geothermometry and geochemistry of aqueous and oil bearing fluid inclusions from fateh field dubai abstract the production of oil from fateh field dubai is principally from the cretaceous mishrif formation porosity in the reservoir facies is partly occluded by late coarse grained calcite cement this cement contains both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry was used to determine the temperature of that cement precipitation and calculate its timing relative to basin burial history these data were related to source rock maturation and from that the timing of oil migration was inferred to be oligocene to mid miocene which is geologically contemporaneous with early petroleum generation r 0 0 5 0 6 in the khatiyah source rock the fluid inclusions were analyzed by a thermal decrepitation gas chromatography technique benzene and low molecular weight paraffins were present and a series of normal alkenes was tentatively identified in the aqueous inclusions fresh oil inclusions consisted of c 1 n c 25 compounds whose light hydrocarbon composition was consistent with derivation from an early mature source rock altered petroleum residues detected in many mishrif samples are contained either in inclusions or along crystal cleavages these materials are the subject of an ongoing geochemical study of fateh field

sunward polar cap convection this is a study of the conditions for which there is sunward convection in the central polar cap the study of convection direction uses digital ionosonde measurements from two central polar cap stations resolute bay corrected geomagnetic cg latitude 83 3 n and eureka cg latitude 88 67 n and presents statistical results about pure sunward convection events the sunward convection events in the central cap region are observed only when the interplanetary magnetic field imf bz is 2 nt for weak northward imf 3 nt sunward convection occurs at all local times indicating the expansion of reverse convection to most of the central polar cap there are very notable imf by effects on the pattern of sunward convection for imf by positive the axis of the pattern of reverse convection appears to rotate toward the postnoon whereas for imf by negative the axis is rotated toward the prenoon these axis orientations are compatible with the expected locations of lobe cell merging another significant imf by effect is that the duration of sunward convection intervals when imf by is negative is about the same as the duration of the northward imf intervals whereas for positive imf by the sunward convection intervals usually last only for a short duration 1 hour however if the northward imf interval is much longer than 1 hour there is a sequence of these l hour sunward convection events the convection pattern during northward imf appears to be compatible with a four cell form

biomarkers in fluid inclusions a new tool in constraining source regimes and its implications for the genesis of mississippi valley type deposits biomarkers in fluid inclusion s can constrain source regimes for hydrocarbons associated with mississippi valley type pb zn deposits significant amounts of hydrocarbons have been detected in fluid inclusions in sphalerite and dolomite intimately associated with pb zn sulfides in the canning basin western australia the hydrocarbons are more mature than those in the host rocks to the ore and are therefore derived from an external source furthermore there are differences between the biomarker components of hydrocarbonas in inclusions in pb zn prospects but they are all different from hydrocarbons in organic rich strata and also in oils from the canning basin yet the hydrocarbons are mature and oil like suggesting that mature organic rich strata deeper in the basin which are less significant as potential source rocks for petroleum generation in the canning basin have contributed to the ore forming fluids

pyrosequencing reveals the dominance of methylotrophic methanogenesis in a coal bed methane reservoir associated with eastern ordos basin in china it is generally believed that biogenic coal bed methane cbm is an end product of coal biodegradation by methanogenic archaea and syntrophic bacteria in this work the archaeal and bacterial communities of cbm reservoir associated with ordos basin in china were investigated using 454 pyrosequencing sampling produced water coal and rock in the reservoir a total of 46 598 sequence reads were obtained all archaea were methanogens with the genus methanolobus predominating the genus consisted of 81 18 of pyrosequencing reads in water sample and 99 in coal and rock samples although the phylum proteobacteria was the main component of all samples bacterial communities in coal and rock samples were similar at the genus level which were distinctly separated with water sample the results strongly suggested that methylotrophic methanogenesis governed the biogenic cbm formation the separation of microbial communities between water and coal rock samples should be considered when investigating the process of coal biodegradation and the generation of new biogenic cbm c 2012 elsevier b v all rights reserved

observations of imf and seasonal effects in high latitude convection the authors describe strong interplanetary magnetic field imf and seasonal effects in the convection of nightside ionospheric plasma the findings are based on a statistical analysis of observations made with the jhu apl hf radar located at goose bay labrador for positive sign of the imf dawn dusk component i e b sub y 0 the dawn cell is more crescent shaped and the dusk cell more round while for b sub y 0 the return flows associated with the crescent shaped cell dominate at midnight mlt magnetic local time the reversal in the zonal velocity in the 67 degrees 69 degrees lambda magnetic latitude interval occurs 2 1 2 hr earlier for b sub y 0 the seasonal dependence of nightside convection resembles in important respects the b sub y dependence greater latitudinal velocity shears occur in the morning afternoon sector for summer winter and the return flow of this sector dominates at midnight the zonal flow reversal occurs 2 1 2 hr earlier in summer than in winter the maximum effects are obtained on the nightside for the pairings b sub y 0 summer and b sub y 0 winter the first produces the more structured cell in the morning the second inmore the evening and this cell dominates the return flow at midnight the difference in the zonal flow reversals for these pairings exceeds 4 hr in mlt 15 refs 4 figs less

hydrocarbon water interactions during brine migration evidence from hydrocarbon inclusions in calcite cements from danish north sea oil fields abstract crude oils in primary and secondary fluid inclusions in calcite from fractures in seven offshore oil fields associated with diapiric salt structures in the danish sector of the north sea were analyzed by capillary column gas chromatography and compared with crude oils produced from the same reservoirs oils from fluid inclusions in all fields show evidence of biodegradation decreased n c17 pristane and n c18 phytane ratios and loss of n c7 2 methyl hexane and 3 methyl hexane relative to methyl cyclohexane and water washing absence of benzene and depletion of toluene some oils in inclusions are extremely enriched in c6 and c7 cyclic alkanes suggesting that these samples contain hydrocarbons exsolved from ascending hotter formation waters compared to inclusion oils the produced oils are less biodegraded but are water washed indicating that both types of oil interacted with large volumes of formation water the carbon isotopic composition of the calcite host of the fluid inclusions in the dagmar and skjold fields is as light as 16 5 pdb and the sulfur isotopic composition of pyrite in and adjacent to the calcite veins in the skjold field is as light as 39 6 cdt indicating that biodegradation of the oils was a source of some of the carbon in the calcite and sulfate reduction was the source of sulfur for the pyrite the evidence for microbial degradation of petroleum is consistent with present day reservoir temperatures 65 96 c but is not consistent with previous estimates of the temperatures of calcite vein filling 95 130 c which are much higher than the temperatures of known occurrences of biodegraded oil

gps tec variations in the polar cap ionosphere solar wind and imf dependence this statistical study examines the solar wind dependence of total electron content tec variations arising from mesoscale tens to hundreds of kilometers structuring of the polar cap ionosphere six years of tec measurements were collected from five high data rate global positioning system gps receivers of the canadian high arctic ionospheric network chain from which high resolution magnetic local time latitude maps of tec variation occurrence rate and amplitude were created ionosonde radars were used to identify tec variations arising from ionization of the e and f region ionospheres statistical tec maps were examined as a function of solar wind and interplanetary magnetic field imf measurements statistical results showed that occurrence rate of tec variations was highest in localized dayside regions with exact local time and latitude of peak occurrence depending primarily on the dayside coupling rate of the solar wind and magnetosphere as well as imf orientation and magnitude in the y z plane occurrence of tec variations throughout the polar cap increased with solar wind magnetosphere coupling rate and imf magnitude the solar wind dependence of occurrence rate largely reflected the location and rate of dayside magnetic reconnection and subsequent particle precipitation and polar cap convection amplitudes of tec variations were largest around noon and increased throughout the polar cap with increased solar wind magnetosphere coupling rate these statistical results improve upon the existing observational picture of the polar ionosphere and will potentially facilitate development of models and techniques for mitigating impacts of the polar ionosphere on navigation signals and communication links

the petroleum characteristics and filling history of the froy field and the rind discovery norwegian north sea abstract the brent group reservoirs of the froy field and the rind discovery norwegian north sea show complex distributions of petroleum and aqueous fluids multiple fluid contacts are present in the rind discovery and the fields show various extent of compartmentalisation due to faulting geochemistry data of core extracts indicate that the two fields have different petroleum sources bhullar karlsen holm backer owe tran 1998 late diagenetic modifications of the reservoir quality consist of quartz cementation followed by carbonate and kaolinite cementation and dissolution of k feldspar fluid inclusion results indicate that filling of the reservoirs occurred after the main phase of quartz cementation at pressure temperature conditions close to the present differences in fluid properties between fault compartments in both fields have been identified fluid inclusion data have proved especially valuable for evaluation of the sealing capacity of faults through time and given evidence for the fault lineament north of both fields to be a time integrated pressure seal except for a lower gas condensate zone in the 25 2 13 compartment of rind the present reservoir fluids are volatile oils close to gas saturation the previous presence of an oil in the lower reservoir zone of 25 2 13 has also been demonstrated the fluid inclusion data indicate that the condensate in 25 2 13 represents a second episode of migration filling rather than phase separation

uv raman spectroscopy of hydrocarbon bearing inclusions in rock salt from the dongying sag eastern china abstract compositions of hydrocarbon bearing inclusions in rock salt halite from the shahejie formation in the dongying sag bohai bay basin eastern china have been analysed by raman spectroscopy coupled with a 244 nm uv laser source the fluorescence effect caused by the conventional visible laser excitation of the aromatic fractions of hc bearing inclusions can be effectively avoided six types of hc bearing inclusions belonging to two generations have been identified in halite according to their hydrocarbon types and petrographic characteristics the presence of hc bearing inclusions in halite provides evidence of crystal fracturing and healing plastic deformation and dynamic recrystallization of rock salt in the dongying sag this proves that rock salt may have repeatedly lost and then recovered its sealing capacity during two stages of oil emplacement water and hydrocarbons were detected by uv raman spectroscopy in the studied samples in both hc bearing inclusions and aqueous inclusions these results are important for understanding the formation conditions of these fluid inclusions and the interactions between the formation water and petroleum in reservoirs our results show that uv raman spectroscopy has a potential to become a powerful tool for analyzing hydrocarbon bearing fluid inclusions trapped in various elements of a petroleum system

chemical changes of fluid inclusion oil trapped during the evolution of an oil reservoir jabiru 1a case study timor sea australia abstract this study of the jabiru oil field timor sea australia shows how the variability of visual properties of fluid inclusions in palaeo oil zones can be mapped to identify internal structures that result from fluid interactions in the reservoir variability in the attributes of oil inclusion assemblages oias is greater within an inferred palaeo gas cap zone 1 and current residual zone zone 3 and less within the current oil zone zone 2 in zone 3 where water imbibed a higher proportion of oias with visual white fluorescing oil inclusions correlates with less mono aromatic compounds and a higher abundance of polar compounds determined on a bulk extract of inclusion oil using high performance liquid chromatography hplc the ch 2 ch 3 ratios and water contents determined by fourier transform infrared spectroscopy ft ir are higher in zone 1 where gas drained there is a higher proportion of oias with visual yellow fluorescing oil inclusions and these correlate with low hplc mono aromatic and moderate polar contents and low ft ir ch 2 ch 3 ratios and water contents interpretation of the grains with oil inclusions goi and pressure volume temperature composition pvtx fluid inclusion data suggests that a gas saturated blue fluorescing palaeo oil was present in the three zones at the same pressure temperature fluid inclusion forming event pt 1 lighter gas saturated blue fluorescing oil was present in zone 2 but was rarer in zones 1 and 3 at the later fluid inclusion forming event pt 2 the yellow and white inclusion oils trapped in zones 1 and 3 respectively are gas depleted and interpreted to result from the interaction between non movable residual oil around grains with the surrounding gas and water respectively comparison between the pvtx data and the published burial curve suggests that most of the fluid inclusions were trapped during two different hot fluid flow events the full oil column is interpreted to have been present during early mid tertiary the palaeo oil column was reduced during the late miocene by imbibition of water in the present residual zone and drainage of gas at the top of the reservoir

organic geochemistry of crude oils from the vienna basin and an assessment of their origin abstract a representative collection of oil samples and neogene rock samples from the vienna basin has been analyzed by organic geochemical methods the relatively high maturity of the crude oils and the characteristics of their hydrocarbon composition makes it unlikely that they are derived from the neogene sediments of the vienna basin furthermore investigation of the rock samples also showed that these sedimentary strata do not have the potential for generation of liquid hydrocarbons however there is some potential for gas generation even the deepest neogene sediments 4000 m depth just have reached the onset of the hydrocarbon generation zone from these results it has to be concluded that the bulk of the oil found so far in the vienna basin originated from pre tertiary sediments below the neogene basin

geochemistry of oil from santa cruz basin bolivia case study of migration fractionation geochemical studies provide important data relevant to the origin of the oils in the santa cruz basin bolivia production from this basin occurs from rocks of devonian carboniferous cretaceous and tertiary ages the productive structures are usually undisturbed by major faulting the devonian sediments are composed of sandstones and dark marine shales the post devonian rocks are generally oxidized and probably nonmarine the tertiary and cretaceous reservoirs usually contain the highest api gravity oils comparison of geochemical data n5 n10 molecular weight range shows that the oils are very similar however systematic compositional trends occur as a function of api gravity these trends are interpreted from gross structural group data isoparaffins and cycloparaffins increase in relative abundance while normal paraffins and aromatics decrease with increasing api gravity a model is proposed that rationalizes these compositional trends by a mechanism of accommodation in water the model requires enrichment of hydrocarbons of intermediate solubility partial exclusion of hydrocarbons of low solubility and retention in solution of the more soluble hydrocarbons processes such as thermal fractionation and biodegradation fail to account satisfacto ily for the observed compositional trends the compositional interrelationships of the oils coupled with the geologic framework suggest that these oils have a common source most probably the devonian differences between the oils are attributed to fractionation occurring during migration exploration risk for areas such as the santa cruz basin can be substantially reduced by use of the knowledge derived from petroleum geochemistry

large scale hot water migration systems around salt diapirs in the danish central trough and their impact on diagenesis of chalk reservoirs abstract fracture filling calcite from the piercement fields of east rosa skjold rolf north arne nils and vagn directly underlain by salt diapirs and the dome field dan overlying a deep seated salt structure have been studied by fluorescence and cathodoluminiscence microscopy fluid inclusion microthermometry and carbon and oxygen isotopes the carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured the temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs the flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments the thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water by combining fluid inclusion thermometry with o isotope data for the fracture filling calcites ranges of o isotopic values of the flushing water are deduced in skjold rolf north arne nils and vagn 18o 1 to 7 smow values typical of sedimentary porewater of sea water origin in east rosa 18o 4 and 4 smow which combined with data on fluid inclusion salinities suggest that the flushing waters were responsible for substantial salt dissolution lower 18o values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields in the case of north arne nils vagn and dan 13c values of the fracture filling calcites are similar to those of normal chalk 0 5 to 3 5 however calcites from rolf skjold and east rosa are depleted by 1 8 6 2 and 16 7 respectively only in east rosa is the matrix chalk itself depleted in 13c range 2 0 to 0 7 the low 13c values are interpreted as the result of biodegration sulphate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons this process produced 13c depleted bicarbonate which was incorporated into the fracture filling calcites

water washing of proterozoic oil in the midcontinent rift system whole oil gas chromatography shows that petroleum inclusions trapped in 1 05 ga veins in the midcontinent rift experienced variable water washing but no significant biodegradation or phase separation by comparing our results with published experimental data we estimate that water petroleum ratios varied from 200 1 to much greater than 9000 1 extreme water washing with water petroleum ratios very much greater than 9000 1 likely produced pyrobitumen solid hydrocarbon that was locally trapped as primary inclusions in vein calcite hydrothermal ore deposits with their extremely high water rock ratios are one of the best places to search for end member water washed petroleum sedimentary basins however with their variable water rock ratios also have a wide range of water petroleum ratios which significantly affect the composition of crude oils along the flow path between source rock and trap water petroleum ratios may be a useful concept to help evaluate crude oil compositions in a variety of settings

seasonal dependence of high latitude electric fields the seasonal dependence of the high latitude electric field was investigated using sondrestrom incoherent scatter radar data average e times b drifts were derived from 5 years of measurements centered around solar minimum the electrostatic potentials that best fit the observed average electric field were calculated it was found that the large scale convection pattern significantly changes with season this change involves the overall shape of the convection pattern as well as the electric field intensity and thus the total dawn dusk potential across the polar cap the cross polar cap potential drop is largest in fall followed by winter spring and summer the small difference found between the summer and winter cross polar cap potential can be attributed to differing field aligned potential drops in view of the well known relationship between field aligned currents and parallel potential drop this is consistent with the observations that birkeland currents are larger in the summer than in winter changes in the overall shape of the convection pattern are consistent with the simple notion that the whole pattern is shifted toward the nightside as well as to a lesser extent toward the dawnside in summer as compared to winter this assumption is based on the following observed effects 1 themore rotation of the overall convection pattern toward earlier local times with respect to the noon midnight direction is maximum for summer on the dayside 2 on the nightside the harang discontinuity is typically located within the radar field of view lambda 67 to 82 in the winter averaged patterns but it is equatorward of the field of view in summer 3 the line that joins the dawn and dusk potential maxima is shifted toward the midnight sector in summer as compared to winter by about 5 degree 4 in the dawn cell the latitude of the convection reversal is the lowest during summer in the dusk cell the latitude of the reversal is the lowest during winter less

large scale convection patterns observed by dmsp the authors present a comprehensive compilation of the average distribution of the electrostatic potential across the high latitude ionosphere the averages are compiled from potentials along the satellite path calculated from thermal ion drift data from instrumentation on the defense meterological satellite program dmsp flights 8 and 9 satellites data were collected from the dmsp f8 satellite during the period september 1987 to december 1990 and from the dmsp f9 satellite during the period march 1988 to december 1990 the potential distributions are separated by geomagnetic position season and orientation of the interplanetary magnetic field imf and then averages of the distributions are calculated the average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawk flanks under the influence of the imf b sub y component the cross cap potential decreases as imf b sub z changes from southward to northward the average distributions indicate that the development of more than two convection cells for northward imf is either uncommon or nonexistent for imf b sub z 0 and b sub z vert bar b sub y vert bar a distorted pattern is observed in the average potential distribution not a four cell pattern as some previous studies suggest it should be for allmore orientations of the imf the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary it is not a shear boundary as suggested by some previous investigations on average the harang discontinuity convection reversal in the auroral zone near midnight is observed to exist weakly or not at all when examining individual passes a strong eastward flow is present sometimes in the region of the harang discontinuity especially on the poleward boundary but not at all times as implied by the heppner maynard model 39 refs 9 figs 2 tabs less

conditions for veining in the barrandian basin lower palaeozoic czech republic evidence from fluid inclusion and apatite fission track analysis abstract the interplay between fracture propagation and fluid composition and circulation has been examined by deciphering vein sequences in silurian and devonian limestones and shales at kosov quarry in the barrandian basin three successive vein generations were recognised that can be attributed to different stages of a basinal cycle almost all generations of fracture cements host abundant liquid hydrocarbon inclusions that indicate repeated episodes of petroleum migration through the strata during burial tectonic compression and uplift the earliest veins that propagated prior to folding were displacive fibrous beef calcite veins occurring parallel to the bedding of some shale beds hydrocarbon inclusions within calcite possess homogenisation temperatures between 58 and 68 c and show that the beef calcites originated in the deeper burial environment during early petroleum migration from overpressured shales e w striking extension veins that postdate beef calcite formed in response to variscan orogenic deformations based on apatite fission track analysis afta data and other geological evidence the veins probably formed 380 315 ma ago roughly coinciding with peak burial heating of the strata folding and the intrusion of variscan synorogenic granites the veins that crosscut diagenetic cements and low amplitude stylolites in host limestones are oriented semi vertically to the bedding plane and are filled with cloudy twinned calcite idiomorphic smoky quartz and residues of hardened bitumen calcite and quartz cements contain abundant blue and blue green fluorescing primary inclusions of liquid hydrocarbons that homogenise between 50 and 110 c geochemical characteristics of the fluids as revealed by gas chromatography mass spectrometry particularly the presence of olefins and parent aromatic hydrocarbons phenonthrene suggest that the oil entrapped in the inclusions experienced intense but geologically fast heating that resulted in thermal pyrolysis of its hydrocarbons this implies that the organic fluids in the fractures may have been partly influenced by heating associated with igneous intrusions that are hidden below the surface subvertical n s striking veins represent the most recent fracturing event s some of these veins are only a few millimeters thick and sparsely mineralised with thin leaf like quartz crystals that contain tiny blue and yellow orange fluorescing hydrocarbon inclusions most of the n s veins however occur as thick calcite veins that generally crystallised at 70 c or less from h2o nacl solutions of variable salinity with admixture of petroleum the origin of these fluids is interpreted in terms of deeply circulating meteoric waters that partially mixed with deep basinal fluids wider structural considerations combined with fission track analysis of adjacent host sediments suggest that n s veins formed during post mesozoic uplift of the area probably in response to major tertiary alpine deformations transmitted far into the bohemian massif

seasonal and imf by effect on the polar cap convection orientation seasonal and imf by effect on the polar cap convection orientation is studied using the canadian advanced digital ionosondes cadi situated at eureka cgm lat 88 67 n and resolute bay cgm lat 83 55 n two polar cap stations in this study we determined the daily convection orientation mlt towards which the convection is directed for each day of 1995 the orientation shows clear seasonal variation being latest in winter and earliest in summer strong northward imf conditions are excluded from the study the convection pattern is rotated clockwise by 4hrs from winter to summer this includes rotation due to the curvature of the flow 2 hours during summer months the convection pattern also shows an imf by dependence the orientation is earlier by about 2 hours when imf by is positive relative to when it is negative the observed seasonal changes in the convection orientation can be broadly explained by the changes in the ratio of the region 1 and region 2 field aligned currents

geochemistry of oil in fluid inclusions in a middle proterozoic igneous intrusion implications for the source of hydrocarbons in crystalline rocks abstract the ca 1280 ma dolerite sill within the mesoproterozoic roper group in the roper superbasin australia contains evidence for at least two episodes of hydrocarbon migration represented respectively by solid bitumen with a ketone rich extract and a mixture of a high maturity gas condensate and a lower maturity oil within oil bearing fluid inclusions the ketone isomers are formed by flash pyrolysis of kerogen during the intrusion of the dolerite sill org geochem 21 1994 829 and represent the first and oldest phase of hydrocarbon migration the gas condensate and oil were subsequently trapped as a mixture within fluid inclusions at diagenetic temperatures and pressures of around 110 c and 250 bars significantly after cooling of the sill and likely during the neoproterozoic reactivation of the roper superbasin either 1 these fluids migrated together and mixed in the reservoir or 2 an earlier oil charge was flushed by a later condensate charge and the oil condensate mixture was trapped within single fluid inclusions oil inclusions occur chiefly within albitised zones of labradorite laths within the dolerite matrix and within transcrystalline microfractures cutting vein calcite and rarely vein quartz oil inclusions trapped in the vein calcite are accompanied by hypersaline ca mg brines gas chromatography mass spectrometry of oil extracted from inclusions within the dolerite matrix shows that the oil is non biodegraded and was therefore trapped relatively quickly within the host minerals trace amounts of biomarkers indicate that the inclusion oil is of a biogenic origin and excludes any abiotic processes that are apparent sources of hydrocarbons in many crystalline rocks monomethylalkanes pentacyclic terpanes chiefly comprising hopanes and diahopanes and very low concentrations of steranes and diasteranes indicate input from cyanobacterial organic matter with a minor contribution from eukaryotes the hydrocarbons are likely derived from proterozoic source rocks such as the directly overlying velkerri formation and or the underlying barney creek formation from the mcarthur group the study has implications for the source of hydrocarbons in non sedimentary rocks and suggests that fluid inclusions can be used not only to distinguish between biogenic and abiogenic sources of hydrocarbons but also to provide critical information about the composition of the biomass fluid migration events and conditions under which hydrocarbons in different geological settings are trapped

substorm associated changes in the high latitude ionospheric convection 1 a study of polar cap dayside convection response to substorm intervals using canadian advanced digital ionosondes cadis situated well within the polar cap and superdarn radars during steady and prolonged southward imf bz conditions showed three distinct features 1 gradual prolonged decrease of dayside polar cap convection speed until the substorm onset 2 sudden decrease of convection following the onset of the substorm and 3 increase of convection during the recovery phase of the substorm we hypothesize that the observed features of the convection are due to the modulation of the region 1 current system associated with the substorm the ground magnetic response of magnetometers situated inside the polar cap is at least consistent with our postulate

fluid inclusion petrography and tectonic burial history of the al ali no 2 well evidence for the timing of diagenesis and oil migration northern oman foredeep cores cut in shallow marine lower and middle cretaceous carbonates in the al ali no 2 well umm al qaiwain united arab emirates display a five stage sequence of calcite cementation fracturing and stylolitization these stages are correlated with the tectonic history of the northern oman orogeny occurrence of fluorescent hydrocarbon fluid inclusions is restricted to stage 2 and stage 3 fracture filling calcites that are crosscut by stylolites stylolite formation during rapid burial beneath abyssal campanian foredeep sediments restricts hydrocarbon migration to post mid cenomanian and pre mid campanian time

geology and geochemistry of crude oils bolivar coastal fields venezuela the bolivar coastal fields bcf are located on the eastern margin of lake maracaibo venezuela they form the largest oil field outside of the middle east and contain oil which is mostly heavy with a gravity less than 22 api lake maracaibo is now in an intermontane basin enclosed on three sides by the andes mountains the area has a complex history and tectonic movement continues today in the cretaceous the area was part of the platform of a large geosyncline but by the eocene it was near a coast where a series of large sandy deltas was deposited with terrestrial sediments on the south and thick marine shales on the north at this time conditions for oil generation in the shales and migration to the sands were established but the subsequent oligocene faultin uplift and erosion may have allowed meteoric water to penetrate into reservoirs during the miocene and pliocene the basin was tilted first west and then south and filled with continental sediments from the rising andes tilting is still continuing and oil is moving up along the oligocene unconformity forming surface seeps most oil fields are located in sands above the unconformity or in fault blocks immediately below it thirty crude oils from the bcf were collected along two parallel and generally southwest northeast trends these oils were characterized by their api gravity percent saturates aromatics nso and asphaltic compounds gas chromatograms for whole oils c4 c7 fractions and aromatics also 24 associated waters were sampled and analyzed for ca mg na hco3 co3 so4 ph and total dissolved solids tds the oils show the classic sequence of biodegradation and range from green 40 api oils with a full suite of n alkanes and isoprenoids to black heavy oils with a gas chromatogram that is an unresolved hump in many respects the oils are chemically simi ar and appear related possibly sharing the same source rock the miocene l 5 reservoir contained two oil types which did not appear to fit the main trend one type is depleted in n alkanes in the range c8 c14 whereas the other type is depleted in n alkanes above c17 benzene and toluene values for these oils were normal in general oils in the eocene reservoirs below the unconformity are less degraded than those in the miocene sands above it the formation waters range from very salty 62 000 mg l to quite dilute 3 000 mg l those associated with the degraded oils are typically meteoric in chemical composition with considerable bicarbonate 20 to 90 meq l small quantities of chloride 2 to 25 meq l and extremely low amounts of magnesium and calcium mostly less than 1 meq l if the amount of bicarbonate is taken as an indicator of the meteoric character of the water then the more meteoric the water the more degraded the oil the presence of at least four classes of waters with different compositions in the area of the bcf suggests that there is no through going flow at present many of the fields have oil water contacts descending toward the south showing that continued tilting southward occurred during the mio ene and pliocene after the oil was emplaced in the reservoir it seems likely that there was large scale secondary migration of oil from south to north probably along the unconformity surface which still leaks oil where it is exposed in the shallower miocene reservoirs along the northeast margin of the field heavy asphaltic oil overlies lighter oil downdip to the west and south this suggests that the oil became more degraded the farther it moved finally becoming viscous and asphaltic possibly even gelled in this immobilized form it acted as a seal trapping the less degraded oil which followed

biogenic and petroleum related ore forming processes in dongsheng uranium deposit nw china abstract sandstone hosted roll type u deposits has recently been found in the middle jurassic zhiluo formation in the dongsheng area north of the ordos basin in order to assess the origin of the uranium mineralization the host sandstone has been investigated with emphasis on 34s values of ore stage pyrite 13c of calcite fluid inclusion oil biomarkers x ray diffraction icp ms as well as studies by electron microprobe and scanning electron microscope the mineralization consists mainly of coffinite some of the coffinite is intimately intergrown with ore stage pyrite indicating co precipitation ore stage pyrite has 34s values from 34 to 17 suggesting the pyrite sulfur originated from bacterial sulfate reduction in the host sandstone calcite cement exhibits 13c values from 27 6 to 2 1 and fluid inclusion oils show evidence of biodegradation these lines of evidence indicate petroleum was likely oxidized by sulfate reducing bacteria srb and thus supplied a source of some of the carbon in the calcite microbial degradation of petroleum is partially supported by the low temperature diagenetic environment

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

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

empirical high latitude electric field models electric field measurements from the dynamics explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn dusk ogo 6 measurements j p heppner 1977 the analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones paralleling the previous analysis the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the y component of the interplanetary magnetic field the objective which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns is met by deriving one pattern model bc for the northern hemisphere with a y interplanetary magnetic field imf and southern hemisphere with a y imf and two patterns models a and de for the northern hemisphere with a y imf and southern hemisphere with a y imf the most significant large scale revisions of the ogo 6 models are 1 on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the imf y component 2 on the nightside where a westward flow region poleward from the harang discontinuity appears under model bc conditions and 3 magnetic local time shifts in the positions of the convection cell foci the modeling above was followed by a detailed examination of cases where the imf z component was clearly positive northward neglecting the seasonally dependent cases where irregularities obscure pattern recognition the observations range from reasonable agreement with the new bc and de models to cases where different characteristics appeared primarily at dayside high latitudes the analysis of these differences for strong bz conditions using passes through different mlt zones led to finding that the deviations from both the bc and de models could be modeled by extending the evening cell foci toward and beyond noon with a deformation that roughly resembles a rotational twist of the extended evening cell the morning cell accommodation to the model bc deformation produces a narrow tongue of eastward convection near 75 invariant latitude on the dayside the model de deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 mlt sector in both cases the deformations of the two cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern thus the nightside dilemmas that plague three and four cell models designed to explain sunward convection in polar regions under bz conditions do not appear

high temperature diagenesis in shallow chalk reservoir skjold oil field danish north sea evidence from fluid inclusions and oxygen isotopes samples of calcite filled fractures from the chalk reservoir of the skjold oil field were studied by fluorescence microscopy cathodoluminescence microscopy fluid inclusion microthermometry and oxygen and carbon stable isotope and trace element analyses two generations of calcite infilling are tentatively related to two major phases of faulting caused by salt movements owing to recrystallization of the first generation of infillings the chemical isotopic and fluid inclusion data only apply to the later generation results of the fluid inclusion studies suggest a precipitation temperature of the infilling calcite significantly above what it should be applying today s geothermal gradient 52 c km or 2 85 f 100 ft to the past this higher temperature indic tes that hot water ascending from deeper strata may have flushed the reservoir apparently during a late miocene to pliocene faulting phase when ring faults guided the water to the reservoir this feature may be typical of most chalk reservoirs in the danish central graben where diapirs have penetrated the chalk

seasonal dependence of large scale birkeland currents the seasonal dependence of large scale birkeland currents has been determined from the analysis of vector magnetic field data acquired by the triad satellite in the northern hemisphere statistical characteristics of single sheet i e net currents and double sheet birkeland currents were determined from 555 triad passes during the summer and 408 passes during the winter more complicated multiple sheet current systems were not included in this study the average kp value for the summer events is 1 9 and for the winter events is 2 0 the principal results include the following 1 the single sheet birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season the single sheet currents are also observed more often in the summer than in the winter as much as 2 to 3 times as often depending upon the mlt sector 2 the intensities of the single and double sheet birkeland currents on the dayside from approximately 1000 mlt to 1800 mlt are larger during the summer in comparison to winter by a factor of about 2 3 the intensities of the double sheet birkeland currents in the nightside the dominant system in this local time do not show a significant difference from summer to winter 4 the single and double sheet currents in the dayside between 0600 and 1800 mlt appear at higher latitudes by about 1 to 3 during the summer in comparison to the winter these characteristics suggest that the birkeland current intensities are controlled by the ionospheric conductivity in the polar region the greater occurrence of single sheet birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it since the intensities of birkeland currents are larger during periods of greater ionospheric conductivity an important source but perhaps not the only source of these currents must be a voltage generator in the magnetosphere possibly related to the convective electric field