and ador are the same as that in the bulk meteorites and are normal the pb isotopic compositions of the acid soluble phases of the allende coarse grained inclusions except c 1 give a mean 207 pb 206 pb model age of4 559 0 015ae which is consistent with the observation of normal u isotopic composition the pb isotopic compositions of coarse grained fun inclusion c 1 and of two fine grained inclusions from allende indicate that the u pb systems of these samples have evolved differently from the rest of the meteorite the 207 pb 206 pb model ages for the whitlockites and for bulk ador are the same as those for st severin whitlockite 4 551 0 004ae the pb results from st severin indirectly constrain the value of the u isotopic abundance to be within 7 4 of normal both the directly measured235u 238u and the pb data on st severin are in complete disagreement with claims of large 235 u excess reported by other workers on the same meteorite the th u ratios of some acid soluble phases of allende inclusions and of meteoritic whitlockite show varying degrees of enrichment of th relative to u by factors of 2 to 25 relative to the bulk meteorites previous studies have shown that 244 pu 238 u ratios in whitlockite are also fractionated relative to the bulk meteorites the observation of no isotopic effects in u reported here does not support the claims of either fractionation of 247 cm 238 u or of a large amount of live 247 cm at the early stage of formation of the solar system using the present data we obtain a limit of 247 cm 235 u 4 10 3 at the time of meteorite formation or differentiation this implies that the last major r process contribution to the material in the protosolar nebula was 10 8 years prior to 26 al formation and injection

pennsylvanian coal and associated bitumen at johnson mills shepody bay new brunswick canada abstract pennsylvanian fluviatile sandstones at johnson mills new brunswick host fossil logs preserved as a result of the paragenetic succession pyritization carbonatization carbonization and overlapping bitumenization carbonatization is the dominant process the coalified material is all overmature as reflected by temperature of maximum pyrolysis tmax in a range of 460 464 c veinlets of once liquid now solid bitumen extend outward from the logs into the surrounding sandstones for several meters present in the bitumen are relict coal macerals that contribute to a microscopic distinctly structured coaly appearance of the material reflectance measurements of coal range from romax 0 78 to romin 0 61 two distinct populations of bitumens are recognized romax 0 78 to romin 0 65 for the main population romax 0 60 to romin 0 48 for the second population transmitted and reflected light microscopy long count energy dispersive spectroscopy eds and rock eval analysis indicate that bitumen was derived from the logs as a result of late stage diagenesis exsudatinite like material is the probable precursor of the bitumen thermal maturity of the bitumen increases directly with inferred migration distance from the logs across the spectrum solid bitumen closest to the logs and within the oil window is least mature tmax 449 c and bitumen furthest from the logs is most mature with tmax 493 c this phenomenon results from differences in the chemistry of the derivative bitumen which is relatively more aliphatic and nso enriched close to the log source and more aromatic distally these differences in bitumen composition may have arisen as a consequence respectively of pre gas and post gas generating conditions

assessment of shale oil potential using a new free hydrocarbon index abstract shale oil is currently a highlight and frontier field in petroleum industry however the assessment and quantitative evaluation of oil content in the shale is challenging which is one of the critical issues in understanding the resource potential here we explore a new free hydrocarbon index based on a case study in the currently most successful shale oil play case in china i e the eocene hetaoyuan formation in the biyang depression of the nanxiang basin eastern china this index s 1 represents the difference between hydrocarbon generation quantity and pyrolysis free hydrocarbon value s 1 it is new in that it considers not only the residual oil contents in the rocks like previous parameters but also the hydrocarbon expulsion and migration conditions that have rarely been focused before when s 1 1 is around 0 it is implied that the generated oil nearly has not expulsed and resided in the shale and thus there is also a good shale oil potential in contrast when s 1 0 it is implied that certain amounts of generated oils have migrated to external reservoirs and thus there is a poor shale oil potential this method has potential general implications and the results in the biyang can be used in the practical shale oil exploration

fracture roughness and gouge distribution of a granite shear band 1 localization of deformation during fracture mechanical tests leads to the development of shear bands we performed triaxial tests using sidobre granite at four different confining pressures from 20 to 80 mpa we compared two sets of tests one set was stopped immediately after the formation of the shear band a second one included additional shear deformation from the analysis of thin sections of these laboratory samples we characterize the typical microstructures in the shear band mode i and ii cracks riedel cracks cataclastic flow statistical properties of rupture surface roughness and gouge grain size reveals scaling invariance using a mechanical profiler the fracture roughness is measured along parallel profiles and shown to be correctly described over up to 3 orders of magnitude by self affine geometry with a roughness exponent close to 0 80 this property is very similar to tensile crack even if local processes are different the influence of the slip is observed fracture surfaces are rougher along the slip direction 0 74 than perpendicular to it 0 80 the confining pressure is shown to have a weak effect on the fracture roughness it smoothes the surface slight increase of the roughness exponent gouge particles extracted from the shear band present a power law distribution with an exponent ranging from 1 44 to 1 91 this exponent appears to increase with the shearing displacement and the confining pressure when a significant shear of the band is combined with a high confining pressure i e impeded dilation of the band the hallmark of fragmentation is observed for the particle distribution and related to a smoothing of the band boundary

analysis of the internal structure of a carbonate damage zone implications for the mechanisms of fault breccia formation and fluid flow abstract a segment of the salzach ennstal fault zone talhof fault eastern alps shows evidence for joint nucleation by layer parallel shear causing the formation of joint bounded slices oriented at high angles 65 85 with respect to the shear zone boundary szb subsequent slice rotation resulted in joint reactivation as antithetic shears slice kinking and breaking up of the individual slices into smaller fragments the latter process due to the longitudinal constraint of slices with impeded shear zone widening marked the transition to cataclasite formation and fault core evolution during shear localization cataclasites were subsequently cemented and underwent continuous shear deformation by re fracturing cement precipitation from fluids therefore played a fundamental role in the evolution of the fault zone with a cyclic change between an open and a closed permeability system during fault evolution stable isotope compositions 13 c 18 o of fault rock cements indicate a continuous equilibration between protolith derived fragments and cements precipitated from those fluids this points to limited fluid amounts only temporally replenished by meteoric water and a hydraulic gradient that directed fluid flow from the damage zone towards the fault core

global volcanism biological mass extinctions and the galactic vertical motion of the solar system summary the recent findings of nearly matching long term cyclicity in biological mass extinctions geomagnetic reversals impact cratering and other terrestrial processes have evoked a major controversy we report here a compilation and analysis of major global magmatic episodes showing a significant enhancement of volcanic activity with a periodicity of 33 million years for the last 250 million years these magmatic episodes match extremely well the best available astronomical estimates of the periodic 31 5 myr galactic disc crossing events during vertical motions of the solar system these events also have a close linkage with the marine biological mass extinctions and other geological rhythms it is argued that the prolonged volcanic activity instead of impact cratering may have been the more immediate primary cause for profound climatic and other environmental deterioration sufficient to create biological crises on a global scale the volcanic periodicity scheme is well supported by the evidence of recent increases in volcanic activity however the alternative hypothesis of the death star nemesis can be rejected since it does not explain the recent increase in volcanism and impact cratering during the last 4 3 myr in view of its quieter apehelion position lying beyond the oort cloud of comets

morphology of hydrocarbon droplets during migration visual example from the monterey formation miocene california in this paper we describe the various morphologies of hydrocarbon residue found in the miocene monterey formation in california scanning electron microscope photomicrographs clearly show various shapes of hydrocarbon droplets in microchannels in the monterey formation and hence provide insight not only into the shape of hydrocarbon droplets during migration but also about the migration pathways themselves the small 5 10 m diameter droplets are observed to have various shapes that include spherical droplets amalgamated droplets sausage shaped droplets and elongate rod shaped droplets observations suggest that hydrocarbon droplets move through the rock matrix into microchannels where they coalesce into larger droplets and then move into larger fractures dif erent morphologies are simply a result of amalgamation of simple droplets during migration

joint development in perturbed stress fields near faults abstract field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories a progressive change in joint direction is observed from unperturbed regions away from faults to strongly perturbed zones adjacent to faults this indicates that the joint pattern can reflect perturbations of the regional stress field around faults in the examples the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock the corresponding joints converge at these points and are sub parallel to the fault along the remainder of the fault plane the possibility that a fault plane acts as a free surface contained within an elastic body is considered in this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault the free surface model seems to explain the metre scale curvature of joints in the vicinity of existing joints but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the earth s surface two examples are investigated from the lias of great britain at nash point and robin hood s bay both comprise sub horizontal strata of relatively homogeneous lithology and bed thickness which provide striking examples of joints developed near faults

a test of terminal mesozoic catastrophe terminal mesozoic catastrophe type extinction models that advocate synchronous marine and terrestrial extinctions spanning short time intervals a few days up to a few millennia have a common foundation the simultaneous terminations of geological ranges of some taxa of marine caco3 producing microplankton and possibly the dinosaurs at the end of the cretaceous gartner and mcguirk 1 propose a new catastrophe theory that at the end of the cretaceous fresh brackish water from the arctic ocean spread over the surface of the world s oceans causing global cooling aridity and the extinctions like other catastrophe models this one also fails to address the possibility of hiatus control of ranges at the end of the cretaceous a well documented seemingly nearly universal hiatus of variable and unknown duration separates cretaceous and tertiary strata documented terminal cretaceous marine regression perhaps 10 times more rapid than a typical regression according to cooper 8 would have caused terrestrial erosion and stripping away of the latest cretaceous stratigraphic record thus truncating geological ranges along a seemingly planar datum the terminal cretaceous marine caco3 dissolution event would have had the same effect on ranges of marine planktonic caco3 producing microplankton the event was a shallow water phenomenon the simultaneous terminations of geological ranges is thus possibly the result of hiatus control and the terminal cretaceous catastrophe an illusion attempts to use cretaceous tertiary transition floras to support global cooling at the time of the extinctions are not based on sound stratigraphic foundations realistic paleobotanical climatic inferences can only be based on the precise correlation of the cretaceous tertiary contact in marine and terrestrial stratigraphic sections and these correlations have not been made with sufficient precision to support catastrophe theory the much used across the cretaceous tertiary boundary glosses over ignorance of the true terminal cretaceous scenario lost forever in most places by the destruction of the terminal cretaceous stratigraphic record for now stable isotope paleotemperature data from marine strata that can be dated radiometrically provide the most reliable estimates of the cretaceous tertiary transition climate boersma et al 5 indicate global warming of deep and shallow oceans across the contact and not surficial cooling only as is required by the spillover model older much cited climate inferences based on leaf physiognomy are suspect in light of dolph and dilcher s 23 work that shows little correlation between leaf physiognomy and climate

extraction of high molecular weight hydrocarbons from source rocks an example from the green river formation uinta basin utah abstract results of extraction experiments performed on immature green river formation source rock samples from the black shale facies uinta basin utah demonstrate the potential of extracting high molecular weight hydrocarbons hmwhc with sequential dichloromethane methanol soxhlet and p xylene sonication techniques the first soxhlet extraction step with dcm meoh removes lower molecular weight alkanes from the source rock while the hmwhc remain in the rock residue sonication of the rock residue with p xylene recovers these hmwhc showing distinct hydrocarbon distributions and preferences in high temperature gas chromatograms extracts obtained by using p xylene soxhlet with original source rocks and sequential soxhlet extraction instead of sonication have relatively lower concentrations of hmwhc sequential extraction of two other source rock types mahogany shale and black shale facies coal did not result in detection of similar hmwhc in the extract this indicates that the presence of these compounds in the black shale facies of the green river formation is a primary source signal and a specific characteristic of this source rock

natural fractures in the spraberry formation midland basin texas the effects of mechanical stratigraphy on fracture variability and reservoir behavior horizontal cores from sandstone siltstone reservoirs in the spraberry formation midland basin west texas have documented two systems of dramatically different yet dynamically compatible natural fractures in reservoirs separated vertically by only 145 ft 44 m each system is capable of producing a different degree of the northeast trending permeability anisotropy recognized in spraberry reservoirs one fracture system consists of two vertical fracture sets with an apparent conjugate geometry striking north northeast and east northeast the other system consists of evenly spaced northeast striking vertical fractures nearly bisecting the acute angle of the first system although lithologically similar differences in quartz overgrowth and clay content in the layers resulted in a yield strength of the lower bed that is only half of that of the upper layer producing different fracture systems in the two reservoirs despite their proximity such differences in the mechanical properties due to variations in diagenetic and depositional histories of the strata are probably widespread within the formation they have the potential to cause significant vertical and lateral variation in the spraberry fracture system across the basin low present day in situ stresses in the reservoirs allow the fractures to open to become more conductive and even to propagate under very low injection pressures

geochemical characterization of solid bitumen in the chesterian mississippian sandstone reservoir of the hitch field southwest kansas solid bitumen was identified within the mississippian chester sandstone reservoir in the hitch field southwest kansas the adjacent etzold field has similar reservoir properties but lacks solid bitumen although the hitch and etzold fields were thought to be in pressure communication and have common source rocks hitch and etzold crude oils and core extracts were characterized geochemically to gain a better understanding of the reservoir filling history and geological and geochemical controls on solid bitumen formation in the hitch reservoir based on a variety of geochemical characteristics we propose that the hitch and etzold oils are mixtures derived from ordovician and late devonian early mississippian woodford shale source rocks the solid bitumen in the hitch reservoir probably results from mixing of oils having different geochemical compositions which filled the reservoir over an extended period no evidence of severe biodegradation or thermal alteration is observed a reservoir filling scenario is proposed in an effort to explain why the hitch oils are geochemically more heterogeneous than etzold oils furthermore gas de asphalting and regional pressure drops as a result of post laramide orogeny may have contributed to a phase change in the reservoir fluid and deposition of solid materials by disturbance of thermodynamic equilibrium the major significance of this study is related to improving our knowledge on the occurrence of the presence of solid bitumen in reservoirs that can introduce barriers into the reservoir complicating waterflood operations and leading to erroneous oil in place calculations and subsequently lower than expected oil recovery

scales and effects of fluid flow in the upper crust two of the most important agents of geological change solar energy and internal heat from the mantle meet and battle for dominance in propelling aqueous and related fluids in the earth s upper crust which prevails and how they interact are subjects of active research recent work has demonstrated that both agents can propel fluids over nearly continental scale distances in a fashion that influences a host of important geological processes and leaves a record in chemical alteration mineral deposits and hydrocarbon resources

micromechanics of shear rupture and the control of normal stress abstract conjugate microfault zones and distributed tensile microcracks were observed in low porosity sandstone samples deformed by shear box rupture at different normal stresses statistical data collected from scanning electron microscopic mapping show that tensile microcracks and microfaults are more frequent in the higher normal stress cases the average thickness of the cataclastic microfault zones increases proportionally to rupture normal stress the density of tensile microcracks increases locally in microfault relay and intersection zones where their formation is an important mode of microfault zone cataclasis concentration of longer en echelon tensile microcracks occurs in process zones ahead of the microfault tips connected by cross cracks in an incipient breakdown zone to further propagate the fault fracture densities are much lower in calcite cement grains whose compliancy serves to arrest microfault growth temporarily yet also aid intragranular microcracking in adjacent stiff grains and at grain boundaries tensile microcrack and microfault average dips from the sample rupture surface increase with rupture normal stress with conjugate microfault orientation variability at higher normal stresses aiding their connectivity results of this investigation demonstrate how the fracture porosity and connectivity around rupture zones increase dramatically at increased rupture normal stress impacting on hydrodynamic properties of rupture zones

shear rupture under constant normal stiffness boundary conditions abstract a grain based distinct element method and its embedded grain based method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive non jointed brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions under these boundary conditions shear rupture zone creation relative to the shear stress versus applied horizontal displacement load displacement curve occurs pre peak before the maximum peak shear strength is reached this is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress due to rupture zone dilation with shear stress producing a complex normal shear stress path that reaches and then follows the rock s yield strength envelope while the yield envelope is followed the shear strength increases further and shear stress oscillations repeated stress drops followed by re strengthening periods in the load displacement curves occur due to fracture creation as the rupture zone geometry smoothens once the maximum peak strength is reached after a series of shear stress oscillations the largest stress drops occur as the ultimate or residual shear strength is approached the simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response as well as the stick slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

lateral migration pathways of petroleum in the zhu iii subbasin pearl river mouth basin south china sea abstract the discovery of the wc13 1 and wc13 2 oil fields in the zhu iii subbasin of the pearl river mouth basin in the south china sea has led to debate as to the oils on horst qionghai hqh are sourced from half graben wenchang a hgwc a or half graben wenchang b hgwc b using the previous findings of sequence stratigraphers this paper further analyzes the sedimentological characteristics of the zhuhai and zhujiang formations and points out that the sandstones deposited on the unconformities basement t 6 and t 7 possess good porosity permeability and lateral connectedness for hydrocarbon migration the depositional systems and facies for the major reservoir rocks had gradually changed from fan delta and semi enclosed bay via barrier islands and washover to tidal flats tidal channels and tide influenced shoreface in response to the rise in sea level in the early miocene the sandy carrier beds of the transgressive systems tract in the zhujiang formation especially in zhujiang formation ii act as the principal migration conduits for the wc13 1 and wc13 2 oil fields measurement of sandstones in drilling holes shows an increase in porosity in the zhujiang formation ii and implies that the oil had ever passed through furthermore the structural morphologies of t 5 and t 4 demonstrate that there are two salient structural noses connecting hqh with the hgwc b and plunging into hgwc b t 5 a regional muddy seal seals the porous standstones underneath and accounts for the key role played by the sandy carrier beds in transporting the oils generated in hgwc b to hqh correlation of oils in hqh and hgwc b supports the plausibility of this migration pathway

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

origin damping and pattern of development of faults in granite observations of brittle fractures in the granite of the massif de la borne as well as in other rocks allow us to discuss the different hypotheses regarding the origin of faults it seems that all faults originate by shear along a preexisting plane which can be an important fracture joint former fault or a microflaw pore grain boundary the shear on the plane gives rise to an array of en echelon cracks that makes the rock less resistant and permits the lengthening of the fault we also found an arrangement of horsetail fractures damping the movements on the faults we then propose a pattern for the development of the faults they originate on preexisting plane and propagate by initiating en echelon cracks the movements are damped by horsetails which permit by faults connection in relays the creation of larger faults

the role of episodic bombardment in geophysics it is shown that cometary or asteroidal impacts strongly perturb the boundary conditions at the core outer mantle and atmosphere of the earth impact episodes occur following the capture or orbital disturbance of these bodies as the solarsystem passes through the spiral arms of the galaxy there is thus a tendency for magnetic field reversals principal plate movements ice ages and mass extinctions to be correlated and to recur on time scales dictated by galactic processes it follows on the basis of a purely astronomical theory that it may be possible to synthesise the major phenomena of geophysics knowledge of the continuous state of the galaxy then becomes a prerequisite for the understanding of terrestrial history

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

introduction to special issue on integrated basin studies ibs a european commission dgxii project this issue contains papers issued from the integrated basin studies project ibs which is part of a larger program of the european commission dgxii entitled geosciences ii the ibs project ec contract jou2 ct92 0110 originated in geosciences consultation meetings the first of them being held in strasbourg in june 1989 under the auspices of mr hubert curien former french minister for research and technology and the subsequent meeting being held in brussels these consultation meetings have resulted in the conclusion that a main axis of future research in geosciences should be the study of sedimentary basins upstream of industrial activities mainly the oil and gas industry but also water resources management the mining industry the storage of undesirable products and coastal engineering they also resulted in the conclusion that future research on sedimentary basins should fulfill two requirements integration of disciplines and modelling such a conclusion may now seem trivial but was not so generally accepted at that time in this spirit the ibs project was designed to provide the oil and gas industry with a new generation of models for basin formation basin evolution and basin fill architecture from basin scale to reservoir scale its main objectives are the linkage of crust thermomechanical behaviour to basin formation and deformation mechanics and the corresponding modelling the quantification of tectonic control on the sedimentary record and the analysis of compaction and mass and heat transfer the ibs strategy is to link subsurface data to field data and an important part of the project is devoted to thematic field studies in european sedimentary basins of different tectonic styles taken as natural laboratories basin research has gone through a rapid evolution during the last decade in particular through the development of new acquisition and processing methods for seismic data and advances in drilling technology modelling provides an important tool to analyse different aspects of basin formation processes and find their tectonic expression in the basin fill the need for 3 d modelling techniques and models capable of linking processes operating on basinwide to subbasin scales is increasingly recognized and a significant effort has been made in the ibs project to develop a new generation of basin formation models coping with these needs see also cloetingh et al 1993a van wees and cloetingh 1994 as many data required to test these models reside in industrial companies ibs has promoted a closer link between academic research and basin studies carried out by industry the participation of the petroleum industry has been vital in this project and ibs has been able to establish a well functioning system of cooperation that not only facilitated data access but most important guaranteed the suitability of the end products of the project this has led to an intensive exchange of modelling concepts and data sets between industry and academia the ibs project has also used extensively the international lithosphere program task force origin of sedimentary basins see cloetingh sassi and task force team 1994 cloetingh et al 1993a b 1994 to implement planning and to discuss preliminary results it also builds partly on joint research through the european commission tempus and peco programs on pannonian basin studies horvath 1993 van balen and cloetingh 1995 van balen et al 1995 horvath and cloetingh 1995 a stimulating aspect of the activity of the ibs group is the creation of a research network in the corresponding field of knowledge which comprises now 30 teams belonging to eight european countries england france germany hungary norway spain switzerland and the netherlands this demonstrates the capacity of the procedures used by the dgxii of the european community to formulate a really european research space phd students and young researchers form an important component of the research groups

destruction of hydrocarbon reservoirs due to tectonic modifications conceptual models and quantitative evaluation on the tarim basin china abstract the tarim basin in china is a complicated superimposed basin with four periods of hydrocarbon accumulations and three periods of modifications due to tectonic movements forming complicated hydrocarbon reservoirs many of which have gone through reservoir migration reservoir scale reformation reservoir damage and phase alterations a result of the tectonic events due to the complexity the hydrocarbon exploration in this region has low success drilling rate it is of great importance to study the destruction to the early hydrocarbon accumulations by the tectonic movements and quantitatively evaluate the remaining resource for understanding the current hydrocarbon distribution and guiding the exploration this study analyzed six periods of large tectonic events in the tarim basin and found the destroyed hydrocarbon volume was mainly controlled by four geological factors including the ratio of the destroyed to the original hydrocarbon amount tectonic event number and sequence and the cap seal capacity larger ratio of destroyed hydrocarbon less tectonic event number later sequence and stronger cap seal capacity lead to more hydrocarbons preserved through the tectonic events based on the geological analysis we established quantitative relationships among the destroyed hydrocarbon volume by the tectonic events ql the volume of primary hydrocarbon accumulation q0 the ratio of destroyed hydrocarbon kl the tectonic event number n and sequence i and cap seal capacity fc using these relationships and the calibrated geological parameters we delineated the hydrocarbon accumulation and destruction history and quantified the hydrocarbon loss due to the tectonic events for both the tazhong area and the whole tarim basin in the tazhong area four major accumulation events occurred at 510 ma 298 ma 227 ma and 38 ma with each accumulation underwent 68 59 28 and 0 of hydrocarbon loss due to later tectonic events in total over 60 of the original hydrocarbon reserves have been destroyed in the tarim basin with an estimate of ca 1 9 billion tons remaining hydrocarbons in the tazhong area at present more than 95 oil and gas reservoirs and over 93 high quality exploration wells are located in the areas with high remaining resource potential predicted in this study whereas 70 non commercial production wells are located outside overall this work shows that a careful evaluation of the damage to reservoirs from tectonic events can considerably enhance the success rate of hydrocarbon exploration

hydrofracturing and episodic fluid flow in shale rich basins a numerical study low permeability sedimentary rocks commonly are fractured direct examination of exposed rock faces and drill cores shows evidence of hydrofracturing the mechanism for hydrofracturing its effects on fluid migration and its dependence on sediment permeability sedimentation rate and sedimentary sequences have not been explored in this study we carry out systematic numerical experiments to study the compaction induced hydrofracturing we show that the compaction induced hydrofracturing commonly may occur in shale rich basins and in sand shale sequences the frequency of such hydrofracturing depends on sediment permeability sedimentation rate and sedimentary sequence an important result is that compaction induced hydrofracturing may occur at relatively shallow depths in shale rich basins but it may mobilize enhanced fluid flow throughout the sedimentary basin over 60 of the total compaction induced fluid flow in the basin may be expelled during hydrofracturing we test the model against field data from the yinggehai basin of the south china margin where abundant hydrofractures in the uppermost quaternary marine mud have been recently detected by seismic imaging we suggest that the compaction induced hydrofracturing may mobilize fluid flow at great depths and affect hydrocarbon migration in shale rich basins

generation and migration of hydrocarbons in the maracaibo basin venezuela an integrated basin study abstract the history of hydrocarbon generation and migration in the maracaibo basin venezuela is closely related to its stratigraphic structural and tectonic evolution during the cretaceous and cenozoic times geochemical evaluation of the possible source rocks within the cretaceous and the tertiary sequences indicates that the argillaceous limestones and calcareous shales of the la luna formation cenomanian coniacian are the most important source rocks in the basin these rocks contain organic carbon ranging from 1 5 to 9 6 c original toc 2 5 10 8 have fluorescent amorphous marine type ii organic matter oil prone and have in the immature stage a h index of 700 mg hc g toc and a h c ratio of 1 5 the beginning of the oil window in these rocks occurs at a relatively low thermal maturity lopatin tti about 10 and the peak of oil generation corresponds to a tti value of 35 geochemistry of oils from the different reservoirs cretaceous paleocene eocene and miocene beds and oil oil and oil source rock correlation studies based on biomarkers have identified three genetic types of oil in the basin a marine type essentially derived from the la luna source a terrestrial type possibly originating either from the cretaceous lisure shales or the paleocene shales and a third type derived from the mixing of the first two types the marine type oil is distributed extensively throughout the basin whereas the terrestrial as well as the mixed marine and terrestrial types are found only in the southwestern part of the basin the marine type oils have been further subdivided based on their alteration and maturity reconstruction of the hydrocarbon generating areas at different geological times using tti maturity diagrams indicates that the generation of oil and gas in the basin took place during two periods the first phase occured during the middle to upper eocene times in the northeastern part of the basin while the second phase occured during the upper miocene to recent times in the central western and southern parts of the basin based on organic geochemical and sedimentological characteristics it is proposed that primary migration of oil from the la luna source rocks took place by expulsion of hydrocarbons through abundant microfractures developed by the pore fluid overpressure during hydrocarbon generation mass balance considerations suggest that the expulsion probably occurred as a hydrocarbon single phase and the expulsion efficiency for oil in la luna source rocks should have been very high 30 50 taking into consideration the development of oil and gas kitchens through time the paleostructures at the time of hydrocarbon generation and the characteristics of oils the migration history of the oil and gas generated from the la luna source has been outlined mixing of oils derived at different times eocene and miocene recent from the la luna source of different areas appeared to have taken place in block iv block 11 lago lamar motatan and bolivar coastal fields

experimental measurements of the diffusion parameters of light hydrocarbons in water saturated sedimentary rocks i a new experimental procedure an automatic experimental set up has been developed for the determination of diffusion parameters of hydrocarbon gases through water saturated rock samples diffusive flow of hydrocarbons through rock slices is monitored by gas chromatography experiments are carried out according to the time lag method yielding diffusion coefficients solubility coefficients and diffusion permeabilities diffusion coefficients down to 10 12 m2 s 1 10 8 cm 2 s 1 may be determined routinely on rock samples of 2 10 mm thickness maximum errors in diffusion coefficients are estimated around 20 and reproducibility was found to range between 10 and 20 specific features of this set up are automatic sampling and data acquistion high sampling frequency and maintenance of water saturation of the rock samples throughout the experiment

tectono sedimentary evolution and petroleum systems of the mundau subbasin a new deep water exploration frontier in equatorial brazil the brazilian equatorial margin bem evolved in response to transform motion between brazil and africa in 2012 petrobras drilled the pecem well in the mundau subbasin ceara basin of the bem to record the first deep water oil discovery in the region this work investigates the deep water evolution of the mundau subbasin focusing on its structural and sedimentary evolution and characterizes the petroleum systems in this new exploration frontier for such purposes poststack seismic reflection borehole and geochemical data were used three tectono stratigraphic sequences representing synrift mundau formation transitional paracuru formation and drift strata ubarana formation were divided into seven seismic units different tectonic domains were interpreted proximal distal and romanche fracture zone typical structures of transform margins such as marginal ridges and marginal plateaus were not identified in the mundau subbasin instead the subbasin was predominantly deformed by transtensional movements the mundau and paracuru formations are mature within the oil window whereas the ubarana formation is immature main reservoir intervals consist of approximately 1 m 3 28 ft thick intercalations of sandstone between shales siltstones and marls the seal rocks comprise shales in the ubarana formation whereas the hydrocarbon trap is related to an unconformity and a normal fault this work concludes that the paracuru formation is the main source and reservoir in the deep water mundau subbasin effectively comprising a paracuru paracuru petroleum system the results have significant implications for petroleum exploration in the bem by proposing a developed transitional petroleum system in the distal parts of northeastern brazil

growth linkage and termination processes of a 10 km long strike slip fault in jointed granite the gemini fault zone sierra nevada california abstract field based structural analysis of an exhumed 10 km long strike slip fault zone elucidates processes of growth linkage and termination along moderately sized strike slip fault zones in granitic rocks the gemini fault zone is a 9 3 km long left lateral fault system that was active at depths of 8 11 km within the transpressive late cretaceous sierran magmatic arc the fault zone cuts four granitic plutons and is composed of three steeply dipping northeast and southwest striking noncoplanar segments that nucleated and grew along preexisting cooling joints the fault core is bounded by subparallel fault planes that separate highly fractured epidote chlorite and quartz breccias from undeformed protolith the slip profile along the gemini fault zone shows that the fault zone consists of three 2 3 km long segments separated by two zones of local slip minima slip is highest 131 m on the western third of the fault zone and tapers to zero at the eastern termination slip vectors plunge shallowly west southwest and show significant variability along strike and across segment boundaries four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at or below greenschist facies conditions taken together we interpret the fault zone to be a segmented linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations complex fault segment interactions and asymmetric slip distance profiles

expulsion of oil from petroleum source rocks inferences from pyrolysis of samples of unconventional grain size oil expulsion efficiencies from different lithologies have been investigated and compared employing pyrolyses of samples of unconventional grain size from 300 mg hc g corg show that liquid range hydrocarbons are expelled from coal when the generated oil exceeds the coal sorption capacity this suggests that expulsion of oil from liptinite poor or in general h poor humic coals is primarily limited by the release of generated liquid hydrocarbons from kerogen because such coals generally do not generate sufficient amounts of liquid hydrocarbons to overcome the coal sorption capacity

development of a self similar strike slip duplex system in the atacama fault system chile abstract fault development models are crucial to predict geometry and distribution of fractures at all scales we present here structures related to the development of the bolfin fault in the atacama fault system afs covering a range of scales of 7 orders of magnitude the afs is a 1000 km long trench parallel fault system located in the andean forearc the bolfin fault is a first order fault of the caleta coloso duplex has a trend 170 and length 45 km it cuts mainly meta diorites and exhibits a 100 200 m thick core of subvertical bands of altered fractured host rock and of foliated cataclasites this foliation is made up of several trend parallel cm thick shear bands composed of plagioclase fragments 0 1 mm surrounded by epidote in the compressive quadrant around the tip point of bolfin fault the lower strain faults exhibit an unusual internal structure consisting of fractures arranged in a multi duplex pattern this pattern can be observed from meters to millimeters scale the fractures in the strike slip duplex pattern can be separated into two types main faults trend parallel longer and with larger offsets and secondary fractures sigmoid shape fractures distributed in the regions between main faults all oriented between 15 and 75 with respect to the main faults measured counterclockwise i e in p diedra on the basis of the distribution of the two types of recognized fractures the relative sequence of propagation can be inferred main faults the more widely distributed propagated earlier the secondary fractures in turn distributed in thinner areas between the larger main faults were propagated later as linking fractures the duplex pattern is self similar multiple core faults with internal structure of multiple duplex are itself in turn secondary faults within a larger km scale duplex caleta coloso duplex the duplex width w and the length l of the main faults forming the duplex show an almost linear relationship for duplexes observed from micro to regional scale for a scale range of seven orders of magnitude the length of the master strike slip faults is about ten times the width of the overlapping duplex area this relationship evidence the self similar nature of the structural system under study and suggests that the same fundamental mechanical processes that build up the small strike slip duplexes operate also at the regional scale

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

organic matter maturation under the influence of a deep intrusive heat source a natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock toarcian shale northern germany four shallow boreholes were drilled in the hils syncline northern germany in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen type ii bearing source rock the holes penetrated the carbonceous lias shales posidonia shale lower toarcian and part of the adjacent dogger and lias mudstones the maturity of the organic matter in the cores recovered ranges from immature 0 48 r0 to overmature 1 45 r0 due to location of the hils syncline in the vicinity of the vlotho massif which is deep seated intrusive body facies variations of the lias within the short geographical distances in the study area are negligible organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the lias shales kerogen bitumen etc and on the evidence of a uniform initial composition of these sediments in the study area dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations about 50 of the initial kerogen was transformed into oil gas and inorganic compounds during the vitrinite reflectance increase from 0 48 to 0 88 ro and only marginally more during the maturity increase from 0 88 to 1 45 ro only a small portion of the generated material remained in the source rock even at a relatively early stage of generation 0 68 ro expulsion efficiency of oil plus gas reached a value of 86 at the end of the main generation stage 0 88 ro

stress fields a key to oil migration a coherent oil migration model based on geomechanical considerations includes both the high molecular kerogen structure and the capillary properties of source rocks oil is squeezed from kerogen by compaction following oil generation this squeezing effect should be created by the differential stress maximum compressive stress minus least compressive stress acting on the kerogen which has been chemically broken up by oil formation in sedimentary bodies whose water is at hydrostatic pressure the migration of oil seems to involve two processes 1 lateral transfer by channeling into the more coarsely microporous layers of the source rocks from the oil generation site toward the geologic structure or lower pressured zone and 2 vertical transfer from source rock to eservoir by the opening or reopening of vertical fractures in the few areas such as structural tops where the least compressive stress is slightly greater than or equal to the pore pressure and where the capillary pressure increment 2 ggr r of oil in the microporosity exceeds the tensile strength of the rock in sedimentary bodies whose water is overpressured the pore pressure should be governed by the least compressive stress and thus migration should begin by oil transfers in a system of small open fractures and eventually in larger fractures the theory demonstrates the impossibility of oil being transferred to the reservoir under true tensile conditions negative effective compressive stress and thus explains the large asphaltic veins of southeastern turkey and the well known bitumen veins of the uinta basin

understanding of hc migration in sedimentary basins present state of knowledge abstract great advances were made during the decade of 1975 1985 in the understanding of hc migration by establishing that the main mechanisms were polyphasic flow whatever its stage and that migration in solution in water and or by molecular diffusion was insignificant except for methane ethane and benzene research is now focusing on points which still have not been satisfactorily answered such as 1 1 behaviour of source rocks during hc expulsion the main driving force for fluid expulsion has been recognized to be excess fluid pressure within the source rock with respect to its surrounding environment of permeable beds the pressure build up is due mainly to accommodation by the fluids of part of the mechanical stresses which are exerted on the rock mainly sedimentary load but also stresses developed by tectonics to thermal expansion of water and to hc formation from kerogen in response to increasing temperatures however it is not clear whether or not petroleum expulsion proceeds preferentially along oil wet networks kerogen or oil wet mineral surfaces nor it is not clear whether or not microfracturing provoked by an internal fluid pressure higher than allowed by the mechanical strength of source rocks is necessary for hc expulsion 2 2 modifications of the compositions of hc phases e g oil versus gas or the distribution of biomarkers during migration and losses of hydrocarbons along the migration pathways although careful observations of natural sample series and also experimentation have been done no clear picture has emerged for the moment however compositional effects seem to be due more to changes in thermodynamic conditions along migration pathways which provoke inter alia hydrocarbon phase separation retrograde condensation than to differential retention by mineral surfaces it is likely that while careful observations on a large variety of source rock samples are needed to more clearly understand source rocks functioning progress in understanding hc migration will come increasingly from modeling and experimentation models which mathematically simulate natural processes are necessary to help the human mind in handling such complex phenomena and therefore are of precious help to focus research on the most important points they replace migration in its geological and historical dimensions with numerical or conceptual tools while observation only describes the present state models are also the tools by which knowledge on migration can be applied to exploration problems however quantitative applications of models require numerous and precise geological data that are difficult to gather at early stages of exploration in the field of experimentation it will be easier to design crucial experiments now that hc migration mechanisms are better understood thanks to experimentation it should also be possible to validate models however so as to reach such aims substantial progress has to be made in the technology of experimental systems

role of diffusion in primary migration of hydrocarbons the following effective diffusion coefficients d cm2 sec were determined for the diffusion of light hydrocarbons through the water saturated pore space of shales methane 2 12 10 6 ethane 1 11 10 6 propane 5 55 10 7 iso butane 3 75 10 7 n butane 3 01 10 7 n pentane 1 57 10 7 n hexane 8 20 10 8 n heptane 4 31 10 8 and n decane 6 08 10 9 on the basis of these new data a deterministic dynamic model was set up to simulate the diffusive transport of light hydrocarbons c1 to c10 from source rocks for eight documented source rock units representing a wid range of geologic conditions maturities of 0 40 to 1 35 mean vitrinite reflectance oil to gas prone kerogens the cumulative amounts of hydrocarbons escaping with time were calculated thus it was shown that diffusion represents an effective process for primary migration of gas but not for oil the rate of mass transport for gas from source rocks with geologic time can be sufficiently high to account for the origin of commercial size gas fields for example a cumulative amount of 109 kg of methane 1 5 109 std m3 or 5 3 1010 scf has escaped by diffusion in 540 000 years from a certain volume 1 000 km2 by 200 m thick of a high mature gas prone mesozoic source rock in western canada the origin of hydrocarbon accumulations with high gas to oil ratios in low mature sediments in geologically young basins early gases and condensates can be explained by an early phase of primary migration predominantly based on diffusion during the initial stages of the accumulation history of those fields extending up to millions of years under certain conditions the reservoir gas changes with geologic time from a methane rich to a wet gas composition at low maturity levels below about 0 6 rm even oil prone source rocks yield methane rich light hydrocarbon mixtures by migration through diffusion compositional trends among reservoir gases of several multiple pay gas fields in louisiana represent evidence for diffusive transport of hydrocarbons the variation in gas composition between the individual pay zones is controlled by increasing distances of diffusive transport of the hydrocarbons from a uniform source rock at depth to their present accumulation sites in the shallow pay zones compounds of high diffusivity are enriched for example in the sligo gas field of louisiana the methane ethane and the iso butane n butane ratios increase from 10 2 to 36 0 and from 0 86 to 1 13 respectively from the deepest to the shallowest of the five productive reservoir sands which are spread over a a depth interval of 5 500 ft 1 676 m diffusion of light hydrocarbons in the subsurface can also have economically adverse effects for example existing gas accumulations can be destroyed by dissipation the rate of this destruction was calculated for the harlingen gas field holland by diffusive loss through 400 m of shale cap rock the initial amount of methane in place of 1 93 109 std m3 6 8 1010 scf is reduced by one half over a period of 4 5 million years this leads us to propose the concept that large gas accumulations can persist through extended periods of geologic time only as dynamic systems reaching some kind of steady state equilibrium between diffusive loss through the cap rock and continuous replenishment from the source rock

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

major marine cycles in the mesozoic the cycles postulated by fischer 1979 are considered in the light of the mesozoic stratigraphical and palaeontological record it is suggested that the most important events were i the late permian regression ii the late mid triassic transgression iii the late late transgression iv the late early jurassic transgression v the late mid jurassic transgression vi the end jurassicre gression vii the late early cretaceous transgression viii the end cretaceous regression these are related to episodicity in ocean floor spreading climatic changes and major happenings in the history of the shallow marine benthos

sequential extraction a useful tool for reservoir geochemistry abstract little is known about the microscale distribution and potential molecular fractionation of bitumen residing in reservoir rocks few data exist on the comparative organic geochemistry of hydrocarbons in authigenic inclusions formed in reservoir rocks and the bitumen in the pore space a three step sequential extraction technique has been applied to clastic petroleum reservoir samples using a suite of solvents with increasing polarity in order to address these questions in the analyzed samples the following main trends were observed i the first extract represents 95 of the total extract ii the relative polar compound content increases going from the first to the last extract iii the last extract has generally a slightly lower apparent maturity as assessed using biomarker parameters additionally a reduction in the degree of biodegradation from the first to the last extracts was observed implying tentatively that biodegradation takes place dominantly in the center of the pores fluid inclusion extracts show distinct source characteristics however the last extract appears to approach the fluid inclusion extract signature in some aspects the use of sequential extraction as a routine tool in the reservoir geochemical context is judged to be limited however it may help to solve specific problems

modelling petroleum migration through microcrack propagation in transversely isotropic source rocks summary to investigate primary petroleum migration through microfracturing of source rocks we develop a theoretical multiphysics model incorporating simultaneous generation of oil and gas from kerogen elastic anisotropy of the source rock and propagation of microcracks filled with oil and gas the variations of excess fluid pressure in the crack and crack propagation distance with time are determined a detailed parametric analysis is performed to study the sensitivity of petroleum migration behaviour to changes in the input parameters including kerogen type chemistry of kerogen to oil gas conversion elastic anisotropy of source rocks geothermal gradient and burial rate numerical results show that a microcrack in type iii kerogen bearing source rocks can attain greater length than in rocks containing type i and ii kerogen which have higher oil potentials and transform to oil gas much faster than type iii kerogen elastic anisotropy of source rocks has a profound influence on the crack propagation distance but only a marginal effect on the duration of crack propagation and the excess fluid pressure the simulation also shows that higher geothermal gradients and fast burial reduce the crack propagation duration significantly but excess pressure and final crack length are not sensitive to the variations of geothermal gradient and burial rate

petroleum migration faults and overpressure part ii case history the haltenbanken petroleum province offshore norway abstract petroleum inclusion and geochemical data from core extracts were applied to deduce a model for oil migration overpressure development and palaeo leakage of oil from currently dry structures in the haltenbanken vest area the existence of fluorescent oil type inclusions in quartz in the smorbukk asgard 2 field suggest that oil migrated into this structure 70 50 million years before present ma bp this is also the case for the dry structures 6506 12 4 6506 11 3 and 6506 11 1 west of the main smorbukk fault zone black oil inclusions with medium gas oil ratio gor occur in these fields together with condensate type petroleum inclusions this suggests that the dry structures transformed from containing oil to condensate before leakage petroleum extracted from inclusions in these structures and in nearby fields have identical marine type ii kerogen signatures source rocks at the spekk formation level in the current drainage area of smorbukk and these dry structures were immature 70 50 ma bp and the smorbukk sor asgard 3 field did not fill at this early time thus oil must initially have entered into smorbukk from areas to the w sw through the currently pressure sealing smorbukk fault zone which today marks the westward limit of the smorbukk field diagenesis in this fault zone caused the much later overpressure development and petroleum was lost from the 6506 12 4 6506 11 3 and 6506 11 1 structures as overpressure built up regionally petroleum loss from these structures with their often thick seals must have occurred via self propagating open fracture induced mechanisms lack of petroleum in the cretaceous strata above these structures suggests that leakage occurred to even shallower strata this could imply that the cretaceous strata in halten vest were overpressured at the time of leakage in contrast the oil in the cretaceous lysing and lange formation above the jurassic reservoirs in smorbukk and smorbukk sor most likely originated based on geochemistry and gors from the jurassic reservoirs below and not from cretaceous strata this migration event would have been facilitated if it occurred before these sands became overpressured as they are today modelling suggests that the spekk formation became mature in the smorbukk sor region

a novel approach for recognition and quantification of hydrocarbon migration effects in shale sandstone sequences a detailed organic geochemical study of over 150 samples from two cores with a total combined length of 320 m 1 050 ft through sequences of interbedded source rock type shales 0 84 rm maturity and reservoir sandstones allowed recognition and quantitation of a number of migration effects detailed gas chromatography mass spectrometry of steranes and triterpanes was used to insure that samples being compared to investigate migration effects contain organic matter of a similar type thin shales interbedded in sands and the edges of thick shale units are depleted in petroleum range hydrocarbons to a much higher degree than the centers of thick shale units for the alkanes expulsion occurs with pronounced compositional fractionation effects shorter chain length n alkanes are expelled preferentially and isoprenoid alkanes are expelled to a lesser degree than their straight chain isomers based on material balance calculations expulsion efficiencies were determined and found to be very high in certain instances for thin interbedded shales they decrease from about 80 around c15 to near zero in the c25 region there is no evidence for significant redistribution of steranes and triterpanes in the two sequences compared to c15 to c25 n alkanes they appear relatively immobile the composition of the hydrocarbons impregnating parts of the reservoir sandstones is in agreement with expulsion occurring with pronounced fractionation based on molecular chain length hence consideration of bulk expulsion efficiencies gives an unrealistic picture furthermore the impregnation of a siltstone cap rock from an underlying hydrocarbon accumulation seems to have occurred by bulk oil migration and without significant fractionation the degree of hydrocarbon depletion of some of the shales of both sequences appears to be controlled by compaction and the primary migration process appears to have occurred with chromatographic separation the migration phenomena observed in both sequences lead us to propose that the main phase of expulsion can be preceded by an earlier sta e during which the edges of thick shales and thin interbedded shales appear to be slowly and continuously depleted by the chromatographic processes the composition of the hydrocarbon product accumulating in the reservoirs at this stage appears to be controlled primarily by physical processes rather than by the type and maturity of the organic matter in the generating source rock by this mechanism the origin of accumulations of light oils and gas condensates in low mature sequences bearing predominantly terrestrial derived organic matter can be explained finally the migration effects documented in this study have some consequences for interpretation of geochemical data e g the pristane n c17 ratio a commonly accepted maturity parameter has been shown to be also controlled by the degree of hydrocarbon expulsion

clean spectral analysis of long term sea level changes a new clean spectral technique has been applied for the first time to analyse a record of long term sea level fluctuation during the last 200 million year myr the technique is based on a one dimensional complex deconvolution algorithm and removes the effects of the data sampling as well as the artifacts arising from the choice of data window the analysis reveals a dominant periodicity of 33 myr in the sea level variations this periodicity compares well with the known half period of the sun s oscillation perpendicular to the galactic plane interestingly a 33 myr periodicity can also be correlated with the reported mass extinction cycles and other geological periodicities the results suggest galactic forcing as a possible driving mechanism for quasi periodic terrestrial processes

effect of water washing on crude oil compositions crude oils from venezuela oklahoma and new mexico were water washed in the laboratory at temperatures from room temperature to 80 c and with water salinities from 0 to 300 000 mg l in experiments lasting from 7 to 338 hours the effects of water washing were determined by gas chromatographic and gas chromatography mass spectrometric analysis of the residual oil these experiments show that water washing is particularly effective for the c15 fraction and hydrocarbons are removed in the sequence aromatics then n alkanes then naphthenes in the c15 fraction no loss of pristane phytane steranes or terpanes occurs but some aromatics and sulfur compounds especially dibenzothiophene are depleted although water washing reduces api gravity water washing is unlikely to produce tar layers the effects of water washing were simulated with a numerical model based on the equation of diffusion predicted oil water ratios were in good agreement with the experimental values for the light ends and the model suggests that water washing is very fast in the subsurface comparison of oils that appeared to have been water washed in nature with the equivalent unwashed oils showed the expected compositional trends water washing is probably the dominant process affecting crude oil composition in the subsurface when water flows past oils under conditions where bacterial degradation is precluded by temperature 80 c or by lack of dissolved oxygen and the temperatures are too low for thermal cracking

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

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

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

the earliest known palaeocene mammal fauna and its implications for the cretaceous tertiary transition several localities in northeastern montana usa representing the earliest known palaeocene mammal sites in the world document a gradual turnover in the mammalian fauna at the cretaceous tertiary boundary these localities in combination with previously known latest cretaceous localities represent the only well documented terrestrial sequence across the cretaceous tertiary boundary this sequence argues for gradual terrestrial extinctions and faunal changes at this boundary

extraction of whole versus ground source rocks fundamental petroleum geochemical implications including oil source rock correlation abstract in petroleum geochemistry extractable hydrocarbons hcs in source rocks have typically been studied by grinding the rock to a fine powder 100 mesh and then extracting the hcs from the rock with a solvent this procedure carries the implicit assumption that the hcs are homogeneously distributed throughout the rock however sequential soxhlet extractions of whole unpowdered source rocks have shown that progressive extracts from the same rock can be quite different and may not even correlate with each other a crude oil like material clearly has been fractionated from indigenous bitumen in these rocks has moved to cracks and parting laminae in the rocks is ready for expulsion from the rocks and is thus most accessible to the first extracting solvents this process which we believe is largely due to hc gases and carbon dioxide generated over all maturation ranks in source rocks carries petroleum geochemical implications of a fundamental nature for oil source rock correlations and gives insight into primary migration mechanisms origin of oil deposits and use of maturity and organic facies indices

impacts and glacio eustasy plate tectonic episodes geomagnetic reversals a concept to facilitate detection of impact events abstract it is suggested that the cretaceous tertiary c t impact destabilised and then profoundly changed the climatic structure of the earth for cenozoic times by establishing freezing conditions at the poles via the c t dust veil and the subsequent h 2 o greenhouse evaporation polar snow fields ice caps see level fall tp1 it is also suggested that the c t impact affected the earth s mantle shock induced phase transitions and via chain reactions also the core mantle boundary this mantle effect could possibly explain the laramian plate tectonic episode 65 ma and reversal t29 r n which occurred 150 000 years after the c t boundary as long term impact effects the combination of these and the multitude of associated events c f faunal breaks appear to correlate episodically in the geological past it is proposed that these repetitions can be used as a potential approach to narrow the search for impact traces also more examples of correlations between impact events and their possible effects are needed to ensure that the implications of the c t impact are generally valid

characterization of oil generation and expulsion from coals and source rocks using diamond anvil cell pyrolysis abstract a visual technique has been developed using a diamond anvil cell to characterize oil prone vs gas prone coals and source rocks and evaluate their oil expulsion efficiency the experiments conducted using 15 humic or shaly coals two boghead coals and eight source rock samples from taiwan turkey north america and australia show that the technique has potential to distinguish oil prone coals from gas prone coals the oil potential of humic coals was estimated from the amounts of total liquid generated during pyrolysis which show correlations with the hydrogen index hi from rock eval pyrolysis and the gas to oil ratio gor determined by py gc analysis the changes of visual area or volume of neoformed liquid as a function of temperature at four heating rates were used to calculate the extents of kerogen to oil transformation for determining the kinetic parameters the results confirm the kinetic controls on the measured transformations but reveal unusually high apparent activation energies and frequency factors the use of this technique as a quantitative tool to predict oil generation kinetics should be treated with caution until this discrepancy has been resolved in addition this study has demonstrated that the expulsion of oil like liquid from coals is generally more efficient than from shales possibly due to the much higher organic content in coal

experimental investigation of oil generation retention and expulsion within type ii kerogen dominated marine shales insights from gold tube nonhydrous pyrolysis of barnett and woodford shales using miniature core plugs abstract although oil retention has recently emerged as a key topic of unconventional shale resource assessment oil retention and expulsion controls in organic rich shales during thermal maturation remain poorly constrained this study presents an experimental comparison of oil generation retention and expulsion in two immature type ii kerogen dominated marine shales the mississippian barnett shale and the upper devonian lower mississippian woodford shale mainly with respect to the combined effects of the organic macerals and rock fabric involved in both cases miniature core plugs drilled from the given samples were isothermally pyrolyzed at 130 to 425 c for 72 h under a confining pressure of 68 mpa during gold tube nonhydrous pyrolysis corresponding to the thermally immature early stage of the oil window the main stage of the oil window the late stage of the oil window the main stage of oil cracking to wet gas and the late stage of oil cracking yields of generated oil retained oil and expelled oil for the two studied samples were systematically quantified on the basis of mass balance calculation of measured oil and gas yields as well as rock eval analyses on pyrolyzed subsamples through the six stages of petroleum formation investigated the principal difference in oil generation was observed in the two studied samples with approximately 38 to 68 greater yields of generated oil equivalent to 130 mg oil g toco for the woodford shale when it evolved into the main and late stages of the oil window these elevated yields of generated oil for the woodford shale were compensated for by additional oil generation resulting from conversion of abundant type i kerogen like algae such as tasmanites and leiosphaeridia which lag in onset and have a shorter period of petroleum generation upon maturation as a response to the difference in oil generation oil retention was found to be significantly enhanced for the woodford shale at equivalent stages with 0 2 to 1 7 times more free oil equivalent to 24 105 mg oil g toco and 0 7 to 3 9 times more sorbed oil equivalent to 58 76 mg oil g toco being retained than that of the barnett shale although this effect was not pronounced for oil expulsion in contrast to the barnett shale relatively low expelled oil yields and expulsion efficiencies both indicate highly limited oil expulsion in the woodford shale implying that the woodford shale whose mineral composition and lithofacies are similar to those of the barnett shale may have a relatively low permeability rock fabric to prevent oil from being expelled furthermore not only significantly higher oil saturation index osi values but also a wider range of maturity at which the oil crossover effect osi 100 mg g toc occurs is expected for the woodford shale when extrapolation to a geological setting occurs these data suggest that the presence of abundant type i kerogen like algae and relatively low permeability rock fabric in the woodford shale are critical to significant oil retention during oil generation and expulsion which jointly raise the possibility of potential commercial shale oil within type ii kerogen dominated marine shales

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

aspects of hydrocarbon migration in the mesozoic in the paris basin as deduced from an organic geochemical survey abstract this paper describes the main results of a study of hydrocarbon migration in the mesozoic in the paris basin as obtained from the geochemical analysis of cuttings from 41 petroleum boreholes the analytical methods used were pyrolysis gas chromatography mass spectrometry and the determination of stable isotopes hydrocarbon formation and migration were simulated using the temispack mathematical model the following results were found concerning the primary migration pyrolysis of numerous samples of freshly cleaned cuttings allowed the computation of a migration efficiency ratio for each sample by comparing the hc contents actually produced with those remaining in the rock they also allowed the compilation of migration maps for each source rock level as indicated by the migration ratios the hc expulsion starts below the beginning of the oil window 2100 m at a depth of about 2350 m for a transformation ratio of the lias om of 25 these migration ratios increase strongly with depth reaching 88 at 2700 m migration maps served to locate the true source rocks at the base of the lias and to calculate the total quantity of oil expelled 2 billion tons of hc analysis of rock extracts from drained levels shows by comparison with the oil analyses that migration occurred without any variation in hc composition concerning the secondary migration the migration maps used to estimate the amounts of migrated hcs revealed lateral migration phenomena in some rocks toarcian with respect to the other secondary migration paths faults played an important role but failed to favor vertical downward migration by more than 50 m below the lias source rocks as shown by the temispack model the deep trias reservoirs could only be filled laterally when the faults like the bray fault placed the mature hettangian sinemurian source rocks in contact with the trias furthermore the hypotheses of a regional hydrodynamic flow trending ne sw were taken into account in the model to explain the lateral hc migrations to distances often far from their oil kitchen and the rarity of shows northeast of the bray fault

extensional deformation assisted by mineralised fluids within the brittle ductile transition insights from the southwestern massif central france abstract extensional deformation assisted by mineralized fluids within the brittle ductile transition is inferred using structural microstructural and textural investigations applied to the sarlande shear zone of the southwestern massif central france the shear zone is a low angle normal fault that bounds the meuzac antiform to the south these structures were formed during the nw se trending synorogenic extension of middle carboniferous age pre existing lithologies involved in the shear zone led to partitioning of behaviour and hydrothermal alteration in response to crustal extension and channelling of mineralising fluids intense fluid rock interactions produce softening and weakening reactions induced by alteration of k feldspar remobilisation of graphite and rutile and growth of white micas chlorite and polymetallic sulphides extensional shear deformation and mineralization progressively and concomitantly developed within the brittle ductile transitional crust 9 13 km depth the derived crustal scale model emphasises the importance of collision which led to the production of large quantities of granite derived fluids and the creation of a crustal permeability that drove these fluids near to the brittle ductile transition late orogenic extension associated with fluid rock interactions led to growth of mineralizing low angle shear zones and footwall domes the role of mineralising fluids fluid pressure appears to be essential in promoting deformation within the brittle ductile transition of the extending crust

constraining the oil charge history of the south pepper oilfield from the analysis of oil bearing fluid inclusions abstract the south pepper oilfield located in the barrow sub basin on the nw margin of the australian continent has experienced a multi phase charge history abundant oil bearing fluid inclusions are present in samples from within the current gas cap suggesting that an oil column existed prior to gas this palaeo oil gas leg fi oil has ts tm and c29 c30 hopane ratios of 1 and the c35 homohopanes are a significant proportion of the extended homohopanes it has lower pr ph and diasterane sterane ratios than the currently reservoired live oil and contains gammacerane a series of peaks tentatively identified as c30 to c34 17 h 30 norhopanes and a large amount of 2 methylhopanes collectively geochemical analysis of the gas leg fi oil suggests that it was generated from a less mature more calcareous source rock deposited under more reducing conditions than the upper jurassic dingo claystone the main source of the live oil in addition the presence of c30 dinosteranes in the gas leg fi oil provides a triassic or younger age constraint this makes palaeozoic carbonates an unlikely source possible source intervals for the gas leg fi oil are thin lower jurassic limestones and marls which occur at the base of the lower dingo claystone or a thin limestone unit the cunaloo member at the base of the triassic locker shale samples from within the present oil leg also contain abundant oil inclusions consistent with high oil saturations at the present day however these oil inclusions exhibit different fluorescence colours suggesting they represent a second oil charge geochemically the oil leg fi oil has an intermediate composition between the live oil and the gas leg fi oil suggesting that gas charge displaced the first oil charge samples of which were preserved as fluid inclusions in the oil leg sample biodegradation of the first oil charge indicated by the presence of 17 h 25 norhopanes in the currently reservoired live oils can be attributed to the ingress of meteoric waters probably during sub aerial exposure of the basin margin during miocene wrenching changing environmental conditions curtailed bacterial activity and allowed unaltered oil sourced from the dingo claystone to accumulate below the gas cap and mix with the biodegraded residues of the first oil charge to achieve the live oil composition the biodegradation event must have preceded the second charge as the live oil contains compounds such as n alkanes which would have been removed had alteration occurred after the second charge complex charge histories are common and the analysis of palaeo oils trapped within fluid inclusions provides the opportunity to achieve a more comprehensive assessment of hydrocarbon charge

compositional modeling of petroleum generation and expulsion trial application to a local mass balance in the smorbukk sor field haltenbanken area norway 1 we present an application of a compositional kinetic model of petroleum generation degradation into gas and residue and simultaneous expulsion petroleum composition is described by four carbon fractions c 1 c 2 c 5 c 6 c 14 c 15 and expulsion is related to a petroleum saturation threshold expulsion is important because rapid expulsion of petroleum from source rocks favors oil whereas late expulsion increases the cracking reactions and favors gas accumulation such a model is tested against field data for the first time by applying it to the smorbukk sor field previously named smorbukk greek beta located in the norwegian sea geometrical and one dimensional thermal reconstructions are performed followed by a computation of a mass balance of expelled and unexpelled products for each source rock throughout the drainage area comparison of the model results is made with rock eval data vitrinite reflectance and actual composition of accumulations lower jurassic coals were the main source expelling gas and oil mainly since 5 ma as the present accumulation accounts for less than 10 of total expelled petroleum major petroleum losses probably occurred through the structural spillpoint this migration scheme is supported by the simila composition of the reservoired petroleum and the petroleum expelled since 0 5 ma although various uncertainties are possible this study shows that our model has the capability to quantify expulsion consistently with the observed amounts of unexpelled petroleum in mature source rocks and with the reported composition of the accumulation

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

geochemical characteristics and implications of hydrocarbons in reservoir rocks of junggar basin china abstract a practical sequential extraction approach has been applied to two core samples collected from oil zones of triassic sandstones in junggar basin northwest china five bitumen fractions were obtained from each sample using this approach these fractions are free oil components in inter granular pores bitumen 1 adsorbed oil components on grain surfaces and liberated by hcl treatment bitumen 2 oil bearing fluid inclusions hosted by grains bitumen 3 and adsorbed oil components on clay mineral surfaces and liberated by hcl and hcl hf treatments bitumens 4 and 5 striking differences have been observed both in bulk compositions and in aliphatic biomarker distributions e g terpanes and steranes among the five bitumen fractions this phenomenon is ascribed to the indigenous compositional variations and differential maturation behaviors between adsorbed oil components in a network of polar compounds resins and asphaltenes and free oil components in even a same oil charge in addition to fractional adsorption effects and compositional changes of the oil charges in reservoir rocks during filling process the molecular compositions and homogenization temperatures of oil bearing fluid inclusions in these two samples indicate that trapping of these types of inclusions apparently ceased in sample a while continued in sample b after the initial oil charge suggesting that the relative content of polar components in the initial oil charge compared to the later oil charges plays a dominant role controlling the trapping of oil bearing fluid inclusions in an oil saturated zone sequential extraction studies are important and useful for reservoir geochemistry especially in the cases where only limited samples of oil and reservoir rocks are available and or where compositional heterogeneity of free oils has disappeared in a reservoir karlsen d a nedkvitne t larter s r bjorlykke k 1993 hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history geochim cosmochim acta 57 3641 3659

the influence of extractable organic matter on vitrinite reflectance suppression a survey of kerogen and coal types abstract the vitrinite reflectance suppression literature shows that while bitumen impregnation of the vitrinite group is often invoked as a significant contributor to suppression its existence is not often supported by petrological evidence this study examines bitumen impregnation as a factor in vitrinite suppression by comparing the vitrinite reflectance of source rock and coal samples before and after solvent extraction bitumen often defined as organic matter soluble or extractable in certain organic solvents should be removed by soxhlet method solvent extraction using chloroform removing the extractable bitumen should restore the suppressed reflectance to its true higher value however the solvent extracted samples averaged 0 014 r v less than that of the unextracted samples we conclude from these results and from other published data that reflectance suppression by bitumen impregnation in the vitrinite maceral group above the huminite stage of gelification is seemingly a rare phenomenon and whose effect on suppressing vitrinite reflectance is typically negligible

ultrasonic and x ray computed tomography characterization of progressive fracture damage in low porous carbonate rocks abstract this paper studies the fracturing process in low porous rocks during uniaxial compressive tests considering the original defects and the new mechanical cracks in the material for this purpose five different kinds of rocks have been chosen with carbonate mineralogy and low porosity lower than 2 the characterization of the fracture damage is carried out using three different techniques ultrasounds mercury porosimetry and x ray computed tomography the proposed methodology allows quantifying the evolution of the porous system as well as studying the location of new cracks in the rock samples intercrystalline porosity the smallest pores with pore radius

practical kinetic modeling of petroleum generation and expulsion abstract models for petroleum generation used by the industry are often limited by a sub optimal laboratory pyrolysis methods for studying hydrocarbon generation b over simple models of petroleum generation c inappropriate mathematical methods to derive kinetic parameters by fitting laboratory data d primitive models of primary migration expulsion and its coupling with petroleum generation and e insufficient use of subsurface data to constrain the models problems a b and c lead to forced compensation effects between the activation energies and frequency factors of reaction kinetics that are wholly artificial and which yield poor extrapolations to geological conditions simple switch or adsorption models of expulsion are insufficient to describe the residence time of species in source rocks yet the residence time controls the thermal stresses to which the species are subjected for cracking to lighter species the shellgenex model for petroleum generation and expulsion has been developed since 1988 in this multi species model the rate limiting step of primary migration is treated as the slow diffusion of the petroleum through the kerogen itself other key aspects of the model are the reaction and transport behaviour of the heavy compounds the role of free radicals in the cracking kinetics of hydrocarbon species in the model and the evolving free volume of the kerogen the last of these has a particularly strong effect on the primary migration of the generated petroleum molecules some implications of this model are that a compositions of expelled petroleum vary more strongly than the standard parallel reaction model suggests and b expulsion is not immediately extinguished by waning temperatures and pressures but continues with decreasing gor of the expelled petroleum and increasing density of the expelled oil

empirical relationship between gas composition and thermal maturity in eagle ford shale south texas organic rich and carbonate rich eagle ford shale is a self sourced oil and gas reservoir with little alteration of gas chemistry as might be affected by petroleum expulsion and migration as such it provides an ideal natural laboratory to quantify the compositional variation of gases generated from oil prone type ii kerogen during thermal maturation the chemical composition of the gas released from rock crushing was conducted and integrated with rock eval pyrolysis to define the empirical relationship between gas compositional parameters and thermal maturity in this study from 10 wells in the eagle ford shale in south texas we collected 74 core samples having a range of thermal maturity the measured maximum temperature tmax values of hydrocarbons generated in rock eval pyrolysis range from 427 c to 494 c 800 f to 921 f and the calculated equivalent vitrinite reflectance roe values range from 0 51 to 1 73 based on tmax values total organic carbon content ranges from 0 3 to 8 53 with an average of 3 12 standard deviation of 1 77 burial depth is from 2989 6 to 13 827 3 ft 911 2 to 4214 6 m our results showed that gas composition in the eagle ford shale is mainly controlled by thermal maturity and three stages of gas generation are identified based on the c1 and c2 concentrations of the gases released by rock crushing from eagle ford shale core samples the three stages of gas generation correspond to the following processes of organic matter conversion 1 kerogen and bitumen thermal cracking to crude oil 2 bitumen and heavy crude oil thermal cracking to light oil and 3 light oil cracking to gas methane rich gas and an abundance of branched butane and pentane are generated in light oil cracking to gas resulting in high c1 c2 c1 c2 c3 i c4 n c4 and i c5 n c5 ratios increased cracking of normal alkanes such as n butane and n pentane occurs in the light oil cracking to gas empirical equations between gas compositional parameters and thermal maturity tmax or roe are obtained for oil prone type ii the c1 c2 c1 c2 c1 c2 c3 and i c4 n c4 ratios are the five best parameters for determining thermal maturity with an exponentially derived r2 value of 0 74 the composition of gas produced from the eagle ford shale following hydraulic fracturing is used to validate the empirical equations calculated thermal regime for the oil production based on the produced gas is located at the peak of oil generation and the beginning of light oil cracking to gas corresponding to tmax from 454 c to 464 c 849 f to 867 f or at an roe ranging from 1 01 to 1 19 empirical equations provide a basis for interpretation of mud gas logging data and produced gas composition

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out