Note: a dual temperature closed loop batch reactor for determining the partitioning of trace gases within CO2-water systems

An experimental approach is presented which can be used to determine partitioning of trace gases within CO2-water systems. The key advantages of this system are (1) The system can be isolated with no external exchange, making it ideal for experiments with conservative tracers. (2) Both phases can be sampled concurrently to give an accurate composition at each phase at any given time. (3) Use of a lower temperature flow loop outside of the reactor removes contamination and facilitates sampling. (4) Rapid equilibration at given pressure/temperature conditions is significantly aided by stirring and circulating the water phase using a magnetic stirrer and high-pressureliquid chromatography pump, respectively

Tracing organic matter composition and distribution and its role on arsenic release in shallow Cambodian groundwaters

Biogeochemical processes that utilize dissolved organic carbon are widely thought to be responsible for the liberation of arsenic from sediments to shallow groundwater in south and southeast Asia. The accumulation of this known carcinogen to hazardously high concentrations has occurred in the primary source of drinking water in large parts of densely populated countries in this region. Both surface and sedimentary sources of organic matter have been suggested to contribute dissolved organic carbon in these aquifers. However, identification of the source of organic carbon responsible for driving arsenic release remains enigmatic and even controversial. Here, we provide the most extensive interrogation to date of the isotopic signature of ground and surface waters at a known arsenic hotspot in Cambodia. We present tritium and radiocarbon data that demonstrates that recharge through ponds and/or clay windows can transport young, surface derived organic matter in to groundwater to depths of 44 m under natural flow conditions. Young organic matter dominates the dissolved organic carbon pool in groundwater that is in close proximity to these surface water sources and we suggest this is likely a regional relationship. In locations distal to surface water contact, dissolved organic carbon represents a mixture of both young surface and older sedimentary derived organic matter. Ground-surface water interaction therefore strongly influences the average dissolved organic carbon age and how this is distributed spatially across the field site. Arsenic mobilization rates appear to be controlled by the age of dissolved organic matter present in these groundwaters. Arsenic concentrations in shallow groundwaters (< 20 m) increase by 1 μg/l for every year increase in dissolved organic carbon age compared to only 0.25 μg/l for every year increase in dissolved organic carbon age in deeper (> 20 m) groundwaters. We suggest that, while the rate of arsenic release is greatest in shallow aquifer sediments, arsenic release also occurs in deeper aquifer sediments and as such remains an important process in controlling the spatial distribution of arsenic in the groundwaters of SE Asia. Our findings suggest that any anthropogenic activities that alter the source of groundwater recharge or the timescales over which recharge takes place may also drive changes in the natural composition of dissolved organic carbon in these groundwaters. Such changes have the potential to influence both the spatial and temporal evolution of the current groundwater arsenic hazard in this region

Determining noble gas partitioning within a CO2–H2O system at elevated temperatures and pressures

Quantifying the distribution of noble gases between phases is essential for using these inert trace gases to track the processes controlling multi-phase subsurface systems. Here we present experimental data that defines noble gas partitioning for two phase CO2–water systems. These are at the pressure and temperature range relevant for engineered systems used for anthropogenic carbon capture and geological storage (CCS) technologies, and CO2-rich natural gas reservoirs (CO2 density range 169–656 kg/m3 at 323–377 K and 89–134 bar). The new partitioning data are compared to predictions of noble gas partitioning determined in low-pressure, pure noble gas–water systems for all noble gases except neon and radon. At low CO2 density there was no difference between measured noble gas partitioning and that predicted in pure noble gas–water systems. At high CO2 density, however, partition coefficients express significant deviation from pure noble gas–water systems. At 656 kg/m3, these deviations are −35%, 74%, 113% and 319% for helium, argon, krypton and xenon, respectively. A second order polynomial fit to the data for each noble gas describes the deviation from the pure noble gas–water system as a function of CO2 density. We argue that the difference between pure noble gas–water systems and the high density CO2–water system is due to an enhanced degree of molecular interactions occurring within the dense CO2 phase due to the combined effect of inductive and dispersive forces acting on the noble gases. As the magnitude of these forces are related to the size and polarisability of each noble gas, xenon followed by krypton and argon become significantly more soluble within dense CO2. In the case of helium repulsive forces dominate and so it becomes less soluble as a function of CO2 density

Noble gases in deepwater oils of the U.S. Gulf of Mexico

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 19(11), (2018): 4218-4235. doi: 10.1029/2018GC007654Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He‐Ne‐Ar‐Kr‐Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover‐Diana) are used to calibrate a model that takes into account both water‐oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two‐phase) oil‐water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios ( urn:x-wiley:15252027:media:ggge21714:ggge21714-math-0001) in Tertiary‐sourced oils from the Hoover‐Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher urn:x-wiley:15252027:media:ggge21714:ggge21714-math-0002 in Hoover‐Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover‐Diana oils and thus have interacted with more water. The ability to determine a robust urn:x-wiley:15252027:media:ggge21714:ggge21714-math-0003, despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.We thank ExxonMobil for funding and providing the samples. In addition, we thank James Scott and two anonymous reviewers for their comprehensive and constructive reviews, as well as Janne Blichert‐Toft for editorial handling.2019-04-1

Use of lithium tracers to quantify drilling fluid contamination for groundwater monitoring in Southeast Asia

Drilling is widely used in groundwater monitoring and many other applications but has the inherent problem of introducing some degree of external contamination into the natural systems being monitored. Contamination from drilling fluid is particularly problematic for (i) wells with relatively low water flow rates which are difficult to flush; and for (ii) hydrogeochemical research studies of groundwaters hosted by incompletely consolidated shallow sediments, which are widely utilized as sources of drinking water and irrigation water across many parts of Asia. Here, we develop and evaluate a method that can be simply used to quantify the extent of drilling fluid contribution to a water sample either to optimize sample collection for reduced contamination, or to allow a correction for contamination to be made. We report the utility of lithium chloride tracers using both field and laboratory analytical techniques to quantitatively evaluate and correct for drilling fluid contamination of casing waters through an investigation of 15 sites in Kandal Province, Cambodia. High analytical errors limit the practicality and resolution of field-based lithium ion selective electrode measurements for purposes other than broad estimates of gross contamination. However, when laboratory analysis is integrated with the method (e.g. via inductively coupled plasma atomic emission spectrometry analysis), lithium tracers can provide a robust and accurate method for evaluating drilling-related contamination if appropriate samples are collected. Casing water is susceptible to contamination from drilling fluid which was shown to be significantly reduced within two to three well volumes of flushing but can still persist above background for greater than seven well volumes of flushing. A waiting period after drilling and prior to water sampling was shown to further decrease contamination due to dilution from the surrounding aquifer, particularly in more permeable wells. Contamination values were generally <3% for 34 monitoring wells across 15 sites after flushing a mean of 4.6 ± 3.8 well volumes, even when lithium-spiked water was directly injected during flushing to remove settled mud/debris. Operational issues can be encountered which can (i) lead to contamination being much higher than the mean if wells are highly unproductive and clay-dominated or (ii) lead to higher flushing volumes than the mean particularly in sandy areas where fine sand may enter the well screening. General correction factors have been provided for typical monitoring wells in poorly consolidated shallow aquifers in Southeast Asia, and examples provided for how to correct other groundwater data for contamination. For most analytes such as sodium or dissolved organic carbon (DOC), specific corrections may not be necessary for the typical magnitude of contamination encountered, particularly when the differences in concentrations between the drilling fluid and groundwater are relatively small. In the particular circumstance where drilling fluid may have much higher DOC than groundwaters, or vice versa with drilling fluid having much lower DOC than groundwaters in organic-rich alluvial sediments, corrections may still be necessary and significant. Similarly, for highly sensitive parameters such as 14C model age or other age-related parameters (such as tritium, chlorofluorocarbons (CFCs) or sulfur hexafluoride (SF6)), corrections can be significant in typical field scenarios particularly when contamination values are high and/or there is a large difference in age between groundwater and drilling fluid. The lithium method was verified with comparison to changes in concentration of a suite of representative and naturally occurring groundwater constituents as a function of well flushing from relatively low and high permeability groundwater monitoring wells to further illustrate the technique

Determining fluid migration and isolation times in multiphase crustal domains using noble gases

Geochemical characteristics in subsurface fluid systems provide a wealth of information about fluid sources, migration, and storage conditions. Determining the extent of fluid interaction (aquifer-hydrocarbon connectivity) is important for oil and gas production and waste storage applications, but is not tractable using traditional seismic methods. Furthermore, the residence time of fluids is critical in such systems and can vary from tens of thousands to billions of years. Our understanding of the transport length scales in multiphase systems, while equally important, is more limited. Noble gas data from the Rotliegend natural gas field, northern Germany, are used here to determine the length scale and isolation age of the combined water-gas system. We show that geologically bound volume estimates (i.e., gas to water volume ratios) match closed-system noble gas model predictions, suggesting that the Rotliegend system has remained isolated as a closed system since hydrocarbon formation. Radiogenic helium data show that fluid isolation occurred 63–129 m.y. after rock and/or groundwater deposition (ca. 300 Ma), which is consistent with known hydrocarbon generation from 250 to 140 Ma, thus corroborating long-term geologic isolation. It is critical that we have the ability to distinguish between fluid systems that, despite phase separation, have remained closed to fluid loss from those that have lost oil or gas phases. These findings are the first to demonstrate that such systems remain isolated and fully gas retentive on time scales >100 m.y. over >10 km length scales, and have broad implications for saline aquifer CO2 disposal site viability and hydrocarbon resource prediction, which both require an understanding of the length and time scales of crustal fluid transport pathways

Investigating the effect of enhanced oil recovery on the noble gas signature of casing gases and produced waters from selected California oil fields

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tyne, R. L., Barry, P. H., Karolyte, R., Byrne, D. J., Kulongoski, J. T., Hillegonds, D. J., & Ballentine, C. J. Investigating the effect of enhanced oil recovery on the noble gas signature of casing gases and produced waters from selected California oil fields. Chemical Geology, 584, (2021): 120540. https://doi.org/10.1016/j.chemgeo.2021.120540.In regions where water resources are scarce and in high demand, it is important to safeguard against contamination of groundwater aquifers by oil-field fluids (water, gas, oil). In this context, the geochemical characterisation of these fluids is critical so that anthropogenic contaminants can be readily identified. The first step is characterising pre-development geochemical fluid signatures (i.e., those unmodified by hydrocarbon resource development) and understanding how these signatures may have been perturbed by resource production, particularly in the context of enhanced oil recovery (EOR) techniques. Here, we present noble gas isotope data in fluids produced from oil wells in several water-stressed regions in California, USA, where EOR is prevalent. In oil-field systems, only casing gases are typically collected and measured for their noble gas compositions, even when oil and/or water phases are present, due to the relative ease of gas analyses. However, this approach relies on a number of assumptions (e.g., equilibrium between phases, water-to-oil ratio (WOR) and gas-to-oil ratio (GOR) in order to reconstruct the multiphase subsurface compositions. Here, we adopt a novel, more rigorous approach, and measure noble gases in both casing gas and produced fluid (oil-water-gas mixtures) samples from the Lost Hills, Fruitvale, North and South Belridge (San Joaquin Basin, SJB) and Orcutt (Santa Maria Basin) Oil Fields. Using this method, we are able to fully characterise the distribution of noble gases within a multiphase hydrocarbon system. We find that measured concentrations in the casing gases agree with those in the gas phase in the produced fluids and thus the two sample types can be used essentially interchangeably. EOR signatures can readily be identified by their distinct air-derived noble gas elemental ratios (e.g., 20Ne/36Ar), which are elevated compared to pre-development oil-field fluids, and conspicuously trend towards air values with respect to elemental ratios and overall concentrations. We reconstruct reservoir 20Ne/36Ar values using both casing gas and produced fluids and show that noble gas ratios in the reservoir are strongly correlated (r2 = 0.88–0.98) to the amount of water injected within ~500 m of a well. We suggest that the 20Ne/36Ar increase resulting from injection is sensitive to the volume of fluid interacting with the injectate, the effective water-to-oil ratio, and the composition of the injectate. Defining both the pre-development and injection-modified hydrocarbon reservoir compositions are crucial for distinguishing the sources of hydrocarbons observed in proximal groundwaters, and for quantifying the transport mechanisms controlling this occurrence.This work was supported by a Natural Environment Research Council studentship to R.L.Tyne (Grant ref. NE/L002612/1) and the U.S. Geological Survey (Grant ref. 15-080-250), as part of the California State Water Resource Control Board's Oil and Gas Regional Groundwater Monitoring Program (RMP)

EJVES vol 34, issue 2 (August 2007) - Spanish Translated Abstracts

Chronic exposure to arsenic (As) through the consumption of contaminated groundwaters is a major threat to public health in South and Southeast Asia. The source of As-affected groundwaters is important to the fundamental understanding of the controls on As mobilization and subsequent transport throughout shallow aquifers. Using the stable isotopes of hydrogen and oxygen, the source of groundwater and the interactions between various water bodies were investigated in Cambodia’s Kandal Province, an area which is heavily affected by As and typical of many circum-Himalayan shallow aquifers. Two-point mixing models based on δD and δ18O allowed the relative extent of evaporation of groundwater sources to be estimated and allowed various water bodies to be broadly distinguished within the aquifer system. Model limitations are discussed, including the spatial and temporal variation in end member compositions. The conservative tracer Cl/Br is used to further discriminate between groundwater bodies. The stable isotopic signatures of groundwaters containing high As and/or high dissolved organic carbon plot both near the local meteoric water line and near more evaporative lines. The varying degrees of evaporation of high As groundwater sources are indicative of differing recharge contributions (and thus indirectly inferred associated organic matter contributions). The presence of high As groundwaters with recharge derived from both local precipitation and relatively evaporated surface water sources, such as ponds or flooded wetlands, are consistent with (but do not provide direct evidence for) models of a potential dual role of surface-derived and sedimentary organic matter in As mobilization

Helium-isotope constraints on palaeoceanographic change and sedimentation rates during precession cycles (Cenomanian Scaglia Bianca Formation, central Italy)

For much of the pelagic sedimentary record, time control is limited to the resolution of precession cycles (ca 20 kyr): the Milankovitch parameter that forms the most detailed metronome for the Cenozoic and Mesozoic Eras. The influence of precession is often detected in lithological alternations, where the duration represented by individual lithologies is not well constrained. Here the novel technique of extraterrestrial helium abundance (3HeET) is used to investigate the sedimentation dynamics and palaeoceanography within individual precessional cycles. High-resolution 3HeET timescales were produced for four precession cycles from the rhythmically bedded Scaglia Bianca Formation, a sequence of Upper Cretaceous (Cenomanian) deep-marine pelagic limestones from central Italy that are well characterized by cyclostratigraphy. Using 3HeET concentrations as a proxy for sedimentation rate allows instantaneous sedimentation rates and organic-carbon mass accumulation rates to be calculated for each bed within a precession cycle. Eccentricity is known to modulate the amplitude of precession forcing, and precession cycles deposited under eccentricity maxima and minima were selected for comparison. Lithological changes through these chert–(black shale)–limestone cycles are explained using the concept of ‘palaeoenvironmental thresholds’; these timescale calculations indicate that when the amplitude of precessional insolation forcing was greatest (at eccentricity maxima) the palaeoenvironmental system spent longer in the more nutrient-rich environment under which siliceous and organic-rich sediments were deposited, reflecting increased time spent above a ‘threshold’ insolation level. Estimates of primary productivity are relatively elevated for organic-rich beds. An increase in the flux of terrestrial helium (4Heterr) during the deposition of cherts may have been coincident with an increase in terrestrially derived nutrients. The presented results indicate great potential for the use of 3HeET to understand past oceanographic, climatic and sedimentological processes at high temporal resolution

Basin architecture controls on the chemical evolution and 4He distribution of groundwater in the Paradox Basin

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tyne, R., Barry, P., Cheng, A., Hillegonds, D., Kim, J.-H., McIntosh, J., & Ballentine, C. Basin architecture controls on the chemical evolution and 4He distribution of groundwater in the Paradox Basin. Earth and Planetary Science Letters, 589, (2022):117580, https://doi.org/10.1016/j.epsl.2022.117580.Fluids such as 4He, H2, CO2 and hydrocarbons accumulate within Earth's crust. Crustal reservoirs also have potential to store anthropogenic waste (e.g., CO2, spent nuclear fuel). Understanding fluid migration and how this is impacted by basin stratigraphy and evolution is key to exploiting fluid accumulations and identifying viable storage sites. Noble gases are powerful tracers of fluid migration and chemical evolution, as they are inert and only fractionate by physical processes. The distribution of 4He, in particular, is an important tool for understanding diffusion within basins and for groundwater dating. Here, we report noble gas isotope and abundance data from 36 wells across the Paradox Basin, Colorado Plateau, USA, which has abundant hydrocarbon, 4He and CO2 accumulations. Both groundwater and hydrocarbon samples were collected from 7 stratigraphic units, including within, above and below the Paradox Formation (P.Fm) evaporites. Air-corrected helium isotope ratios (0.0046 - 0.127 RA) are consistent with radiogenic overprinting of predominantly groundwater-derived noble gases. The highest radiogenic noble gas concentrations are found in formations below the P.Fm. Atmosphere-derived noble gas signatures are consistent with meteoric recharge and multi-phase interactions both above and below the P.Fm, with greater groundwater-gas interactions in the shallower formations. Vertical diffusion models, used to reconstruct observed groundwater helium concentrations, show the P.Fm evaporite layer to be effectively impermeable to helium diffusion and a regional barrier for mobile elements but, similar to other basins, a basement 4He flux is required to accumulate the 4He concentrations observed beneath the P.Fm. The verification that evaporites are regionally impermeable to diffusion, of even the most diffusive elements, is important for sub-salt helium and hydrogen exploration and storage, and a critical parameter in determining 4He-derived mean groundwater ages. This is critical to understanding the role of basin stratigraphy and deformation on fluid flow and gas accumulation.This work was supported by a Natural Environment Research Council studentship to R.L. Tyne (Grant ref. NE/L002612/1). We gratefully acknowledge the William F. Keck Foundation for support of this research, and the National Science Foundation (NSF EAR #2120733). J.C. McIntosh and C.J. Ballentine are fellows of the CIFAR Earth4D Subsurface Science and Exploration Program. The authors would like to acknowledge the U.S. Bureau of Reclamation, Paradox Resources, Navajo Petroleum, US Oil and Gas INC, Anson Resources, Lantz Indergard (Lisbon Valley Mining Co.), Ambria Dell'Oro and Mohammad Marza for help with sampling