correlation of oil and asphaltite in ouachita mountain region of oklahoma geologic notes several chemical characteristics of oils and asphaltites in the frontal and central ouachita mountains have been examined results indicate that the three oils and six asphaltites examined from atoka pittsburg and pushmataha counties in southeastern oklahoma originated from a common source carbon isotope ratios for oil and asphaltite suggest that the asphaltite is neither a protopetroleum nor a thermally degraded crude oil results of metallic and elemental analyses are consistent with an oil alteration origin for ouachita solid bitumens it is proposed that low temperature near surface alteration phenomena such as biodegradation and water washing have degraded crude oil to produce asphaltite in the frontal and central areas these results suggest that previous assu ptions of a high temperature history are unwarranted

origin of tar mats in petroleum reservoirs part ii formation mechanisms for tar mats abstract tar mats and oil legs from several marine source rock derived oil fields including the ula and oseberg fields in the north sea and an unidentified north american example have been analysed geochemically in all cases the tar mats were derived from the same petroleum system as the oil leg oils and were found in the most porous and permeable portions of the reservoir comparing case history data with published data on the subsurface solubility characteristics of asphaltenes in petroleums it is possible to eliminate some potential tar mat formation mechanisms and suggest the most likely causative mechanisms thus the adsorption of asphaltenes on reservoir clays and light to moderate levels of biodegradation are considered unlikely to contribute to tar mat formation in the ula field thermal degradation of the oil in the carrier and reservoir causing asphaltene precipitation may be a major contributing factor to the tar mats there in the oseberg field increased gas solution in the oil leg may have contributed to deasphaltation tentative mass balance calculations the extreme pressure dependence of asphaltene solubility in subsurface crude oils the occurrence of tar mats in zones of elevated permeability plus a simple transport model suggest that during secondary migration an asphaltene rich petroleum phase may be produced in dipping carrier beds and may be carried into the reservoir contributing in some instances to tar mat formation

processes and rates of recent holocene basin filling in an active transform margin santa monica basin california continental borderland abstract santa monica basin an inner basin of the california continental borderland is a deep margin basin presently receiving sediments under high sea level conditions since the slowing of the last transgression the basin has been receiving primarily suspended load contributions with rare turbidites except in the most headward parts of the two principal canyons one turbidite found throughout the basin was laid down about 200 years bp and was probably deposited by a turbidity current generated by mass movement of slope sediments in the slope apron adjacent to the major active canyons similar basin wide events have occurred throughout holocene time at intervals of about 500 1000 years and these represent the effects of big earthquakes major floods or other exceptional happenings not commonly recorded in historic time except for these exceptional events the basin has received fine clastic sedimentation derived from the mainland rivers and transported by nepheloid plumes near bottom and in the surface mixed layer biogenic carbonate and organic carbon input from areas of high productivity fed by upwelling is masked by the fine detrital influx over the major fans by dilution from the rain of particulates from the major surface and near bottom turbid plumes that pass over the basin center a maxima of carbonate and organic content occurs in the basin floor sediments most distant from the combined diluting effects of these two major detrital inputs the basin slope fan and shelf bank top sediments are differentiated on the basis of mean particle size and skewness changes in sand and silt content are related to the pattern of the prevailing surface and near bottom water circulation with their reservoirs of fine suspended particulates the principal process removing the fine particles from the surface plumes is biological filtering and pelleting sedimentation rates of major sediment components show that near bottom nepheloid plumes are trapped by the closed deep basin and their load settles out as the turbid waters circle over the central basin floor sedimentation rates vary from 40 80 cm 1000 years average sediment delivery is about 106 tons but exceptional floods can deliver several fold more sediment at 10 30 year intervals

evidence for gloeocapsomorpha prisca in late devonian source rocks from southern alberta canada abstract organic rich intervals within the late devonian camrose member of southern alberta canada show optical and chemical characteristics very similar to those of ordovician samples whose organic matter is dominated by gloeocapsomorpha prisca derived alginite this includes saturate fraction gas chromatograms dominated by n alkanes with a pronounced odd carbon number up to c19 and much lower abundances of c19 n alkanes acyclic isoprenoids and biomarkers microscopy reveals these samples contain g prisca like alginite with a morphology that previously has been suggested for the growth of this organism under higher salinity conditions which is in agreement with the depositional environment of the camrose member one unusual feature of the g prisca rich samples is the very high concentration of c21 and c23n alkylnaphthalenes and n alkylbenzenes in the aromatic fractions of their extracts the origin of these compounds is not known but their occurrence could be related to the high concentrations of c21 and c23n alkyl phenols that have been noted in pyrolysates of estonian kukersites by previous workers other camrose member extracts show very different distributions that are more typical for carbonates deposited under anoxic higher salinity conditions many oils that occur in nisku formation reservoirs in the enchant hays field in southern alberta show saturate fraction gas chromatograms and other evidence that indicate an important contribution to these oils from the g prisca rich intervals these are thought to have a contribution from camrose member source rocks hence caution should be used in only attributing g prisca geochemical characteristics to cambro ordovician oils as on rare occasions they can also occur in younger source rocks and their derived oils

heat flow and thermal history of the anadarko basin and the western oklahoma platform abstract the average geothermal gradient in the anadarko basin and the oklahoma platform estimated from 856 corrected bottom hole temperatures bhts is 21 c km analysis of previously published thermal maturation data indicates that the anadarko basin has undergone from 1 to 3 km of erosion starting about 40 to 50 ma the average thermal gradient at the time of maximum burial was in the range of 22 to 25 c km there is no evidence that the thermal state of the anadarko basin has changed significantly since the late paleozoic 250 ma to estimate heat flow in the anadarko basin and the oklahoma platform we made 652 thermal conductivity measurements on drill cuttings from 9 oil and gas wells all measurements were corrected for the effects of anisotropy temperature and porosity matrix conductivities perpendicular to bedding at 22 c range from 1 7 w m 1 k 1 for permian age sandstone and shale to 2 6 w m 1 k 1 for devonian silurian age limestone and shale in situ thermal conductivities vary from 1 3 w m 1 k 1 to 1 9 w m 1 k 1 estimated heat flow 20 ranges from 30 mw m2 to 42 mw m2 with a mean of 36 mw m2 we found no evidence for heat flow to increase significantly from the anadarko basin in the south to the oklahoma platform to the north these results contradict a previous study which found heat flow increases from south to north with heat flow in the oklahoma platform as much as 50 greater than heat flow in the anadarko basin at the present time we do not know if these differences are related to spatial variations or reflect methodological errors if our results are averaged with those reported in previous work mean heat flows in the anadarko basin and oklahoma platform are 39 mw m2 and 51 mw m2 respectively

composition and stable isotope geochemistry of natural gases from kansas midcontinent u s a abstract more than 28 1012 ft 3 79 1010 m3 of natural gas and 5 3 109 bbl 8 4 108 m3 of oil have been produced in kansas u s a from paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the anadarko basin a heavily explored geologically well characterized state kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases immature to marginally mature rocks of eastern kansas cherokee and forest city basins produce mixed microbial and thermogenic gases gases in this region have wetness 0 03 51 methane 13c 65 to 43 and methane d 260 to 150 gases from central and western kansas nemaha uplift to hugoton embayment are entirely thermogenic and have wetness 4 51 methane 13c 48 to 39 and methane d 195 to 140 ethane and propane 13c values throughout kansas vary from 38 to 28 and from 35 to 24 respectively mature thermogenic gas generated from source rocks in southwestern kansas and the anadarko basin with 1 0 ro 1 4 is recognized throughout the state lateral migration into shallow reservoirs on the central kansas and northern nemaha uplifts and in the cherokee basin probably occurred along basal pennsylvanian conglomerates and weathered lower paleozoic carbonates at the regional sub pennsylvanian unconformity early thermogenic gas generated by local source rocks with ro 0 7 is recognized in isolated fields in the salina and forest city basins in ordovician reservoirs beneath the sub pennsylvanian unconformity in the cherokee basin and in reservoirs generally above the unconformity in the cherokee and sedgwick basins the eastern central kansas uplift and the hugoton embayment

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

biochemical evolutionary significance of ordovician oils and their sources abstract geochemical data from several ordovician oils and kerogens from distinct basins in canada united states estonia and australia show some unique compositional characteristics the oils analyzed by gas chromatography and gas chromatography mass spectrometry are characterized by an odd dominance in the c9 c19 molecular weight range of normal paraffins and an odd dominated homologous series of cyclohexyl substituted normal paraffins the oils contain an unusually small amount of c20 components and pristane and phytane are conspicuous by their virtual absence the compositions of the oils and kerogens correlate closely and display characteristics that have not been observed in younger sediments the predominant organism found in the source kerogens for these unique oils is gloeocapsamorpha prisca a primitive prokaryotic organism data from the analysis of gloeocapsamorpha rich kerogens and the association of this organism with ordovician source rocks indicate a genetic relationship exists between the organism and the unusual oil chemistry the chemistry of the oils and kerogens suggests that gloeocapsamorpha was either non photosynthetic or that it fixed light using a chlorophyll that did not contain a phytyl side chain e g a bacteriochlorophyll the widespread occurrence of oils and kerogens possessing such a uniform composition appears unique to the ordovician certainly to the early paleozoic this suggests that paleocological conditions of ordovician anoxic environments were very similar and g prisca was particularly well adapted to these conditions

middle ordovician organic matter assemblages and their effect on ordovician derived oils two distinct middle ordovician oil prone organic matter assemblages occur in thermally immature to marginally mature petroleum source rocks from iowa the substantially more oil prone assemblage a generates the unique ordovician oil fingerprint which has been associated with the organic walled microfossil gloeocapsamorpha prisca the second assemblage b generates a more ordinary signature the two assemblages which are mixed or interbedded in many ordovician sediments of north america explain the variations in oils derived from ordovician source rocks these mixtures also aid in interpretation of the chemistry of g prisca core samples examined are from three wells in iowa penetrating the primarily carbonate sequence from the guttenberg member of the decorah formation down to the st peter sandstone microscopy rock eval pyrolysis and capillary gas chromatography on source rock bitumen extracts and nearby oils were used to evaluate the two assemblages solvent extracts from rocks containing predominantly assemblage a have the diagnostic ordovician gas chromatographic signatures with an odd preference in c11 c19 normal alkanes low amounts of heavier normal alkanes and virtual absence of isoprenoids including pristane and phytane although assemblage a occurs only in very thin beds it is potentially so oil generative that thicknesses in inches may be significant extracts from r cks containing predominantly assemblage b show reduced odd preference a full profile of normal alkanes and conspicuous occurrence of isoprenoids including pristane and phytane these samples from iowa are representative of middle ordovician source rocks found in most paleozoic basins of north america as well as baltic europe and australia therefore the conclusions drawn from these middle ordovician rock samples from iowa provide a basis to explain variations in ordovician derived oils found in many other areas

nicolas and eel submarine fans california continental borderland nicolas and eel submarine fans occur in the san nicolas basin an outer basin of the california continental borderland that has a low sedimentation rate nicolas fan lies southeast of san nicolas island and the broad san nicolas bank the upper fan is characterized by numerous channels the midfan region may be divided into three distinct areas a central midfan and two subfans the central midfan depositional system is typical of normark s suprafan the subfans are essentially flat sandy lobes eel fan lies west of san clemente island and is fed by an erosional valley its midfan region may also be characterized as a flat sandy lobe box core data show that holocene turbidity currents have occurred on the central nicolas fan whereas the subfans and eel fan are nearly nactive the local tectonic regime influences these fans by determining slope trends creating bathymetric obstacles controlling canyon location and triggering mass movements sea level changes affect sedimentation patterns of the fans by increasing the mean grain size and the amount of sediment delivered to the fan during lowstands these changes may in turn affect the morphology of the fan the characteristics of these fans represent variations of the generalized fan models described in the literature

overpressures in the anadarko basin southwestern oklahoma static or dynamic fluid pressures were estimated from mud weights and wellhead shut in pressures along a north south linear trend through the anadarko basin in southwest oklahoma fluid pressures above hydrostatic start at a depth of about 2 5 km on a normalized scale where hydrostatic pressure equals 0 and lithostatic pressure equals 1 estimates of fluid pressures were found to range from 0 4 to 0 8 over a depth range of 4 7 km using scale analyses and a simple numerical model we evaluated two end member hypotheses compaction disequilibrium and hydrocarbon generation as possible causes of overpressuring in the anadarko basin if compaction disequilibrium is the primary cause of present day overpressures in the anadarko basin the anadarko basin is required to have an average permeability of 10 23 m2 10 8 md or lower if geopressures in the anadarko basin result from hydrocarbon generation average basin permeabilities can be as high as 10 21 m2 10 6 md scaling these average permeabilities down to thicknesses of 100 m or less implies permeabilities lower than 10 25 m2 10 10 md are required in the most optimistic scenario the lowest permeabilities ever measured on sedimentary rocks are in the neighborhood of 10 22 10 23 m2 10 7 10 8 md thus it is not possible to reconcile the existence of overpressures in the anadarko basin with classic hydrodynamic theories that maintain that aquicludes do not exist either some unknown process is generating excess fluid pressures or the anadarko basin contains pressure seals geopressure models that invoke compaction disequilibrium and are commonly applied to cenozoic basins undergoing rapid sedimentation e g the gulf coast basin of the southeastern united states do not appear to apply to the anadarko basin the anadarko basin belongs to a group of cratonic basins that are tectonically quiescent and characterized by the association of abnormal pressures with natural gas begin page 146

structural controls on submarine fan geometry and internal architecture upper la jolla fan system offshore southern california la jolla fan offshore of san diego california is a well studied example of submarine fan sedimentation yet the internal architecture of the fan has remained poorly known high resolution seismic data recorded in a 1 by 2 mi 1 6 by 3 3 km grid over much of the fan allow better understanding of upper and middle fan features and processes and of structural controls on fan sedimentation three bathymetrically prominent conduits supply sediment to the upper la jolla fan system from stream and nearshore littoral drift cell sources la jolla canyon and contiguous la jolla fan valley is the main feeder to the fan seismic profiling data confirm the previously reported erosional character of the channel and constructional nature of flanking levees these data also reveal that the position of the channel is controlled by the geometry of a buried hard rock structure newport canyon channel northerly feeder to the upper la jolla fan system is a single well defined channel with flanking constructional levees where it lies in a structurally controlled trough in contrast the channel splays into multiple broad poorly defined channels where sedimentation is unconstrained a buried pliocene pleistocene ancestral version of newport channel displays the same structural control the position of loma sea valley southern feeder to la jolla fan system is tightly controlled by the structure of the steep flank of coronado bank thus loma sea valley trends parallel with the shore and is fed by an orthogonal set of tributary channels which drains the san diego shelf to the east at intersections with these tributaries abnormal thicknesses of sediment partially clog loma sea valley these channel fills may be analogous to those occurring in terrestrial trunk stream intermittent tributary systems like the colorado river in the grand canyon seismic data demonstrate that the la jolla fan system comprises a complex interleaved set of sediment wedges derived from multiple sources and woven around the wrench tectonic fabric of uplifts and basins of the southern california borderland thus la jolla fan system presents an expansion from the simple radial growth pattern of fan sedimentation to a complex fan system built of a number of smaller interwoven radial growth components despite these complexities lithofacies patterns are in part predictable for the la jolla fan system fault bounded uplifts form long lived barriers to sediment dispersal and enhance channel development along their flanks multistory channel complexes detectable seismically commonly occur in these structurally controlled positions adjacent to wrench elated uplifts

compound specific isotope analysis as a tool for characterizing mixed oils an example from the west of shetlands area abstract the origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources or when multiple episodes of charging are involved in this study oils from the clair field west of shetland islands which are mixtures of nonbiodegraded oil added to biodegraded oil are characterized by comparing the carbon isotope ratios of the gasoline range hydrocarbons grh of the oil to the grh released from the pyrolysis of the asphaltenes in the oil this comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir information useful in assessing the source potential of the basin

a recent turbidity current event hueneme fan california reconstruction of flow properties a recent 100 yr old turbidite is described from hueneme fan california continental borderland dense sampling over the fan surface has allowed excellent delineation of the characteristics of this deposit it exhibits bouna de sequences and has a distinctly bimodal sandy silt grain size distribution through the use of generalized fluid dynamics equations it is possible to reconstruct original flow properties of the current which deposited this material the calculated velocities ranged from 10 90 cm s 1 and excess density above ambient seawater from 0 001 0 005 g cm 3 in the lower midfan and upper fan channel regions respectively height of the current ranged from 5 15 m on slopes from 1 5 to 0 15 a total of 107 m3 of sediment was deposited during 10 days the turbidity current is conjectured to have originated from direct river input during the floods of 1884 an older event is also described which has distinctly different properties and origins the grain sizes of this older deposit are much coarser and sedimentary structures suggest higher flow regimes this turbidite is conjectured to have been deposited from a higher density faster current thought to have been generated by slumping the need for a better understanding of the controls on the characteristics of turbidity currents and their effect on fan morphology is emphasized

small turbidite systems in a complex tectonic setting sw mediterranean sea morphology and growth patterns abstract three small turbidite systems almeria sacratif and guadiaro each tens of kilometres long are developed in the complex morpho structural setting of the northern alboran sea and have similar primary architectural elements canyons channel levee systems lobes however comparison reveals differences in the axial gradients of their canyons depth physiographic location morphological framework and lateral and longitudinal sedimentary shifts of turbidite deposition the depositional architecture and sedimentary evolution from late pliocene to quaternary seems to be conditioned by number of submarine feeding sources canyons sea level fluctuations and local tectonic e g margin canyon channel gradients faults we group the alboran turbidite systems into two models mud sand rich submarine point source and mud sand rich multiple submarine source ramp

effect of co2 flood on geochemistry of mcelroy oil abstract geochemical characterization has been completed on a series of oil samples collected over time from the mcelroy field texas where a pilot co 2 flood project was initiated a few years ago a non waxy 31 gravity o api oil is produced from carbonate reservoirs within the permian grayburg formation the samples were taken from various wells over a time span of one and one half years for monitoring changes in oil composition induced by co 2 injection over time the oil samples taken from about 40 wells shortly after the start of co 2 injection showed a marked reduction 50 in the asphaltene content indicating co 2 induced asphaltene deposition had occurred mapping asphaltene reduction could provide information on the flow direction of co 2 in the reservoir hydrocarbon profiles of the oils from some wells also showed a significant reduction in the heavy paraffin content i e c 25 suggesting deposition of heavy hydrocarbons within the reservoir the observation of a slight increase in oil api gravity is also consistent with precipitation of heavy components from the oil phase due to co 2 injection the organic deposits or flocs which can cause restriction of fluid flow in the reservoir by reducing porosity and permeability have probably contributed to reduction in injectivity experienced by some injection wells shortly after the start of co 2 injection field observations have been duplicated in laboratory core flood experiments to mimic the field recovery process the experiments show that most of heavy organics were deposited near the co 2 injection port suggesting organic deposition in the field occurs near the injection wells rather than producing wells despite the continued co 2 flood some molecular properties such as sterane and hopane distributions remain relatively unchanged these geochemical parameters are commonly derived from ratios of compounds with similar molecular properties and are generally not affected by the co 2 flood as precipitation of heavy hydrocarbons causes little fractionation among these compounds thus oil samples from fields under the gas flood are still viable for correlation source evaluation and maturity determination

origin and occurrence of 25 norhopanes a statistical study abstract the alkane fraction of more than 200 rocks biodegraded oils and non biodegraded oils have been analysed by means of computerized gc ms in order to investigate the effect of natural biodegradation on the occurrence of demethylated hopanes i e 17 25 norhopanes the results obtained indicate that 25 norhopanes are preexisting biomarkers the concentration of which is enhanced by selective biodegradation of more readily degradable homologs i e regular hopanes rather than by demethylation of hopanes in reservoirs however the use of 25 norhopane enrichment as a palaebiodegradation indicator in apparently non biodegraded oils is still valuable providing the initial background content in the corresponding source rocks is known furthermore 25 norhopanes appear to be diagnostic of specific environmental conditions marine and lacustrine source rocks dysoxic and not very hypersaline lastly one other novel bacterially resistant rearranged hopanoic compound namely a c29 neohopane is applicable for both biodegradation and maturation evaluation

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

holocene sediment budgets for the basins of the california continental borderland abstract two holocene sediment budgets have been compiled for the california continental borderland the first detailed budget includes the six northern inshore and central basins that capture almost 40 of the total sediment input to the entire borderland in the second budget the data for the six basins has been added to estimates of accumulation for the remaining borderland area to produce a total regional budget of lower precision than the smaller six basin region natural river influx to the borderland approximates 13 1010 tons for the holocene epoch and biological input has been estimated at about 2 1010 tons eolian and ocean current influx have each been estimated at about 1 1010 tons in sum the total deposited volume for 104 yrs is about 14 1010 tons and the estimated total influx is of the order of 17 1010 tons which suggests that a net of 1 3 101010 tons for the holocene high sea level period the six high accumulation rate basins are located adjacent to the largest river sources the major zones of coastal upwelling and the main northern eddies of the california current these high accumulation sites are typically also areas where mass movement and fan development are localized the sediment accumulation rate is much larger than subsidence rate and flat floored basins are typical in contrast the southern and outer low accumulation basins are areas of draped sediment with accumulation rate less than subsidence rate and are the sites of penecontemporaneous deformation of the accumulating fine hemipelagic sediments few fans or major mass movements are seen significant sedimentation is mainly confined by topography to less than 20 of total margin area thus the moderate to low total sediment influx is amplified by the restricted receiving area to produce locally thick deposits of limited areal extent this pattern is characteristic of neogene southern california basins and illustrates that stratigraphic thickness is not a valid indicator of sediment influx

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

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

geochemical effects of asphaltene separation procedures changes in sterane terpane and methylalkane distributions in maltenes and asphaltene co precipitates asphaltene precipitation either natural or artificial may be an important cause of observed compositional differences in oils of identical source and maturity we studied variations in both the bulk and molecular compositions of maltenes and asphaltene co precipitates prepared from six different oils using different procedures the first procedure used a single treatment with n pentane iptc to separate asphaltenes from maltenes the second procedure applied four sequential n pentane extractions of the iptc asphaltenes four times 4ptc analyses of resulting fractions included thin layer chromatography tlc gas chromatography gc and gas chromatography mass spectrometry gc ms these asphaltene separation processes resulted in changes in geochemical parameters previously considered to be influenced solely by source or thermal maturity maltene geochemical parameters not significantly affected by multiple n pentane extractions of the n pentane precipitated asphaltenes were the c 15 c 35 n paraffin distributions except for a small increase in higher n alkanes hopane and homohopane distributions tm ts ratios and c 27 c 28 c 29 sterane distributions maltene geochemical parameters which were affected by multiple n pentane washes of the n pentane precipitated asphaltenes were increases in the c 21 and c 22 sterane pregnane to c 27 c 28 c 29 and c 30 sterane and c 20 to c 24 tricyclic terpane to c 29 to c 35 hopane ratios the n pentane precipitated asphaltene co precipitates showed an increasing ratio of methylalkanes to n alkanes in the range from c 25 to c 36 following multiple extractions with n pentane these results suggest mechanisms of molecular interactions between maltenes and asphaltenes

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

southern california inner basin sediment trap calibration the deployment of particle interceptor traps pits in the three inner basins of the southern california bight santa barbara santa monica and san pedro where preserved laminated bottom sediments occur provides a natural calibration between the parameters determined with the pits and those derived from the historical sedimentary deposits the accumulation rates and chemical composition of the pit materials compare favorably with these recently deposited bottom sediments the ratio of the measured particle collection rate to the sediment accumulation rate for these three basins averaged0 93 0 20 radionuclide 210pb 228th 232th and trace element fe cu zn cd pb compositions of the pit materials and surface sediments agree within generally 30 in each basin an application of pits as a sampling system in an outer basin san nicolas where the sedimentary record has been obscured by bioturbation is also presented to further demonstrate the utility of pits for spatial and temporal studies of various aspects of particle transport and sediment deposition based on the calibration of the pits in the three inner basins we conclude from the comparison of the radionuclide and trace element compositions between the pit materials and surface sediments from the san nicolas basin that recently deposited sedimentary material has been mixed by bioturbation with older material from the last several hundred years excess210pb and the228th 232th activity ratio in the pit material are 6 and 15 times higher than in the surface sediment total pb and1n hno3 leachable pb are 4 and 8 fold higher in the pit material

pyrobitumen occurrence and formation in a cambro ordovician sandstone reservoir fahud salt basin north oman the cambro ordovician barik sandstone reservoirs in the fahud salt basin in oman contain bitumen which may fill up to 40 of the porosity in well jaleel 1 this bitumen was isolated according to kerogen procedure and typed by nmr elemental analysis and density measurements the isolated bitumen is characterized by 1 a highly aromatic character nmr 75 caro h c atomic ratio 0 65 2 a very high sulphur content 4 2 and 3 a relatively high density 1 3 1 4 g cm3 the insolubility and the reflectivity of the bitumen 1 2 vr qualify it as a low mature pyrobitumen the combination of rock eval and density data was used to calculate the actual volume of the pyrobitumen in the rock as a percentage of porosity it was found that the pyrobitumen volume shows a negative correlation with total porosity indicating that small pores are more invaded by bitumen than larger ones finally closed system pyrolysis experiments performed on oils with different nso contents indicate that an in situ oil with a very high content of nso compounds is required to generate such large amounts of pyrobitumen in the pore system these observations suggest that the precursor oil of the current pyrobitumen was a very heavy oil tentatively assumed to be the result of a severe biodegradation basin modeling shows that the reservoir was charged already in devonian times a major uplift brought the oil accumulation near the surface during the carboniferous and a rather regular burial to the present day position 4500 m 140 c loosveld et al 1996 this scenario involving a residence time at shallow depth strengthens the biodegradation hypothesis the numerical modeling which involves the ifp kinetic model for secondary oil cracking suggests that pyrobitumen formation is a very recent event inclusion of pyrobitumen particles within quartz overgrowth containing fluid inclusions provides an upper temperature limit for the beginning of pyrobitumen formation which comforts the result of kinetic modelling

a dynamic model for the permian panhandle and hugoton fields western anadarko basin panhandle hugoton the largest north american gas field has long been controversial because of extreme subnormal pressures variable gas composition and tilted fluid contacts commonly attributed to hydrodynamic flow despite the absence of an effective updip aquifer these anomalies are addressed in terms of a basin scale petroleum system history largely independent of the geographically underlying pre permian system hydrocarbons were already being generated in the deep anadarko basin during the early permian with efficient southward migration from all potential source rocks via bounding faults and pennsylvanian permian alluvial fans giant amarillo uplift drape structures trapped hydrocarbons immediately following permian evaporite deposition the pre laramide panhandle field at maximum burial depth and pressure contained most of the oil and gas now found in mid continent permian reservoirs the early tertiary laramide orogeny redistributed panhandle field fluid columns possibly spilling gas into the hugoton embayment subsequent erosion of permian reservoir facies in eastern kansas allowed water discharge to outcrops at elevations below the regional hydraulic head as regional pressure dropped in response the panhandle field gas cap expanded rapidly forcing a late tertiary quaternary mass movement of gas northward to fill hugoton and associated fields panhandle hugoton pressures upon discovery were subnormal relative to drilling depth but normal relative to reservoir outcrop elevations in eastern kansas indicating that pressures are controlled by aquifer communication with the surface instead of burial depth variations in fluid contacts pressure and gas composition suggest that reservoir fluids are still moving driven by decompression and the rapid volumetric expansion of a supergiant gas accumulation

petroleum migration alteration and remigration within troll field norwegian north sea troll field represents the largest petroleum discovery within the entire north sea area in oil equivalents with 74 of the accumulated petroleum present as dry gas and 26 as a heavy biodegraded oil leg the field is divided into several provinces based on the distribution of gas and oil and the gas and oil have been suggested to be cogenetic the migration and filling model presented in this paper suggests that the oil and gas represent two different migration phases and that gas migration and filling predate oil emplacement two different oil populations have been characterized and mapped in troll field applying conventional geochemical techniques we suggest that the two oil populations migrated into the structure through two different migration systems oil and gas were subsequently biodegraded within the reservoir the two oil populations have been found in neighboring oil and gas discoveries and an oil oil correlation with these discoveries has been used to determine the location of field filling points and regional migration routes when oil biodegradation terminated fresh oil continued to migrate into the reservoir and mixed with the residue of the biodegraded oil the field was tilted downward to the west in the neogene and oil and gas remigrated within the field with a possible spillage of gas tilting resulted in a dominantly upward movement of the oil phase whereas gas migrated laterally residual oils in the water zone copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received july 18 1995 revised manuscript received march 14 1996 final acceptance august 16 1996 2saga petroleum a s kjorboveien 16 p o box 490 n 1301 sandvika norway 3newcastle research group drummond building university of newcastle upon tyne newcastle upon tyne ne1 7ru united kingdom we would like to thank the partners in the troll license who allowed us to publish these results per erling johansen and tone molvik are acknowledged for the analytical work and snorre olaussen nigel mills and terje hellem are thanked for helpful discussions and for assistance with the back tilting of the irap reservoir field model jill sonrier is acknowledged for typing we acknowledge k m wolgemuth john f brint and two anonymous reviewers for helpful comments that improved the paper significantly

geochemical study of potential source rocks and crude oils in the anadarko basin oklahoma paleozoic source rocks and crude oils from the anadarko basin oklahoma have been characterized by means of a variety of organic geochemical techniques the potential source rocks investigated include the viola group sylvan shale lower mississippian limestone chester group springer formation and morrow group the woodford shale which is an important source rock in the basin and has been discussed extensively in the literature was used as a laboratory standard in this study the crude oils examined in this study were obtained from reservoir formations of various ages from throughout the basin the source rock screening analysis indicates that the lower and middle subfacies of the viola especially from the southeastern part of the basin have substantial oil generation potential the sylvan is not a source rock although the black shales in the springer and morrow have substantial oil and especially gas generation potential the results of this study support the proposal for multiple sources of oil and gas generation in the anadarko basin selected source rock and oil samples were characterized in more detail and the distributions and concentrations both relative and absolute concentrations of biomarkers in different source rocks and oils were determined the biomarker characteristics were combined with other geochemical and geological data to interpret the sources depositional environments diagenesis and catagenesis processes migration and weathering oil source rock correlations were made between source rocks and a number of crude oils based on quantitative and qualitative biomarker distributions petrographic descriptions and graptolite reflectance measurements were used to evaluate copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received november 1 1995 revised manuscript received april 8 1996 final acceptance september 13 1996 2arco international oil and gas company 2300 w plano parkway plano texas 75057 3school of geology and geophysics university of oklahoma norman oklahoma 73019

the shir kuh pluton central iran magnetic fabric evidences for the coalescence of magma batches during emplacement abstract the 136 ma nw se elongate shir kuh pluton is one of the most poorly understood geological feature of central iran it is composed of peraluminous rocks corresponding to ilmenite bearing s type granites compositionally ranging from granodiorites to leucogranites these rocks show a continuum in their chemistry attributed to progressive differentiation this allows using the anisotropy of magnetic susceptibility technique to tempt establishing the relative chronology between emplacements of magma batches in the pluton the rather low susceptibility magnitudes km

south eubank field haskell county kansas a case of field redevelopment using subsurface mapping and 3 d seismic data a portion of recent field development efforts in the hugoton embayment of western kansas has focused on deeper less drilled mississippian sandstone reservoirs of the chesterian series such efforts have yielded particular successes in the case of south eubank field haskell county kansas new core data combined with subsurface mapping and three dimensional 3 d seismic information have led to over 30 new producers being drilled in this field reservoirs are best developed in fine grained well sorted chesterian sandstones filling a narrow incised paleovalley system that runs north south through the field although new core information contributed to improved reservoir characterization in the area 3 d seismic data were required to accurately delineate the paleovalley system and thus locate specific prospects a number of such prospects remain to be drilled success at south eubank suggests that other portions of the same valley system also might be similarly developed this system extends at least 50 mi 80 km from northern haskell county to the oklahoma border through a number of existing field areas

monocyclic alkanes in ordovician organic matter abstract the major compounds in the c 15 branched cyclic alkane fractions of two ordovician oils pine unit and midland farms oils and an immature ordovician rock guttenberg oil rock are monocyclics one series of these compounds was identified as n alkylcyclohexanes and another tentatively identified as methyl n alkylcyclohexanes the carbon number distribution of these compounds resembled those of the n alkanes found in these samples with an odd carbon number predominance it is suggested that the monocyclic alkanes in these ordovician samples may be principally derived from the cyclisation of straight chain algal fatty acids by mechanisms that involve decarboxylation however there is evidence from the m z 97 fragmentograms of these samples to indicate that methyl n alkylcyclohexanes can also be derived from fatty acids by a less preferred mechanism that does not involve decarboxylation or from other precursors in addition a sample of kerogen from the guttenberg oil rock was hydrously pyrolysed the saturated hydrocarbon products of this experiment showed very similar distributions including monocyclics to those observed in the ordovician oils this suggests that although the oils and the guttenberg oil rock come from widely differing geographical locations their precursor algal derived organic matter was very similar