alternative workflow for three dimensional basin modeling in areas of structural complexity case study from the middle magdalena valley colombia basin modeling in structurally complex areas involves several difficulties associated with its geometric and thermal history approaches there have been multiple developments concerning the structural geometry in doing three dimensional 3 d basin modeling in these settings however their applicability is limited because most of these improvements require 3 d structural restorations which is an input that is not always available at basin scale although a traditional basin model using backstripping could give a faster overview of the petroleum system elements it is an alternative method that may distort the structural evolution and consequently the petroleum potential evaluation equally important are the thermal history uncertainties in these environments where several factors disturb the thermal regime despite these difficulties traditional 3 d basin modeling could be a reliable tool when we are able to understand the geometric and thermal histories and implement the proper adjustments we propose alternative methods to tackle common problems when building 3 d basin models and we demonstrate their validity with an example in the middle magdalena valley colombia this hydrocarbon province located in the northern andes corresponds to an intermountain basin that has undergone a complex evolution its structural configuration represents a modeling challenge by means of the backstripping method additionally a high variability exists in the present day basal heat flow related to its structural evolution the result of our model not only fits the calibration data but also reflects the geological processes better the proposed methodology intends to aid basin modelers in providing additional options when modeling in structurally deformed basins

methane leakage from evolving petroleum systems masses rates and inferences for climate feedback abstract the immense mass of organic carbon contained in sedimentary systems currently estimated at 1 56 10 10 tg des marais et al 1992 bears the potential of affecting global climate through the release of thermally or biologically generated methane to the atmosphere here we investigate the potential of naturally occurring gas leakage controlled by petroleum generation and degradation as a forcing mechanism for climate at geologic time scales we addressed the potential methane contributions to the atmosphere during the evolution of petroleum systems in two different petroliferous geological settings the western canada sedimentary basin wcsb and the central graben area of the north sea besides 3d numerical simulation different types of mass balance and theoretical approaches were applied depending on the data available and the processes taking place in each basin in the case of the wcsb we estimate maximum thermogenic methane leakage rates in the order of 10 2 10 3 tg yr and maximum biogenic methane generation rates of 10 2 tg yr in the case of the central graben maximum estimates for thermogenic methane leakage are in the order in 10 3 tg yr extrapolation of our results to a global scale suggests that at least as a single process thermal gas generation in hydrocarbon kitchen areas would not be able to influence climate although it may contribute to a positive feedback conversely only the sudden release of subsurface methane accumulations formed over geologic timescales can possibly allow for petroleum systems to exert an effect on climate

modelling generation and dissipation of overpressure in sedimentary basins an example from the halten terrace offshore norway a pressure simulator modelling the dynamic overpressure history in sedimentary basins is developed using a pressure compartment methodology simple models for porosity reduction are used for controlling pressure generation and different empirical models are used to estimate the lateral and vertical sealing dissipation mechanisms the equations describing the flow of formation water between the pressure compartments are used to calculate the resulting pressure dissipation on a geological time scale the methodology is tested and applied to the jurassic fangst group in the halten terrace area offshore norway dynamic allocation and an explicit numerical solution technique ensure a fast and accurate solution of the flow equations the results suggest a the probable mechanisms and processes that have generated the overpressure b the timing and location of hydraulic fracturing and c the nature and behaviour of the overpressure in addition to the overpressure history

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

incipient subduction and deduction along the eastern margin of the japan sea the eastern margin of the japan sea has been under convergent tectonics since sometime after the pliocene the suture line is on the ocean continent boundary between the japan yamato basins and the tohoku northeast japan arc incipient subduction and obduction of the oceanic and sub oceanic crust are observed along the suture line with the occurrence of numerous n s trending fault bounded ridges and troughs focal mechanism solutions of several compressional type earthquakes with magnitudes of m 6 9 to 7 7 which have occurred along the zone are consistent with the observation of geological thrust faults the convergent stresses in the japan sea may be due to india eurasia collision and its associated intra plate or inter microplate movements in east asia the eastward movement of the amurian plate causes baikal extension along its western margin and the japan sea convergence along its eastern margin

thermal history model for the south central graben north sea derived using both tectonics and maturation abstract the thermal history modelling of basins is essential for petroleum systems analysis the methodology involves the derivation of the heat flow history by calibration using a kinetic model to match the predicted and observed vitrinite reflectance values in wells although this method is almost universally used by basin modellers a simple check using two independent methods with tectonic subsidence history being the second method shows that the thermal histories derived from the subsidence history do not match those predicted by the vitrinite reflectance method for any point in a basin there can only be one thermal history and the derivation of two different thermal histories indicates that there is a problem that has been ignored by geochemists and basin modellers the thermal history must predict the tectonic subsidence history and this heat flow history must also account for the maturation data e g vitrinite reflectance sediments subside under the action of forces and energy e g heat is a function of force during subsidence the downward force exceeds the upward force and the heat flow supplied to the basin must be reduced as the upward force is reduced while force and heat flow must be increased during uplift applying this relationship to the central graben north sea a heat flow history is derived that accounts for the rifting and subsequent subsidence tectonic history of two wells the british 23 26 2z and the danish lulu 1 the vitrinite reflectance predicted by this thermal history and the easy ro kinetic vitrinite reflectance model are higher than the measured values in both wells both wells are overpressured and the problem with the vitrinite reflectance calibration method is that the kinetic parameters used do not correctly account for the retardation produced by pressure le chatelier s principle without the pressure retardation effect incorporated into the kinetic parameters the modeller has to use lower temperatures to simulate retardation using the presro vitrinite reflectance model which incorporates pressure retardation as required by thermodynamics the thermal history derived from the rifting subsidence history can also be used to model the vitrinite reflectance data in the british 23 26 2z and danish lulu 1 wells this method of deriving an unknown e g thermal history using two independent models is widely used in physical sciences as an essential check on any prediction and this scientific rigor has to be followed by geoscientists modelling the thermal history of basins

pore fluid evolution in the kimmeridge clay formation of the uk outer moray firth implications for sandstone diagenesis abstract carbonate concretions in upper jurassic kimmeridge clay formation from three overpressured wells provide a detailed record of pore fluid evolution in the outer moray firth northern central graben the concretions contain multiple generations of septarian cements with morphologies ranging from simple cracks to complex fractures discrepancy exists between diagenetic studies which indicate these concretions formed during the initial 1 1 5 km of burial and palaeotemperature predictions based on a thermal history calibrated from the vitrinite reflectance kinetic model which indicate formation at much greater depths of between 1 5 and 2 5 km modelling undertaken for this study indicate that the concretions formed during the initial stages of burial under high heat flows fitting the early diagenetic model for their formation these conclusions have important implications for understanding the cementation of adjacent sandstone reservoirs where cement sequences have similar mineralogy and isotopic compositions with precipitation in the same temperature range from mudrock derived pore fluids early cementation of these sandstones is implied by analogy with the mudrock concretions

fluorescence alteration and the suppression of vitrinite reflectance abstract vitrinite reflectance is a highly important thermal maturity indicator in petroleum exploration but there are a number of problems in its successful application which are basically the consequence of it being a single parameter technique fluorescence alteration of macerals which can be conveniently measured with the laser raman microprobe is a multi parameter technique which can be used to overcome some of these limitations on a fluorescence alteration diagram most vitrinite plots on or close to a line which may be called the normal vitrinite line fluorescence alteration data for a suite of randomly selected macerals from coal or dispersed organic matter plot along a curve which cuts the normal vitrinite line at the equivalent vitrinite reflectance of the sample as determined by calibration againsta suite of reference coals the technique posseses a high degree of objectivity and can be employed to determine the equivalent vitrinite reflectance of samples in which the vitrinite is difficult to identify or even absent perhydrous vitrinites with suppressed vitrinite reflectance are readily recognized as they plot in a field laterally displaced with respect to the normal vitrinite line the method is exemplified by a study of coals from the greta and pelton seams sydney basin which provides a classic example of vitrinite reflectance suppression and is further illustrated by a study of the dampier 1 well from the north west shelf of australia which contains both perhydrous macerals and dispersed organic matter in which vitrinite is difficult to identify

mirror symmetry of the crust in the oil gas region of shengli china abstract the concept of mirror image symmetry describes the correlation between the bottom of a sedimentary basin and the top of the underlying mantle the degree of mirror symmetry is analyzed here using thickness data from mesozoic cenozoic sedimentary basins and the moho depth with the purpose of investigating the implications for tectonics and exploratory practices in oil gas bearing basins our attention is focused on different tectonic elements of a multi scale tectonic partition in the oil gas region of shengli southeast of bohai bay china by applying standard least squares analysis methods to both datasets we obtained the average thickness h of the consolidated crust and the mirror symmetry factor a for every tectonic unit thereby allowing us to explore the correlation between the bottom depth of a sedimentary basin and the top of the underlying mantle a detailed analysis of data uncertainties and their potential effects led to small fluctuations of h and a within a narrow band around the mean values of 33 26 km and 1 43 respectively thus the results can be considered valid if they are constrained by these error bounds the issues of crust mantle interaction and the deviation of the crust from isostatic equilibrium are also addressed for their tectonic implications other structural parameters related to the deep rooted crust beneath the tectonic elements that make up the study region such as the ratio r of the thickness of the consolidated crust to the absolute value of the symmetry factor the ratio k of the maximum sediment thickness to the maximum uplift of the mantle and the product kh are also evaluated for their implications in geophysical prospecting the symmetry signature of the crust is compared to the symmetry of other sedimentary basins in china and in the world suggesting symmetry as a feasible prognostic tool in exploration for oil gas reservoirs the key result is that those locations where oil gas reservoirs have been found to date are basins in which the crust mantle interaction is active and the crust is isostatically compensated both of those parameters can be quantitatively constrained conversely oil and gas reserves are poor or nonexistent in regions where the crust mantle interaction is inactive and the crust is far from isostatic equilibrium however an intermediate case between these two extreme scenarios wherein the crust mantle interaction is rather moderate but the crust is in a state close to isostasy cannot be entirely ruled out

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

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

elastic anisotropy of source rocks implications for hydrocarbon generation and primary migration we combined acoustic velocities and anisotropy measurements with x ray diffraction mineralogy rock eval organic geochemical analyses vitrinite reflectance and scanning electron microscope observations on 69 cores of hydrocarbon source rocks collected from eight sedimentary basins the velocity data indicate the lamellar distribution of solid organic matter kerogen in compacted black shales and show a strong correlation between their elastic anisotropy and organic richness the experimental results are consistent with the two component anisotropic model of black shales with a continuous kerogen network in both bedding parallel and bedding normal directions beginning from relatively low toc values the strong elastic anisotropy of tight thermally mature source rocks i further enhanced by overpressure induced bedding subparallel microcrack development during the main stage of hydrocarbon hc generation and primary migration at r0 greater than 0 75 in agreement with published petrographic observations these microcracks significantly aid primary hc migration particularly horizontally elastic anisotropy of medium to high porosity illite smectite shales is weaker than in lower porosity predominantly illite shales however the overall positive trend of elastic anisotropy with kerogen content remains unchanged

estimates of virgin rock temperature derived from bht measurements bias and error virgin rock temperatures are important to hydrocarbon exploration as these temperatures are necessary for the computation of source rock temperatures and for hydrocarbon generation computations several methods have been developed for determination of virgin rock temperatures from maximum temperatures recorded during logging in the past decades this paper describes an investigation where the calculated virgin rock temperatures from several different methods were examined for bias and accuracy using 18 different measurement series at the oseberg field the temperatures were corrected for different depths of burial and then compared with each other and with drill stem test dst measurements to investigate the inaccuracy of the methods the most advanced methods gave values close to the dst temperatures on average but with standard deviations as high as 9 degrees c the less advanced models like the horner plot method have systematically too low virgin rock temperatures by about 8 degrees c for the oseberg field with standard deviations of 8 degrees c the errors in calculated virgin rock temperatures are large enough to completely alter predictions of hydrocarbon generation in an area the large errors are attributed to poor quality data and to physical effects that are not properly taken into account in the temperature calculations improved sampling of temperature data can probably reduce the errors to some extent

should fluorescence alteration replace vitrinite reflectance as a major tool for thermal maturity determination in oil exploration abstract the fluorescence alteration multiple macerals famm technique is closely related to vitrinite reflectance until recently fluorescence alteration study of dispersed organic matter dom in sedimentary rocks has been regarded as technically difficult with the introduction of optical microprobes equipped with small continuous wave gas lasers having a very stable output of blue radiation readily focused to 1 2 m on the sample this work has now become routine famm has important advantages over vitrinite reflectance stemming from the possibility of resolving the data into two parameters one related to the level of maturation and the other related to the hydrogen richness of a maceral this enables the resolution of what are often difficult problems for the single parameter vitrinite reflectance technique namely the identification of indigenous vitrinite in dom the recognition of caved and reworked organic matter and the suppression of vitrinite reflectance for these reasons famm is a powerful tool for investigating vitrinite reflectance anomalies especially those associated with unconformities it is also well suited to investigate the tacit assumption in the vitrinite reflectance technique that all telocollinite matures along a single compositional pathway the famm technique is not without problems the range is restricted to equivalent mean random vitrinite reflectance rm o 0 4 1 2 the results are more sensitive to ambient temperature oxidation than vitrinite reflectance and the technique demands a high level of technical expertise the famm technique is calibrated on coals and it is therefore more likely to give high quality results on types ii and iii kerogens rather than type i kerogens which have not yet been intensively investigated although famm is unlikely to replace vitrinite reflectance considerable confidence may be had in a maturation assessment when consistent results are obtained from these two closely related but independent techniques

burial and exhumation history of the galilee basin australia implications for unconventional hydrocarbon prospectivity this multidisciplinary study describes the burial and exhumation history of the frontier galilee basin in central queensland australia with implications for understanding its geohistory and unconventional gas prospectivity seismic interpretation stratigraphic mapping and an analysis of exhumation through quantifying overcompaction show total subsidence of approximately 2 km 6600 ft from the carboniferous to the late cretaceous punctuated by two major exhumation events triassic exhumation was less than 600 m 1970 ft whereas late cretaceous exhumation was in the order of 1000 m 3300 ft increasing eastward to greater than 1600 m 5250 ft geohistory reconstructions show that permian coal measures generated up to 45 m3 t 1590 ft3 t of gas when modeled temperatures exceeded 100 c 210 f during maximum burial of 1 5 2 km 4920 6560 ft in the late cretaceous in the carboniferous to the mid cretaceous the basin was situated to the west of the eastern australian subduction zone where proto pacific oceanic lithosphere was subducted until circa 100 ma when subduction ceased our study shows that the geohistory of the basin is characterized by rapid subsidence of 50 m m y 165 ft m y followed by rebound at circa 95 ma resulting in an uplift and erosion phase the undersaturation of the coals at present day is explained by this uplift event carbon isotopes indicate that the remaining gas 8 m3 t 280 ft3 t is of mixed biogenic and thermogenic origin therefore dynamic surface topography driven by subduction dynamics and slab breakoff had a profound effect on the subsidence uplift and resource potential of the galilee basin

semi periodic sequences and extraneous events in earthquake forecasting ii application forecasts for japan and venezuela in order to analyze observed seismicity in central japan and venezuela we applied a new method to identify semi periodic sequences in the occurrence times of large earthquakes which allows for the presence of multiple periodic sequences and or events not belonging to any sequence in the time series we also explored a scheme for diminishing the effects of a sharp cutoff magnitude threshold in selecting the events to analyze a main four event sequence with probability p c 0 991 of not having occurred by chance was identified for earthquakes with m 8 0 in central japan venezuela is divided from west to east into four regions for each of these the magnitude ranges and identified sequences are as follows region 1 m 6 0 a six event sequence with p c 0 923 and a four event sequence with p c 0 706 region 2 m 5 6 a five event sequence with p c 0 942 region 3 m 5 6 a four event sequence with p c 0 882 region 4 m 6 0 a five event sequence with p c 0 891 forecasts are made and evaluated for all identified sequences having four or more events and probabilities 0 5 the last event of all these sequences was satisfactorily aftcast by previous events whether the identified sequences do in fact correspond to physical processes resulting in semi periodic seismicity is of course an open question but the forecasts properly used may be useful as a factor in seismic hazard estimation

hydraulic fracturing stress measurements and in situ stress field in the kanto tokai area japan abstract hydraulic fracturing stress measurements have been made in fifteen boreholes of various depths from 100 to 800 m in the kanto tokai area since 1978 about 90 sets of in situ stresses have been obtained successfully the maximum and minimum horizontal compressive stresses increase linearly with depth in each borehole the difference between the maximum and minimum principal stresses also increases with depth the increase of stress difference with depth is interpreted in terms of large stress relaxation in shallow parts of the boreholes where low confining pressure and many pre existing microcracks are dominant the maximum shear stress at a depth of 400 m ranges from 1 to 8 mpa depending on the site it is not always the case that the regions of small shear stresses are inactive in microseismicity and crustal movement this phenomenon is attributed to the relaxation of shear stress at the measured depths and to the regional variation in increasing rate of shear stress the maximum compressive stress direction is obtained from detection of the fracture azimuth after hydraulic fracturing stress direction measured at each borehole agrees well with that estimated from geologic and seismic methods near the measurement site several stress provinces where the stress directions appear almost uniform are defined in the kanto tokai area the regional distribution of the stress directions is understood in terms of the relative movement of three plates the philippine sea pacific and eurasian plates which are in contact with each other in this area

forecast of large earthquakes through semi periodicity analysis of labeled point processes large earthquakes have semi periodic behavior as a result of critically self organized processes of stress accumulation and release in seismogenic regions hence large earthquakes in a given region constitute semi periodic sequences with recurrence times varying slightly from periodicity in previous papers it has been shown that it is possible to identify these sequences through fourier analysis of the occurrence time series of large earthquakes from a given region by realizing that not all earthquakes in the region need belong to the same sequence since there can be more than one process of stress accumulation and release in the region sequence identification can be used to forecast earthquake occurrence with well determined confidence bounds this paper presents improvements on the above mentioned sequence identification and forecasting method the influence of earthquake size on the spectral analysis and its importance in semi periodic events identification are considered which means that earthquake occurrence times are treated as a labeled point process a revised estimation of non randomness probability is used a better estimation of appropriate upper limit uncertainties to use in forecasts is introduced and the use of bayesian analysis to evaluate the posterior forecast performance is applied this improved method was successfully tested on synthetic data and subsequently applied to real data from some specific regions as an example of application we show the analysis of data from the northeastern japan arc region in which one semi periodic sequence of four earthquakes with m 8 0 having high non randomness probability was identified we compare the results of this analysis with those of the unlabeled point process analysis

geology and geothermal origin of grant canyon and bacon flat oil fields railroad valley nevada eastern nevada s grant canyon and bacon flat oil fields show strong evidence of formation in a still active moderate temperature geothermal system modern manifestations of this system include unusually elevated oil reservoir temperature at shallow depth 116 122 c at 1 1 1 6 km and dilute na hco3 cl thermal waters directly associated with hot oil hydrogen and oxygen isotopic compositions indicate that these thermal waters are meteoric in origin but were probably recharged prior to the holocene before 10 ka the waters apparently ascended to oil reservoir elevations after deep heating in response to the normal regional thermal gradient there is no evidence for a modern magmatic heat source the beginning of oil reservoir evolution at both fields is recorded by late stage fracture filling quartz in the vuggy brecciated paleozoic dolostone reservoir rocks oil and aqueous solutions were trapped as fluid inclusions in the quartz at temperatures comparable to those now prevailing in the reservoirs apparent salinities of the aqueous inclusions closely match the actual concentrations of current oil field waters and the quartz has the oxygen isotopic composition predicted for its crystallization from these waters at contemporary temperatures present day and fluid inclusion temperatures define essentially coincident isothermal profiles through and beneath the oil reservoir interval a phenomenon consistent with near constant convective heat transfer since inception of the eothermal system textural and mineralogic clues indicate that hot waters circulating in this system also increased porosity by dissolving carbonate minerals and helped seal reservoir margins by precipitating silica and kaolin more importantly the rising thermal waters may have aided oil transport and accelerated source rock maturation through an increase in the shallow 3 km local thermal budget along with the aforementioned fluid inclusion and isotopic evidence radiometrically dated life spans for numerous extinct geothermal systems epithermal ore deposits in the basin and range make it likely that the grant canyon bacon flat system and associated oil reservoirs are no older than 2 5 ma

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

correction criteria for the suppression of vitrinite reflectance in hydrogen rich kerogens preliminary guidelines abstract thermal maturity is an important factor when assessing the petroleum potential of a basin or particular source rocks although the vitrinite reflectance vr technique provides excellent results from coal samples it has limitations when source rocks are used one problem is the anomalously low vrs the suppression of vr vr suppression in hydrogen rich kerogens the anomalously low suppressed vrs discussed in this article are mainly caused by the problems that organic petrographers encounter in finding and measuring appropriate vitrinite particles in hydrogen rich kerogens vr suppression is recognized when lower than normal vrs are measured on exinite rich or amorphous rich intervals in a vr well profile vr vs depth it can also be recognized when anomalously low vrs relative to the regional coalification maturation pattern or to regional oil gas occurrences are encountered in an interval although vr suppression in organic rich rocks coals and oil shales is well documented guidelines for its correction are lacking a preliminary model fig 1 is presented to help correct the vr suppression in hydrogen rich kerogens measured suppressed vr in r o along with original when immature hydrogen index hio estimated via rock eval pyrolysis and or organic petrography data of a sample can be used to estimate the maximum true unsuppressed vr although the vr and hio data for an individual sample is sufficient to estimate the maximum true vr we recommend the use of data from several closely spaced samples the model was tested with examples from published data and found to reasonably correct vr suppression in hydrogen rich kerogens we plan to refine the model using data from rock samples suppressed unsuppressed pairs and pyrolysis data

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

basin modelling how well have we done model developers have been highly successful in building usable useful and reliable one dimensional models and in convincing explorationists to use them development of convenient universal software played an instrumental role in the acceptance of 1 d modelling the remaining weaknesses in technology and training while serious can be resolved through a few years of intensive work in certain specific areas 2 d and 3 d fluid flow modelling in contrast finds itself today largely in the position occupied by 1 d modelling more than a decade ago the concept of fluid flow modelling has not yet been adequately sold to explorationists mainly because existing software is often inadequate to meet the real needs of exploration personnel development of appropriate software will probably have to precede widespread popularization of fluid flow modelling to improve existing software two major areas must be addressed 1 making models more comprehensive by including all relevant geologic phenomena and 2 making software easier to use