the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

osmium in the rivers there is a large uncertainty in our understanding of the behavior of osmium during weathering and transport into deep oceans and the osmium budget of the oceans the problem stems chiefly from the lack of osmium data on the dissolved load in the rivers and in the estuaries in this study the concentration and isotopic composition of osmium have been determined in three north american rivers the mississippi the columbia and the connecticut and one river draining central europe and flowing into the baltic sea the vistula osmium concentration in the mississippi and the vistula is about 45 femto mol kg 1 it is about 14 and 15 femto mol kg 1 for the connecticut and the columbia respectively the 187 os 186 os ratios estimated for the mississippi and the vistula are 10 4 and 10 7 respectively for the connecticut and the columbia 187 os 186 os 8 8 and 14 4 respectively of all the rivers examined the mississippi is by far the largest supplying 1 6 of the total annual world river flow its osmium isotopic composition is identical to the upper mississippi valley loesses esser and turekian 1993a indicating 1 congruent dissolution of the bedrock and 2 little or no impact of anthropogenic sources on the osmium isotopic composition of the dissolved load the latter observation indicates that the upper limit of the anthropogenic input in the dissolved osmium load of the mississippi outflow is about 250 g yr 1 while the osmium concentration of the vistula is high the isotopic composition does not appear to have been affected by substantial pollution the river data can be used to put limits on the mean residence time of osmium in the oceans t os and on the osmium budget of the oceans if the bulk river influx of dissolved osmium into the oceans is similar to that of the mississippi we get a value for the net riverine inflow of osmium of 1680 mol yr 1 if there were no sequestering of osmium in the estuaries this would give a value of t os of 1 3 10 4 years as the estuaries may trap a significant amount of river osmium this is a lower limit so that t os 1 3 x 10 4 years using the iridium data by anbar et al 1996 the os ir ratio for the vistula is 2 8 we infer that there is no large fractionation between osmium and iridium during the transport of these elements from the continents into the oceans it follows that the high os ir ratio 22 observed in seawater must be related to the different rain out mechanisms of these elements in the estuaries or in the oceans

osmium geochemistry of modern estuarine sediments from the tama and yasaka rivers in japan concentrations of re and os and 187 os 188 os ratios were obtained on the modern sediment samples from two estuarine areas the tama river in tokyo and the yasaka river in oita japan the shallow depth 25 cm intervals are 99 2 105 5 ppt os that are more than 3 times higher than ucc however all samples have 187 os 188 os ratios within a relatively narrow range of 0 3029 0 4035 much lower than that of ucc 1 0 1 3 indicating a similar source of os in both parts the lower 187 os 188 os ratios and high os concentrations of the sediments in the tama river suggest the impact from human activities the sudden enrichment of os at the deep interval may be related to the redox condition change in addition the os concentration is vertically constant in either the upper and lower intervals of the sediment profile suggesting constant burial fluxes of os in the sediment the os in the yasaka river estuary sediments 9 22 29 4 ppt are generally lower than that of the tama river either similar or much lower 1 3 than the average ucc os concentrations the samples with high os concentrations have lower 187 os 188 os ratios whereas the samples with lower os concentrations have relatively higher 187 os 188 os ratios probably indicating different os sources the relatively higher 187 os 188 os ratios and lower os concentrations in some yasaka river estuarine sediments than the tama river may also suggest less pollution from human activity to the yasaka river compared to the tama river there is a large decrease of re concentrations with depth in the yasaka river estuarine sediment whereas less variations of re in the tama river estuarine sediments the ratio of re os is also sharply different between the two estuarine sediments also indicating different sedimentary environments the tama river sediments may receive much more anthropogenic influence while the yasaka river sediments get strong impact from modern volcanic activity due to their different geographical and geological surroundings the tama river flows through a heavily industrial metropolitan area whereas the yasaka river flows through a volcanic active but less industrial area

re os isotope systematics and weathering of precambrian crustal rocks implications for the marine osmium isotope record the effects of weathering of freshly exposed precambrian rocks on the mobility of osmium were studied on soils developed on a chronosequence of glacial moraines from the western wind river range in wyoming the os budget of the precambrian granitoid source rocks is dominated by os rich trace phases such as magnetite amongst the major silicates biotite or a trace phase in biotite carries most of the os and re and is also the most radiogenic mineral with 187os 186os of 113 and 187re 186os of 2 000 re os isotope systematics of source rocks and soils indicate that rapid oxidation of magnetite mobilizes os with an isotopic composition similar to the isotopic composition of the bulk soils a very radiogenic fraction of os is mobilized through preferential weathering of biotite radiogenic runoff from precambrian shields inferred from osmium isotope analyses of freshwater fe mn nodules suggests that high latitude precambrian shields are important source areas of radiogenic os in seawater we propose that glacial scouring and weathering of glacial tills exposed after deglaciation of precambrian shields surrounding the north atlantic provides a mechanism for the slightly more radiogenic nature of north atlantic seawater compared to other seawater masses glacial interglacial variations in the osmium isotopic composition of seawater seem plausible and may be triggered by changes in weathering regimes on glacial interglacial time scales in high latitude shield areas surrounding the north atlantic

tracing the migration of mantle co2 in gas fields and mineral water springs in south east australia using noble gas and stable isotopes abstract geochemical monitoring of co2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of co2 during injection storage and any subsequent migration here we analyse a natural analogue of co2 storage migration and leakage to the atmosphere using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the co2 we present the most comprehensive evidence to date for mantle sourced co2 in south east australia including well gas and co2 rich mineral spring samples from the otway basin and central victorian highlands cvh 3he 4he ratios in well gases and co2 springs range from 1 21 to 3 07 ra and 1 23 3 65 rc ra respectively we present chemical fractionation models to explain the observed range of 3he 4he ratios he ne ar kr xe concentrations and 13c co2 values in the springs and the well gases the variability of 3he 4he in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4he accumulation 3he 4he in co2 springs decrease away from the main mantle fluid supply conduit we identify one main pathway for co2 supply to the surface in the cvh located near a major fault zone solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and 13c co2 values measured in the mineral spring samples this process is also responsible for low 3he concentrations and associated high co2 3he which are commonly interpreted as evidence for mixing with crustal co2 the elevated co2 3he can be explained solely by solubility fractionation without the need to invoke other co2 sources the noble gases in the springs and well gases can be traced back to a single end member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing this work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected co2 to the shallow subsurface

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

noble gases in formation fluids from deep sedimentary basins a review abstract atmospheric ne ar kr and xe are observed in fluids occurring in deep basins modifications of their abundance patterns reveal modes of recharge and brine formation phase separations during boiling and association of natural gas with water or oil radiogenic 4 he and 40 ar serve as age indicators of entrapped fluids effective over a significant portion of the geological time scale simultaneous application of 13 c atmospheric noble gases and radiogenic 4 he and 40 ar is recommended to identify a recent bacterial natural gas formation not accompanied by oil and b natural gas formed along with oil in a mature source rock

widespread distribution of ascending fluids transporting mantle helium in the fore arc region and their upwelling processes noble gas and major element composition of deep groundwater in the kii peninsula southwest japan abstract chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire kii peninsula which is located in the fore arc region of southwest japan groundwater of na cl hco3 na hco3 cl and na cl types was shown to be distributed across the whole area groundwater in the inland central part of the peninsula shows relatively low salinity whereas groundwater from the area along the ene trending median tectonic line mtl on the north side of the peninsula shows high salinity up to 18 800 mg l of cl and the presence of unusual heavy oxygen isotopes this trend is similar to that documented in saline waters from the arima region the so called arima type thermal water high 3he 4he ratios relative to the atmospheric value up to 6 7 ra were recorded throughout the kii peninsula covering a wider area than documented previously the saline groundwater is also strongly depleted in 20ne and heavy noble gases from the wide distribution of high 3he 4he values and the associated 20ne and cl concentrations we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire kii peninsula these aqueous fluids may ascend along the major north dipping boundary faults the isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration derived fluids is relatively small in this region however volatile components e g noble gases and co2 in the groundwater of this area may originate from the dehydration derived fluids upwelling of arima type thermal water of the na cl hco3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends the variety of water types documented may be due to this water gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater the observed high 3he 4he ratios in the absence of a mantle wedge below the southern part of the kii peninsula may reflect the oblique ascent of these fluids along north dipping boundary faults

effect of compaction pressure on consolidation behaviour of unsaturated silty soil the effect of compaction pressure on subsequent soil behaviour during isotropic consolidation has been investigated by conducting controlled suction triaxial tests on samples of an unsaturated compacted silty soil a comprehensive set of laboratory experiments was carried out in a double walled triaxial apparatus on samples of unsaturated soil that were prepared using two different compaction pressures the axis translation technique was used for creating the desired suctions in the samples in the experiments the soil samples were subjected to isotropic consolidation under constant suctions the results show that different compaction pressures produce different fabrics in a soil and therefore affect the behaviour of the soil the results also show that the value of yield stress and the location of the loading collapse lc yield curve are functions of soil fabric furthermore it is shown that the slopes of normal consolidation lines for densely and loosely compacted samples differ in unsaturated condit

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

the osmium isotopic composition of organic rich marine sediments abstract the osmium os concentration and 187 os 186 os ratio of several recent marine organic rich sediment samples from three widely separated sites have been measured os concentrations range from 0 095 to 0 212 ppb and 187 os 186 os ratios range from 8 2 to 8 9 the calculated fraction of hydrogenous os exceeds 78 in all samples thus the 187 os 186 os ratio of these samples reflects os isotopic composition of seawater the small range in measured 187 os 186 os ratio indicates that the os isotopic composition at these sites is fairly homogeneous the large magnitude of the os burial flux at these sites indicates the os burial in association with organic rich sediments is an important sink in the marine cycle of os these data also suggest that ancient organic rich sediments may provide a record of past variations in the os isotopic composition of seawater

the transport of osmium and strontium isotopes through a tropical estuary abstract we have determined the concentration and isotopic composition of os and sr in the estuarine waters from the godavari delta in peninsular india additionally we have obtained the concentration and isotopic composition of os and al concentration in selected suspended particulate matter recovered on 0 45 m filters the na k mg and ca concentrations of water samples obtained along salinity gradients from two distributary channels in the delta display a general two component mixing between river and sea water the data also reveal that al behaves non conservatively and is affected by interactions with suspended particulates the 87 sr 86 sr ratio of the riverine end member is 0 716303 and shows a linear decrease with salinity to seawater value and sr isotope systematics indicate that its behavior is conservative in the estuary the 187 os 188 os ratio of the godavari river end member is 1 24 and within error of the average eroding upper continental crust the concentration and isotopic composition of os through the two salinity transects shows that its behavior in the godavari estuary is complex and non conservative by comparing the al os ratios and os isotopes in the waters with those of the suspended particulate we find that both os gains and losses occur in the water column however in one of the distributaries vasishta the os concentration of suspended load increases and that of dissolved load decreases with increasing salinity towards the bay of bengal end member we infer that there is removal of seawater os at higher salinities the estimated mean residence time of os in the oceans is 37 14 2 kyr a comparison of the os concentration of the bay of bengal and the indian ocean waters indicates that the rainout rate of os in bay of bengal is 30 faster than that in the open ocean and suggests that the observed discrepancy between the mean residence time calculated from mass balance considerations and that estimated from the relaxation of the os isotopic ratio in marine record may not be real as the relaxation time experiments likely estimate the residence time for a basin sub basin and not for the entire ocean

dating ultra deep mine waters with noble gases and 36cl witwatersrand basin south africa abstract concentrations and isotopic ratios of dissolved noble gases 36cl d and 18o in water samples from the ultra deep gold mines 0 718 to 3 3 km below the surface in the witwatersrand basin south africa were investigated to quantify the dynamics of these ultra deep crustal fluids the mining activity has a significant impact on the concentrations of dissolved gases as the associated pressure release causes the degassing of the fissure water the observed under saturation of the atmospheric noble gases in the fissure water samples 70 98 normalized to asw at 20 c and 1013 mbar is reproduced by a model that considers diffusive degassing and solubility equilibration with a gas phase at sampling temperature corrections for degassing result in 4he concentrations as high as 1 55 10 1cm3stp4he g 1 40ar 36ar ranging between 806 and 10331 and 134xe 132xe and 136xe 132xe ratios above 0 46 and 0 44 respectively corrected 134 136 xe 132xe and 134 136 xe 4he ratios are consistent with their production ratios whereas the nucleogenic 4he 40ar and 134 136 xe 40ar ratios generally indicate that these gases are produced in an environment with an average u th k content 2 3 times above that of crustal average in two scenarios one considering only accumulation of in situ produced noble gases the other additionally crustal flux components the model ages for 14 individual water samples range from 13 to 168 ma and from 1 to 23 ma respectively the low 36cl ratios of 4 37 10 15 and comparatively high 36cl concentrations of 8 350 10 15 atoms 36cl l 1 reflect subsurface production in secular equilibrium indicating an age in excess of 1 5 ma or 5 times the half life of 36cl in combination the results suggest residence times of the fluids in fissures in this region up to 3 3 km depth are of the order of 1 100 ma we cannot exclude the possibility of mixing and that small quantities of younger water have been mixed with the very old bulk

fingerprinting coal derived gases from the uk abstract the large scale extraction of unconventional hydrocarbons in the united states has led to fears of methane contamination of shallow groundwaters differentiating between the deep gas released during extraction shale gas coal bed methane and underground coal gasification and natural shallow sourced methane is imperative for the monitoring and managing of environmental risks related to the extraction process here for the first time we present measurements of the major gas and stable and noble gas isotope composition of coal bed methane cbm from central scotland and coal mine methane cmm from central england uk the molecular c1 c2 c3 21 to 121 and stable isotope compositions 13cch4 39 5 to 51 1 dch4 163 to 238 indicate a thermogenic origin for the methane they are distinct from the majority of shallow sourced gases in uk both sample suites exhibit high he concentrations 338 to 2980 ppmv that are considerably above atmospheric and groundwater levels simple modelling shows that these high 4he concentrations cannot be solely derived from in situ production since coal deposition and hence the majority is derived from the surrounding crust the scottish cbm contains a resolvable mantle he ne and ar contribution that may originate from melts in the deep crust demonstrating the uk coals have acted as a store for deep volatiles for 10s of millions of years the high 4he in the coal derived gases has the potential to be used as a novel diagnostic fingerprint to track fugitive release of deep methane from future unconventional gas extraction operations in the uk

the undrained shear strength of soils containing large gas bubbles measurements of undrained shear strength are reported from a series of triaxial tests on reconstituted soil samples containing large bubbles of methane gas the experimental results indicate that the undrained strength can be either increased or reduced by the presence of large gas bubbles depending upon the values of the consolidation pressure and the initial pore water pressure a conceptual model for soils containing large gas bubbles developed in the companion paper is analysed to provide theoretical predictions for the undrained shear strength the analysis leads to theoretical upper and lower bounds for the undrained strength which show good agreement with the experimental data the experimental and theoretical developments have led to a better understanding of the strength of soils containing large gas bubbles this could be of considerable benefit to the offshore construction industry if platforms pipelines and other structures are to be built in areas of gas bearing sediments l article pre

multiple atmospheric noble gas components in hydrocarbon reservoirs a study of the northwest shelf delaware basin se new mexico the northwest shelf of the delaware basin se new mexico is the site of several large and productive oil and gas fields the most productive reservoirs are located in the late pennsylvanian morrow and early permian abo formations production from the latter more important play is predominately from fluvial abo red beds of the pecos slope field the oxidizing conditions implied by the reddish color of the formation require an external hydrocarbon source to test the existing migration model for the region and constrain the location of potential hydrocarbon sources we measured the elemental and isotopic composition of noble gases produced along with the hydrocarbons we found the hydrocarbons to be highly enriched in radiogenic 4he 40 ar and nucleogenic 21 ne f 4he 44 000 250 000 40ar 36ar 400 3145 21ne 22ne 0 044 0 071 the greatest enrichments occur in the pecos slope gas fields the hydrocarbons also contain three independent nonradiogenic noble gas components each with an atmospheric isotopic composition one component is most likely air saturated water asw the second component is enriched in the heavy noble gases f 130xe 8 5 and is derived from the hydrocarbon sources the third component is enriched in ne f 20ne 0 8 that we believe is degassed from sources within the reservoirs this component is correlated with but decoupled from the dominant source of radiogenic 4he and 40 ar very high concentrations of 4he up to 1 by volume in the pecos slope reservoirs require a source external to the reservoirs such as the underlying precambrian basement granites and sedimentary equivalents structural buckles cutting through the pecos field may act as high flux vertical pathways for the radiogenic 4he if the hydrocarbons in the pecos slope fields have migrated northward from the deeper delaware basin as suggested by compositional trends then perhaps the buckles also play an important role in the distribution and filling of the pecos slope reservoirs

the behavior of natural and anthropogenic osmium in long island sound an urban estuary in the eastern u s abstract the os concentration and 187 os 186 os distributions in surface sediments of long island sound eastern u s provide a way of determining the sources and estuarine transport of os the contribution of anthropogenic os from sewer outfalls from the new york city region supplies a tracer with a characteristic 187 os 186 os of about 1 the os concentration of the bulk surface sediment increases steeply moving toward new york city in the westernmost sound and generally follows the concentration of organic carbon the 187 os 186 os ratio of bulk surface sediment increases from west to east in the westernmost part of the sound and is effectively constant in the central sound we interpret these results as indicating that the surface bulk sediments of the sound contain a low 187 os 186 os component perhaps as a reduced coating associated with organic remains from sewer outfalls the acid hydrogen peroxide leach fraction has an average 187 os 186 os of 9 5 in the central sound significantly higher than both the bulk sediment value and the probable sea water value of about 8 the leach fraction in the westernmost part of the traverse is less radiogenic than the central sound and follows the os wsotope trend of the bulk sediment liquid effluent from a new york city sewer outfall contains 30 pg l 1 of dissolved os with a 187 os 186 os of about 2 5 consistent with its being an end member of the west east sediment pattern recorded in the leach fractions of the westernmost cores the leachable os from the central sound predominantly reflects os in ferromanganese oxyhydroxide coatings from continentally derived sediments with 187 os 186 os ratios more radiogenic than seawater the distribution patterns of anthropogenic and natural os with their characteristic isotopic signatures in the sound and the insights gained from the behavior of other particle reactive species indicates that very little os in solution may pass through the estuarine gauntlet

the behavior of loose gassy sand methane gas found in loose deltaic deposits can contribute to the triggering of flow liquefaction of submarine slopes the behavior of loose gassy sand is studied in the laboratory using monotoni

evidence for bacterially generated hydrocarbon gas in canadian shield and fennoscandian shield rocks hydrocarbon rich gases found in crystalline rocks on the canadian and fennoscandian shields are isotopically and compositionally similar suggesting that such gases are a characteristic feature of precambrian shield rocks gases occure in association with saline groundwaters and brines in pressurized pockets formed by sealed fracture systems within the host rocks when released by drilling activities gas pressures as high as 5000 kpa have been recorded typical gas flow rates for individual boreholes range from 0 25 l min to 4 l min the highest concentrations of ch4 are found in the deepest levels of the boreholes associated with ca na cl and na ca cl brines n2 is the second major component of the gases and with ch4 accounts for up to 80 to 90 vol higher hydrocarbon c2 concentrations range from 1 to 10 vol with c1 c2 c3 ratios from 10 1000 isotopically the gases show a wide range of values overall 13c 57 5 to 41 1 d 245 to 470 but a relatively tight cluster of values within each sampling locality the enonkoski mine methanes are unique with 13c values between 65 4 and 67 3 and d values between 297 and 347 the shield gases are not readily reconcilable with conventional theories of methanogenesis the range of c1 c2 c3 ratios for the shield gases is too low to be consistent with an entirely bacterial origin in addition dch4 values are in general too depleted in the heavy isotope to be produced by thermogenic methanogenesis or by secondary alteration processes such as bacterial oxidation or migration however isotopic and compositional evidence indicates that bacterially derived gas can account for a significant component of the gas at all shield sites conventional bacterial gas accounts for 75 94 vol of the occurrences at enonkoski mine in finland at each of the other shield sites bacterial gas can account for up to 30 50 vol of the total gas accumulation this study and other recent evidence of active bacterial communities in deep hydrogeological environments emphasize the need for more comprehensive investigation of the role of microorganisms in the deep subsurface

regional groundwater focusing of nitrogen and noble gases into the hugoton panhandle giant gas field usa the hugoton panhandle giant gas field located across sw kansas and the texas and oklahoma panhandles in the usa is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations we collected 31 samples from producing wells in a north south traverse of the 350 km long field the samples reflect the previously observed north south change in 4he n2 with values changing from 0 020 to 0 049 respectively 3he 4he 21ne 22ne and 40ar 36ar vary between 0 14 0 25 ra 0 0373 0 0508 and 818 1156 respectively and are caused by quantifiable contributions from mantle crustal and atmosphere derived sources the atmosphere derived 20ne 36ar ratios are indistinguishable from groundwater values the crustal 4he 21ne and 4he 40ar ratios show a 60 excess of 4he compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust the mantle 3he n2 and groundwater recharge 36ar n2 ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field n2 which is dominantly crustal in origin correlated 20ne n2 and 4he n2 shows mixing between two distinct crustal n2 components one n2 component n2 is associated with the crustal 4he and groundwater derived 20ne and the other with no resolvable noble gas contribution measured 15nn2 values vary from 2 7 to 9 4 the n2 and non he associated n2 endmembers are inferred to have 15nn2 3 and 13 and contribute from between 25 60 and 75 40 of the nitrogen respectively the non he associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column the 15nn2 value is not compatible with a crystalline or high grade metamorphic source and similar to the 4he is inferred to be from a shallow or low metamorphic grade source rock 4he mass balance requires a regional crustal source its association with significant magmatic 3he pointing to a tectonically active source to the west of the hugoton system the volume of groundwater required to source the 20ne in the gas field demonstrates the viability of the groundwater system in providing the collection transport and focusing mechanism for the 4he and n2 the n2 20ne ratio shows that the n2 transport must be in the aqueous phase and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase

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

osmium isotopes and silver as tracers of anthropogenic metals in sediments from massachusetts and cape cod bays high concentrations of osmium os and silver ag and low 187os 186os ratios in boston sewage make these elements sensitive tracers of the influence of sewage on marine sediments in massachusetts and cape cod bays pristine marine sediments have ag concentrations more than 200 times lower than sewage sludge os concentrations 10 40 times lower and 187os 186os ratios six times higher surface sediments from both massachusetts and cape cod bays exhibit both high ag concentrations and low 187os 186os ratios indicating the influence of sewage particles on marine sediments in this region extends some 70 km from the point of sewage release in detail the distribution of os and ag do not support a model of simple physical mixing of sewage particles with normal marine sediments deviations from the mixing model may be the result of fractionation of os and ag in the marine environment and or independent temporal variations in the os and ag content of the waste stream the results of this investigation suggest that osmium isotopes may be widely applicable as tracers of the influence of sewage on sediments in estuarine environments and that subtle variations in the isotopic composition of os in the waste stream may help constrain the sources of os and other metals delivered to the environment

los angeles metro rail project geologic and geotechnical design and construction constraints the los angeles metro rail project is part of a planned 30 year transportation system development that will include over 480 km of light rail heavy rail and commuter trains spanning the greater los angeles area the backbone of the system and focal point of this paper is the red line project which consists of a heavy rail subway system with 37 km of twin 6 6 meter diameter tunnels numerous geologic and geotechnical related issues involving regional seismicity active faults high groundwater toxic and potentially explosive subsurface gases abandoned oil wells and oil fields and both soft ground and hard rock conditions above and below the groundwater surface have imposed constraints on the design and construction of the subway project complicating design and construction matters further the project is routed through the heart of a major metropolitan area and has tunneled under freeways and high rise buildings beneath busy city streets and through oil fields and contaminated groundwater innovative solutions to natural and man made problems have included unique tunnel support designs to accommodate or mitigate risks associated with earthquakes chemical and compaction grouting to enhance ground performance and reduce surface settlements during tunneling containment treatment and disposal of contaminated groundwater sophisticated gas monitoring equipment for tunneling in gassy ground and use of magnetometers to detect abandoned oil well casings in front of advancing tunneling machines

coupled use of carbon isotopes and noble gas isotopes in the potiguar basin brazil fluids migration and mantle influence abstract we used the carbon isotope ratios of hydrocarbons and co 2 and the proportions of noble gas isotopes of associated gases from several geological provinces of the potiguar basin brazil for gas source rock correlation and to determine maturity post genetic processes migration leakage biodegradation and to assess the possible interactions between hydrocarbons and surrounding waters barriers of permeability at the basin scale the amount of water interacting with the accumulated hydrocarbons proportion of meteoric water and contamination of the fluids by the mantle were quantified for the distinct petroleum systems defined in this basin four hydrocarbon provinces have been defined in the potiguar basin the first is located in the southern part of the basin and the other three are in the northern part with offshore pods of generation migration occurred along ne sw horst and grabben structures all gases are mainly thermogenic 13 c of methane between 49 and 34 except for biodegraded gases with isotopically lighter methane generated in the oil window and only two fields from one of the trends seem to have been significantly biodegraded 13 c of propane up to 5 8 per mil the source rocks were lacustrine for the gases from the southwest of the basin and mixed marine lacustrine for two trends the third trend as well as an offshore field appears to have a lacustrine source rock and the hydrocarbon generation and accumulation are older than for the other fields each of the three trends is generally isolated in terms of fluid migration except in one location where noble gas isotopes indicate that the guamare trend is invaded by fluids of the macau trend an important contamination by mantle fluids has been confirmed for all the hydrocarbon fields close to the shore 3 he 4 he ratios up to 1 6 times the atmospheric ratio the mantle contribution as high as 20 of total helium decreases inland the mantle contribution provides some chronological constraints for the hydrocarbon accumulations and may have had an influence in hydrocarbon generation due to an igneous activity associated influence in the hydrocarbon generation pod

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

rare gas isotopic compositions in natural gases of japan isotopic and elemental compositions of rare gases in various types of gas samples collected in the japanese islands were investigated excess3he was found in most samples many samples showed a regionally uniform high3he 4he ratio of about 7 times the atmospheric ratio the he concentrations varied from 0 6 to 1800 ppm and they were low in co2 rich gases and high in n2 rich gases ne isotopic deviations from the atmospheric ne were detected in most volcanic gases the deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements ar was a mixture of mass fractionated ar atmospheric ar and radiogenic ar and the contribution of radiogenic40ar was small in all samples except for he elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere several samples were highly enriched in kr and xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water the component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust

sources and sinks of unradiogenic osmium runoff from papua new guinea the fly and sepik are two of the largest rivers draining the island of new guinea and among the world s large rivers in discharge and sediment yield sediment from the upper fly river and its delta have low 187os 188os of 0 511 0 560 and sediments from the upper and lower sepik river have even lower ratios of 0 294 0 418 filtered waters 1 2 burial of os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the gulf of papua there is a negative correlation between the os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on c isotopes the systematic relationship between c and os isotopic compositions in these samples indicates that organic matter is the major host of os in tropical estuarine sediments the os corg of gulf of papua surface sediments is intermediate between that of other modern and ancient sediments approximately 1011 mol yr of corg and 20 57 mol yr of os are buried in the inner shelf 50 m depth of the gulf of papua over an area of only 21 000 km2 corresponding to 1 3 of the global marine os burial flux in 0 006 of the total sea surface area these results suggest that a large proportion of the global burial flux of os may take place in conjunction with the deposition of low corg sediments lowering of the os isotopic composition of ambient seawater due to a large flux of unradiogenic riverine os may be indicated by the os isotopic composition of water from the coral sea 187os 188os 0 844 and marine sediments within the gulf of papua the island of new guinea is estimated to provide 4 5 of the global riverine os flux given the very large particulate and dissolved flux to the oceans from rivers in the wet tropics the effect of the weathering of young arc related crust in the sw pacific is an important source of unradiogenic os to modern seawater

horizontal and vertical motion at surface of a gassy ocean sediment layer induced by obliquely incident sv waves free gas is ubiquitous at shallow sediment depths of the continental margins of the worldwide oceans however theoretical study of the dynamic behavior of gassy seafloor under the action of earthquake has been rare in this paper a theoretical model for the analysis of the horizontal and vertical motion at the surface of a gassy ocean sediment layer induced by sv waves is developed based on the multiphase poroelasticity theory the marine sediment layer with finite thickness is assumed to between seawater and underlying elastic solid seabed the pores of sediment are filled by two compressible and viscous fluids i e liquid and gas the theoretical formulation is derived for the computation of horizontal and vertical motion in forms of displacement amplitudes displacement ratios and amplification coefficients which are defined as a function of incident angle wave frequency thickness of porous layer and saturation degree of sediment numerical results show that even a slight decrease of full saturation of the porous sediment may lead to significant influence on sediment s displacement amplitudes displacement ratios as well as the amplification coefficients apart from saturation degree this influence also depends on the incident angle wave frequency and thickness of sediment layer

a conceptual model for soils containing large gas bubbles offshore site investigations have indicated the presence of undissolved gas bubbles in the soils forming the sea bed at various locations throughout the world the gas bubbles are typically much larger than the normal void spaces so they cannot be considered as occluded bubbles within the pore water which simply change the compressibility of the pore fluid the effect of these large bubbles on the engineering properties of the soil must be understood if offshore construction is to take place in areas of gas bearing sediments this paper describes a conceptual model for soils containing large gas bubbles the model consists of a matrix of saturated soil surrounding isolated gas filled cavities the cavities forming the bubble sites are fixed within the soil so that gas drainage occurs only by the movement of dissolved gas the behaviour of the model is complicated by the processes of localized consolidation and bubble flooding des recherches conduites en mer ont indique qu il y a partout dans le monde d

fossil brines preserved in the st lawrence lowlands quebec canada as revealed by their chemistry and noble gas isotopes abstract brines in cambrian sandstones and ordovician dolostones of the st lawrence lowlands at becancour quebec canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path in addition to quantifying their residence time major ion chemistry indicates that the brines are of na ca cl type possibly derived from halite dissolution 87 sr 86 sr ratios and ca excess indicate prolonged interactions with silicate rocks of the proterozoic grenville basement or the cambrian potsdam sandstone the brines constrain a 2 3 contribution of mantle 3 he and large amounts of nucleogenic 21 ne and 38 ar and radiogenic 4 he and 40 ar 4 he 40 ar and 21 ne 40 ar ratios corrected for mass fractionation during incomplete brine degassing are identical to their production ratios in rocks the source of salinity halite dissolution plus the occurrence of large amounts of 40 ar in brines constrain the residence time of becancour brines as being older than the cretaceous evaporites in the st lawrence lowlands likely existed only during devonian silurian time brines might result from infiltration of devonian water leaching halite penetrating into or below the deeper cambrian ordovician aquifers during the devonian the basin reached temperatures higher than 250 c allowing for thermal maturation of local gas prone source rocks utica shales and possibly facilitating the release of radiogenic 40 ar into the brines the last thermal event that could have facilitated the liberation of 40 ar into fluids and contributed to mantle 3 he is the cretaceous monteregian hills magmatic episode for residence times younger than the cretaceous it is difficult to find an appropriate source of salinity and of nucleogenic radiogenic gases to the becancour brines

the isotopic composition of leachable osmium from river sediments the 187os186os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of os delivered to sea water from the continents the 187os186os values for river sediment leaches from the eastern and central u s the ganges river and the rio maipo range from 10 1 to 21 5 these results suggest that the 187os186os of the soluble river load delivered from the major continental areas to the oceans is on average more radiogenic than average currently eroding continental crust 10 5 sediment leaches from three rivers from the western u s that drain ophiolitic peridotites have distinctly lower 187os186os values 1 4 7 1 such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187os186os of 8 6

osmium isotope geochemistry of a tropical estuary abstract fundamental aspects of the estuarine geochemistry of os were investigated by analysis of the os isotope composition and concentration variations in filtered water samples from a salinity transect taken in the estuary of the tropical fly river of new guinea 187os 188os of the waters in the salinity transect increase with salinity from 0 6165 in the river endmember 0 1 salinity to a maximum of 0 913 in the most saline water 33 these values are distinctly lower than the 187os 188os of 1 06 reported for open ocean waters from the indian and pacific oceans sharma et al 1997 levasseur et al 1998 woodhouse et al 1999 the os concentrations in the waters range from a minimum of 4 59 pg os g in the river to a maximum of 5 66 pg os kg at 12 salinity these concentrations are all significantly lower than the open ocean range of 6 6 to 10 86 pg os kg levasseur et al 1998 woodhouse et al 1999 the isotopic results indicate that the rivers draining the new guinea landmass provide unradiogenic dissolved os to the oceans and led to a lowering of the 187os 188os of the local seawater the os concentration salinity relationship indicates that the mixing process is not conservative and that removal of os from the dissolved state has taken place the proportion of os lost from solution increases with salinity resulting in removal of a large proportion of seawater os in the estuary high concentrations of os in marine sediments within the gulf of papua were previously interpreted to be due to incorporation of seawater derived os into organic matter martin et al 2000 earth planet sci lett 183 261 274 and are the likely complement to the processes observed in the dissolved state enhanced removal of seawater os in estuaries could help to resolve the differences in estimates of os residence time made on the basis of oceanic deposits versus those based on measured river water concentrations

the behavior of natural and anthropogenic osmium in the hudson river long island sound estuarine system abstract the extent to which riverine os is trapped in a temperate estuary was the aim of this study the behavior of os through the hudson river east river and the long island sound lis system is addressed using both natural os and anthropogenically mobilized os the os concentration os and isotopic composition 187os 188os of the mid atlantic bight as inferred from the analysis of a water sample of 31 salinity s at vineyard sound ma are 46 fm and 1 070 respectively in comparison the hudson river at newburgh ny has os 68 fm and 187os 188os 1 265 the os concentration of the east river at the whitestone bridge is 51 fm and remains essentially constant proceeding eastward in the lis despite the increase of salinity from 20 towards the higher value of the mid atlantic bight the 187os 188os ratio of water at whitestone bridge is 0 945 and increases eastward through the sound to 0 979 at 7 km and then to 1 019 at 39 6 km the behavior of os through lis appears to be conservative at s 20 on the basis of os concentration and isotopic composition we infer that anthropogenic os is being added to the east river through sewers with the likely isotopic ratio of 0 13 and that about 24 of riverine os must be removed at s 20 there is a net transport of about 0 4 1 mole of anthropogenic os per year from the east river into the lis the residence time of os in the ocean at present must be about 39 000 years unless an independent source of supply of os can be identified

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

effect of gas hydrates melting on seafloor slope instability we present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature pressure pore water chemistry and the mean pore size distribution the model uses a new formulation based on the enthalpy form of the law of conservation of energy the developed model shows that due to a temperature and pressure increase hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water this original result confirms what has been already shown through experiments the second part of the paper presents an application of the model through a back analysis of the giant storegga slide on the norwegian margin two of the most important changes during and since the last deglaciation hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature were considered in the calculation simulation results show that melting of gas hydrate due to the change of the gas solubility can be at the origin of a retrogressive failure initiated at the lower part of the storegga slope once again the developed model leads to predictions which are supported by laboratory experiment results but contradictory to previous interpretations and beliefs considering that hydrate dissociation occurs only at the bottom of the gas hydrate stability zone

release of gas bubbles from lake sediment traced by noble gas isotopes in the sediment pore water abstract the release of gas bubbles from lacustrine or oceanic sediments into the overlying water ebullition is a major mechanism for the discharge of biogenic or geogenic gases into the water body ebullition of methane or carbon dioxide for instance contributes considerably to the release of these potent greenhouse gases through the sediment water interface depending on the rate of ebullition the pore water will show a depletion in dissolved atmospheric noble gases because the poorly soluble noble gases escape from the pore water into the gas bubbles in this study the depletion of dissolved noble gases in sediment pore water was analyzed for the first time to study bubble formation and ebullition in sediments the noble gases in the pore water of the sediments of soppensee switzerland show a distinct depletion due to ebullition of biologically produced methane this depletion is lowest in the deep sediment and increases towards the sediment surface the noble gas isotope ratios in the pore water indicate that vertical diffusion barely affects the observed noble gas profiles the isotope ratios further show that the methane bubbles remain long enough in the sediment to attain noble gas solubility equilibrium before escaping into the overlying water the volume of gas released from the sediment by ebullition can therefore be reconstructed from the extent of the noble gas depletion in the pore water using a simple gas equilibration model the noble gas profiles in the sediment indicate that ebullition increased in soppensee during the holocene and that ebullition contributed strongly to the release of methane from the sediment our case study thus illustrates that noble gases are sensitive proxies for the release of gas from lacustrine and marine sediments or similar aquatic environments

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

air xe enrichments in elk hills oil field gases role of water in migration and storage hydrocarbons from the elk hills naval petroleum reserve npr 1 bakersfield ca are enriched in heavy noble gases the 132xe 36ar ratios are as high as 576 times the ratio in air and represent the largest relative xe enrichments ever observed in terrestrial fluids the xe isotopic composition is indistinguishable from air we show that these samples cannot be explained by equilibration of oil with air saturated water and secondary enrichment via a rayleigh distillation gas stripping process based on laboratory studies of others with potential petroleum source rocks we believe the source of this enriched heavy noble gas component was adsorbed air initially trapped in on the source rocks that was expelled and mixed with the hydrocarbons during expulsion and primary migration kr and xe enrichments decrease with increasing 36ar concentration we propose a model in which an initial kr xe enriched hydrocarbon becomes diluted with noble gases extracted from air saturated groundwater during expulsion migration and storage the model generates an integrated water hydrocarbon ratio for the production fluid which indicates a minimal role for water in hydrocarbon expulsion and migration the results are interpreted to provide time geometrical constraints on the mechanisms by which hydrocarbons can migrate as a separate phase

basin scale natural gas source migration and trapping traced by noble gases and major elements the pakistan indus basin he ne and ar concentrations he and ar isotopic ratios carbon isotopic ratios and chemical compositions of hydrocarbon gases were measured in natural gas samples from gas producing wells in the indus basin pakistan where no oil has ever been found 3he 4he ratios are in the range 0 01 0 06 ra ra is the atmospheric value of 1 38 10 6 indicating the absence of mantle derived helium despite the trias extension 40ar 36ar ratios range from 296 to 800 consistent with variable additions of radiogenic argon to atmospheric groundwater derived argon rare gas concentrations show large variations from 6 10 5 to 1 10 3 mol mol for 4he and from 3 10 7 to 3 10 5 mol mol for 36ar in general 36ar concentrations are high compared to literature data for natural gas co2 and n2 concentrations are variable ranging up to 70 and 20 respectively mantle derived he is not observed therefore co2 and n2 are not mantle derived either hydrocarbon gas maturity is high but accumulation efficiency is small suggesting that early produced hydrocarbons including oil were lost as well as mantle helium this is consistent with the generally late pliocene trap formation and explains the high n2 concentrations since n2 is the final species generated at the end of organic matter maturation based on 13c data co2 originates from carbonate decomposition very elevated 20ne 36ar ratios are found reaching a maximum of 1 3 compared to 0 1 0 2 for air saturated water and 0 5 for air and these high values are related to the lowest rare gas concentrations we suggest that this highly fractionated signature is the trace of the past presence of oil in the basin and appeared in groundwater we propose a model where oil water contact is followed by gas water contact both with rayleigh distillation for rare gas abundance ratios thereby generating the fractionated 20ne 36ar signature in groundwater first and transferring it to gas later assuming the gas water contact occurred shallower than present reservoir depths this model explains the generally high 36ar concentrations and low ch4 36ar ratios compared to other studies on younger basins it thus provides a historical perspective on fluid transfer in a sedimentary basin where a gas accumulation may have been buried to greater depth since formation rare gas and major element data point to mixing between two gas pulses produced successively the very co2 n2 rich gases are terminal products of organic matter maturation which have been trapped after important migration this gas was followed by a more typical thermogenic gas which mixed with it

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

mechanical behaviour of gas charged marine plastic sediments understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue special triaxial tests were carried out on natural sediments recovered from the gulf of guinea special attention was devoted to the laboratory preparation procedure involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of a the increase in the isotropic compressibility and decrease in the preconsolidation pressure and b the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing the experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments

critical state for overconsolidated unsaturated silty soil the critical state concepts have been investigated for an overconsolidated unsaturated silty soil through a comprehensive set of controlled suction triaxial laboratory experiments the experimental

halogens and noble gases in sedimentary formation waters and zn pb deposits a case study from the lennard shelf australia abstract halogen ratios br cl and i cl and concentrations provide important information about how sedimentary formation waters acquire their salinity but the possible influence of organic br derived from sedimentary wall rocks is rarely quantified here it is demonstrated that br cl versus i cl mixing diagrams can be used to deconvolve organic br contributions that organic matter has a limited range of br i ratios and that organic br is a more significant component in zn pb deposit ore fluids than previously recognised the significance of these findings is illustrated for the lennard shelf zn pb deposits of western australia fluid inclusions related to lennard shelf zn pb mineralisation have variable salinity and hydrocarbon contents the halogen data from these fluid inclusions require mixing of three fluid end members 1 an evaporated seawater bittern brine 30 wt nacl equiv with greater than seawater br cl ratio 2 a lower salinity pore fluid 5 wt nacl equiv with moderately elevated br cl and i cl and 3 fluids with br cl ratios of 5 times seawater and extremely elevated i cl ratios of 11 500 times seawater the first two fluids have 40 ar 36 ar of 300 400 and greater than air saturated water 36 ar concentrations that are typical of fluid inclusions related to zn pb mineralisation the third organic rich fluid has the highest 40 ar 36 ar ratio of up to 1500 and a depleted 36 ar concentration mineralisation is interpreted to have resulted from mixing of zn rich evaporitic brines and h 2 s present in hydrocarbons it is suggested that aqueous fluids acquired organic br and i from hydrocarbons and that hydrocarbons exsolving from the aqueous fluid removed noble gases from solution interaction of variably saline brines and hydrocarbons could account for the variable br cl and i cl composition and 36 ar concentrations recorded by lennard shelf fluid inclusions the distinct 40 ar 36 ar signature of the fluid with the highest i cl ratio suggests the hydrocarbons and brines were sourced independently from different parts of the sedimentary basin these data indicate the complementary nature of halogen and noble gas analysis and provide new constraints on important mixing processes during sediment hosted zn pb mineralisation

himalayan uplift and osmium isotopes in oceans and rivers previous studies have shown that 187 os 188 os in seawater has become increasingly radiogenic over the last 40 ma in a manner analogous to strontium this rapid rise in the marine 187 os 188 os over the last 17 ma has been attributed to an increase in the bulk silicate weathering rates resulting from the rise of the himalayas and or selective weathering and erosion of highly radiogenic organic rich ancient sediments the key test of this hypothesis is the 187 os 188 os and the total osmium concentration of the himalayan rivers we report the concentration and isotopic composition of osmium in the ganges the brahmaputra and the indus rivers the 187 os 188 os of the ganges close to its source at kaudiyal 30 05 n 78 50 e is 2 65 and os 45 fm kg a second sample of the lower reaches of the ganges at patna 25 30 n 85 10 e gives 187 os 188 os 1 59 and os 171 fm kg the 187 os 188 os of the brahmaputra at guwahati 26 10 n 91 58 e is 1 07 and os 52 fm kg a sample of the indus besham 34 55 n 72 51 e has a 187 os 188 os of 1 2 and os 59 fm kg we infer that the himalayas do not provide either a high flow of osmium or a highly radiogenic osmium component to the oceans the overall trend for osmium and strontium could be explained by a regularly increasing input of global continental weathering sources but the himalayas themselves appear not to be the dominant source

thermal constraints on crustal rare gas release and migration evidence from alpine fluid inclusions the palfris marl of the helvetic alpine nappes contains four distinct vein fill generations ch4 rich gas is found in abundant fluid inclusions within these carbonate veins while free ch4 gas has also been produced from exploratory boreholes through this formation the stable isotope and helium neon and argon isotopic composition of these fluids has been determined a constant radiogenic 40ar concentration of 1 25 0 13 1 ppm in these differently sited fluids requires an intimate association between the 40arrad source and the hydrocarbon phase this can only be reasonably explained if the 40arrad was input into the hydrocarbon phase during hydrocarbon generation migration or storage prior to entrapment in the fluid inclusions stable isotope results constrain the maturity of hydrocarbon production while fluid inclusion formation pressures and temperatures record values of up to 2 5 kbars and 250 c these values place limits on the range of thermal conditions in which the hydrocarbon 40arrad relationship was established all fluids within inclusions also contain radiogenic 4he40ar values at predicted crustal production ratios these observations provide the first evidence that both 4herad and 40arrad can be quantitatively released on a regional scale bounded by the thermal conditions required to produce the hydrocarbon phase and the conditions under which the fluid inclusions were formed t 190 250 c these results require that negligible quantities of excess 40arrad decoupled from 4herad have been released into this system given the wide array of mechanisms which can potentially cause decoupling of these two species this result provides an important constraint on the role of these processes within the sedimentary fluid regime in contrast the free borehole gas contains excess radiogenic 4he and 21ne relative to 40arrad in proportions which can be accounted for by local production and subsequent diffusion from the surrounding marl the latter pattern is consistent with rare gas migration in lower temperature environments a conceptual model which considers both diffusional and metamorphic release of helium and argon and the ability of the surrounding fluid regime to transport the rare gases from their respective mineral production sites is consistent with both these results and data from regional rare gas studies

dissolved rhenium in the yamuna river system and the ganga in the himalaya role of black shale weathering on the budgets of re os and u in rivers and co 2 in the atmosphere extensive measurements of dissolved re and major ion abundances in the yamuna river system yrs a major tributary of the ganga have been performed along its entire stretch in the himalaya from its source near the yamunotri glacier to its outflow at the foothills of the himalaya at saharanpur in addition re analysis has been made in granites and precambrian carbonates some of the major lithologies of the drainage basin these data coupled with those available for black shales in the lesser himalaya allow an assessment of these lithologies contributions to the re budget of the yrs the re concentrations in the yrs range from 0 5 to 35 7 pm with a mean of 9 4 pm a factor of 4 higher than that reported for its global average concentration in rivers dissolved re and cations na k ca mg are strongly correlated in the yrs indicating that they are released to these waters in roughly the same proportion throughout their course the re cations in most of these rivers are one to two orders of magnitude higher than the re na k mg ca measured in granites of the yamuna basin this leads to the conclusion that on average granites crystallines make only minor contributions to the dissolved re budget of the yrs on a basin wide scale though they may be important for rivers with low dissolved re similarly precambrian carbonates of the lesser himalaya do not seem to be a major contributor to dissolved re in these rivers as their re ca mg is much less than those in the rivers the observation that re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite black shale carbonate layers in phosphorite mines are high and that re and so4 are significantly correlated in yrs seems to suggest that the bulk of the dissolved re is derived from black shale carbonaceous sediments material balance considerations based on average re of 30 ng g 1 in black shales from the lesser himalaya require that its abundance in the drainage basin of the yrs needs to be a few percent to yield average re of 9 4 pm furthermore the positive correlation between re and cations would require that these re rich sediments e g black shales and re poor lithologies e g crystallines precambrian carbonates contribute re and cations in roughly the same proportion throughout the drainage basin the available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met the annual fluxes of dissolved re at the base of the himalaya from the yamuna are 150 mol at batamandi and 100 mol at saharanpur compared to 120 mol from the ganga at rishikesh the total flux from the yamuna and the ganga account for 0 4 of the global riverine re flux much higher than their contribution to global water discharge this is also borne out from the mobilization rate of re 1 to 3 g km 2 y 1 in the ganga and yamuna basins in the himalaya compared to the global average of 0 1 g km 2 y 1 black shale weathering can also significantly influence the budgets of os and u in rivers and co2 in rivers and the atmosphere using dissolved re in rivers as a proxy it is estimated that 6 9 108 kg y 1 of black shales are being weathered in the ganga and yamuna basins in the himalaya weathering of such amounts of black shales can account for the reported concentrations of os and u in these rivers furthermore if the weathering results in the conversion of organic carbon in the black shales to co2 it would release 2 105 mol of co2 km 2 y 1 in the yamuna and ganga basins in the himalaya comparable to the co2 consumption from silicate weathering

the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters noble gases inert elements having isotopes produced by the decay of long half life radionuclides offer a powerful approach for tracing fluid circulation and dating groundwaters the u th 4he water ages calculated from the accumulation rate in water of radiogenic 4he produced by decay of u and th contained in the aquifer rocks is frequently higher than the hydrological ages this discrepancy is generally interpreted by two contrasting models i heterogeneities of the aquifers which allow water stagnation and accumulation of large amounts of radiogenic 4he or ii addition of 4he produced in deeper regions of the continental crust in this contribution we propose that the apparent contrast between u th 4he ages and hydrological ages in the paris basin reflects the mixing of different types of water having different residence times we show using the helium isotopic signatures of waters that this mixing occurs between three aquifers the middle jurassic the triassic and the palaeozoic basement which have contrasting helium contents and heterogeneous chemical compositions and permeabilities the difference of radiogenic 4he 4 ratios between the aquifers of triassic and middle jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks this implies residence times for groundwaters circulating in the middle jurassic carbonate aquifer much longer than those obtained from hydrological studies independent fluid age estimates based on the ground palaeotemperatures recorded in the same groundwaters by the atmospherederived noble gases seem to confirm the presence of very old groundwaters in the paris basin the estimation of the residence time of ancient groundwaters is the most challenging problem in basin hydrology e g chapman 1987 typical water residence times of 104 108 years outreach the range of half lives of most of the geochronometers available in hydrology e g 3h 14c and prolonged water rock interactions alter the chemical and isotopic signature of water preventing the identification of the fluid sources on the other hand hydrological modelling faces serious problems of estimating space and time variations of critical parameters such as the permeability due to the petro physical heterogeneities of the aquifers and fluid velocity estimates can be valid only on a local scale e g alexander et al 1987 because noble gases are inert and have isotopes produced by natural decay of long halflife radionuclides these elements have received increasing attention as tracers of groundwater movements in deep aquifers e g marine 1979 andrews et al 1982 1985 bottomley et at 1984 1990 torgersen clarke 1985 zaikowski et al 1987 ballentine et al 1991 stute et al 1992 marty et al 1993 o nions ballentine 1993 groundwaters contain noble gases derived from the atmosphere the crust and the mantle fig 1 studies on water dating are focused mainly on the crustal derived radiogenic noble gas component for obvious reasons although the mantle derived component has the capacity of tracing fluid sources oxburgh et al 1986 and the atmosphere derived component can provide independent estimates on the water residence times pinti et al 1997 in continental environments mantle derived noble gases are generally observed in regions of active volcanism or extensional tectonics ballentine et al 1991 the source is probably sub continental magma intrusion and underplating with successive episodic and tectonically controlled advective transport in the crust torgersen 1993 mantle derived helium can be easily identified from its isotopic signature indeed the mantle is enriched in primordial 3he as indicated by 3he 4he ratios greater than 10 5 whereas the atmospheric ratio is l a x 10 6 and crustalderived radiogenic helium has 3he 4he ratios in the range of 10 8 consequently the geographical distribution of the 3he 4he ratios in sedimentary fluids can be used to identify the fluids pinti d l marty b 1998 the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters in parnell j ed 1998 dating and duration of fluid flow and fluid rock interaction geological society london special publications 144 53 68 by guest on january 5 2014 http sp lyellcollection org downloaded from

effect of gassy sand lenses on a deep excavation in a clayey soil abstract gas venting mainly methane was encountered during a deep excavation in a 40 m thick clayey deposit with silty sand lenses overlying a shale layer believed to be the source of biogenic gas the upward diffusion of methane and chloride from the bedrock aquifer through the clay till is modeled and the potential for chloride migration contributing to the exsolution of methane due to a reduction in methane solubility is discussed two approaches to modeling the lenses are examined where gas exsolution either occurs prior to the excavation or during the excavation both approaches lead to similar conclusions although sand lenses were more prone to liquefaction if the methane was present in its gaseous state prior to unloading the results suggest that while liquefaction of a sand lens near the base of the excavation may have contributed to the formation of the seeps and vents the gassy response of sand lenses due to the exsolution of gas during unloading cannot explain the level of venting that was observed in the field

forensic numerical analysis of gas venting in southwestern ontario abstract a forensic modeling study examines the potential causes of gas and water venting observed during the excavation of a landfill in a 40 m thick clayey till deposit in southwestern ontario canada the clayey till is known to be underlain by permeable natural gas bearing rock and gas has been diffusing through the clayey deposit over about the last 13 000 15 000 years attention is focused on 2d modeling of hydrofracturing as well as gassy soil behavior the model examines the predicted location of venting with and without the presence of gassy sand lenses and a discontinuous layer of basal till between the bedrock and the low permeability till the modeling shows that hydrofracturing alone can explain the occurrence and location of the observed venting in one of the sub cells in the other sub cell hydrofracturing explains the occurrence but not the location of the observed venting or the presence of the sand in the venting water at this location modeling of appropriately placed gassy sand lenses is shown to explain the occurrence and location of the observed venting as well as the presence of both waters with different geochemistry from the bedrock and the till in the venting waters

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

sampling of volcanic gases the role of noble gas measurements a case study of vulcano south italy abstract collection of volcanic gases during a workshop at vulcano south italy revealed that the atmospheric noble gases are sensitive monitors to air contamination whereas indigenous deep seated compounds such as he co 2 hcl and h 2 s are insensitive to such contaminations fumaroles at the vulcano crater contained high concentrations of he 1 3 10 3 cm 3 stp g h 2 o and he ne equaled 1000 in the least contaminated sample compared to 0 2 in air saturated water 40 ar 36 ar was up to 692 radiogenic 40 ar was 11 10 4 cm 3 stp g h 2 o and radiogenic 4 he 40 ar equaled 1 2 these characteristics resemble those of steam separated from boiling geothermal fluids occurrences of vigorous bubbling drowned fumaroles were studied at the vulcano beach and at the adjacent hippopotamus pond he ne was 20 40 indicating the presence of some radiogenic he accompanied by no significant radiogenic ar the ratio of atmospheric noble gases to dry gas was 10 times higher in the drowned fumaroles at the beach than in the crater fumaroles the water of the hippopotamus pond contained 9690 mg 1 1 cl 11 800 mg 1 1 so 2 4 the ph measured in the laboratory was 1 2 these characteristics indicate that the fumaroles loose reactive gases co 2 h 2 s hcl while passing shallow water

determining fluid migration and isolation times in multiphase crustal domains using noble gases geochemical characteristics in subsurface fluid systems provide a wealth of information about fluid sources migration and storage conditions determining the extent of fluid interaction aquifer hydrocarbon connectivity is important for oil and gas production and waste storage applications but is not tractable using traditional seismic methods furthermore the residence time of fluids is critical in such systems and can vary from tens of thousands to billions of years our understanding of the transport length scales in multiphase systems while equally important is more limited noble gas data from the rotliegend natural gas field northern germany are used here to determine the length scale and isolation age of the combined water gas system we show that geologically bound volume estimates i e gas to water volume ratios match closed system noble gas model predictions suggesting that the rotliegend system has remained isolated as a closed system since hydrocarbon formation radiogenic helium data show that fluid isolation occurred 63 129 m y after rock and or groundwater deposition ca 300 ma which is consistent with known hydrocarbon generation from 250 to 140 ma thus corroborating long term geologic isolation it is critical that we have the ability to distinguish between fluid systems that despite phase separation have remained closed to fluid loss from those that have lost oil or gas phases these findings are the first to demonstrate that such systems remain isolated and fully gas retentive on time scales 100 m y over 10 km length scales and have broad implications for saline aquifer co2 disposal site viability and hydrocarbon resource prediction which both require an understanding of the length and time scales of crustal fluid transport pathways

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

the noble gas isotope record of hydrocarbon field formation time scales abstract noble gases may be considered as the most prominent tracers of natural fluids including hydrocarbons the atmosphere is the only source of 20ne 36ar 84kr 130xe in subsurface environments and their concentrations in pore waters after recharge are known from the solubility data this allows modelling of noble gas partitioning between coexisting gas oil and water phases in the course of hydrocarbon formation migration and storage radiogenic isotopes 4he 21ne 40ar 136xe after being released from source rocks are mixed with air derived noble gases already present in the pore space concentrations of radiogenic species in the pore space of typical hydrocarbon fields are generally so high that they can hardly be accumulated in situ and thus indicate noble gas transfer from ground waters the time bearing ratios 4he 20ne 21ne 20ne 4he 40arair 40ar 40arair in hydrocarbon fields are thus proportional to the time interval between the ground water recharge and noble gases partitioning into the hydrocarbon phase s the recharge partition interval the largest available data set allows the recharge partition intervals to be constrained for a large number of hydrocarbon fields situated in different tectonic settings ancient plates young plates mobile belts these intervals increase systematically with the ages of hydrocarbon source and trap lithologies and are comparable with these ages this important feature valid in general for different hydrocarbon fields implies i local sources of radiogenic noble gas isotopes in ground waters ii relatively recent formation of hydrocarbon fields and iii their short formation time scales in some cases the duration of formation of a hydrocarbon field can be constrained for example nearly constant 21ne 20ne 40ar 40arair ratios measured in samples from the magnus oil field north sea give an accumulation time scale 10 ma it should be emphasized that the above noble gas isotope ratios give the time estimates which are independent of geological reconstructions sometimes the noble gas inventory in a hydrocarbon field and ground waters allows characterization of the source rock volume involved in formation of the field generally this volume exceeds that of the hydrocarbon field rocks by orders of magnitude

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature

stress dilatancy behaviour of bubbled fine grained sediments abstract although the strength and stiffness of fine grained gassy soil have been relatively well characterised its dilatancy remains poorly understood this study aimed to understand and formulate the stress dilatancy behaviour of fine grained gassy soil through a series of triaxial tests 19 in total conducted on fine grained gassy specimens where different initial gas volume fractions 0 and initial pore water pressures uw0 were considered compared to the stress dilatancy relation of saturated fine grained soil the addition of gas bubbles was found to result in more contractive or dilative soil behaviour depending on the combination of 0 and uw0 these distinct features cannot be captured by the existing stress dilatancy functions for fine grained saturated soils which solely depend on the stress ratio therefore a new stress dilatancy function is proposed within the framework of critical state soil mechanics to quantify the distinct modification effects of bubbles which either suppress or enhance dilatancy on the dilatancy of gassy soils with different 0 and uw0 values in a unified manner this new function has been validated and can be readily implemented in critical state based constitutive models for predicting the shear behaviour of fine grained gassy soil and therefore the response of various offshore structures i e foundations and pipelines founded on a gas bearing seabed

simple models for the geochemical response of the ocean to climatic and tectonic forcing abstract simple models for the geochemical response of the ocean to periodic forcing are used as a framework to discuss the shortest periods of change resolvable by present analytical precision of elemental or isotopic ratio measurements of the chemical evolution of seawater for chemical properties whose budget is dominated by fluxes into and out of the ocean we show that the geochemical response to changing fluxes is strongly attenuated at periods shorter than the residence time and that the response at these periods is also phase shifted so as to lag the forcing by one quarter cycle the amplitude response as a function of period is used to estimate the periods of forcing resolvable by present analytical precision in measuring the 87sr 86sr and 234u 238u evolution of seawater and we find that the shortest periods resolvable are of the order of 1 myr if variations at periods shorter than this are found we would argue that these are very likely of local as opposed to global origin we illustrate the importance of phase shifts as a function of forcing period by discussing some recently published data that show a high degree of correlation over the last 300 kyr between changes in 87sr 86sr and 18o measured in the same sediment core at first sight this correlation might be taken as good evidence that both 87sr 86sr and 18o are responding to some common climatic forcing but given the long residence time of sr in the ocean sr and o should in fact have different phase shifts relative to any proposed common forcing thus the apparent correlation between 87sr 86sr and 18o over the past several 100 ma is not necessarily an indication that they are responding to a common cause amplitude response curves are also used to place limits on permissible global seawater 234u 238u variations and these are then compared with published data to identify local diagenetic effects application to 187os 186os and u records in seawater detectors is proposed

the glacial interglacial variation of seawater osmium isotopes as recorded in santa barbara basin abstract the pleistocene deposits of santa barbara basin sbb show laminations during interglacial periods typical of an anoxic or suboxic depositional environment and more sporadically laminated deposits during glacial times indicating a more oxic environment of deposition the 187os 188os value of sediment leaches varies as a function of climate consistent with a more radiogenic os signal during interglacial times and less radiogenic os values more typical of glacial times the signal is confounded by contributions from a high os detrital component with a variable 187os 188os value but generally agrees with prior result from deposits from other marine environments

effect of initial pore pressure on undrained shear behaviour of fine grained gassy soil many of the world reserves of fossil fuels are located at various water depths in fine grained sediment under the seabed the fine grained sediment contains relatively large biogas bubbles which has been posing challenges to the stability of offshore foundations supporting oil and gas platforms although fine grained gassy soil was found to exhibit different undrained shear strengths cu by altering the initial pore pressure ui relevant to water depth systematic studies concerning the effect of ui on undrained shear behaviours of the soil are still lacking this study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine grained gassy soil with the same consolidation pressure p c but at a wide range of varying ui 0 1000 kpa the shearing induced excess pore pressure u in the gassy specimens highly depends on ui it can be either smaller than that of the saturated specimen with the same p c due to partial dissipation of u int

osmium behavior in estuaries the lena river example the behavior of dissolved osmium at the river ocean interface was studied in the lena river estuary dissolved osmium removal is observed at very low salinities the loss is estimated to be 28 of the dissolved concentration of the river the removal cannot be related to the flocculation of iron oxide organic matter colloids but occurs simultaneously with the loss of aluminum the proposed mechanism is the adsorption of dissolved osmium on suspended particles in the maximum turbidity zone if this is correct then the removal of osmium in estuaries is probably a common phenomenon no contribution of osmium from the sediments is detected but neither the samples nor the stratified nature of the estuary are favorable to the study of a flux from sediments if this finding can be generalized the estimated global riverine flux of osmium to the ocean has to be recalculated and the osmium residence time in the ocean would change from 3 3 104 yr to 4 6 104 yr