the upper limit of maturity of natural gas generation and its implication for the yacheng formation in the qiongdongnan basin china abstract vitrinite reflectance vr ro measurements from residual kerogen of pyrolysis experiments were performed on immature maoming oil shale substituted the samples for the gas prone source rocks of yacheng formation of the qiongdongnan basin in the south china sea the work was focused on determination an upper limit of maturity for gas generation ulmgg or the deadline of natural gas generation ro values at given temperatures increase with increasing temperature and prolonged heating time but ro value given a definition of the difference of all values for vr related to higher temperature and adjacent lower temperature in open system non isothermal experiment at the heating rate of 20 c min is better than vr and representative examples are presented in this paper it indicates that the range of natural gas generation for ro in the main gas generation period is from 0 96 to 2 74 in which ro is in concordance with the stage for the onset and end of the main gas generation period corresponding to 0 02 up to 0 30 and from 0 30 up to 0 80 respectively after the main gas generation period of 0 96 2 74 the evolution of vr approach to the ulmgg of the whole rock for type ii kerogen it is equal to 4 38 of vr where the gas generation rates change little with the increase of maturation ro is the maximum of 0 83 corresponding to vr of 4 38 ro and the source rock does not nearly occur in the end process of hydrocarbon gas generation while ro is over 4 38 it shows that it is the same the ulmgg from the whole rock for type ii kerogen as the method with both comparison and kinetics by comparing to both the conclusions of pyrolysis experiments and the data of vr from the source rock of yacheng formation on a series of selected eight wells in the shallow water continental shelf area it indicate that the most hydrocarbon source rock is still far from reaching ulmgg from the whole rock for type ii kerogen the source rock of yacheng formation in the local areas of the deepwater continental slope basin have still preferable natural gas generative potential especially in the local along the central depression belt namely the ledong lingshui songnan and baodao sags from southwest to northeast from the depocenter to both the margin and its adjacent areas it help to evaluate the resource potential for oil and gas of the hydrocarbon source rock in the deepwater continental slope of the qiongdongnan basin or other basins with lower exploration in the northern of the south china sea and to reduce the risk in exploration

reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

organic matter maturity in northern italy some determining agents abstract in previous agip studies concerning the origin of oil in northern italy thematurity evolution of the source rocks beneath a thrust plate and the anomalous depth trends of maturity parameters were exained this paper focuses on the possible effects of different thermal histories and of high pressure on the catagenesis of kerogen the effects of overthrusting on the degree of maturity of source rocks is investigating in two areas of the northern apennines near the cortemaggiore oil and gas field and ponte del olio no 1 well respectively the model by angevine and turcotte is used for reconstructionof the temperature evolution and that by tissot and espitalie to model the hydrocarbon generation in addition it was examined how different thermal histories affect the oil to gas ratio computed according to tissot espitalie the results for sediments beneath thrust plates which are subjected to rapid increases in temperature are compared to those typical of regularly subsiding basin in the po basin intervals of abnormally pressured sediments were drilled in the lombardy area the organic matter appears immature in early jurassic and late triassic sediments at depth even down to 6000 m as recognized by different maturity parameters possible causes for the low maturity levels of the organic matter are examined with particular emphasis on the effects of high pressures

role of overpressures and in situ stresses in fault controlled hydrocarbon migration a case study abstract two wells no 1 and no 2 separated by 2 km and situated in the upper prospective zone of a tertiary basin in south east asiat cross the same mio pleistocene shaly sandy series from 1500 m downwards these series are subject to significant overpressures related to an active margin comparison of well data in terms of sonic compaction profiles anomalous pressures and temperatures has provided evidence of both a positive pressure and a temperature anomaly below a vertical depth of 1800 m in well 2 this anomaly is closely associated with the presence of liquid hydrocarbons in the 1900 2000 m reservoir interval the confirmed deep source of these fluids and the amounts that have migrated during a short time interval can be explained only by the transitory dynamics of active transfers along faults and fractures the episodic nature of this movement is the result of hydromechanical mechanisms in which the interactions between the high pressure regime and principal in situ stresses appear to be fundamental the processes which induce open faulting and fluid pressure build up in the direction of reservoirs with lower pressure regimes occur preferentially during phases of lateral tectonic stress relaxation as soon as the effective minimum stress component becomes negative the analysis of this case study gives a better understanding of the dynamic phenomena involving secondary hydrocarbon migration and caprock efficiency the results obtained will help to optimize the overpressure prediction approach in comparable geological contexts

a two dimensional model of overpressure development and gas accumulation in venture field eastern canada 1 we used a basin scale model to reconstruct the development of overpressures in a sedimentary basin the area of application is the venture gas field nova scotia canada it is in an overpressured zone in which sedimentation rates have been relatively low since 90 ma and where large horizontal stresses have been evidenced we investigated the importance of overpressure mechanisms using the institut francais du petrole temispack model which integrates compaction hydraulic fracturing fluid flow heat transfer and the formation and migration of hydrocarbons we first constructed a reference model using geological geochemical and physical data second we studied sensitivity of the model to several input parameters and from this deduced additional constraints the modeled permeability along faults and of shaly beds interlayered in the reservoirs must be very low to enable both the local and regional distributions of overpressure and gas to be reproduced several runs of the reference model studying the relative importance of possible overpressuring mechanisms and the relative contribution of plausible source rocks to gas accumulations showed that gas generation and accumulation and lateral compression contribute little to overpressuring which is mainly accounted for by compaction disequilibrium in spite of low sedimentation rates faults and shaly beds play an important role in maintaining the overpressure gas generation in the reservoir units or close to them does not contribute significantly to the field gas accumulations gas sources are likely to be found in the underlying formations

quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

are time and temperature the only constraints to the simulation of organic matter maturation abstract confined pyrolysis hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples toarcian shale and kerogen woodford shale and kerogen manakam coal and under different experimental conditions in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter results show that i experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models ii increasing confining pressure 300 1300 bars in gold cell experiments performed on woodford samples has a limited influence on the reduction rate of the oil potential the tsom total soluble organic matter yield and the structure of the polars iii the presence of excess liquid water 0 100 weight in confined pyrolysis experiments does not significantly influence organic matter maturation however comparisons with classic hydrous pyrolysis 200 weight water could indicate major differences in timing and composition of the tsom bitumen expelled fraction as well as of the solid residue it appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined hydrous pyrolysis conditions low partial pressure of products delay woodford kerogen conversion in addition results concerning the mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect iv increasing water pressure in hydrous conditions 220 1300 bars drastically lowers and delays woodford kerogen maturation quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis this study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation

oil and gas developments in western canada in 1989 there were 5513 wells drilled in western canada during 1989 30 fewer than in 1988 total meterage drilled was 6 459 797 m for an average well depth of 1172 m exploratory drilling in 1989 dropped by 13 and development drilling by 40 from 1988 levels british columbia was the only area in western canada with increased activity the industry continued to acquire more acreage for less total bonus at provincial crown sales throughout western canada during 1989 3 564 827 ha were acquired for a total bonus of 484 872 000 footnote 5 although the total disposition of crown lands decreased only 4 the average bonus dropped to 136 ha down 26 from 1988 in alberta the most active exploration areas were the southern and eastern mesozoic gas play the western deep devonian gas play the oil plays on and adjacent to the peace river arch and the middle devonian carbonate oil plays in the northwest in british columbia the most active exploration areas were the mesozoic and paleozoic gas plays in the northeastern portion of the province for the first time in 5 years crown drilling rights were issued within the fraser valley in the southwest there was a focus on gas exploration in the province as pipeline reversal was implemented permitting access to canadian and california markets through the alberta transportation network in manitoba exploration and development activity continued to decline in northern canada exploratory drilling success offering of crown lands for exploration approval of gas exports and indications that many of the native lands claims may be approaching settlement all provided exploration encouragement for the next decade exploration activities occurred throughout the northwest territories from the offshore beaufort to the southern border in saskatchewan active exploration areas were shallow mesozoic gas plays in the western portions of the province and deep paleozoic oil plays in the south

hydrocarbon generation and migration from jurassic source rocks in the e shetland basin and viking graben of the northern north sea in the e shetland basin oil generation began 65 ma ago peak oil generation maturity occurs today at 3250 m 0 7 r 0 and was first reached 40 50 ma ago the oil generation threshold is at 2500 m highest oil saturations in the kimmeridge clay occur at 0 8 r 0 oil expulsion efficiencies are 20 30 oil phase migration has probably occurred through oil wet kerogen laminae and through interconnected large pores aided by low oil water interfacial tensions oil migrated along strong lateral fluid pressure gradients from overpressured source rocks in half grabens to jurassic reservoirs in tilted fault blocks in the viking graben the kimmeridge clay is at oil floor maturity below 4500 m oil and peak oil generation began 7c 80 and 55 65 ma ago respectively 40 ma ago the kimmeridge clay passed through peak generation and gas generation by cracking of oil had begun peak dry gas generation from brent coals occurs today below 5000 m and began 40 ma ago the frigg field gas probably generated from late jurassic source rocks migrated through microfractures in overpressured mudstones below 3500 m above 3500 m methane probably migrated in aqueous solution and was exsolved in the early tertiary aquifer

the faroe shetland basin a regional perspective from the paleocene to the present day and its relationship to the opening of the north atlantic ocean the faroe shetland basin is located offshore nw scotland on the se margin of the atlantic ocean and comprises numerous sub basins and intra basin highs that are host to a number of significant hydrocarbon discoveries the principal hydrocarbon discoveries are in palaeocene eocene strata though earlier ones are known and therefore their existence is intimately linked to the opening and evolution of the north atlantic from 54 ma the final rifting and separation of greenland from eurasia is commonly attributed to the arrival of a mantle plume which impacted beneath greenland in the early tertiary moreover the ensuing plate separation is commonly described in terms of instantaneous unzipping of the north atlantic whereas in reality proto plate boundaries were more diffuse during their inception and the linked rift system including connections with the arctic which we see today was not established until late palaeogene early neogene time from a regional analysis of ocean basin development including the stratigraphic record on the adjacent continental margins the significance of the greenland iceland faroe ridge and the age and role of iceland we propose a dual rift model whereby north atlantic breakup was only partial until the oligo miocene with true final breakup only being achieved when the reykjanes and kolbeinsey ridges became linked as final breakup coincides with the appearance of iceland this model negates the need for a plume to develop the north atlantic with rifting reliant on purely plate tectonic mechanisms lithospheric thinning and variable decompressive upper mantle melt along the rifts

some pragmatic perspectives in source rock geochemistry abstract conceptual advances in petroleum source rock geochemistry made during the last decade are reviewed and some problem areas in analytical geochemistry are outlined areas of discussion include views of source rocks based on assessment of hydrocarbon expulsion kinetic models of kerogen maturation vitrinite reflectance evolution and a discussion of the data dilemma facing modern source rock geochemistry the increased application of petroleum geochemistry to the quantitative solution of geological problems is stressed

an examination of the formation of linear lee waves generated by giant martian volcanoes abstract the vertical wave displacement generated by a martian volcano at heights comparable with and above the altitude of the topography is investigated in this paper an examination is made of the leakage of this displacement into atmospheric heights well above the topography and consideration is given to two large martian volcanoes olympus mons and ascraeus mons viking orbiter imagery portraying wave clouds in the vicinity of these volcanoes is compared with theoretical results obtained by considering a simple one layer atmosphere in which the ratio of the stability factor to the square of the atmospheric velocity profile is deemed to be constant at all vertical levels it is found that a wave plume phenomenon is predicted by this theory and by comparing with visual observations information can be deduced as to the atmospheric mean structure of velocity and stability when these cloud formations occur

an interlaboratory comparison of vitrinite reflectance measurement a vitrinite reflectance vr round robin analysis was undertaken by the society for organic petrology tsop research committee fourteen laboratories from five countries participated in the study which involved samples of one shale and three coals ranging in rank maturity from lignite to high volatile a bituminous the main objective was to evaluate interlaboratory comparability and accuracy of vr measurements in a context of practical data interpretation e g maturity determination of petroleum source rocks the between laboratory standard deviations x of the vr data are 0 033 0 048 for mean random and 0 037 0 049 for mean maximum measurements the results suggest that at a moderate level of confidence 68 assuming normally distributed populations a vr differential of 0 1 is significant in indicating different thermal maturities within the rank range studied a differential of 0 2 vr is required if a high level 95 of confidence is desired at the 5 significance level between laboratory consistency tests h statistic show that the random vr data of one out of fourteen laboratories for each sample are found to be inconsistent with the main population whereas the other thirteen laboratories are consistent with each other the maximum vr data are shown to be consistent at the same significance level of 5 except for one data point the within laboratory standard deviations are relatively high from 0 023 to 0 110 with an average ranging from 0 037 to 0 070 the relatively high is likely related to natural variations in the vitrinite macreal which can result in the inconsistent selection of vitrinite particles for measurements by the operators maximum vr measurements are found to give rise consistently to slightly higher interlaboratory and average within laboratory standard deviations compared to those of corresponding random vr results this may be related to experimental errors introduced during maximum vr analyses e g imperfect focusing of the sample and centering of the stage however this observation by no means suggests that random analysis is a more precise measurement

impact of high water pressure on oil generation and maturation in kimmeridge clay and monterey source rocks implications for petroleum retention and gas generation in shale gas systems this study presents results for pyrolysis experiments conducted on immature type ii and iis source rocks kimmeridge clay dorset uk and monterey shale california usa respectively to investigate the impact of high water pressure on source rock maturation and petroleum oil and gas generation using a 25 ml hastalloy vessel the source rocks were pyrolysed at low 180 and 245 bar and high 500 700 and 900 bar water pressure hydrous conditions at 350 c and 380 c for between 6 and 24 h for the kimmeridge clay kcf at 350 c rock eval hi of the pyrolysed rock residues were 30 44 mg g higher between 6 h and 12 h at 900 bar than at 180 bar also at 350 c for 24 h the gas expelled oil and vitrinite reflectance vr were all reduced by 46 61 and 0 25 ro respectively at 900 bar compared with 180 bar at 380 c the retardation effect of pressure on the kcf was less significant for gas generation however oil yield and vr were reduced by 47 and 0 3 ro respectively and rock eval hi was also higher by 28 mg g at 900 bar compared with 245 bar at 12 h the huge decrease in gas and oil yields and the vr observed with an increase in water pressure at 350 c for 24 h and 380 c for 12 h maximum oil generation were also observed for all other times and temperatures investigated for the kcf and the monterey shale this shows that high water pressure significantly retards petroleum generation and source rock maturation the retardation of oil generation and expulsion resulted in significant amounts of bitumen and oil being retained in the rocks pyrolysed at high pressures suggesting that pressure is a possible mechanism for retaining petroleum bitumen and oil in source rocks this retention of petroleum within the rock provides a mechanism for oil prone source rocks to become potential shale gas reservoirs the implications from this study are that in geological basins pressure temperature and time will all exert significant control on the extent of petroleum generation and source rock maturation for type ii source rocks and that the petroleum retained in the rocks at high pressures may explain in part why oil prone source rocks contain the most prolific shale gas resources

kinetic models of vitrinite kerogen and bitumen reflectance abstract vitrinite reflectance is perhaps the most widely used property to calibrate paleothermal histories and the most common model for that purpose is easy ro this paper reviews the origin of easy ro as a simplification of vitrimat weaknesses of the original versions are discussed as are historical attempts to improve them new versions of vitrimat and easy ro are presented that use substantially higher frequency factors and activation energies and variations of these versions are derived for vitrinite itself and hydrogen rich macerals and bitumen the vitrimat models are based on the original premise that reflectance correlates primarily with h c ratio and secondarily with o c ratio with this approach the reflectance of different types of organic matter is automatically calculated based on the initial composition of that organic matter this general approach may also serve as a pathway with appropriate cross reaction terms to calculate suppression of true vitrinite reflectance matured in oil prone rocks containing significant concentrations of liptinite

geology and diagenetic history of overpressured sandstone reservoirs venture gas field offshore nova scotia canada deep exploratory wells in the scotian basin offshore nova scotia canada have encountered overpressured formations with pressures 1 9 x the normal hydrostatic gradient the overpressures occur over an area of approximately 10 000 sq km in the venture field the abnormal pressures are confined below a depth of 4500 m and are associated with upper jurassic lower cretaceous gas and condensate bearing sandstone reservoirs the overpressures occur within normally compacted shales containing numerous overpressured sandstone reservoir beds the development of overpressures seals and secondary reservoirs are all diagenetically driven the volumetric increase achieved by kerogen to petroleum gas conversion and hydrocarbon expulsion are believed to be the main driving forces or venture overpressures three secondary porosity depth levels which top at 2500 m 65 degrees c 3700 m 95 degrees c and 4600 m 130 degrees c correlate with major steps in the organic matter maturation in the basin secondary porosity is initially achieved by alumosilicate dissolution with ferroan sparry calcite cement dissolution dominating below 4000 m porosity enhancement and preservation is not the result of a single diagenetic event but instead the result of a series of diagenetic events that overlapped in time formation of dynamic diagenetic barriers within the zone of peak gas generation helps retard the diffusive migration of hydrocarbons and other fluids expelled during shale diagenesis resulting in pressure build up the preservation of up to 32 percent porosity under 500 1000 atm of pressure could not be achieved without simultaneous pressuring of developing voids thus the expansion of secondary reservoirs in the overpressured zone also had to be late 50 ma or younger and about synchronous with pressurizing of the reservoirs significant for hydrocarbon exploration is that venture type diagenetic overpressures are not associated with undercompacted sediments and hence they cannot be predicted from compaction trends during drilling petrographic diagenetic and lithofacies studies can be instrumental in predicting potential areas of deep subsurface secondary reservoirs development

some observational constraints on the global scale wind systems of mars wind direction measurements from a variety of indicators taken over several mars years and covering the entire planet have been collected these include observations of lee wave clouds not previously studied the data exhibit a high degree of consistency and seasonal reproducibility making it possible to interpret most of the observations in terms of the zonally symmetric circulation of mars we examine these data in the context of the constraints the observed wind directions place upon the thermal and polar cap mass flux fields which force the flows within the limitations of the data set mid and high latitude winds appear to be controlled by the thermal field during mid and late summer and winter and in the northern hemisphere during early spring and early summer at other times the cap flows dominate at high latitudes the strongest yearly winds are probably generated by cap formation in the north and cap recession in the south the hemispheric asymmetry seems to result primarily from the effects of global dust storms on the north polar cap turning of the prograde wind from poleward to equatorward in midautumn is observed consistent with reduced poleward mass flux and increased meridional temperature gradient at that time the latitudinal extent of the equatorial hadley cell when observed is probably larger than that predicted by nearly inviscid models of low latitude circulation the cross equational hadley cell and high latitude poleward flows which occur in both hemispheres during the summer seasons may set additional constraints on the thermal forcing mechanisms at these times

an investigation of the in reservoir conversion of oil to gas compositional and kinetic findings from closed system programmed temperature pyrolysis abstract the thermal alteration of reservoired petroleum upon burial was simulated by closed system non isothermal pyrolysis samples of a medium gravity oil from the norwegian north sea central graben were pyrolysed in microscale sealed glass or quartz vessels at heating rates of 0 1 0 7 and 5 0 k min 1 up to temperatures varying from 300 to 650 c the composition of the oil and gas in each vessel was determined by a single step on line gas chromatographic analysis with increasing rate of heating the onset of all oil degradation reactions was shifted to higher temperatures the same successive compositional changes occurred in each case increase in the total yield of gc detectable compounds significant gas c1 c4 generation accompanied by a decrease in yield of heavy components aromatisation and attainment of maximum gas yield and finally a cracking of the c2 gas components the stable final mixture consisted of methane aromatic hydrocarbons pyrobitumen and possibly hydrogen kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal mol assigning 35 of the total gas potential 460 mg per g of oil to an energy of 66 kcal mol and 29 to 67 kcal mol pre exponential factor 1 1 1016 s 1 by extrapolation to natural maturation conditions the onset of gas generation is predicted to occur between 160 and 190 c for geological heating rates between 0 53 and 5 3 k ma 1 predictions from the model are in accordance with the observed preservation of liquid hydrocarbons in a deep hot 165 c petroleum reservoir from the saga 2 4 14 well norwegian continental shelf

a vitrinite reflectance kinetic model incorporating overpressure retardation abstract the models currently used to predict maturation and hydrocarbon generation in petroleum basins use time and temperature as controlling parameters a small number of studies have indicated that overpressure can retard maturation although some of the published information from experimental investigations appears to be conflicting careful examination of the experimental conditions shows that both vitrinite reflectance and hydrocarbon generation are retarded by overpressures overpressure appears to result in the retention of volatiles within the molecular structure which prevents the molecular reorganisation necessary to produce higher reflectance values using a database containing vitrinite reflectance from both overpressured and normally pressured wells a kinetic model presro has been developed in which overpressure modifies the arrhenius a factor the model has been tested on two different basins south china sea and sable exhibiting a range of time temperature overpressure characteristics the results suggest that the maturity and timing of the onset of hydrocarbon generation differ significantly from those predicted by current models

the application of famm fluorescence alteration of multiple macerals analyses for evaluating rank of parana basin coals brazil abstract combining vitrinite reflectance vr and fluorescence alteration of multiple macerals famm analyses provide insights into the chemical nature of vitrinites i e perhydrous vs orthohydrous vs subhydrous compositions in permian gondwana coals of the parana basin brazil the famm derived equivalent vr eqvr values and relationships with vr can be determined according to calibration curves based largely on permian gondwana coals of eastern australia the analytical results indicate that vitrinites in the parana basin coals studied generally range from orthohydrous to perhydrous with interpreted vr suppression ranging up to 0 2 absolute for the most perhydrous case the eqvr values of the santa catarina coals which range from about 0 85 to 0 95 differ from vr values by about 0 10 0 15 absolute potentially having significant implications on coal utilization the causes of vitrinite reflectance suppression in the parana basin coals are as yet poorly understood but are likely to be related to a combination of factors

geopressure evolution hydrocarbon generation and migration in the beaufort mackenzie basin canada results from two dimensional quantitative modelling abstract three cross sections of onshore and offshore areas of the beaufort mackenzie basin were used to simulate geopressure evolution hydrocarbon generation and migration processes of the tertiary section using a two dimensional model two analytical approaches were used 1 adjusting geological geophysical and geochemical parameters to obtain the best fit between the model results and regional geological data in a one dimensional manner and 2 reconstructing the basin evolutionary history in a two dimensional manner the model results indicate that the present day distributions of geopressure and maturity levels at different locations have been modified by late miocene uplift and erosion followed by rapid deposition of the late miocene pleistocene lperk sediments although the occurrence of oil and gas has no obvious relationship to geopressure at the present day the evolution of geopressure in strata older than the mackenzie sequence plays an important part in the maturation of tertiary source rocks geopressure in these older formations caused an increase in thermal gradient and porosity in the deep formations the analysis indicates that the timing of hydrocarbon generation and the evolution of geopressure are critical factors in the development of horizontal migration reindeer reservoirs versus vertical migration kugmallit reservoirs

geopressured jurassic reservoirs in the viking graben modelling and geological significance abstract formation pressure data from jurassic and triassic reservoirs of 192 wells 68 in the norwegian sector 124 in the uk sector in the viking graben have been analysed several different pressure regimes are distinguished an open system consists of hydropressured reservoirs adjacent to the east shetland platform in the west and the horda platform in the east a restricted system consists of moderately geopressured reservoirs overpressure typically lower than 1500 psi located at greater distance from the platforms and is interpreted to be in partial pressure communication with the open system through lateral or vertical pressure drainage a closed system consists of geopressured reservoirs practically isolated from the open system in this system formation pressure is assumed to be representative of the various overpressuring mechanisms active locally pressure data analysis suggests that pore pressure is mainly controlled by rapid loading aquathermal pressuring oil generation and possibly by shale dewatering above the depth for the onset of gas generation formation overpressure typically in the range 1500 2500 psi gas generation is interpreted to constitute a major overpressuring mechanism below that depth formation overpressure higher than 2500 3000 psi in the former case a pore pressure gradient approximately 50 higher than the hydrostatic gradient is estimated in the latter case a much more drastic overpressure increase with depth is suggested this model also applies to the norwegian central graben where only a limited number of wells tested jurassic reservoirs despite unavoidable simplification and approximation this model is believed to provide a better understanding of the areal distribution of geopressured jurassic reservoirs in the viking and central grabens it may be used to impose constraints on hydrocarbon migration models and for prediction of porosity preservation in relation to reservoir overpressuring

overpressure retardation of organic matter maturation and petroleum generation a case study from the yinggehai and qiongdongnan basins south china sea three superimposed pressure systems developed in the yinggehai basin south china sea as indicated by seismic data well logs and direct pressure measurements the organic maturation profile is nonlinear with three nonparallel segments that correspond to the shallow normal pressured system the intermediate overpressured system and the deep strongly overpressured system respectively the intermediate and deep overpressured systems have abnormally low r0 gradients the organic maturity of these overpressured rocks is significantly lower than the maturity of normal pressured source rocks in nearby wells with similar thermal histories and does not match the thermal histories of the rocks such an organic maturity anomaly is distinctly different from those aused by variation in activation energies conductivity contrasts and hydrologic effects and is confirmed to be the result of overpressure retardation the degree to which the organic matter maturation is retarded expressed as the difference between predicted and measured vitrinite reflectance increases exponentially with increasing fluid pressure confirming that pressure increases the activation energies of organic matter maturation reactions overpressure retardation has been proven to be conditional and quite important for clearly understanding petroleum generation migration and accumulation in overpressured sedimentary basins

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

thermal alteration of organic matter in an impact crater and the duration of postimpact heating the 24 km diameter tertiary haughton impact structure formed in rocks that contained preexisting liquid hydrocarbons biomarker ratios in the hydrocarbons show a consistent pattern of variation in degree of heating across the structure the heating reached a maximum at the crater center and is attributed to hydrothermal activity following impact kinetic modeling suggests a time scale of 5 k y for the heating at a maximum temperature of 210 c the short time scale suggests that in moderate sized craters which are abundant on mars heating is not so extensive that fossil or extant organic matter would be obliterated

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

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

venture gas field offshore nova scotia case study of overpressuring in region of low sedimentation rate the venture gas field is a deep overpressured gas reservoir on the scotian shelf off eastern canada overpressuring occurs at depths below 4 5 km and is associated with significant quantities of gaseous hydrocarbons the overpressured zone is composed of high porosity sandstones interbedded with low porosity low permeability shales which have nearly normal levels of compaction pore pressures in this zone show a step wise increase with depth where pressure jumps correlate with low permeability 10 20m2 where 10 12m2 1 01 d shale beds petrophysical and lithological data for sandstones and shales in the overpressured zone are used to constrain a one dimensional single phase model of pore pressure development the con ersion of kerogen to hydrocarbons is simulated by simple kinetic reaction theory estimates of the effects on overpressuring of sediment compaction temperature changes and hydrocarbon generation were obtained from this model using the above data 2 disequilibrium compaction apparently is responsible for much of the overpressuring in the venture gas field in our simple single phase model the contribution of hydrocarbon generation to overpressuring was slight

palynomorph optical analyses for thermal maturity assessment of upper ordovician katian hirnantian rocks from southern estonia abstract application of integrated multi proxy optical analytical techniques for the assessment of thermal maturity of organic matter was tested in katian to hirnantian upper ordovician sediments from a subsurface succession in southern estonia the investigated valga 10 drill core section consists of a biostratigraphically well constrained succession deposited in the outer part of a carbonate shelf livonian basin the diverse and well preserved palynological assemblages permitted the analysis of thermally induced modifications of optical properties of small and large acanthomorph acritarchs qualitative methods such as uv fluorescence and acritarch alteration index aai were calibrated against the quantitative palynomorph darkness index pdi the occurrence of vitrinite like organoclasts allowed reflectance measurements in some of the investigated samples the strong fluorescence and pale to yellow colour of acritarchs combined with low pdi and organoclast reflectance values suggest thermally immature kerogen and a limited burial diagenesis in the study area moreover pdi showed a good correlation with uv fluorescence allowing a calibration of these two techniques and proving the reliability of pdi for thermal maturity estimation in sedimentary rocks unsuitable for rock eval pyrolysis and vitrinite reflectance furthermore the applied methodologies permitted the differentiation of reworked from in situ organic matter and highlighted the potential of the former for sequence stratigraphic investigations

results from the ism experiment the imaging spectrometer ism operating in the near infrared is the first ever flown in space for planetary observation with a spectral range of 0 76 3 14 m its main goals were to obtain information on the mineralogical composition of the surfaces of mars and phobos and on the composition spatial and temporal variations of the martian atmosphere the infrared imaging spectrometer ism acquired 40 000 spectra of mars and phobos here we present the first results on the surface mineralogy of mars and phobos and the atmospheric composition of mars

observation of pressure variations in the martian atmosphere 1 pressure waves in the martian atmosphere could so far be observed only in the presence of clouds thanks to the mars global surveyor mars orbiter laser altimeter mgs mola a direct observation is now possible with the method presented here many more events are thus potentially observable we compare altimetry measurements from mgs mola and spectral observations from ism the infrared spectrometer aboard the phobos 2 spacecraft to infer pressure variations in the martian atmosphere we identify variations of pressure above martian volcanoes and we observe lee vortices of wavelength 200 250 km and amplitude 0 05 mbar in two different occasions the application of this technique should constrain martian meteorology with data from future imaging spectrometers

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

determination of paleoheat flux from vitrinite reflectance data a method is presented for determining paleoheat flux from the reflectance of vitrinite collected from wells the maturation of vitrinite is modeled using a time temperature integral that assumes pseudo first order kinetics in testing the numerical algorithm it was necessary to introduce a critical temperature of 295 k below which vitrinite does not mature this result is consistent with the latest findings of independent researchers the degree of consistency obtained from a number of wells is not perfect much of the inconsistency can be attributed to large uncertainties in the vitrinite reflectance readings to test the method heat flow history was determined for the north sea basin and the national petroleum reserve of alaska quantitative results were obtained detailing the increase and or decrease of heat flux with time and were consistent with the qualitative behavior inferred for paleoheat flow from current geologic models

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

geochemical modelling in rapidly subsiding basins abstract geochemical modelling in rapidly subsiding basins presents some puzzling questions in trying to clarify them two african basins related to different domains were studied the high tertiary and quaternary sedimentation rate is a common feature of the two basins in each of them present heat flow values were computed in different wells on the basis of temperature stratigraphic and petrophysical data using a one dimensional finite element mathematical model the resulting distributions show in some cases irregular patterns which are examined in detail to outline their possible causes extrapolation of the present thermal regime to the past generally gives computed maturity values considerably higher than those obtained experimentally the experimental data include vitrinite reflectance values rock eval pyrolysis results sterane and hopane isomerization and sterane aromatization hypotheses about thermal history are made in order to explain the areal maturity distribution they are checked comparing computed maturity values and experimental ones by combining experimental data and results of the modelling exercise we conclude that the high sedimentation rate independent of the tectonic domain in which it occurs can induce noticeable and peculiar thermal anomalies

the relationship between aromaticity vitrinite reflectance and maceral composition of coals implications for the use of vitrinite reflectance as a maturation parameter abstract previous studies on the aromaticity f a of coals have either limited themselves to the effects of rank or to differences between the macerals and generally conclude that f a and rank increase simultaneously although not necessarily linearly this study contains 13 c cp mas nmr analysis data of more than 70 coals obtained from different coal basins these are combined with published data to produce a data base with more than 130 analyses the aim is to determine the influence of rank and maceral composition on the measured f a of coals a plot of f a vs r o vitrinite reflectance shows a non linear relationship that can be described by a polynomial equation the shape of the curve produced by this equation is determined by the processes that occur during maturation only approx 50 of the coals in the data base have f a values that are accurately predicted by the vitrinite reflectance this is an indication of the large spread of values observed in the plot of f a vs r o as a result of the processes that occur during maturation the influence of the maceral composition on the f a was restricted to coals with r omax values 0 70 r o the equation generated shows that more than 80 of the coals tested with this level of rank have f a values that can be accurately predicted by an equation containing the r omax value the total vitrinite content and the contents of fusinite semifusinite and macrinite in the coals comparison of the f a values obtained from vitrinitic type iii kerogen with the f a values obtained from liptinitic sporinites and type ii kerogens reveals a pattern which illustrates the structural changes that occur during maturation both vintrinites and liptinites show a change in the slope in an f a vs r o plot although the reflectance level at which the change in slope occurs differs between the two kerogen types the changes in molecular structure that occur within the two kerogen types during maturation are discussed the implications of the f a r o relationship of vitrinites on the use of vitrinite reflectance as a maturation parameter are also discussed

experimental study on the pressure dependence of vitrinite maturation we conducted the first systematic experiments over a pressure range of 0 5 to 20 0 kbar at temperatures of 200 to 350 c and run durations of 2 4 and 7 days to investigate the influence of pressure on vitrinite reflectance the data indicate that applied pressure lowers vitrinite reflectance the suppression appears to be stronger under wet than under dry conditions in addition high pressure favors liptinite preservation at temperatures 300 c whereas at the same temperature range yet at low pressure liptinite is decomposed our data fit an empirical rate equation which expresses rr as a function of pressure temperature and time the derived equation satisfactorily describes our experiments and enables extrapolations to geological timescales values of rr calculated for a pressure of 0 5 kbar are remarkably consistant with previous numerical pressure independent models a literature review shows that previous experimental data and field observations are inconsistent regarding the effect of pressure on vitrinite maturation this and some previous studies suggest that vitrinite maturation is suppressed by increased pressure whereas other workers regarded pressure as having little influence on the rate of coalification we suggest that original virinite composition experimental design and natural environment tectonic regime play important roles regarding the effects of pressure on vitrinite maturation interpretation of geothermal histories of sedimentary rocks based on vitrinite reflectance data must therefore include evaluation of the pressure otherwise vitrinite reflectance data from high pressure terranes should be interpreted with caution if used as a quantitative paleogeothermometer

identifying potential gas accumulation sites from oligocene overpressure data in the qiongdongnan basin offshore south china overpressure in oligocene formations in southern qiongdongnan basin offshore china can be determined either by actual measurements in wells or by calculations using data derived from well logs and seismic surveys the overpressure is mainly the result of undercompaction of oligocene rocks during rapid loading by pliocene and quaternary sedimentation and of the subsequent thermal expansion of fluids in the oligocene strata every formation possesses its own normal compaction trend plot of shale interval acoustic transit times vs depth the actual fluid pressures and potential pressures can be computed by the equilibrium depth method this method must be corrected for the thermal expansion of fluid the pressure corrections are based on shale interval transit times from well logs interval velocities interpreted from vertical seismic profile vsp surveys and stacking velocity from sonic log data of nearby wells gas generated from source rocks is assumed to have moved vertically from strata of higher hydraulic pressure potential to those of lower potentials and to have moved laterally and accumulated within areas where the contour closures of a gas equipotential hydraulic pressure surface u curves have lower values in the study area the vicinity of the yacheng gas field the potential maps u gas and v water maps and hydraulic head profiles can be plotted from values derived either from actual pressure measurements or from calculations these maps and profiles show prospective areas of gas accumulation

hierarchies of overpressure retardation of organic matter maturation case studies from petroleum basins in china the effects of overpressure on different aspects of organic matter maturation have been examined in three basins using multiple parameters overpressure in the yinggehai basin has retarded kerogen maturation hydrocarbon generation and thermal cracking of long chain normal hydrocarbons as well as evolution of isoprenoid hydrocarbons overpressure in the dongpu depression bohai bay basin seems to have retarded the maturation of bulk kerogens reflected by rock eval tmax the thermal cracking of long chain normal hydrocarbons and the evolution of isoprenoid hydrocarbons but seems to have had no detectable effects on vitrinite reflectance overpressure in the qiongdongnan basin has had no detectable retardation effects on all aspects of organic matter maturation the observed phenomena suggest differential retardation of organic matter maturation that is different organic matter maturation reactions and different maturity parameters have been retarded by overpressure to different degrees in the same overpressured system and four hierarchies of overpressure retardation hierarchy i retardation is defined as the state where the overpressure has retarded all aspects of organic matter maturation and is proposed to have been caused by the combination of high formation pressure and excess pressure a high water organic matter ratio and strong retention of reaction products in an early developed strong persistent overpressured system hierarchy ii retardation refers to the case in which all aspects of organic matter maturation except the maturation of hydrogen poor kerogens especially vitrinite have been retarded and seem to have been caused by early developed moderate to strong persistent overpressure hierarchy iii retardation refers to the situation where overpressure has retarded only the thermal cracking of liquid hydrocarbons but has had no detectable effect on the maturation of both hydrogen rich and hydrogen poor kerogens and is proposed to have been caused by moderate to strong persistent overpressures that began to develop around peak oil generation hierarchy iv retardation is defined as the situation where overpressure has had no detectable retardation on all aspects of organic matter maturation and may have been caused by cases wherein the overpressure developed too late the intensity of the overpressure was too low the duration of the overpressure was too short or overpressured fluids had been expelled frequently resulting from both the diversities of organic matter maturation reactions and the complexities of overpressure generation and development the hierarchies of overpressure retardation in different basins may be quite different and it is necessary to use multiple parameters to understand the evolution of the petroleum systems in overpressured basins

petroleum generation and migration in the cambro ordovician laurentian margin succession of nw scotland fluid inclusion and organic biomarker data show that there was formerly a hydrocarbon system in the cambro ordovician laurentian margin rocks of nw scotland oil fluid inclusions occur in stylolitized eriboll formation sandstone in k feldspar cements with an 40 ar 39 ar age of 415 5 5 5 8 ma 2 analytical precision full external precision organic extracts from durness group black limestones yield biomarker ratios characteristic of high thermal maturity organic maturation to yield oil probably occurred during orogenic deformation along the moine thrust zone the recognition of a hydrocarbon system in scotland adds to a huge hydrocarbon province in laurentian rocks including north america and greenland supplementary material technical data for ar ar dating are available at https doi org 10 6084 m9 figshare c 3879616

a north indonesian basin geo thermal and hydrocarbon generation histories abstract geohistory thermal history oil generation and accumulation have been examined in an early pliocene basin which is located offshore north of indonesia the basinal sediments are 4500 m thick and were deposited in about 5 million years leading to development of high excess fluid pressures up to 170 atm at 2000 m mainly due to strong undercompaction the successive deltaic platforms in the basin are controlled by a major growth fault system which is probably related to a large overpressured shale diapir a one dimensional study of two wells was undertaken using an inverse non linear scheme to determine dynamic and thermal parameters and then to reconstruct the geohistories and thermal histories at the well sites the two thermal histories suggest a major heating event about 4 million years before present probably tied to revewed volcanism which boosted the maturation of organic matter so that the development of hydrocarbons was massively enhanced without the heating event hydrocarbon generation would have been very unlikely in such a young basin

implications for organic maturation studies of evidence for a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature cerro prieto geothermal system mexico discussion a short term rapid heating and cooling of the rock in well m 94 below 1300 m was caused by a pulse of hot water passing through the edge of the cerro prieto mexico geothermal system below 1300 m the peak paleotemperatures were about 225 250 degrees c but equilibrium well log temperatures indicate a decrease to 150 210 degrees c at present this hot water pulse sharply increased vitrinite reflectance to levels comparable to those measured in the central part of the system even though studies of apatite fission track annealing indicate that the duration of heating was only 10 0 10 1 yr in m 94 in contrast to 10 3 10 4 yr in the central part of the system these data indicate that sedimentary organic matter chemically reacts quickly to temperature increases of about 125 degrees c above ambient even when the higher temperature existed for only 10 0 10 1 yr the quick change of the vitrinite reflectance geothermometer indicates that thermal maturation reactions can stabilize after a geologically short period of heating to a level consistent with peak temperature under moderate to high temperature diagenesis in open fluid rich geothermal systems cerro prieto is one of the most intensively studied and well known geothermal systems in the world thus data from cerro prieto are a benchmark to compare with the predictions of published thermal maturation models such as those formulated by j karweil n v lopatin and a k burnham and j j sweeney these thermal maturation models inaccurately predict duration of heating at cerro prieto the kinetic equations used in these models explicitly allow thermal maturation to continue indefinitely at peak temperature which does not seem to be the case at cerro prieto

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

tectonic history from vitrinite reflectance summary the degree of organic metamorphism of carbonaceous matter is expressed in terms of the reflectance of vitrinite vitrinite reflectance is a function of temperature and time a model relating vitrinite reflectance to temperature and time is proposed from published vitrinite reflectance temperature time nomograms a plot of the logarithm of vitrinite reflectance versus depth gives a linear curve for vitrinite reflectance greater than 0 3 per cent in a sedimentary basin which has had a constant geothermal gradient throughout its tectonic history the geothermal gradient c km 1 is equal to the slope of the curve multiplied by 194 8 the model is also applied to sedimentary basins with decreasing geothermal gradient with time i e cooling continental margin basins the vitrinite reflectance model is demonstrated to be consistent with observed reflectance data and tectonic information from the sydney bowen surat and gippsland basins in eastern australia

suppression of thermal maturity indicators in lacustrine source rocks a case study of dongying depression eastern china abstract the paleogene shahejie formation of the dongying depression in eastern china is a unique region and can offer insights into the suppression of thermal maturity in a large set of successive lacustrine shales this study focuses on the paleogene shahejie formation of n 38 well in the dongying depression the unusual distribution of thermal maturity indicators such as vitrinite reflectance vro and c29 sterane thermal parameters was investigated through geochemical analysis the research interval 2770 3376 m was divided into three parts the upper part of es32 2770 2990 m the lower part of es32 2990 3190 m and the es31 3190 3376 m the es31 mainly contained organic matter type i and some type ii which included mostly good and excellent source rocks meanwhile the upper es32 mainly contained organic matter type iii which included mostly poor and moderate source rocks the parameters g c30h c35h c31 35h c31m c31h c29 20s 20s 20r c31 22s 22s 22r and c32 22s 22s 22r showed a different distribution corresponding to the different lake sedimentary environments various organic facies were developed at the different evolution stages of the lake basin which showed a noticeable influence on the parameters the thermal maturity indicator vro and molecular thermal parameters such as c29 20s 20s 20r c31 22s 22s 22r c32 22s 22s 22r and c31m c31h presented abnormal distributions in the large set of lacustrine shales especially in the es31 this observation suggested suppression of several thermal maturity indicators vro suppression positively correlated well with the corrected hydrogen index and alginite content in maceral composition the high content of alginite group was considered to be the primary reason behind the evident negative vro anomaly

cenozoic exhumation on the southwestern barents shelf estimates and uncertainties constrained from compaction and thermal maturity analyses abstract the barents sea is believed to have been influenced in most parts by cenozoic uplift and erosion episodes the rocks in the area are not currently at their maximum burial depth the exhumation of the sedimentary rocks has had large effects on rock physical properties and hydrocarbon maturation and migration the current study seeks to estimate exhumation from shale compaction and thermal maturity techniques and discuss its implications for hydrocarbon exploration in the uplifted barents sea area this study uses well logs and thermal maturity data together with widely distributed shot gather data along long offset seismic reflection lines the use of shale compaction techniques to estimate exhumation was focused particularly on the regionally preserved aptian albian kolmule formation and paleogene torsk formation shales normal compaction reference curves were established for these units in areas currently at their maximum burial depth e g sorvestsnaget basin and vestbakken volcanic province the results suggest widespread cenozoic exhumation throughout the southwestern barents sea the exhumation magnitudes increase towards east and northeast the average exhumation estimates from the three data sources range from 800 to 1400 m within the hammerfest basin 1150 1950 m on the loppa high 1200 1400 m on the finmark platform and 1250 2400 m on the bjarmeland platform the marked differences in glacial erosion from mass balance and average erosion estimates from the current study suggest a significant pre glacial uplift and erosion in the southwestern barents sea area the observed stratigraphy and presence of significant volumes of late oligocene middle miocene sediments in basins at the outer margin and increased erosion rates at the same time in source areas suggest that maximum burial in the southwestern barents sea may have occurred sometime during the oligocene or even earlier in the eocene the results from this study are useful input for modelling of source rock maturation generation migration and trapping of hydrocarbons in the area these results are also an important input for the prediction of more precise reservoir and seal rock properties in frontier areas away from the exploration wells and provide valuable knowledge for the use of interval velocities in the uplifted areas

quantifying paleosecular variation insights from numerical dynamo simulations abstract thanks to advances in dynamo modelling it is now possible to produce numerical sequences of magnetic polarity reversals over periods of time equivalent to several tens of millions of years using a set of five numerical models integrated over the equivalent of 40 50 myr we generated synthetic data analogous to paleomagnetic data derived from volcanic flows we find that the distributions of directions are remarkably similar to those observed in the paleomagnetic database paleosecular variation among the five models is best discriminated by the relative variability in paleointensity e f and the relative dispersion of directions or poles as defined by the precision parameter k whether the geodynamo operated in different regimes in its past can be best tested with these parameters in combination roughly one million years of time with 200 time independent samples is required to achieve convergence of e f and k the quantities e f and k correlate well with the average chron duration chr which suggests that excursions and reversals are an integral part of paleosecular variation if applicable to the geodynamo the linear dependence of k on chr could help to predict chr for the earth during geologic times with no available reversal frequency data it also predicts much higher average k for directions during superchrons k 2500 for the cretaceous normal superchron than during actively reversing times k 35 for the last 80 myr as such high k values are not observed either this family of dynamo models is not applicable to the geodynamo or the geodynamo regime acting during superchrons is independent of that acting during times with frequent reversals

future uses of fossil fuels a global view of related emissions and depositions abstract the flow of fossil fuels through contemporary civilizations and the related emissions and depositions of sulphur and nitrogen compounds can no longer be considered to be of only local importance the size of these flows compares with and even exceeds natural cycles this leads to a problem whose future evolution in time is not clear the question becomes more difficult with the present tendency to increase use of fossil fuels whereas this was considered a problem of the quantity of available resources in the 1970 s it may now turn out to be a problem of the quality of resources the procedure applied in the present study highlights the lack of data and knowledge particularly striking are lack of data on quality of resources the chemistry of the atmosphere and the transport of aerosols and the lack of standards by which to judge effects of nox and so2 deposition

optical properties of organic matter in relation to thermal gradients and structural deformation the general response of macerals to the coalification process the effectiveness of organic geochemical and petrological parameters as estimators of coalification and the applicability of different microscopical parameters in the assessment of rank are reviewed the central role of vitrinite reflectance as the most widely used estimator of coalification from brown coals to the low grade metamorphic zone is established on the basis of its relatively uniform variation with rank specificity ease and rapidity of measurement and cheapness factors influencing the optical properties ofvitrinites are considered temperature has the dominant influence in modifying optical properties with rank but time static pressure and stress can all have significant influences upon the course of optical properties depending upon particular geological conditions static pressure has a retarding effect on the coalification process but it is also responsible for creating increasing anisotropy within the condensing aromatic structures as rank rises hydrostatic pressures and pore pressures can contribute to the overpressuring of sediments thus affecting their thermal conductivities and consequently the rate of coalification stress is responsible for the development of biaxicity in the reflectance indicatrix fast and high levels of heating from igneous bodies cause textural effects on vitrinites as a result of carbonization that are quite different from those of coalification recognizing these different influences upon the optical properties of vitrinites examples are given of the use and application of vitrinite reflectance in the preparation of rank maps in the burial histories of basins in the timing of coalification in relation to orogenesis and igneous activity and in the zones of anchimetamorphism and low grade metamorphism consideration is also given to the problem of provincialism in correlations between chemical and physical parameters and to the future development of optical studies in organic petrology and their relation to organic geochemical investigations

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

suppressed vitrinite reflectance in the ferron coalbed gas fairway central utah possible influence of overpressure chemical and thermoplastic properties of coals in the ferron coalbed methane fairway indicate that coals in the north are of higher rank than coals in the south measured vitrinite reflectance does not accurately show this variation of coal rank although vitrinite reflectance in the southern and central part of the fairway is consistent with other measures of coal rank suppressed vitrinite reflectance is observed in the north where methane contents are relatively high this coincidence of suppressed reflectance and relatively high coalbed methane yields may be significant we speculate that the suppressed reflectance values result from a burial history where overpressure developed during the early stages of coalification and persisted until recent uplift and cooling such instances may be diagnostic of prospective coalbed methane targets elsewhere

winter clouds over the north martian polar cap the mars orbiter laser altimeter mola experiment carried on the mars global surveyor spacecraft has observed echoes from cloud tops on roughly 2 5 of the total data taken above 70 n over the northern winter martian polar hood from march to june 1998 sloping wavefronts are commonly seen at latitudes above 70 n implying the presence of propagating buoyancy waves since these wavefronts frequently extend from the surface up to 10 km at a time when co2 is known to be condensing on the polar surface it seems likely that the laser scattering particles consist primarily of co2 ice and that the near surface temperature lapse rate is 0 85 k km 1 set by the vapor pressure of dry ice from the observed wavelengths where available we have calculated the corresponding phase velocities some of these waves appear to be correlated with surface discontinuities and may represent lee waves

kinetic method for modeling vitrinite reflectance a kinetic method for the prediction of vitrinite reflectance is outlined its application allows the effect of spatially variable syndepositional and postdepositional processes to be considered through geologic time the model can be used for deterministic and probablilistic analyses and allows the determination of the temporal and spatial relationship between hydrocarbon generation and vitrinite reflectance in a basin

organic geochemistry of core samples from an ultradeep hot well 300 c 7 km south texas cores of lower cretaceous rocks from a depth of 6400 8 to 7544 6 m at present day temperatures of 262 296 c have high concentrations of c15 hydrocarbons bitumen coefficients range from 105 to 367 mg g and c15 extractable bitumen ranges from 500 to 2200 ppm some generation potential remains associated with the kerogen of these rocks in addition to exhibiting the above organic geochemical properties characteristic of the zone of intense hydrocarbon generation these rocks also have organic geochemical properties attributed to the zone of hydrocarbon extinction or greenschist metamorphism these characteristics are high vitrinite reflectance r0 values 4 4 4 8 low h c ratios 0 30 0 58 high saturate aromatic hydrocarbon ratios 7 05 20 6 high hydrocarbon nso ratios 2 65 4 66 and high transformation index ratios s1 s1 s2 0 61 0 87 the data from this and other wells we have studied show that high concentrations of c15 hydrocarbons are thermally stable to high temperatures at least 300 c in abnormally pressured semi closed systems over geologic time concepts prevelant among petroleum organic geochemists concerning the thermal fate of hydrocarbons with subsequent graphite formation and greenschist metamorphism are in sharp contradiction to these data conventional concepts of the distribution of heavy hydrocarbons with increasing temperature and depth apparently require further review and revision

a data driven model for studying kerogen kinetics with application examples from canadian sedimentary basins abstract source rock is an essential element in unconventional resource play evaluation while kerogen kinetics is one of the most important components in source rock evaluation traditional approach for determining oil generation kinetics is done through laboratory pyrolysis analysis by mimicking the hydrocarbon generation processes with variable accelerated heating rates thus the thermal energy required for hydrocarbon generation under geological conditions is inferred study suggests that for a given kerogen type numerical kinetic models derived from a limited number of laboratory tests may result in unacceptable errors because of under representation of variation in activation energy related to organic facies change and source rock heterogeneity as economic margin of developing an unconventional resource play can be small business success often depends on early identification of favourable area a quick and robust method for resource play evaluation is critical this study proposes a data driven statistical approach that utilizes existing rock eval toc data by fitting the measured hydrogen index and tmax to an exponential model the model is designed so that all parameters have an explicit physical meaning and the ranges of parameter values are predictable once the empirical statistical model is established hydrocarbon transformation ratio can be calculated to represent the hydrocarbon generation kinetics of the source rock the main advantage of the proposed approach is the utilization of widely available rock eval datasets so that 1 no additional specifically designed laboratory pyrolysis experiments are required 2 the uncertainty due to facies variation or source rock heterogeneity nature and poor data quality human can be quantified through the statistical analysis of a large dataset and 3 validation for temperature and geothermal rates in situ pressure and other environmental conditions is not necessary as the input data for the model are all based on naturally matured samples rock eval datasets from four well known canadian source rock intervals representing the most common kerogen types are tested and used as examples to demonstrate the application of the proposed method the examined source rocks with different kerogen types show distinct kinetic behaviours and this is consistent with models derived from laboratory tests applications also indicate that the proposed method appears to be robust and convenient for modelling kerogen kinetics from rock eval data directly

overpressure retardation of organic matter maturation a kinetic model and its application abstract a kinetic model t p ro has been developed to address the issue that overpressure increases the activation energies during organic matter maturation and that the retardation of organic matter maturation by overpressure is due to the fact that organic matter is hindered from progressive molecular ordering under overpressured conditions the mean effective stress i e mean stress minus pore pressure is much lower and the pore pressure is usually higher than under hydrostatic pressure conditions as a result the progressive molecular ordering of the vitrinite such as the aromatization is retarded and the vitrinite reflectance can hardly be increased the reflectance values predicted by t p ro model as it has been applied to the well ld3011 at yinggehai basin in south china sea are similar to the measured ones the kinetic model predicts that overpressure can cause the oil window floor and the peak oil generation to shift to greater burial depth in the case of yinggehai basin the local geological conditions are prone to generate light hydrocarbons and natural gas instead of oil hence they constitute the predominant products in this high temperature heating rate basin

the influence of pressure on petroleum generation and maturation as suggested by aqueous pyrolysis because fluid pressures are transient in sedimentary basins over geologic time the effect of increasing fluid pressure on organic matter metamorphism is difficult to determine and conflicting opinions exist concerning its influence properly performed aqueous pyrolysis experiments can closely simulate hydrocarbon generation and maturation in nature and thus offer an excellent way to study the influence of pressure such experiments carried out on the retort phosphatic shale member of the lower permian phosphoria formation type ii s organic matter at different constant temperatures demonstrated that increasing pressure significantly retards all aspects of organic matter metamorphism including hydrocarbon generation maturation and thermal destruction this conclusion results from detailed quantitative and qualitative analyses of all products from hydrocarbon generation from the c1 to c4 hydrocarbon gases to the asphaltenes and also from analyses of the reacted rocks we have documented that our aqueous pyrolysis experiments closely simulated natural hydrocarbon generation and maturation thus the data taken as a function of pressure have relevance to the influence of normal and abnormal fluid pressures as related to 1 depths and temperatures of mainstage hydrocarbon generation 2 the thermal destruction of deposits of gas or light oil or their preservation to unexpectedly high maturation ranks and 3 the persistence of measurable to moderate concentrations of c15 hydrocarbons in fine grained rocks even to ultra high maturation ranks

remote sensing of surface pressure on mars with the mars express omega spectrometer 2 meteorological maps 1 surface pressure measurements help to achieve a better understanding of the main dynamical phenomena occurring in the atmosphere of a planet the use of the mars express omega visible and near ir imaging spectrometer allows us to tentatively perform an unprecedented remote sensing measurement of martian surface pressure omega reflectances in the co2 absorption band at 2 m are used to retrieve a hydrostatic estimation of surface pressure see companion paper by forget et al 2007 with a precision sufficient to draw maps of this field and thus analyze meteorological events in the martian atmosphere prior to any meteorological analysis omega observations have to pass quality controls on insolation and albedo conditions atmosphere dust opacity and occurrence of water ice clouds and frosts for the selected observations registration shifts with the mola reference are corrected sea level surface pressure reduction is then carried out in order to remove the topographical component of the surface pressure field three main phenomena are observed in the resulting omega surface pressure maps horizontal pressure gradients atmospheric oscillations and pressure perturbations in the vicinity of topographical obstacles the observed pressure oscillations are identified as possible signatures of phenomena such as inertia gravity waves or convective rolls the pressure perturbations detected around the martian hills and craters may be the signatures of complex interactions between an incoming flow and topographical obstacles highly idealized mesoscale simulations using the wrf model enable a preliminary study of these complex interactions but more realistic mesoscale simulations are necessary the maps provide valuable insights for future synoptic and mesoscale modeling which will in turn help in the interpretation of observations

effects of early petroleum charge and overpressure on reservoir porosity preservation in the giant kela 2 gas field kuqa depression tarim basin northwest china kela 2 is a giant gas field with a proven reserve of 597 tcf in the kuqa depression northern tarim basin widespread overpressures have been encountered in the eocene and cretaceous sandstone reservoirs of the field with pressure coefficients up to 2 1 from drill stem tests and well log data analysis disequilibrium compaction associated with horizontal tectonic compression may be the dominant overpressure mechanism in the sandstone reservoirs because the overpressured sandstone with a maximum burial depth over 6000 m 19 685 ft displays anomalously high porosity and low density the causes for sandstone reservoirs with anomalously high porosity in the kela 2 gas field were studied based on an integrated investigation of sandstone reservoir characteristics paleo oil water contact petroleum charge history and overpressure evolution collective evidence indicates that early oil charge had retarded the porosity reduction of the reservoir sandstone and resulted in disequilibrium compaction from overburden rocks and overpressure from disequilibrium compaction and horizontal tectonic compression at the beginning of the rapid subsidence and deposition in the kela 2 gas field again contributed to the preservation of the reservoir porosity 1 overpressured mudstones in the kela 2 gas field are characteristic of normal compaction and overpressure was generated by horizontal tectonic compression instead of disequilibrium compaction 2 the reservoir sandstones with high porosity and permeability are associated with high paleo oil saturation as indicated by quantitative grain fluorescence qgf responses and anomalous qgf on extract intensity 3 sandstone units below the paleo oil water contact have very low porosity and permeability and 4 three episodes of oil and one episode of gas charge are identified in the sandstone reservoirs of the kela 2 gas field and the later two episodes of oil charge occurred circa 5 5 4 5 ma which corresponds to the beginning of the rapid tectonic subsidence and deposition in the kuqa depression the initially charged oil in the sandstone reservoirs was subsequently displaced by gas at circa 3 2 ma through fault activation at the edge of the anticline trap the overpressure evolution for the k1bs reservoir sandstone in the kela 2 gas field indicates that the apparent overpressure development in the sandstone reservoir began at 5 ma following the major oil charge and has been maintained to the present overpressure development from 5 ma in the sandstone reservoirs of the kela 2 gas field is believed to be the dominant cause of the porosity preservation

overcoming pitfalls of vitrinite reflectance measurements in the assessment of thermal maturity the case history of the lower congo basin abstract vitrinite reflectance has been always considered the most reliable thermal maturity indicator in sedimentary basins nevertheless the reliability of vitrinite reflectance measurements can be affected by many external factors that change from basin to basin e g organic facies temperature and pressure conditions leading to wide uncertainties in thermal modelling calibration and thus in the evaluation of timing and amount of hydrocarbons generation we demonstrate that in case of vitrinite suppression and or retardation in siliciclastic successions the classical sweeney and burnham kinetics do not match the actual thermal evolution of the basin in these cases thermal evolution can be successfully modelled using a complementary approach based on smectite illitization kinetics or more appropriate kinetics e g presro tm and t p ro to evaluate the effect of pressure on organic matter maturation where pressure data are available this approach was applied in the lower congo basin where 32 cuttings from a 5 km deep well drilled in the upper oligocene miocene malembo formation have been analysed to derive organic and inorganic constraints to model the basin thermal evolution vitrinite and bitumen reflectance measurements show values between 0 3 and 1 0 along the well whilst the illite content of mixed layer i s ranges between 35 and 88 passing from r0 to r1 to r3 stacking order with increasing depth present day temperature distribution through the well indicates a geothermal gradient of about 40 c km and measured pressures show an overpressured interval between 3 and 4 km depth retardation and suppression phenomena affected vitrinite reflectance in this interval but did not influence smectite illitization the comparison between thermal maturity scenarios constrained by organic and inorganic thermal indicators shows differences in the calculation of the depth of the onset of hydrocarbon generation that is overestimated of about 500 m in the lower miocene interval when only suppressed retarded vitrinite reflectance values are used to calibrate models

global patterns in cloud forms on mars abstract mariner 9 images and all viking orbiter images through july 1979 were searched for cloud forms a computer accessible catalog was assembled consisting of a classification of cloud type lee wav wave for example and properties directionality wavelength for example lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor lee waves are rare at equatorial latitudes plumes probably dust occur preferentially at locations where strong boundary layer convection is expected