tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

geologic framework of the mississippian barnett shale barnett paleozoic total petroleum system bend arch fort worth basin texas this article describes the primary geologic characteristics and criteria of the barnett shale and barnett paleozoic total petroleum system tps of the fort worth basin used to define two geographic areas of the barnett shale for petroleum resource assessment from these two areas referred to as assessment units the u s geological survey estimated a mean volume of about 26 tcf of undiscovered technically recoverable hydrocarbon gas in the barnett shale the mississippian barnett shale is the primary source rock for oil and gas produced from paleozoic reservoir rocks in the bend arch fort worth basin area and is also one of the most significant gas producing formations in texas subsurface mapping from well logs and commercial databases and petroleum geochemistry demonstrate that the barnett shale is organic rich and thermally mature for hydrocarbon generation over most of the bend arch fort worth basin area in the northeastern and structurally deepest part of the fort worth basin adjacent to the muenster arch the formation is more than 1000 ft 305 m thick and interbedded with thick limestone units westward it thins rapidly over the mississippian chappel shelf to only a few tens of feet the barnett paleozoic tps is identified where thermally mature barnett shale has generated large volumes of hydrocarbons and is 1 contained within the barnett shale unconventional continuous accumulation and 2 expelled and distributed among numerous conventional clastic and carbonate rock reservoirs of paleozoic age vitrinite reflectance ro measurements show little correlation with present day burial depth contours of equal ro values measured from barnett shale and typing of produced hydrocarbons indicate significant uplift and erosion furthermore the thermal history of the formation was enhanced by hydrothermal events along the ouachita thrust front and mineral wells newark east fault system stratigraphy and thermal maturity define two gas producing assessment units for the barnett shale 1 a greater newark east fracture barrier continuous barnett shale gas assessment unit encompassing an area of optimal gas production where dense impermeable limestones enclose thick 300 ft 91 m barnett shale that is within the gas generation window ro 1 1 and 2 an extended continuous barnett shale gas assessment unit covering an area where the barnett shale is within the gas generation window but is less than 300 ft 91 m thick and either one or both of the overlying and underlying limestone barriers are absent

mechanical properties of shale gas reservoir rocks part 1 static and dynamic elastic properties and anisotropy abstractunderstanding the controls on the elastic properties of reservoir rocks is crucial for exploration and successful production from hydrocarbon reservoirs we studied the static and dynamic elastic properties of shale gas reservoir rocks from barnett haynesville eagle ford and fort st john shales through laboratory experiments the elastic properties of these rocks vary significantly between reservoirs and within a reservoir due to the wide variety of material composition and microstructures exhibited by these organic rich shales the static young s modulus and dynamic p and s wave moduli elastic parameters generally decrease monotonically with the clay plus kerogen content the variation of the elastic moduli can be explained in terms of the voigt and reuss limits predicted by end member components however the elastic properties of the shales are strongly anisotropic and the degree of anisotropy was found to correlate with the amount of clay and organic content as well as the shale fab

impact of thermal maturation on nano scale elastic properties of organic matter in shales abstract the properties of organic matter change during diagenesis and catagenesis potentially altering the way shales deform and fracture although kerogen in mudrocks is thought to become stiffer during thermal maturation few studies have been able to confirm this by direct measurement as standard mechanical testing techniques cannot easily be used to measure the micrometer sized organic components in shales here we use a new non destructive atomic force microscopy technique to map the elastic modulus of organic and inorganic components at the nanometer scale in shales containing type ii kerogen from three different levels of thermal maturation we found that when vitrinite reflectance increases from 0 40 to 0 82 the average young modulus of kerogen increases from 6 1 gpa to 16 0 gpa however as ro increases further from 0 82 to 1 25 the modulus values for kerogen do not change significantly a high degree of variance is registered in the elastic moduli particularly at higher levels of thermal maturation probably reflecting the inherent heterogeneity in the depositional organic matter present in the shales the mean modulus for bitumen in the same samples identified as void filling organic matter that was present only at intermediate and higher levels of maturation was relatively constant with mean values of 7 5 gpa and 8 5 gpa respectively in the samples that experienced catagenesis the modulus maps reveal that individual kerogen macerals possess soft regions interpreted as exuded bitumen which act to soften the overall structure of the kerogen as well as providing high resolution mechanical data this technique could be used to track the way bitumen and other compounds are generated from kerogen during catagenesis

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

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

petroleum source rocks of the tarfaya basin and adjacent areas morocco abstract this work characterizes the source rock potential of the tarfaya basin and enabled us to reconstruct its geochemical history outcrop samples covering different stratigraphic intervals plus the northwestern part of the zag tindouf basin bas draa area were analyzed for total organic carbon corg and total inorganic carbon contents and total sulfur content rock eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis corg content a set of 45 samples were extracted and non aromatic hydrocarbons were analyzed by way of gas chromatography flame ionization detection gc fid and gc mass spectrometry gc ms non isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks high quality petroleum source rocks with high corg content and hydrogen index hi values were found for samples of eocene coniacian turonian and cenomanian age most samples were carbonate rich and organic sulfur values were high to moderate various maturity parameters indicated immature or possibly early mature organic matter based on organic geochemical and petrological data the organic matter is of marine aquatic origin cenomanian or a mixture of aquatic and terrigenous material eocene the early cretaceous interval did not contain high quality source rocks but indications of petroleum impregnation were found

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

effect of thermal maturity on elastic properties of kerogen abstractwe have performed spatially continuous nanodynamic mechanical analysis on four organic rich shale samples with different thermal maturities to extract the elastic modulus of the kerogen particles aliquots were rigorously prepared and three scans were acquired from each aliquot subcritical nitrogen adsorption pore characterization was performed to determine the abundance of kerogen hosted porosity to fully characterize the pore system of samples from the oil window toluene and then chloroform extraction were performed to remove the pore filling hydrocarbons prior to nitrogen adsorption the statistical distribution of the measured modulus values was analyzed to extract the properties of the shale particles in mature samples from the peak oil generation or gas window the kerogen porosity was the dominant pore morphology we found that significant lowering of the kerogen particle modulus resulted from intraparticle kerogen porosity the kerogen particle modulus in mature samples was measured a

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

marine black shale deposition and hadley cell dynamics a conceptual framework for the cretaceous atlantic ocean understanding the controls that determine the spatial distribution and internal heterogeneities of black shales in the mesozoic ocean has been a focal point of research over many decades the consensus is that atmosphere land ocean interactions influenced variations in marine biogeochemistry and sediment supply thus exerting fundamental controls on the richness and quality of sedimentary organic matter om and ultimately on petroleum source rock distribution and its generation potential internal small scale heterogeneities in black shales that have been reported from all ocean settings were often linked to orbitally driven fluctuations in continental runoff and marine upwelling the two processes are generically related under the ascending tropical and descending subtropical limbs of the palaeo hadley cells with fluctuations at variable time seasonal orbital geological and spatial shelf margin deep basin scales these dynamic variations translate into characteristic patterns of om quantity and quality best preserved near the continents where the forcing effects are strongest the expression of these orbital scale interactions are not well constrained at the basin scale however they may hold a key to better understand the distribution of heterogeneities in black shales this study presents a conceptual framework that links om quality and quantity in cretaceous atlantic sediments with the dominant processes that operated under the hadley cells using a comprehensive compilation of bulk organic geochemical data total organic carbon concentration toc hydrogen index hi oxygen index oi and kerogen type we explore how basic geochemical patterns can be used to identify the underlying generic processes we utilise published and new data from deep ocean sites of the dsdp odp program as well as one palaeo shelf setting tarfaya spanning a latitudinal transect from the outer subtropics to the palaeo equator during the albian the cenomanian turonian and the coniacian santonian this study emphasises the potential of integrating orbital scale datasets and wide spatial coverage as a predictive tool for black shale formation across ocean basins

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

mechanical properties of organic matter in shales mapped at the nanometer scale abstract the mechanical properties of organic matter strongly affect the way shales deform and fracture however the way organic matter responds to mechanical stresses is poorly understood representing a critical obstacle to assessing oil and gas production in shale formations little is known about the mechanical properties of organic matter in fine grained rocks primarily because it often occupies tiny nanometer scale voids between the mineral grains which cannot be accessed using standard mechanical testing techniques here we use a new atomic force microscopy technique peakforce qnm to map the mechanical properties of organic and inorganic components at the nanometer scale we find that the method is able to distinguish between different phases such as pyrite quartz clays and organic matter moreover within the organic component young s modulus values ranged from 0 to 25 gpa in 3 different samples all of which come from thermally mature type ii iii source rocks in the dry gas window a modal value of 15 16 gpa was measured with additional peaks measured at 10 gpa in addition the maps suggest that some porous organic macerals possess a soft core surrounded by a harder outer shell 50 100 nm thick thus our results demonstrate that the method represents a powerful new petrographic tool with which to characterize the mechanical properties of organic rich sedimentary rocks

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

delivery of upper basin sediment to the lower neuse river north carolina u s a extensive storage of upper basin piedmont sediment and apparent low sediment supply to streams in lower basin coastal plain areas generates questions as to the source of alluvium in lower reaches of rivers of the u s atlantic drainage this was investigated on the neuse river north carolina using a mineralogical indicator of sediment source areas the utility of mica flakes for discriminating between piedmont and non piedmont sources of sediment in the lower coastal plain reaches of the neuse was established on the basis of an examination of the u s national soils database and of 26 soil surveys of the north carolina coastal plain from the neuse river estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments mica flakes become more common upstream this suggests that a very small proportion of the sediment eroded in the piedmont portion of the watershed is delivered to the river mouth the small amounts which presumably do reach the lower coastal plain are so diluted by coastal plain derived alluvium that no piedmont origin can be discerned this demonstrates a dominantly coastal plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems more importantly results suggest that upper and lower basin sediment dynamics are not only non linearly related but may be virtually decoupled

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

a continental weathering control on orbitally driven redox nutrient cycling during cretaceous oceanic anoxic event 2 the cretaceous period 145 65 m y ago was characterized by intervals of enhanced organic carbon burial associated with increased primary production under greenhouse conditions the global consequences of these perturbations oceanic anoxic events oaes lasted up to 1 m y but short term nutrient and climatic controls on widespread anoxia are poorly understood here we present a high resolution reconstruction of oceanic redox and nutrient cycling as recorded in subtropical shelf sediments from tarfaya morocco spanning the initiation of oae2 iron sulfur systematics and biomarker evidence demonstrate previously undescribed redox cyclicity on orbital time scales from sulfidic to anoxic ferruginous fe rich water column conditions bulk geochemical data and sulfur isotope modeling suggest that ferruginous conditions were not a consequence of nutrient or sulfate limitation despite overall low sulfate concentrations in the proto north atlantic instead fluctuations in the weathering influxes of sulfur and reactive iron linked to a dynamic hydrological cycle likely drove the redox cyclicity despite the potential for elevated phosphorus burial in association with fe oxides under ferruginous conditions on the tarfaya shelf porewater sulfide generation drove extensive phosphorus recycling back to the water column thus maintaining widespread open ocean anoxia

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

pyrolysis induced p wave velocity anisotropy in organic rich shales abstractthe sources of elastic anisotropy in organic rich shale and their relative contribution therein remain poorly understood in the rock physics literature given the importance of organic rich shale as source rocks and unconventional reservoirs it is imperative that a thorough understanding of shale rock physics is developed we made a first attempt at establishing cause and effect relationships between geochemical parameters and microstructure rock physics as organic rich shales thermally mature to minimize auxiliary effects e g mineralogical variations among samples we studied the induced evolution of three pairs of vertical and horizontal shale plugs through dry pyrolysis experiments in lieu of traditional samples from a range of in situ thermal maturities the sensitivity of p wave velocity to pressure showed a significant increase post pyrolysis indicating the development of considerable soft porosity e g microcracks time lapse high resolution backscattered electron scanning electron

fixed recurrence and slip models better predict earthquake behavior than the time and slip predictable models 1 repeating earthquakes 1 the behavior of individual events in repeating earthquake sequences in california taiwan and japan is better predicted by a model with fixed inter event time or fixed slip than it is by the time and slip predictable models for earthquake occurrence given that repeating earthquakes are highly regular in both inter event time and seismic moment the time and slip predictable models seem ideally suited to explain their behavior taken together with evidence from the companion manuscript that shows similar results for laboratory experiments we conclude that the short term predictions of the time and slip predictable models should be rejected in favor of earthquake models that assume either fixed slip or fixed recurrence interval this implies that the elastic rebound model underlying the time and slip predictable models offers no additional value in describing earthquake behavior in an event to event sense but its value in a long term sense cannot be determined these models likely fail because they rely on assumptions that oversimplify the earthquake cycle we note that the time and slip of these events is predicted quite well by fixed slip and fixed recurrence models so in some sense they are time and slip predictable while fixed recurrence and slip models better predict repeating earthquake behavior than the time and slip predictable models we observe a correlation between slip and the preceding recurrence time for many repeating earthquake sequences in parkfield california this correlation is not found in other regions and the sequences with the correlative slip predictable behavior are not distinguishable from nearby earthquake sequences that do not exhibit this behavior

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores