noble gases in crude oils from the paris basin france implications for the origin of fluids and constraints on oil water gas interactions in order to investigate the potential of noble gases to trace the dynamics of oil reservoirs we have analysed the abundance and isotopic composition of all noble gases he ne ar kr and xe in crude oils from the paris basin france using a new extraction and purification procedure the main oil reservoirs are presently located in the jurassic dogger limestone and in the triassic keuper sandstone but hydrocarbons originated from a common source rock formation located in the interbedded liassic sequence despite this common origin the abundance and isotopic ratios of the noble gases differ between the dogger and the keuper the isotopic compositions of kr and xe are indistinguishable from that of air 3he 4he ratios higher than those predicted from radiogenic production in the sediments or in the crust are attributed to the occurrence of mantle derived 3he in the basin each sedimentary sequence is characterised by well defined and homogeneous 21ne 22ne and 40ar 36ar ratios which average 0 0306 0 0008 and 312 10 for the dogger and 0 0367 0 0012 and 664 30 for the keuper respectively the main source of radiogenic noble gases appears to be the continental crust underlying the basin with possible regional contributions of noble gas isotopes produced in the sediments the helium and argon isotopic ratios of the dogger oils are very similar to those observed in geothermal waters flowing in the dogger aquifer throughout the basin demonstrating that noble gases in oils derive from associated groundwaters oil reservoirs in the paris basin therefore accumulate noble gases from wide regions of the continental crust through cross formational flow of groundwaters and subsequent partitioning into oil this observation implies that noble gases cannot be directly used to date oils but can provide time constraints if 1 water oil interactions are quantified and 2 the residence time as well as the noble gas characteristics of associated groundwaters are known oil water gas partitioning processes are well recorded in the fractionation of noble gas elemental abundance two distinct processes have been identified 1 accumulation of atmosphere derived ang and radiogenic noble gases both initially dissolved in groundwaters resulting in a positive correlation between absolute amount of ang and the extent of heavy noble gas fractionation and 2 subsequent fractional degassing resulting in a negative correlation between ang abundance and heavy noble gas fractionation degassing is particularly evident for the keuper oils and might have occurred in the reservoirs following hydrodynamic gas stripping the ang abundance in the dogger reservoirs requires that about one order of magnitude more water than presently observed has interacted with the oil given current estimates of the residence time for groundwaters in the dogger aquifer the duration of oil water interaction is in qualitative agreement with a palaeocene oligocene age for the major episode of secondary oil migration in the paris basin high xenon contents in keuper reservoirs suggest that they have experienced hydrodynamic interactions between flowing waters and oils for long time and that the trias might have reached hydrostatic condition only recently

noble gas geochemistry in thermal springs abstract the composition of noble gases in both gas and water samples collected from horseshoe spring yellowstone national park was found to be depth dependent the deeper the sample collection within the spring the greater the enrichment in kr xe radiogenic 4he and 40ar and the greater the depletion in ne relative to 36ar the compositional variations are consistent with multi component mixing the dominant component consists of dissolved atmospheric gases acquired by the pool at the surface in contact with air this component is mixed in varying degree with two other components one each for gas and water entering the bottom of the pool the two bottom components are not in equilibrium in horseshoe spring the bubbles entering at the bottom strip the atmospheric derived pool gases from the surrounding water while en route to the surface if the original bottom bubbles are noble gas poor as in the case of horseshoe the acquired pool gases can then quickly obliterate the original bubble composition these results are used to demonstrate that yellowstone spring surface gas samples and perhaps similarly sampled thermal springs from other hydrothermal systems have gas abundances that depend more on spring morphology than processes occurring deeper in the hydrothermal system

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

stable isotope conservation and origin of saline waters from the middle jurassic aquifer of the paris basin france abstract seventy nine samples of formation water from geothermal boreholes oil field and ground water wells tapping the dogger middle jurassic limestone reservoir of the paris basin have been analyzed for their 2h 18o tds bromide and chloride contents geostatistical mapping of 2h and of 18o contents and their variations with chloride content indicate that both isotopes have a common origin and a similar behaviour within the aquifer the 2h and 18o values increase progressively from the outcrops toward a zone where temperature cl and tds values are high the 2h and 18o values are very uniform in this zone and do not show any relation with formation temperature in contrast to what is generally observed in other sedimentary basins a discussion of isotopes exchange with the carbonate matrix for oxygen and with h2s for deuterium shows that such processes are not controlling the heavy isotope contents of groundwaters this is attributed to the relatively short residence time of groundwaters in the aquifer both 2h and 18o contents of groundwater may thus be considered as conservative tracers in the dogger aquifer of the paris basin and their initial contents are modified only by fluid mixings complex mixing processes account for stable isotope composition tds cl and br values of the dogger fluids all mixtures include a brine component meteoric water percolated and dissolved halite in the triassic aquifer secondary brine this saline solution mixed with some residual primary brine then migrated via vertical faults into the dogger aquifer such migration is found to be in agreement with data from fluid inclusions in late carbonate cements from the liassic and dogger strata the requirement that these units were exposed implies that meteoric invasion could not have occurred before the tertiary successive mixings of the brine with several types of meteoric waters depleted in heavy isotopes account for the present isotope and chemical compositions of the dogger fluids

helium accumulation in groundwater ii a model for the accumulation of the crustal 4he degassing flux abstract a model of 4 he accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4 he into the bottom of a confined aquifer the model is consistent with the measurements of 4 he concentration in the great artesian basin australia torgersen and clarke 1985 and also with the measurements of 4 he concentration in the auob sandstone of namibia heaton 1981 the measured value of the crustal degassing flux of 4 he from these two areas is comparable with the 4 he degassing flux calculated from the atmospheric budget of 4 he wasserburg et al 1963 ozima and podosek 1983 a literature review suggests that a crustal degassing 4 he source may account for the 4 he accumulation in many other groundwater systems it is concluded from the literature review the detailed modelling of 4 he accumulation in gab and the auob sandstone and the atmospheric budget that crustal degassing of 4 he may be a common and widespread phenomena

natural gas association with water and oil as depicted by atmospheric noble gases case studies from the southeastern mediterranean coastal plain a model for the equilibrium distribution of atmospheric noble gases ang between natural gas and water phases was extended to include the gas oil relationship the basic assumption is that the ang are introduced into hydrocarbon systems via recharge or seawater theoretical ang patterns of natural gas at equilibrium with water fall between the air pattern and that of air saturated water theoretical ang patterns of natural gas degassed from oil which had previously equilibrated with a water phase cover a wide range including the range calculated for gas water equilibration ang patterns in natural gas which fall outside the overlapping range may thus indicate association of the gas with oil the model was tested in the case of hydrocarbon systems of the southeastern mediterranean coastal plain other geochemical evidence indicates that the ashdod sadot shallow gas wells are not related to oil the relative ang abundances in gas samples from these wells lie within the range predicted for gas water association the relative ang abundances in samples degassed from oils of the helez kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water published and new analyses of methane dominated natural gas samples from california japan and northern israel also reveal ang patterns of the type predicted by the model the results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems this forms the basis for identification of oil associated natural gases via ang study

flow of formation water in the jurassic of the paris basin and its and discussion effects the jurassic of the paris basin is a major target for oil and geothermal exploitation interpretation of data from numerous wells reveals that the spatial distribution of fluid and reservoir parameters is heterogeneous with correlated anomalies for temperature and geochemistry the multidisciplinary approach used to describe these typical characteristics shows that hydrodynamics provides the key to explain observed deviations from the usual correlations with depth as a consequence of the coupling between hydrodynamics and fluid properties the analysis of induced effects is a calibration criterion which can be used to improve the numerical simulation of the regional flow path compared to the results of the constant density approach the new computer flow scheme both gravity and density driven is more consistent with the thermal and chemical anomalies observed the refined analysis including density effects confirms the existence of a confined area and a mixing zone around paris previously identified by geochemical investigations

continental strike slip rifts and their stratigraphic signature application to the bangong nujiang zone tibet and the south penninic zone alps our literature studies show that the thermal regime along continental strike slip rifts is inconspicuous and that they are low volcanicity rifts at best along with that young continental strike slip rifts exhibit no signs of major thermally controlled doming we suggest that the larger the strike slip component of a rift is the less likely major thermal doming is causally associated with the rift zone since vertical lithosphere movements are reflected in the stratigraphic record of a rifted area different rift modes strike slip dip slip may be distinguished by analyzing the relevant sequences two ancient and especially suitable strike slip rift margins in tethyan mountain belts the bangong nujiang zone of tibet and the south penninic zone of the alps were analyzed with regard to their uplift history the results confirm recent regional rift models which indicate in both cases that rifting was dominated by strike slip the stratigraphic approach may provide significant clues as to the mode of paleorifting when structural data are unavailable

carbon helium neon and argon isotopes in a po basin northern italy natural gas field the abundance and isotopic composition of he ne and ar have been determined in 19 gas samples taken from the dosso degli angeli hydrocarbon gas field between 3000 and 3750 m depth in the po basin carbon isotope ratios in these samples vary between 13c ch4 67 5 and 73 4 indicating a predominantly biogenic source for the methane c2 c2h6 c3h8 concentrations increase systematically from 0 04 to 0 17 by volume with depth suggesting that there is a small additional thermogenic or diagenetic hydrocarbon contribution to these gases ch4 36ar ratios in the dosso degli angeli gases are in the range predicted for a groundwater which has derived its rare gas by equilibration with the atmosphere and is ch4 saturated under reservoir conditions there is also up to 10 excess of ch4 which is not associated with the groundwater these results are consistent with 90 of the ch4 in the dosso degli angeli reservoir originating from ch4 saturated groundwater measured 20ne 36ar ratios depart from the predicted ratio in air equilibrated groundwater this fractionation is consistent with water gas phase equilibration under reservoir conditions and is similar to that observed in gas reservoirs in the vienna and pannonian basins austria and hungary respectively the he in the dosso degli angeli gases is almost entirely radiogenic and derived from the crust the concentration of 4he in the reservoir gases requires that he is mostly sourced from outside the reservoir volume radiogenic 4he 40ar ratios input into the reservoir gas must be much higher than averaged crustal production ratios as no shift from the atmospheric 40ar 36ar ratio is observed preferential release of 4he over 40ar from the sites of their production is the preferred explanation this observation contrasts with previous studies from active extensional basins in which radiogenic 4he and 40ar appear to have been stored released and transported at near production ratio on a regional scale the most obvious difference between these studies is the comparatively low thermal gradient of the po basin

physical processes occurring in tight gas reservoirs from western canadian sedimentary basin noble gas signature abstract noble gases have become a powerful tool to constrain the origin of fluids as well as the rates of fluid migration in sedimentary basins the aim of this study was to apply these tracers to understand the genesis and the evolution of unconventional gas reservoirs basin centered gas reservoirs also called tight gas reservoirs a natural laboratory for this study is the methane rich gas field in cretaceous tight sands from the western canadian sedimentary basin wcsb the selection of the wcsb was motivated by an easy access to wells that cover an extensive area from deep to shallow parts of the basin as well as the relatively well documented geology and hydrology of the area the elemental noble gas signature he ar kr and xe of natural gas from 18 wells of the basin shows a mixture between the original low content noble gas signature of the hydrocarbon gas after its charge into the reservoir and water trapped in intergranular volumes igv which is comparatively rich in noble gases this difference in relative contents can be used to estimate the geographical position of the contact between the gas reservoir and the shallower igv water furthermore the original noble gas signature which is defined as the noble gases generated in the source later transferred and mixed with in situ produced noble gases in the reservoir is mainly composed of radiogenic isotopes 40ar and 4he the comparison of 4he 40ar ratios with an average value for potential source rocks and reservoir rocks production ratio estimated with u th and k concentrations allows us to understand how the gas was transferred from the source rock to the reservoir rock these results combined with the geological and hydrological knowledge of the wcsb affords a new method to better understand the dynamics of unconventional gas reservoirs

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

3 he 4 he ratios in ch 4 rich natural gases suggest magmatic origin natural gas and oil fields commercially exploited since the 1950s are distributed in the zonal area facing the sea of japan in north east japan we report here measurements of the 3he 4he ratios in 27 ch4 rich natural gases obtained from commercial oil and gas wells in the area we observed extraordinarily high 3he 4he ratios up to 8 65 10 6 in gases from wells drilled into deep reservoirs in volcaniclastic rock formations the so called green tuff fig 1 these values are almost identical to those of volcanic fumaroles in the japanese islands in contrast gases in shallower sedimentary rock reservoirs have low 3he 4he ratios with a minimum value of 0 3 10 6 these low values are similar to those of natural gases originating from biological materials this suggests that the formation of natural gas reservoirs in the volcaniclastic rock may be attributed to large scale magmatic activities which occurred in the middle miocene

noble gas and methane partitioning from ground water an aid to natural gas exploration and reservoir evaluation the partitioning of noble gases and methane from oil field brines can provide valuable information about the redistribution of gas phase constituents the alterations in fluid compositions produced by closed system phase changes are predictable with pronounced differences from original compositions if these alterations commonly occur in sedimentary basins then a new aid for natural gas exploration and reservoir evaluation can be developed

helium isotope fluxes and groundwater ages in the dogger aquifer paris basin the dogger aquifer of the paris basin has been shown to be first order homogeneous in its helium concentration and its helium isotopic ratio although slight differences are noted in relation to specific chemical water types the helium isotopic composition of the dogger aquifer contains a small component of mantle helium that is associated with a magmatic input although the heat accompanying this magma is small constraints on the age of the overlying albien aquifer are used to calculate the flux of helium out of the dogger this constraint allows a calculation of the residence time of waters in the dogger aquifer of 4 myr 50 which is significantly longer than estimates derived from hydrologic models and hydrologic testing it is possible that the hydrologic ages and the helium ages can be reconciled by a vertically layered dogger aquifer with gradients in he salinity and fluid flow vertical profiles of fluid composition helium concentration and permeability are required in the paris basin to resolve this question

mantle derived volatiles in continental crust the massif central of france co2 rich gases and groundwaters from springs and boreholes originating within the basement of the massif central have variable3he 4he ratios with correspondingr ra values ranging from 0 8 to 5 5 and 0 3 to 2 8 respectively indicating the presence of a significant component of mantle helium molar concentrations of rare gases in the co2 rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near surface henry s law fractionation has occurred between exsolving co2 and water 13c values of the co2 rich gases are in the range 4 2 to 6 1 i e in that range normally attributed to mantle carbon but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources c 3he ratios show 4 orders of magnitude variation from 1 4 1012 to 5 108 and compared to a mantlec 3he ratio of 109 indicate that either a complex fractionation has occurred between mantle helium and mantle co2 or more likely that mantle rare gases have been diluted by large quantities of co2 with an average crustal carbon isotope composition the regional distribution of3he and c does not show any obvious relationship to age or proximity of volcanic centres or major faults suggesting that mantle derived c and he components decoupled from their silicate melt sources at some depth the results from this area of active fluid circulation suggest that c isotope data derived from metamorphic terrains should be interpreted with great caution but that input of some mantle derived carbon is expected to accompany crustal extension

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

numerical modeling of neotectonic movements and the state of stress in the north caucasus foredeep 1 this paper examines modern tectonic processes and the state of stress in the north caucasus along three profiles that cross its eastern central and western parts using the models of crustal structure along these profiles we solved the following inverse problem to find boundary conditions in this study velocity at side boundaries and bottom of the model that provide the best fit of calculated vertical movements at the top of the model and vertical neotectonic movements during the late quaternary our modeling shows that during the late quaternary geodynamics of the eastern and central parts has been controlled by regional intraplate compression normal to the greater caucasus belt the western part has been strongly influenced by tectonic processes taking place in the eastern black sea the calculated slow flow patterns and stress fields showed good agreement with the distribution of seismic events results of focal mechanisms inversions and gps data

noble gas composition of deep brines from the palo duro basin texas deep groundwaters in sedimentary basins can be sufficiently old 10 m y to have accumulated both radiogenic 4he and 40ar differences in the ratio of u th k for aquifer lithologies lead to variations for 4he40ar in the groundwater these variations can be used to resolve chronologically significant noble gas components application of a binary model to brine samples from the palo duro basin texas yields u th 4he residence times of 100 to 300 m y concentrations of two non radiogenic noble gases 20ne and 36ar provide information on the salinities of the water that recharged these aquifers

aspects of hydrocarbon migration in the mesozoic in the paris basin as deduced from an organic geochemical survey abstract this paper describes the main results of a study of hydrocarbon migration in the mesozoic in the paris basin as obtained from the geochemical analysis of cuttings from 41 petroleum boreholes the analytical methods used were pyrolysis gas chromatography mass spectrometry and the determination of stable isotopes hydrocarbon formation and migration were simulated using the temispack mathematical model the following results were found concerning the primary migration pyrolysis of numerous samples of freshly cleaned cuttings allowed the computation of a migration efficiency ratio for each sample by comparing the hc contents actually produced with those remaining in the rock they also allowed the compilation of migration maps for each source rock level as indicated by the migration ratios the hc expulsion starts below the beginning of the oil window 2100 m at a depth of about 2350 m for a transformation ratio of the lias om of 25 these migration ratios increase strongly with depth reaching 88 at 2700 m migration maps served to locate the true source rocks at the base of the lias and to calculate the total quantity of oil expelled 2 billion tons of hc analysis of rock extracts from drained levels shows by comparison with the oil analyses that migration occurred without any variation in hc composition concerning the secondary migration the migration maps used to estimate the amounts of migrated hcs revealed lateral migration phenomena in some rocks toarcian with respect to the other secondary migration paths faults played an important role but failed to favor vertical downward migration by more than 50 m below the lias source rocks as shown by the temispack model the deep trias reservoirs could only be filled laterally when the faults like the bray fault placed the mature hettangian sinemurian source rocks in contact with the trias furthermore the hypotheses of a regional hydrodynamic flow trending ne sw were taken into account in the model to explain the lateral hc migrations to distances often far from their oil kitchen and the rarity of shows northeast of the bray fault

helium isotopes in north sea gas fields and the rhine rift the popular assumption that all natural hydrocarbon accumulations are biogenic in origin has recently been questioned1 2 with the suggestion that deep source mantle derived hydrocarbons may contribute to accumulated biogenically produced hydrocarbons and also give rise to hydrocarbon deposits in unexpected parts of the crust the possibility that deep source volatiles are present in significant quantities in the hydrocarbon bearing parts of the crust of western europe is assessed here using analyses of 3he abundances in groundwaters and natural gas accumulations within the uk mainland and continental shelf for comparative purposes analyses are also presented for groundwaters from the southern part of the rhine graben a region that has been relatively active tectonically and the site of tertiary and quaternary volcanic activity in contrast the north sea sedimentary basins and central graben have no recorded tertiary or younger volcanic activity helium associated with north sea gas fields and groundwaters on the uk mainland is dominantly radiogenic produced by decay of u and th in the continental crust even where heat flow exceeds 100 mw m 2 a minor component 15 in groundwater samples fault structures seem to be important for the transport of mantle helium through the brittle upper crust the results are entirely consistent with a biogenic origin for north sea hydrocarbons

noble gases solubility models of hydrocarbon charge mechanism in the sleipner vest gas field abstract noble gases are chemically inert and variably soluble in crustal fluids they are primarily introduced into hydrocarbon reservoirs through exchange with formation waters and can be used to assess migration pathways and mechanisms as well as reservoir storage conditions of particular interest is the role groundwater plays in hydrocarbon transport which is reflected in hydrocarbon water volume ratios here we present compositional stable isotope and noble gas isotope and abundance data from the sleipner vest field in the norwegian north sea sleipner vest gases are generated from primary cracking of kerogen and the thermal cracking of oil gas was emplaced into the sleipner vest from the south and subsequently migrated to the east filling and spilling into the sleipner ost fields gases principally consist of hydrocarbons 83 93 co2 5 4 15 3 and n2 0 6 0 9 as well as trace concentrations of noble gases helium isotopes 3he 4he are predominantly radiogenic and range from 0 065 to 0 116 ra reported relative to air ra 1 4 10 6 clarke et al 1976 sano et al 1988 showing predominantly 98 crustal contributions consistent with ne 20ne 22ne from 9 70 to 9 91 21ne 22ne from 0 0290 to 0 0344 and ar isotopes 40ar 36ar from 315 to 489 air derived noble gas isotopes 20ne 36ar 84kr 132xe are introduced into the hydrocarbon system by direct exchange with air saturated water asw the distribution of air derived noble gas species are controlled by phase partitioning processes in that they preferentially partition into the gas i e methane phase due to their low solubilities in fluids therefore the extent of exchange between hydrocarbon phases and formation waters that have previously equilibrated with the atmosphere can be determined by investigating air derived noble gas species we utilize both elemental ratios to address process i e open vs closed system and concentrations to quantify the extent of hydrocarbon water exchange i e volumetric gas water ratios these data are discussed within the framework of several conceptual models i total gas stripping model which assumes all noble gases have been stripped from the water phase thus defining the minimum volume of water to have interacted with the hydrocarbon phase ii equilibrium model which assumes equilibration between groundwater and hydrocarbon phase at reservoir p t and salinity and iii open and closed system gas stripping models using concentrations and elemental ratios by applying these models to ne ar data from sleipner we estimate volumetric gas water ratios v g v w between 0 02 and 0 07 which are lower than standard geologic gas water estimates of 0 24 estimated by combining gas in place estimates with groundwater porosity estimates sleipner vest data can be best approximated by an open system model which predicts more than an order of magnitude more groundwater interaction during migration than geologic estimates indicating a dynamic aquifer system and or a hydrous migration pathway in an open system the extent of gas loss can be estimated to be between 8 and 10 reservoir volumes which have passed through the system and been lost i e filled and spilled