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

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

diffusive separation of noble gases and noble gas abundance patterns in sedimentary rocks the mechanisms responsible for noble gas concentrations abundance patterns and strong retentivity in sedimentary lithologies remain poorly explained diffusion controlled fractionation of noble gases is modeled and examined as an explanation for the absolute and relative abundances of noble gases observed in sediments since the physical properties of the noble gases are strong functions of atomic mass the individual diffusion coefficients adsorption coefficients and atomic radii combine to impede heavy noble gas xe diffusion relative to light noble gas ne diffusion filling of lithic grains half spaces by diffusive processes thus produces ne enrichments in the early and middle stages of the filling process with f ne values similar to that observed in volcanic glasses emptying lithic grains half spaces produces a xe enriched residual in the late but not final stages of the process producing f xe values similar to that observed in shales exotic but unexceptional shales that exhibit both f ne and f xe enrichments can be produced by incomplete emptying followed by incomplete filling this mechanism is consistent with literature reported noble gas abundance patterns but may still require a separate mechanism for strong retention a system of labyrinths with constrictions and or c si nanotubes when combined with simple adsorption can result in stronger diffusive separation and non steady state enrichments that persist for longer times enhanced adsorption to multiple c atoms inside c nanotubes as well as dangling functional groups closing the ends of nanotubes can provide potential mechanisms for strong retention we need new methods of examining noble gases in rocks to determine the role and function of angstrom scale structures in both the diffusive enrichment process and the strong retention process for noble gas abundances in terrestrial rocks

geological storage of carbon dioxide carbon dioxide co2 is the main compound identified as affecting the stability of the earth s climate a significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change geological storage of co2 or the injection and long term stabilization of large volumes of co2 in the subsurface in saline aquifers in existing hydrocarbon reservoirs or in unmineable coal seams is one of the more technologically advanced options available a number of studies have been carried out and are reported here they are aimed at understanding the safety physical and chemical behaviour and long term fate of co2 when stored in geological formations until efficient alternative energy options can be developed geological storage of co2 the subject of this volume provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy

determination of crustal fluid residence times using nucleogenic 39ar abstract argon 39 is a radioactive isotope of ar with a half life of 269 years there are two natural sources of 39 ar on earth cosmogenic production in the upper atmosphere and nucleogenic production in rocks cosmogenic 39 ar has been recognized as an ideal tracer for groundwater residence times and oceanic circulation nucleogenic 39 ar has generally been considered problematic for groundwater studies in this work we developed simple models for the evolution of 39 ar 40 ar ratios where 40 ar denotes radiogenic 40 ar produced in the model system in rocks and fluids in rocks both 39 ar and 40 ar are produced and a fraction of the 39 ar and 40 ar is released into the mobile fluid phase in both reservoirs 39 ar reaches production or supply decay equilibrium whereas 40 ar accumulates with time thereby the 39 ar 40 ar ratio in rocks and fluids generally decreases with time our models suggest that the co evolution of these two isotopes in rocks and fluids provides a new chronometer of fluid migration and reaction in the crust this chronometer is relevant to a much wider time range than that limited by radioactive decay of cosmogenic 39 ar i e 1400 years at the current detection limit of 3 modern atmospheric value the 39 ar 40 ar chronometer is applicable to estimating residence times of very old groundwater as well as for studying fluid rock interactions and fluid migration rates such as those occurring during co 2 sequestration and the formation of hydrocarbon reservoirs

using 3he 4he isotope ratios to identify the source of deep reservoir contributions to shallow fluids and soil gas abstract one strategy to counteract rising atmospheric co 2 levels is the capture and subsequent geological storage of anthropogenic co 2 legislation will require the monitoring and early identification of any leakage to the near surface from the storage site owing to their low concentrations and unreactive nature noble gases are well established as key tracers of crustal fluid systems ballentine et al 2002 the 3 he 4 he and noble gas content of soil gases and groundwater may provide the opportunity to detect identify and quantify a weak deep sourced signal that contributes to a larger near surface biological signal we present 3 he 4 he ne ar kr and xe data from near surface soil gases two of which exhibit hydrocarbon microseepage from deeper oil reservoirs from the teapot dome oil field wyoming usa we also present a noble gas characterisation of the oil reservoirs beneath the seepages a helium excess 4 he excess up to 37 7 ppm relative to air concentrations 4 he air 5 24 ppm is found in soil gases at both microseepage sites error propagation demonstrates that it is possible to unambiguously resolve the 3 he 4 he of the deep helium source and allows us to explore the limits of this technique at one seep the resolved deep 3 he 4 he 0 055 0 009ra where ra 1 40 10 6 is indistinguishable from the range observed in the subsurface hydrocarbon system of 0 046 to 0 109ra notably the soil gas 4 he ch 4 1 8 10 3 at this microseepage site compares similarly with the lower subsurface source 4 he ch 4 1 4 to 3 4 10 4 and demonstrates the conservative nature of helium as a tracer we show that the sensitivity of helium as a deep fluid tracer should be increased by up to two orders of magnitude in groundwater compared to soil gases studied here due to the low solubility of helium in water groundwater rather than soil gas should be the priority in any monitoring strategy that plans to use helium as an early indicator of deep fluid microseepage

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

impact of human activities on the central mediterranean offshore evidence from hg distribution in box core sediments from the ionian sea total hg concentrations have been measured for five box core sediments collected seawards of the augusta industrial area se sicily in more coastal sediments upcore increasing hg concentrations exceeding the hg background concentration estimated for the strait of sicily indicate hg contamination over time due to the industrial area development strong correlation between total organic c toc and hg concentrations was found only for core bx2 that displays organic c to total n c n ratios indicative of autochthonous organic matter for other sediments high hg enrichment factors with respect to toc indicate in addition to hg trapping by toc other factors as responsible for hg accumulation in the presence of some contribution of detrital organic matter hg is mainly adsorbed onto the mineral component of the bottom sediments probably because toc is saturated by hg excess contaminant impact affected also the open sea environment main drivers of hg flux towards the offshore were dredged materials which repeatedly discharged sediment resulting in substantial increases in toc contents and high c n ratios consistent with the geochemistry of recent turbidites these anomalous sedimentary inputs induced sediment redox environment modifications constrained by mn peaks which affected hg distribution

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

tracer applications of noble gas radionuclides in the geosciences noble gas radionuclides including 81kr t1 2 229 000 years 85kr t1 2 10 8 years and 39ar t1 2 269 years possess nearly ideal chemical and physical properties for studies of earth and environmental processes recent advances in atom trap trace analysis atta a laser based atom counting method have enabled routine measurements of the radiokrypton isotopes as well as the demonstration of the ability to measure 39ar in environmental samples here we provide an overview of the atta technique and a survey of recent progress made in several laboratories worldwide we review the application of noble gas radionuclides in the geosciences and discuss how atta can help advance these fields specifically determination of groundwater residence times using 81kr 85kr and 39ar dating old glacial ice using 81kr and an 39ar survey of the main water masses of the oceans to study circulation pathways and estimate mean residence times other scientific questions involving a deeper circulation of fluids in the earth s crust and mantle are also within the scope of future applications we conclude that the geoscience community would greatly benefit from an atta facility dedicated to this field with instrumentation for routine measurements as well as for research on further development of atta methods

noble gas and carbon isotopic evidence for co2 driven silicate dissolution in a recent natural co2 field secure storage of anthropogenic carbon dioxide co2 in geological reservoirs requires predicting gas water rock interactions over millennial timescales noble gases and carbon isotope measurements can be used to shed light on the nature of competing dissolution precipitation processes over different timescales from the fast dissolution of gaseous co2 in groundwater to more sluggish reactions involving dissolution and precipitation of newly formed minerals in the reservoir here we study a compilation of gas analyses including noble gases and 13c of co2 from nine different natural co2 reservoirs amongst these reservoirs the bravo dome co2 field new mexico usa shows distinct geochemical trends which are explained by degassing of noble gases from groundwater altering the composition of the gas phase this groundwater degassing is synchronous with the dissolution of co2 in groundwater progressive creation of alkalinity via co2 promoted mineral dissolution is required to explain the observed positive correlation between co2 3he and 13c of the gas phase a unique feature of bravo dome the differences between bravo dome and other natural co2 reservoirs are likely explained by the more recent filling of bravo dome reflecting co2 water rock interactions over thousands of years rather than over millions of years in older reservoirs

gas geochemistry of the macuspana basin mexico thermogenic accumulations in sediments impregnated by bacterial gas a gas survey was performed in the macuspana basin south of mexico two distinct gas families were identified family 1 is represented by homogeneous and purely thermogenic gas associated with condensates expelled at the end of the oil window and family 2 is composed of a mixture of bacterial dry gas and thermogenic gas derived from source rocks at high maturity chemical and isotopic parameters as well as noble gas data provided information about the sources the proportions of mixing and directions of hydrocarbon migration of these two families considering the risk associated with further oil and gas exploration in the basin deeper zones present higher exploratory interest for family 1 gas fields and associated oil accumulations in contrast the bacterial gas fields should be considered a less promising target for future oil and gas exploration

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

helium and carbon isotope variations in liaodong peninsula ne china chemical and c he isotopic compositions have been measured for n2 rich hydrothermal gases from the liaodong abbreviation of east liaoning province peninsula from which the oldest crustal rocks in china with 3 8 ga outcrop with the exception of one sample containing tritogenic 3he and atmospheric 4he in liaoyang the observed 3he 4he ratios from 0 1 ra to 0 7 ra indicate 1 8 helium from mantle 92 98 from crust and 0 1 0 8 from atmosphere despite the lack of quaternary volcanism such 3he 4he ratios suggest together with geophysical evidences the existence of intrusive magmas that contain mantle helium and heat within the liaodong middle lower crust the 3he 4he ratios are high along the ne trending jinzhou faults and gradually decrease with the increase of distance from the faults such a spatial distribution suggests that the mantle helium exsolves from magmatic reservoir in the middle lower crust becomes focused into the root zones of jinzhou faults and subsequently traverses the crust via permeable fault zones when transversely migrated by groundwater circulation in near surface mantle helium with high 3he 4he ratio may have been further diluted to the observed values by addition of radiogenic helium produced in the crust this pattern shows strong evidence that the major faults played an important role on mantle derived components transport from mantle upwards

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 long term fate of co2 in the subsurface natural analogues for co2 storage abstract co 2 is a common gas in geological systems so that planned storage of co 2 in the subsurface may do no more than mimic nature natural co 2 has a wide number of sources that can be at least partly identified by carbon stable isotope geochemistry three pairs of case studies with different reservoir characteristics and co 2 contents have been examined to assess the natural impact of adding co 2 to geological systems carbonate minerals partially dissolve when co 2 is added simply because the co 2 dissolves in water and forms an acidic solution therefore carbonate minerals in the subsurface are not capable of sequestering secondary co 2 the addition of co 2 to a pure quartz sandstone or a sandstone in which the supply of reactive aluminosilicate minerals has been exhausted by excess natural co 2 addition will have no consequences the co 2 will simply saturate the water and then build up as a separate gas phase the addition of co 2 to carbonate cemented sandstone without reactive aluminosilicate minerals will induce a degree of carbonate mineral dissolution but no solid phase sequestration of the added co 2 when co 2 is naturally added to sandstones it will induce combined aluminosilicate dissolution and carbonate cementation if the aluminosilicate minerals contain calcium or magnesium or possibly iron examination of a co 2 filled porous sandstone with abundant reactive aluminosilicate minerals that received a huge co 2 charge about 8000 to 100 000 years ago reveals minimal evidence of solid phase sequestration of the added co 2 this indicates that either dissolution of reactive aluminosilicates or precipitation of carbonate minerals is relatively slow it is very likely that the slow dissolution of reactive aluminosilicates is the rate limiting step solid phase sequestration of co 2 occurs only when reactive aluminosilicates are present in a rock and when the system has had many tens to hundreds of thousands of years to equilibrate the two critical aspects of the behaviour of co 2 when injected into the subsurface are 1 that the rock must contain reactive ca and mg aluminosilicates and 2 that reaction to produce carbonate minerals is extremely slow on a human timescale the reactive minerals include anorthite zeolite smectite and other fe and mg clay minerals such minerals are absent from clean sandstones and limestones but are present in dirty standstones lithic arenites which are mineralogically immature and some mudstones the analysis of geological analogues shows that injection of co 2 into carbonate bearing rocks that do not contain reactive minerals will induce dissolution of the carbonate whether it is a matrix cement rock fragment fault seal or part of a top sealing mudstone

the active southwest margin of the colorado plateau uplift of mantle origin during cenozoic time the colorado plateau was raised about 2 km above sea level the most recent and best documented uplift of the plateau 1 km has been concentratedatitssouthwestmarginbetween6 and 1 ma whereas the eastern colorado plateau may have been at high elevations sinceeocenetime tobetterunderstandthe recent tectonic activity at the southwest marginofthecoloradoplateau wecompile detailed crustal thickness and density informationfromseismicandgravitydatafor a region that includes northwest arizona and the southern tip of nevada this information is used to isolate the mantle contribution to uplift wefind that there is relatively low density mantle underlying the southernmarginoftheplateauinnorthwest arizona which could result from about 60 80 km of thinning of the dense mantle lithosphere combined with about 100 cof heating through a 100 km thick mantle layer the available estimates from earthquake source seismology in or near the studyareaarecompatiblewiththisestimate of lithospheric thinning we speculate that uplift may result from subduction related thinning of the continental lithosphere

in reservoir mixing of mantle derived co2 and metasedimentary ch4 n2 fluids noble gas and stable isotope study of two multistacked fields pannonian basin system w hungary abstract several multistacked gas fields located in very different parts of hungary display a large variation in their gas composition the shallow position of the mantle beneath the basement of the pbs is responsible for the high heat flux it facilitates that the co 2 intensely released from the ascending upper mantle derived melts could reach the basin system in this work the results of a geochemical study of the main components and noble gases of the multistacked repcelak co 2 hc n 2 and mihalyi co 2 fields are presented and discussed the vertical variations of gas composition in the repcelak and mihalyi fields fit well with in reservoir mixing of two end members a mantle related magmatic co 2 fluid and a n 2 rich hc gas fluid of crustal origin however it is very likely that other processes modified to some extent the gas composition of the two fields carbon isotopic composition of the co 2 of the samples studied agrees with both the carbonate decomposition and mantle degassing origins it is very likely that the marked difference in helium isotopic composition between the neighbouring repcelak and mihalyi fields also reflects this heterogeneity

the fate of mantle derived carbon in a continental sedimentary basin integration of c he relationships and stable isotope signatures abstract the isotopic composition and abundances of the rare gases he ne and ar and active gases co2 ch4 have been determined in a series of commercial gas reservoirs in the pannonian and vienna basins of hungary and austria respectively in these zones of continental extension significant components of mantle derived 4he up to 39 8 and 21ne up to 58 are identified the results of this study indicate a major component of mantle derived carbon in these systems as well ranging in composition from close to 100 co2 to ch4 dominated reservoirs with trace concentrations ppm of co2 these gas reservoirs provide a unique opportunity to examine the relationship of the conservative rare gases to the active gas components and to examine the sources and sinks for mantle and crustal derived carbon phases with the exception of kismarja gas field which shows evidence of addition of 3he depleted crustal co2 all gas fields exhibit a trend whereby the most co2 rich samples approach co 2 3 he mntl values similar to morb 2 109 to 7 109 while co2 depleted samples extend to co 2 3 he mntl values as low as 105 the lack of any correlation of co 2 3 he mntl ratios with r ra values indicates the observed trends are not a function of mixing between crustal and mantle derived endmembers but instead reflect progressive loss of the mantle derived co2 carrier phase during volatile transport and emplacement in the continental crust based on stable isotopic signatures from the kismarja field a crustal co2 endmember with an isotopic composition of 6 8 and a mantle co2 endmember with an isotopic composition no more depleted in 13c than 5 0 can be identified one of the few instances where the isotopic signatures of mantle and crustal derived co2 can be reliably distinguished in a continental setting covariation in 13cco2 and 13cch4 values in the gas fields is used to place constraints on two alternative models whereby the trends in percent co2 and co 2 3 he mntl ratios can be accounted for by 1 loss of the mantle derived co2 carrier phase 2 addition of crustal derived co2 3 addition of crustal derived thermogenic ch4 and potentially 4 conversion of the co2mntl carrier phase to mantle derived ch4 based on an estimated total mantle 4he flux for the pannonian basin of 4 2 108 atoms m 2 s 1 mantle carbon flux estimates for this basin alone range from 3 108 g c yr to 1 109 g c yr which over the lifetime of the basin is only 4 5 orders of magnitude less than flux estimates based on the total area of the spreading ridges clearly the addition of mantle derived carbon to the crust in areas of continental extension is significant and may have been previously underestimated we demonstrate here that integration of 13c data with rare gas isotopic tracers provides an important tool in constraining models of mantle carbon sources and sinks in continental settings

mantle and crustal gases of the colorado plateau geochemistry sources and migration pathways abstract the colorado plateau hosts several large accumulations of naturally occurring non hydrocarbon gases including co2 n2 and the noble gases making it a good field location to study the fluxes of these gases within the crust and to the atmosphere in this study we present a compilation of 1252 published gas composition measurements the data reveal at least three natural gas associations in the field area which are dominated by hydrocarbons co2 and n2 he ar respectively most gas accumulations of the region exhibit compositions that are intermediate between the three end members the first non hydrocarbon gas association is characterized by very high purity co2 in excess of 75 mol hereafter many of these high purity co2 fields have recently been well described and interpreted as magmatic in origin the second non hydrocarbon gas association is less well described on the colorado plateau it exhibits he concentrations on the order of 1 10 and centered log ratio biplots show that he occurs proportionally to both n2 and ar overall ratios of n2 to he to ar are 100 10 1 and correlation in concentrations of these gases suggests that they have been sourced from the same reservoir and or by a common process to complement the analysis of the gas composition data stable isotope and noble gas isotope measurements are compiled or newly reported from 11 representative fields previously published data from 4 fields and new data from 7 fields gas sampled from the harley dome gas field in utah contains nearly pure n2 he ar the various compositional and stable and noble gas isotopic data for this gas indicate that noble gas molecule isotope ratios are near crustal radiogenic production values and also suggest a crustal n2 source across the field area most of the high purity n2 he ar gas accumulations are associated with the mapped surface trace of structures or sutures in the precambrian basement and are often accumulated in lower parts of the overlying phanerozoic sedimentary cover the high purity gas association mostly occurs in areas interior to the plateau that are characterized by a narrow range of elevated moderate heat flow values 53 74 mw m2 in the ancient 1 8 1 6 ga basement terranes of the region collectively the geochemical and geological data suggest that 1 the n2 he ar gas association is sourced from a crustal reservoir 2 the gas association migrates preferentially along structures in the precambrian basement and 3 the sourcing process relates to heating of the crust prospecting for noble gas accumulations may target areas with elevated cenozoic heat flow ancient crust and deep crustal structures that focus gas migration high purity co2 gas may also migrate through regional basement structures however there is not always a clear spatial association rather co2 accumulations are more clearly associated with zones of high heat flow 63 mw m2 that sit above hot upper mantle and are proximal to cenozoic volcanic rocks near the plateau margins these observations are consistent with previous interpretations of a magmatic gas source which were based on geochemical measurements

natural h2 in kansas deep or shallow origin a geochemical study of gas coming from three wells in northeastern kansas supplements previous studies from the 1980s and points to a persistent regional phenomenon of h2 production in 2008 a new well showed just after drilling a free gas phase with more than 80 mole of h2 followed by water production associated with gas this gas is mainly composed of n2 he h2 and occasionally ch4 with changing proportions through time a drastic decrease in h2 at the well was observed since the aquifer is produced along with occasional recharges in h2 evidenced notably in the early phases of gas sampling we demonstrate that this evolution of gas composition is closely associated to the well completion story accordingly two distinct origins of h2 are proposed 1 deep crustal h2 water reduction associated to iron oxidation in the precambrian basement 2 reactions occurring in the tubing primarily attributed to high contents of reduced iron and or dissolved organic carbon doc 4 1 mg l 1 in the water the low d values averaging 760 are attributed to a low temperature process possibly a re equilibration with water furthermore the suggested origins are supported by the observed gas associations a deep crustal h2 with radiogenic gases 4he and 40ar and metamorphic n2 15n averaging 2 5 b surficial h2 with methane produced in the sedimentary aquifer and the tubing by methanogenic organisms

dolomite in permian paleosols of the bravo dome co2 field u s a permian reflux followed by late recrystallization at elevated temperature abstract lower permian abo tubb subsurface strata of northeastern new mexico u s a consist of 30 to 120 m of fluvial and eolian deposits containing numerous dolomitic paleosols dolomite in the abo tubb interval occurs in discrete intervals interpreted as paleosols on the basis of recognizable horizonation and the presence of associated features such as ped structures and rhizoliths the dolomite commonly forms veins rhizoliths and discrete and coalesced nodules petrographic analysis indicates four dolomite types present in paleosol horizons microsparitic pseudospherulitic clear cement and cloudy inclusion rich cement microsparitic dolomite constitutes most of 70 the dolomite and is stoichiometric with relatively low sr and na and elevated fe and mn pseudospherulitic dolomite forms 15 of the dolomite and consists of stoichiometric microspar and spar with abundant fluid inclusions low sr na and fe and elevated mn clear dolomite cement constitutes approximately 12 of the dolomite and is finely to coarsely crystalline with a relatively calcian composition low sr and na and elevated fe and mn the cloudy cement forms a minor 2 phase of very coarsely crystalline rhombs with a calcian composition low sr and na values and relatively high fe and mn all dolomite types exhibit a mottled texture of moderate to bright orange and red luminescence fluid inclusion analysis was not possible on the most common microsparitic dolomite type but analyses on the coarser varieties reveal homogenization temperatures typically ranging from 70 c to 110 c and final melting temperatures of ice ranging from 20 c to 34 c suggesting fluids of high 25 by weight salinity bulk rock carbon and oxygen isotopes of carbonate nodules and rhizoconcretions from four paleosol profiles most commonly exhibit mean values typically ranging between 3 to 5 5 vpdb and 0 5 to 2 8 vpdb respectively sulfur isotopes were analyzed for the overlying cimarron anhydrite interval and an anhydrite nodule near the base of the study interval both samples yielded similar results suggesting that brines that precipitated the cimarron anhydrite also influenced the study interval the dolomite in the abo tubb interval is interpreted to have precipitated in multiple stages solid calcite microinclusions in microsparitic and pseudospherulitic dolomite suggest that pedogenensis and groundwater penecontemporaneous with early permian deposition led to precipitation of calcite rather than dolomite oxygen and sulfur isotope data indicate dolomitization from later reflux of brines associated with deposition of the overlying leonardian cimarron anhydrite petrographic relations and elevated temperatures and salinities recorded by the fluid inclusions in the coarse dolomite are consistent with recrystallization of the earlier dolomite and precipitation of dolomite cement from warm saline fluids of a possible tertiary hydrothermal origin just predating migration of mantle derived gas into the bravo dome reservoir these findings offer insight into questions about the climate significance of dolomite in paleosols origin of dolomite in hydrothermally altered hydrocarbon reservoirs and the long term effect of co2 sequestration in saline aquifers the results show that dolomitic nodules in paleosols may form as replacements of paleosol calcite long after the paleosol formed primary pedogenic dolomite would undoubtedly have climatic and paleoenvironmental significance but recognizing it as forming during soil formation as opposed to later dolomitization is key in establishing that significance also this study provides an example of high temperature recrystallization of low temperature dolomite a process hotly debated in discussions of dolomitized hydrocarbon reservoirs with evidence for hydrothermal fluid flow finally as a natural co2 reservoir the bravo dome system shows that the long term result of dissolution of co2 into brines is predominantly carbonate mineral dissolution

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

quantifying the helium and hydrocarbon accumulation processes using noble gases in the north qaidam basin china abstract limited reserves and insecure resource supply have led to global shortage crises in helium a vital gas for cryogenic engineering and other countless industrial manufacturing processes despite the attention drawn by global supply disruptions the helium accumulation mechanism in natural gas fields remains poorly understood noble gases are excellent tracers for studying migration and accumulation processes of fluids in the subsurface and can be used to investigate the influence of subsurface fluids on helium accumulation we present noble gas isotope and abundance data as well as major gas compositional data from 10 producing wells in three gas fields in the north qaidam basin china helium is more concentrated in the mabei and dongping gas fields 2 06 48 4 10 4 cm3 stp cm3 than in the niudong gas field 1 15 1 42 10 4 cm3 stp cm3 the helium is mainly radiogenic with 3he 4he ratios of 0 01 0 05 ra where ra is the atmospheric value of 3he 4he and lacks significant contribution from the mantle 0 03 0 67 the noble gases derived from air saturated water 20ne 36ar 84kr and 130xe can be explained by an oil modified groundwater exsolution model with excess heavy noble gases the calculated voil vwater and vgas vwater ratios indicate that the mabei region is the most oil rich area and the dongping region has the driest natural gas which is consistent with the geological context these ratios further support the fractionation models the strong linear relationship between 4he and 20ne r2 0 98 suggested that 4he was dissolved into groundwater before migrating into the oil or gas phase the initial 4he concentrations in groundwater can accumulate within 0 31 2 78 myr assuming a 4he flux from the entire crustal section according to the fractionation model helium in groundwater partitions into the gas phase when contacting hydrocarbons the different volume ratios among oil gas and water during the equilibration process cause much greater variability in the helium concentrations in the gas phase e g 6 08 10 4 to 2 01 10 3 cm3 stp cm3 in mabei than those in the groundwater phase e g 9 18 10 3 to 1 39 10 2 cm3 4he stp cm3 h2o in mabei hydrocarbons play a critical role in helium accumulation and dilution helium rich natural gas fields are characterized by old groundwater systems and moderate hydrocarbon abundance this study has succeeded in quantitatively assessing the helium accumulation process in natural gas fields in the north qaidam basin and revealed that both groundwater and hydrocarbon phases control the helium accumulation in the subsurface environment this outcome has broad implications for the prediction of hydrocarbon and helium as resources

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

pulses of carbon dioxide emissions from intracrustal faults following climatic warming carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels an analysis of a 135 000 palaeorecord shows that pulses of carbon dioxide leakage from a natural reservoir in utah are associated with episodes of glacial unloading

neon excess in pumice volcanological implications abstract we measured the noble gas abundance and ne and ar isotopic compositions in pumice samples from japan and the eolian islands italy the goal was to give clues on the mechanism of air incorporation into pumice and its relationship with eruption processes the samples contain large excesses of atmospheric ne over ar with 20 ne 36 ar ratios up to 600 times the atmospheric ratio this excess is produced by the preferential diffusion of ne over ar in pumice vesicles during volcanic eruptions the 20 ne 36 ar ratios measured in pumice reflect the initial quenching temperature the cooling rate of the eruption column and the bubble s wall thickness the final ne amount is likely to be proportional to the volume of preserved vesicles in pumice calculations indicate that the fraction of isolated vesicles are less than 10 of the total suggesting that a few amount of gas is preserved in pumice after deposition

the distribution of thermogenic bacterial and inorganic fluid sources in the petroleum systems of the llanos basin colombia insights from the noble gases and carbon stable isotopes abstract the colombian andean foreland is a rich petroleum province where various source rocks and an active circulation of fresh water are present in the subsurface resulting in a complex fluid mixture within the reservoirs moreover some of the traps are shallow and low api gravity oils are found massive meteoric water infiltration and local biodegradation have been proposed to explain these observations but require some in depth investigation to be confirmed in order to provide some new insights into the llanos basin petroleum system we performed a natural gas geochemical survey over different areas of the basin including stable isotopes of hydrocarbon non hydrocarbon and noble gases results show that the influence of meteoric water infiltration is dominant in the shallow area eastward but decreases towards the deepest part of the basin westward a general gas oil phase separation differentiates gas depleted biodegraded shallow reservoirs from deep gas rich less altered reservoirs data suggest that there is a shallow biodegradation associated with meteoric water circulation in the carbonera fm while some of the deeper heavy oils mirador une fms were more likely produced by an early mature source rock however biodegraded oil later mixed with less altered oil and associated gas are plausible this study also indicates a contribution of mantle fluids in the deepest parts of the basin near the contact with the guaycaramo fault system there older rift sequences may have recorded mantle fluid fluxes or alternately the presence of diffuse mantle fluxing along the deep rooted thrust front during the formation of the llanos basin

geochemical monitoring for potential environmental impacts of geologic sequestration of co2 carbon dioxide sequestration is now considered an important component of the portfolio of options for reducing greenhouse gas emissions to stabilize their atmospheric levels at values that would limit global temperature increases to the target of 2 c by the end of the century pacala and socolow 2004 ipcc 2005 2007 benson and cook 2005 benson and cole 2008 iea 2012 romanak et al 2013 increased anthropogenic emissions of co2 have raised its atmospheric concentrations from about 280 ppmv during pre industrial times to 400 ppmv today and based on several defined scenarios co2 concentrations are projected to increase to values as high as 1100 ppmv by 2100 white et al 2003 ipcc 2005 2007 eia 2012 global ccs institute 2012 an atmospheric co2 concentration of 450 ppmv is generally the accepted level that is needed to limit global temperature increases to the target of 2 c by the end of the century this temperature limit likely would moderate the adverse effects related to climate change that could include sea level rise from the melting of alpine glaciers and continental ice sheets and from the ocean warming increased frequency and intensity of wildfires floods droughts and tropical storms and changes in the amount timing and distribution of rain snow and runoff ipcc 2007 sundquist et al 2009 iea 2012 rising atmospheric co2 concentrations are also increasing the amount of co2 dissolved in ocean water lowering its ph from 8 1 to 8 0 with potentially disruptive effects on coral reefs plankton and marine ecosystems adams and caldeira 2008 schrag 2009 sundquist et al 2009 sedimentary basins in general and deep saline aquifers in particular are being investigated as possible repositories for the large volumes of

experimental determination of noble gases and sf6 as tracers of co2 flow through porous sandstone abstract in order to label the co2 injected underground for geological storage and allow it to be differentiated from natural sources a panoply of additive chemical tracers have been proposed yet the transport of these tracers relative to co2 in pore space is currently poorly constrained this leads to uncertainty as to whether tracers will act as an early warning of co2 arrival or be preferentially retained in the pore space making them ineffective here we present the factors affecting transport of noble gases and sf6 relative to co2 in a porous rock using a porous sandstone core each of the tracers were loaded into a sample loop and injected as discrete gas pulses into a co2 carrier stream at five different experiment pressures 10 50 kpag upstream to ambient pressure downstream tracer arrival profiles were measured using a quadrupole mass spectrometer significantly our results show that peak arrival times of helium were slower than the other noble gases at each pressure gradient the differences in peak arrival times between helium and other noble gases increased as the pressure gradient along the system decreased and the curve profiles for each noble gas differ significantly the heavier noble gases kr and xe along with sf6 show an earlier arrival time and a wider curve profile compared to he and ne curves through the co2 carrier gas stream this shows that kr and xe could be substituted for sf6 a potent greenhouse gas in tracer applications for comparison co2 pulses were passed through a n2 carrier gas resulting in significantly slower peak arrival times compared to those of noble gases and sf6 hence all investigated tracers when co injected with co2 could potentially act as early warning tracers of co2 arrival though we find that kr xe and sf6 will provide the most robust advance warning analysis of our experimental results shows that they cannot be explained by a simple one dimensional flow model through a porous medium we outline a conceptual model that incorporates different preferential flow paths depending on flow velocities of individual gas streams this model can explain the observed dataset and shows that the flow of noble gases and sf6 tracers is influenced by pore scale heterogeneity

geological carbon storage storage of the carbon dioxide that is produced by burning fossil fuels is one way to avoid the damaging consequences of climate change a range of observations suggests that geological carbon storage is much less risky than unabated carbon emissions to the atmosphere

high resolution δ18o and δ13c records during the past 65 ka from fengyu cave in guilin variation of monsoonal climates in south china abstract the 18 o and 13 c records of a 230 th u dated 2 2 m long stalagmite from fengyu cave in south china provide a continuous decadal resolution with 3698 measurements proxy for regional climatic and environmental conditions during 4 65 ka this single stalagmite reveals all heinrich cold events most dansgaard oeschger warm events deglaciation and holocene optimum generally supporting the hulu and dongge records on 5000 10000 year time scales the 18 o and 13 c variations show strongly positive correlations r 0 7 reflecting that a common climatic factor controls both 18 o and 13 c of f 1 the comparison of the speleothem ice core insolation and marine records reveals strong linkages between n atlantic temperature and the asian summer monsoon over most of the study period however there are some regional discrepancies between the stalagmite 18 o records following the deglaciation although the nh summer insolation provides the major forcing on asian monsoon variability over orbital time scales the weakest summer monsoon intensity during the last glacial occurred ca 16 ka corresponding to the heinrich event 1 a 5 6 ky lag from the minimum insolation during the last glacial maximum variations in the monsoonal climate of the study area over the past 700 years have been reconstructed from the 18 o and 13 c records of a 14 6 cm long stalagmite f4 in fengyu cave showing wet conditions between ad 1550 and ad 1850 the little ice age and relatively dry conditions before and after this interval human impacts on local vegetation since ad 1700 were recorded by the 13 c record of stalagmite f4

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

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

supercritical carbon dioxide brine rock reactions in the madison limestone of southwest wyoming an experimental investigation of a sulfur rich natural carbon dioxide reservoir abstract the madison limestone on the moxa arch southwest wyoming usa is a sulfur rich natural co 2 reservoir a series of hydrothermal experiments was performed to evaluate multi phase co 2 h 2 o brine rock reactions and processes in this reservoir and to test the hypothesis that this reservoir is a natural analog for geologic carbon sulfur co sequestration idealized madison limestone dolomite calcite anhydrite pyrite and na cl so 4 2 brine i 0 5 molal reacted at 110 c and 25 mpa for approximately 81 days 1940 h supercritical co 2 was then injected and the experiment continued for approximately 46 days 1100 h a parallel experiment was performed without supercritical co 2 to provide a basis of understanding for the interaction of supercritical co 2 with the brine rock system two additional experiments were conducted in the same manner but without anhydrite in the starting mineral assemblage to examine supercritical co 2 sulfur reactivity injection of supercritical co 2 decreases ph by 2 5 to 3 3 units increases eh by 0 19 to 0 23 v and drives reaction pathways along the pyrite anhydrite saturation boundary of an eh ph diagram the dolomite calcite anhydrite mineral assemblage and reaction textures that are produced are consistent with those observed in the natural co 2 reservoir the mineral assemblage does not change following emplacement of supercritical co 2 instead minerals dissolve mobilize and re precipitate anhydrite precipitates in the dolomite calcite pyrite experiment following injection of supercritical co 2 and provides a mineral trap for sulfur anhydrite precipitation decreases so 4 2 activity ultimately leading to mineralization of co 2 experimental results support the hypothesis that the madison limestone on the moxa arch is a natural analog for geologic carbon sulfur co sequestration

a geologic deconstruction of one of the world s largest natural accumulations of co2 moxa arch southwestern wyoming geologic sequestration of anthropogenic carbon dioxide co2 is one of the most promising approaches to safely and effectively reduce emissions of co2 created through the oxidation of fossil fuels methods used by the petroleum industry in the characterization of hydrocarbon accumulations can be used to assess potential subsurface traps for sequestration purposes in this article we use these approaches to evaluate the characteristics of a naturally occurring accumulation of co2 in western wyoming the moxa arch is a 200 km 124 mi long basement involved anticline the mississippian madison formation and the ordovician bighorn dolomite contain the most co2 within the structure relict anhydrite in these and other paleozoic units was an important factor in evolving hydrocarbons into co2 through inorganic thermal sulfate reduction and more importantly in creating a seal to hold large columns of buoyant gas fluid inclusion data sets have been particularly useful in understanding the sealing characteristics of the units within the moxa arch and affirming that the devonian jefferson mississippian amsden and triassic dinwoody and woodside formations have been very effective seals existing pressure data reveal that the two gas columns in the madison and bighorn formations lie on a similar gradient and share a common gas water contact yet are likely not in hydraulic communication currently all available data suggest that both reservoirs share a fault dependent spill point by reconciling the spill points of the gas in the madison and bighorn reservoirs their compositions their initial and current pressures their seal and the uncertainties associated with injection of co2 can be identified and potentially derisked with additional information if the madison and bighorn are filled to their fault dependent spill point it implies that additional storage capacity in the reservoir can only be obtained by production of the original gas column this uncertainty may be abated if data from future drilling demonstrates that neither the madison formation nor the bighorn dolomite have a fault dependent spill point suggesting that these structures are underfilled with respect to their closure and possess additional storage capacity

continental smokers couple mantle degassing and distinctive microbiology within continents abstract the discovery of oceanic black and white smokers revolutionized our understanding of mid ocean ridges and led to the recognition of new organisms and ecosystems continental smokers defined here to include a broad range of carbonic springs hot springs and fumaroles that vent mantle derived fluids in continental settings exhibit many of the same processes of heat and mass transfer and ecosystem niche differentiation helium isotope 3he 4he analyses indicate that widespread mantle degassing is taking place in the western u s a and that variations in mantle helium values correlate best with low seismic velocity domains in the mantle and lateral contrasts in mantle velocity rather than crustal parameters such as gps proximity to volcanoes crustal velocity or composition microbial community analyses indicate that these springs can host novel microorganisms a targeted analysis of four springs in new mexico yield the first published occurrence of chemolithoautotrophic zetaproteobacteria in a continental setting these observations lead to two linked hypotheses that mantle derived volatiles transit through conduits in extending continental lithosphere preferentially above and at the edges of mantle low velocity domains high co2 and other constituents ultimately derived from mantle volatiles drive water rock interactions and heterogeneous fluid mixing that help structure diverse and distinctive microbial communities

man made versus natural co2 leakage a 400 k y history of an analogue for engineered geological storage of co2 to evaluate sites for long term geological storage of co2 and optimize techniques for monitoring the fate of injected co2 it is crucial to investigate potential co2 migration pathways out of a reservoir and surface leakage magnitudes for the first time we calculate co2 leakage rates and volumes from ancient fault related travertines and from an abandoned borehole u th dated travertine along two faults near green river utah western united states shows that leakage has occurred in this area for over 400 k y and has switched location repeatedly over kilometer scale distances one individual travertine was active for at least 11 k y modern leakage is predominantly through the active crystal geyser which erupts from an abandoned exploration well using age data and travertine volume we calculate magnitudes and rates of co2 emission fault focused leakage volume is twice as great than diffuse leakage through unconfined aquifers the leakage rate from a poorly completed borehole is 13 times greater than the long term time averaged fault focused leakage although magnitudes and rates of any leakage from future storage sites will be highly dependent on local geology and pressure regime our results highlight that leakage from abandoned wells is likely to be more significant than through faults introduction carbon dioxide could potentially migrate from underground storage sites through boreholes poor cap rocks or faults and fractures storage formation integrity and effects of leaking co2 on the surface environment is commonly investigated stevens et al 2001 kirk 2011 however the overburden between the storage formation and the surface is a poorly studied part of the co2 storage system gaus 2010 understanding flow through potential migration pathways in the overburden such as faults or high permeability strata is crucial for evaluating long term storage security the integrity of well bores and their long term ability to retain co2 has also been recognized as a significant risk to the long term security of geological storage ieaghg 2005 storage operators will be legally required to monitor the fate of injected co2 european commission 2009 effective monitoring and engineered remediation depends on the likely nature of migration pathways through the overburden and on the locations and likely fluxes of co2 shallow leakage pathways cortis et al 2008 benson and hepple 2005 we investigate a unique location in the paradox basin utah western united states where fossil travertine mounds allow us to compare ancient co2 flux via fault associated fracturing and diffuse leakage through an aquifer with modern leakage from abandoned wells the paradox basin hosts at least nine natural co2 accumulations most of which have contained co2 for millennia gilfillan et al 2008 co2 charged springs along the little grand wash lgw and salt wash graben swg normal faults fig 1 demonstrate that co2 is leaking to the surface through fault zones and abandoned wells doelling 1994 the springs are fed from a shallow aquifer overlain by low permeability siltstones and shales and charged by co2 from depth making this setting analogous to heterogeneous and variably permeable overburden above a geological co2 storage site we use u th dating of travertine formed by out gassing of co2 from springwater to determine flow history along the faults combining travertine age and volume allows us to estimate volumes and rates of co2 emission to the surface through time and compare fault focused diffuse and borehole leakage in a single hydrogeological setting

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

noble gas tracing of groundwater coalbed methane interaction in the san juan basin usa the san juan basin natural gas field located in northwestern new mexico and southwestern colorado in the usa is a case type coalbed methane system groundwater is thought to play a key role in both biogenic methane generation and the co2 sequestration potential of coalbed systems we show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas we collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin and the underpressured low producing region as having a significant admix of thermogenic coal gas 3he 4he ratios increase from 0 0836ra at the basin margin to 0 318ra towards the center indicating a clear but small mantle he signature in all gases coherent fractionation of water derived 20ne 36ar and crustal 4he 40ar are explained by a simple rayleigh fractionation model of open system groundwater degassing low 20ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater associated gas by desorbed coalbed methane this rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well the quantified water volumes in both underpressured and overpressured zones range from 1 7 103 m3 to 4 2 105 m3 with no clear distinction between over and underpressured production zones these results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds there is no requirement of continuous groundwater flow for renewing the microbes or nutrient components we furthermore observe strong mass related isotopic fractionation of 20ne 22ne and 38ar 36ar isotopic ratios this can be explained by a noble gas concentration gradient in the groundwater during gas production which causes diffusive partial re equilibration of the noble gas isotopes it is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air derived noble gases can occur when such concentration gradients are established during gas production excess air derived xe and kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if xe and kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form ch4

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

estimating carbon dioxide residence time scales through noble gas and stable isotope diffusion profiles the study of natural carbon dioxide reservoirs provides fundamental insight into processes involved in carbon capture and storage however the calculations of process rates such as dissolution of co2 into formation water remain uncertain due to indirectly determined ages of the co2 influx the proposed ages for the bravo dome gas field in new mexico usa vary from 56 ka to 1 5 ma here we demonstrate that residence times can be estimated from simple modeling of noble gas and stable isotope diffusion profiles from the gas water contact through the gas column the bravo dome gas field shows a gradient in noble gas concentrations and isotopic ratios from east to west across the 70 km wide field a mantle like end member with a 3he 4he r ra ratio of up to 4 7 is found in the west in contrast to a groundwater end member with high concentrations of air and crustal derived noble gases in the east the air and crustal derived noble gases decrease gradually toward the west stable isotope compositions c and o also vary across the field diffusion modeling of he ne ar kr xe and 13c data yield residence times for the co2 between 14 1 0 2 ka and 16 9 1 1 0 5 ka this is far less than the previous estimates of 1 2 1 5 ma based on apatite u th he thermochronology leading to a dissolution rate of 29 900 11 800 10 700 t a to 35 900 12 300 t a implying that 28 of the total emplaced co2 dissolved this new method can be applied to a wide variety of gas fields with variation in the concentration of groundwater derived noble gases and allow a better assessment of the time scale of other diffusive fluid fluid interactions

constraining the timing of microbial methane generation in an organic rich shale using noble gases illinois basin usa abstract at least 20 of the world s natural gas originates from methanogens subsisting on organic rich coals and shales however in situ microbial methane production rates are unknown methanogens in the upper devonian new albany shale in the illinois basin extract hydrogen from low salinity formation water to form economic quantities of natural gas because of this association constraining the source and timing of groundwater recharge will enable estimation of minimum in situ metabolic rates thirty four formation water and gas samples were analyzed for stable isotopes oxygen and hydrogen chloride tritium 14 c and noble gases chloride and 18 o spatial patterns reveal a plume of water with low salinity 0 7 to 2154 mm and 18 o values 0 14 to 7 25 penetrating 1 km depth into evapo concentrated brines parallel to terminal moraines of the laurentide ice sheet suggesting glacial mediated recharge however isotopic mixing trends indicate that the recharge endmember 7 18 o is higher than the assumed bulk ice sheet value 18 o and similar to modern local precipitation 7 5 to 4 5 18 o continental paleoprecipitation records reveal that throughout the pleistocene 18 o of precipitation in the region ranged from 10 to 5 suggesting that the dilute groundwater was primarily sourced from paleoprecipitation with minor contributions from glacial meltwater for the majority of samples the atmosphere derived 4 he contribution is negligible and the 4 he is dominated by a crustal radiogenic source with near complete transfer of dissolved noble gases to the gas phase in addition mantle derived helium is negligible for all samples 18 o data however all groundwater in the study area was influenced by pleistocene recharge estimated in situ microbial methane production rates range from 10 to 1000 tcf ma 10 4 to 10 6 times slower than average laboratory rates from coals findings from this study have implications for targeting undeveloped microbial gas accumulations improving natural gas reservoir estimates the potential of in situ methanogen stimulation and understanding biologic cycling of carbon in subsurface reservoirs

evolution of fault permeability during episodic fluid circulation evidence for the effects of fluid rock interactions from travertine studies utah usa faults are known to be important pathways for fluid circulation within the crust the transfer properties along faults can evolve over time and space the little grand wash and salt wash normal faults located on the colorado plateau are well known examples of natural co2 leakage systems from depth to surface previous studies dated and established a chronology of co2 enriched fluid source migration along the fault traces and linked the aragonite veins observed close to crystal geyser to co2 pulses however multiple circulation events recorded along a given fault segment deserve to be studied in minute detail in order to unravel the chronology of these events precipitation processes and associated mechanisms a combination of structural geology petrography u th dating oxygen and carbon isotope analysis were used to study the fault related co2 enriched paleo circulations in order to build a conceptual model of co2 circulation along the faults this study resulted in the precise descriptions of the features attesting co2 enriched fluid circulation by a characterization of their relationship and architecture at the outcrop scale these features are witnesses of a large range of circulation sealing mechanisms as well as changes in fluid chemistry and thermodynamic state of the system providing evidence for i the evolution of the fluid through a pathway from depth to the surface and ii different cycles of fault opening and sealing large circulation events linked with fault opening sealing are observed and calibrated in nature with millennial circulation and sealing time lapses numerical modelling indicates that such sealing timescale can be explained by the introduction of a fault sealing factor that allows modifying permeability with time and that is calibrated by the natural observations

the spar lake strata bound cu ag deposit formed across a mixing zone between trapped natural gas and metals bearing brine ore formation at the spar lake red bed associated strata bound cu deposit took place across a mixing and reaction zone between a hot oxidized metals transporting brine and a reservoir of sour h2s bearing natural gas trapped in the host sandstones fluid inclusion volatile analyses have very high ch4 concentrations 1 mol in most samples and a sample from the fringe of the deposit has between 18 and 36 mol ch4 the ratio of ch4 co2 in fluid inclusions appears to vary regularly across the deposit with the lowest ch4 co2 ratios from high grade chalcocite bearing ore and the highest from the chalcopyrite bearing fringe the helium r ra isotope ratios 0 23 0 98 and concentrations define a mixture between crustal and atmospheric helium the volatiles in fluid inclusions ch4 co2 h2s so2 h2 h2o and other organic gases and values of f o2 and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone other volatiles from the fluid inclusions hcl hf 3he 4he n2 ar characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences the brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest northeast and northwest metals transporting brines may have been fed into the host sandstones from the east fault but that remains uncertain abundant ore stage fe and mn calcite cements from the reduced fringe have 13c values as low as 18 4 and many values less than 10 which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas the zone of calcite cements with very low 13c values approximately envelopes chalcocite bearing ore sulfur isotope data of cu pb and fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas h2s that sour gas h2s had developed in steps known from other sedimentary basins starting with 1 bacterial sulfate reduction bsr of seawater sulfate having 34s of about 20 and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks followed by 2 maturation of the sulfide bearing organic matter into liquid petroleum with relatively homogeneous sulfide having 34s of 5 5 then by 3 thermal cracking of the oil to ch4 and h2s with relatively homogeneous sulfide having 34s closely distributed about 6 the ch4 and h2s migrated and were trapped in sandstones of the upper member of the revett formation where they were later met by the 200 c metals transporting brine there was additional contribution of sulfide to ore from later thermochemical sulfate reduction tsr operating on sulfate 34s of 20 to 29 in both formation waters and metals transporting solutions a large range of 34s in sulfides resulted as the 6 sour gas sulfide was supplemented with varying proportions of 20 to 29 sulfide from tsr

noble gas fractionation during subsurface gas migration abstract environmental monitoring of shale gas production and geological carbon dioxide co2 storage requires identification of subsurface gas sources noble gases provide a powerful tool to distinguish different sources if the modifications of the gas composition during transport can be accounted for despite the recognition of compositional changes due to gas migration in the subsurface the interpretation of geochemical data relies largely on zero dimensional mixing and fractionation models here we present two phase flow column experiments that demonstrate these changes water containing a dissolved noble gas is displaced by gas comprised of co2 and argon we observe a characteristic pattern of initial co enrichment of noble gases from both phases in banks at the gas front followed by a depletion of the dissolved noble gas the enrichment of the co injected noble gas is due to the dissolution of the more soluble major gas component while the enrichment of the dissolved noble gas is due to stripping from the groundwater these processes amount to chromatographic separations that occur during two phase flow and can be predicted by the theory of gas injection this theory provides a mechanistic basis for noble gas fractionation during gas migration and improves our ability to identify subsurface gas sources after post genetic modification finally we show that compositional changes due to two phase flow can qualitatively explain the spatial compositional trends observed within the bravo dome natural co2 reservoir and some regional compositional trends observed in drinking water wells overlying the marcellus and barnett shale regions in both cases only the migration of a gas with constant source composition is required rather than multi stage mixing and fractionation models previously proposed

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

the noble gas systematics of late orogenic h2o co2 fluids mt isa australia abstract the noble gases he ne ar kr and xe are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere crust and mantle this study illustrates how noble gases can be used to trace fluid origins in high temperature metamorphic and mineralising environments and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously we report data for h2o and co2 fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the proterozoic mt isa inlier of australia sulphide fluid inclusions are dominated by crustal 4he however co variations in fluid inclusion 20ne 22ne 21ne 22ne 40ar 36ar and 136xe 130xe indicate noble gases were derived from three or more reservoirs in most cases the fluid inclusions elemental noble gas ratios e g ne xe are close to the ranges expected in sedimentary and crystalline rocks however the elemental ratios have been modified in some of the samples providing evidence for independent pulses of co2 and interaction of co2 with high salinity aqueous fluids compositional variation is attributed to mixing of i magmatic fluids or deeply sourced metamorphic fluids characterised by basement derived noble gases with 20ne 22ne 8 4 21ne 22ne 0 4 40ar 36ar 40 000 and 136xe 130xe 8 ii basinal metamorphic fluids with a narrow range of compositions including near atmospheric values and iii noble gases derived from the meta sedimentary host rocks with 20ne 22ne 8 9 8 21ne 22ne these data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in mt isa s largest ore deposits in addition the data show how noble gases in fluid inclusions can provide information on fluid origins the composition of the crust s major lithologies fluid rock interactions and fluid fluid mixing or immiscibility processes

the degassing character of a young volcanic center cerro negro nicaragua cerro negro volcano is a young basaltic cinder cone which is part of the nicaraguan volcanic arc eruptive activity at cerro negro is characterized by explosive strombolian to subplinian eruptions driven by volatile rich basaltic magma ascending rapidly from various crustal depths 15 to 6 km resulting in the onset of precursory activity only 30 min before an eruption in this paper we present a comprehensive degassing characterization of the volcano over a 4 year period aimed at improving our understanding of the magmatic plumbing network and its relationship with regional tectonics a total of 124 individual soil gas samples were collected between 2010 and 2013 and analyzed for stable carbon isotopes 13c from co2 high temperature fumaroles were sampled for 18o d and 3he 4he isotope analysis and major degassing zones were mapped using soil co2 flux measurements gases at cerro negro are characterized by a strong 3he 4he mantle signature 6 3 to 7 3 ra magmatic 13c ratios 2 3 to 3 0 meteoric 18o and d ratios and stable co2 fluxes 31 t d 1 the lack of 13c fractionation and an increase in the relative mantle component from 2002 to 2012 suggest that the volatile flux at cerro negro originates from the mantle and ascends to the surface via a series of crustal fractures that act as permeable conduits despite the lack of new eruptions the hydrothermal system of cerro negro continues to evolve due to seasonal inputs of meteoric water slope failures that expose and bury sites of active degassing and bursts of regional seismicity that have the potential to open up new conduits for gas release as well as magma continuing geophysical and geochemical monitoring of the main edifice and the recently formed south zone is essential as the volcano remains overdue to erupt

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

hydrogeochemistry of the middle rio grande aquifer system fluid mixing and salinization of the rio grande due to fault inputs abstract deeply derived fluids influence river and groundwater hydrochemistry at the socorro constriction in the central new mexico rio grande rift new hydrochemical transects in the rio grande rift provide three dimensional perspectives on sources contributing to surface and groundwaters in addition to abrupt salinity increases in the rio grande major and trace ion chemistry 18o d 13c 87sr 86sr 3h and 3he 4he variations in springs and wells across the rift are best explained by mixing of deeply derived endogenic fluids containing both mantle and crustal inputs with shallow groundwater endogenic fluids ascend along rift bounding and intra rift faults and can cause increased salinity accompanied by an increase in metals and overall degradation of water quality our data reinforce models that attribute a downstream increase in salinity to geological not agricultural influences hydrochemical mixing of endogenic waters along faults in shallow aquifers has a major influence on groundwater and surface water quality and variability in arid tectonically active regions with important ramifications for water management

follow the water connecting a co2 reservoir and bleached sandstone to iron rich concretions in the navajo sandstone of south central utah usa concretions with thick iron oxide cemented rinds and lightly cemented iron poor sandstone cores are abundant within the navajo sandstone near the southeast fl ank of the escalante anticline utah united states previous workers suggested the spheroidal concretions as analogs for martian blueberries hematite concretions and linked the origin of concretions and bleaching of the navajo sandstone to the buoyant rise of hydrocarbons toward anticlinal crests we measured azimuths of 163 pipe like pipy joint associated concretions and those of 58 comet tails that extend from some spherical concretions both data sets have vector magnitudes 90 and subparallel southeast directed resultant vectors our data indicate that groundwater transported and deposited iron over a fl ow path that spanned more than 100 km from the anticlinal crest to the colorado river buoyant fl uids could not have transported iron from bleached rock to sites of concretion growth however because iron moved downdip we propose that iron was transported southeastward by reducing groundwater that fl owed through a co 2 and methane charged reservoir within the escalante anticline iron rich carbonates precipitated during co 2 degassing after methane was fl ushed from the aquifer microaerophiles oxidized fe 2 in concretions dissolving the carbonates and forming the iron oxide rich rinds and iron poor cores these concretions defi ne the fl ow direction and geochemical evolution of a paleoaquifer this approach could be used to follow the water on other planets

supercritical carbon dioxide and sulfur in the madison limestone a natural analog in southwest wyoming for geologic carbon sulfur co sequestration article i nfo the madison limestone on the moxa arch southwest wyoming usa contains large volumes 65 95 of supercritical co2 that it has stored naturally for 50 million years this reservoir also contains supercritical h2s aqueous sulfur complexes so4 2 and hs and sulfur bearing minerals anhydrite and pyrite although so2 is not present these sulfur bearing phases are known products of so2 disproportionation in other water rock systems the natural co occurrence of so4 2 s 2 supercritical co2 and brine affords the opportunity to evaluate the fate of a carbon sulfur co sequestration scenario mineralogic data was obtained from drill core and aqueous geochemical data from wells outside and within the current supercritical co2 sulfur brine rock system in addition to dolomite calcite and accessory sulfur bearing minerals the madison limestone contains accessory quartz and the aluminum bearing minerals feldspar illite and analcime dawsonite naalco3 oh 2 predicted as an important carbon sink in sequestration modeling studies is not present after confirming equilibrium conditions for the madison limestone system reaction path models were constructed with initial conditions based on data from outside the reservoir addition of supercritical co2 to the madison limestone was simulated and the results compared to data from inside the reservoir the model accurately predicts the observed mineralogy and captures the fundamental changes expected in a madison limestone brine system into which co2 is added ph decreases from 5 7 to 4 5 at 90 c and to 4 0 at 110 c as expected from dissolution of supercritical co2 creation of carbonic acid and buffering by the carbonate rock the calculated redox potential increases by 0 1 v at 90 c and 0 15 v at 110 c due to equilibrium among co2 anhydrite and pyrite final calculated eh and ph match conditions for the co existing sulfur phases present in produced waters and core from within the reservoir total dissolved solids increase with reaction progress mostly due to dissolution of calcite with an accompanying increase in dissolved bicarbonate the madison limestone is a natural example of the thermodynamic end point that similar fluid rock systems will develop following emplacement of a supercritical co2 sulfur mixture and is a natural analog for geologic carbon sulfur co sequestration

roles of fault structures on the distribution of mantle derived co2 in the bohai bay basin ne china abstract based on studies on the contents origin and filling history of co2 and the seismic interpretation of the bohai sea the sea area of the bohai bay basin the distribution of mantle derived co2 and roles of fault structures have been examined in this study mantle derived co2 is mainly distributed in the structures within the bozhong area the center of the bohai sea laser raman spectrum shows that co2 inclusions are symbiotic with hydrocarbon inclusions with a charging time no earlier than 5 1 ma late stage 5 1 0 ma active basement faults are the major pathways for the migration of mantle derived co2 the intensity of the activity influences the co2 content abundant co2 occurs in the structures with basement faults that have relatively high fault activity rate far values along the basement fault high co2 content appears near the segments with high far values fault combination patterns affect the accumulation layers of mantle derived co2 structures with fault combination patterns that resemble a flower or y commonly accumulate co2 in cenozoic shallow layers as well the branch faults that intersect with basement faults facilitate the adjustment of co2 from deep to shallow layers the uplifted mantle is the deep tectonic context and the upwelling mantle magma is the source of the development of mantle derived co2 below the middle crust mantle derived co2 may be vertically transported along the lithosphere scale strike slip faults within the middle and upper crust the late stage active basement faults are the major conduits for mantle derived co2