Tracer Applications of Noble Gas Radionuclides in the Geosciences

The noble gas radionuclides, including 81Kr (half-life = 229,000 yr), 85Kr (11 yr), and 39Ar (269 yr), 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 deeper circulation of fluids in the Earth's crust and mantle also are 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

The state of the art in monitoring and verification— ten years on

In the ten years since publication of the IPCC Special Report on CCS, there has been considerable progress in monitoring and verification (M&V). Numerous injection projects, ranging from small injection pilots to much larger longer-term commercial operations, have been successfully monitored to the satisfaction of regulatory agencies, and technologies have been adapted and implemented to demonstrate containment, conformance, and no environmental impact. In this review we consider M&V chiefly from the perspective of its ability to satisfy stakeholders that these three key requirements are being met. From selected project examples, we show how this was done, and reflect particularly on the nature of the verification process. It is clear that deep-focussed monitoring will deliver the primary requirement to demonstrate conformance and containment and to provide early warning of any deviations from predicted storage behaviour. Progress in seismic imaging, especially offshore, and the remarkable results with InSAR from In Salah are highlights of the past decade. A wide range of shallow monitoring techniques has been tested at many sites, focussing especially on the monitoring of soil gas and groundwater. Quantification of any detected emissions would be required in some jurisdictions to satisfy carbon mitigation targets in the event of leakage to surface: however, given the likely high security of foreseeable storage sites, we suggest that shallow monitoring should focus mainly on assuring against environmental impacts. This reflects the low risk profile of well selected and well operated storage sites and recognizes the over-arching need for monitoring to be directed to specific, measureable risks. In particular, regulatory compliance might usefully involve clearer articulation of leakage scenarios, with this specificity making it possible to demonstrate “no leakage” in a more objective way than is currently the case. We also consider the monitoring issues for CO2-EOR, and argue that there are few technical problems in providing assurance that EOR sites are successfully sequestering CO2; the issues lie largely in linking existing oil and gas regulations to new greenhouse gas policy. We foresee that, overall, monitoring technologies will continue to benefit from synergies with oil and gas operations, but that the distinctive regulatory and certification environments for CCS may pose new questions. Overall, while there is clearly scope for technical improvements, more clearly posed requirements, and better communication of monitoring results, we reiterate that this has been a decade of significant achievement that leaves monitoring and verification well placed to serve the wider CCS enterprise

Tracer applications of noble gas radionuclides in the geosciences

pre-printNoble gas radionuclides, including 81Kr (t1/2 = 229,000 yr), 85Kr (t1/2 = 10.8 yr), and 39Ar (t1/2 = 269 yr), 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 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

Further developments of radio-noble gas groundwater dating – assessment of 39Ar and 37Ar underground production, and development of a new 85Kr sampling technique

Groundwater supplies billions of people with freshwater for domestic, agricultural, energy, and industrial purposes. Understanding its recharge rates, flow paths, and residence times is essential for protecting the resource in terms of quantity and quality and implementing management policies that ensure equitable and sustainable access to clean water. In this context, assessing the age of the water allows for a better understanding of the water cycle at all scales. Dating methods using radioactive noble gas isotopes rely on the accumulation and/or decay from a known atmospheric activity, which dissolves in the recharge. The focus of this thesis is the application of these dating methods for the radioactive isotopes of argon (39Ar and 37Ar) and krypton (85Kr). Subsurface production of radioactive isotopes is an inherent problem associated with these methods. Taking this phenomenon into account is essential to avoid biasing the ages concluded from the dissolved activities towards young values. For the methods based on argon-39 (39Ar) and argon-37 (37Ar), some processes are now clearly understood and documented. This is the case of the interactions with neutrons originating from cosmic rays or from the naturally present radioactivity in rocks. In contrast, reactions involving muons, which are different cosmogenic particles, are documented for other applications but have never been considered in the context of groundwater dating methods. In this thesis, the significant impact of muon-induced reactions on 39Ar and 37Ar activities could be demonstrated for the first time. The activities measured in aquifers in Denmark could be compared with those theoretically produced by the documented and/or the newly-assessed muon processes. For this purpose, a review of all nuclear processes involved in the production of radioargon in the underground was required. In addition, the emanation, which is the transfer process for the atoms produced in the rock to the pore space, was assessed by irradiation experiments in a particle accelerator. These results were then combined with information on depth-dependent recharge residence time to compute the activities accumulating during the infiltration of a water particle. Finally, using numerical modeling tools, the significance of subsurface production processes was extrapolated to a broader context. The simulation of various recharge scenarios allowed a better understanding of the situations where groundwater production is susceptible to induce significant age biases. In parallel, the use of 37Ar as an indicator of surface water-groundwater interactions was investigated in a pumping experiment in an alluvial aquifer in Emmental (CH). The combination of multiple tracers (222Rn and 4He) allowed to distinguish the mixing fraction and the travel time of the freshly infiltrated river water from the regional component. 85Kr is a tracer commonly used to date young (< 50 years) groundwater. Conventionally, its sampling is associated with logistical and practical challenges, such as disruption of the age stratigraphy in the well and preferential drainage of permeable aquifer fractions. As part of this thesis, a new in-situ sampling method was developed for the 85Kr. The latter consists of small quasi-passive samplers placed directly in the well, thus avoiding the need to pump water to the surface. Thereby, the fieldwork is facilitated, and the accessibility of this dating method is improved. This new technique has been tested and validated in a porous aquifer of the Swiss Plateau

Workshop on Mars Sample Return Science

Martian magnetic history; quarantine issues; surface modifying processes; climate and atmosphere; sampling sites and strategies; and life sciences were among the topics discussed

Tracking the interaction between injected CO2 and reservoir fluids using noble gas isotopes in an analogue of large-scale carbon capture and storage

Industrial scale carbon capture and storage technology relies on the secure long term storage of CO2 in the subsurface. The engineering and safety of a geological storage site is critically dependent on how and where CO2 will be stored over the lifetime of the site. Hence, there is a need to determine how injected CO2 is stored and identify how injected CO2 interacts with sub-surface fluids. Since July 2008 ∼1 Mt of CO2 has been injected into the Cranfield enhanced oil recovery (EOR) field (MS, USA), sourced from a portion of the natural CO2 produced from the nearby Jackson Dome CO2 reservoir. Monitoring and tracking of the amount of recycled CO2 shows that a portion of the injected CO2 has been retained in the reservoir. Here, we show that the noble gases (20Ne, 36Ar, 84Kr, 132Xe) that are intrinsic to the injected CO2 can be combined with CO2/3He and δ13CCO2 measurements to trace both the dissolution of the CO2 into the formation water, and the interaction of CO2 with the residual oil. Samples collected 18 months after CO2 injection commenced show that the CO2 has stripped the noble gases from the formation water. The isotopic composition of He suggests that ∼0.2%, some 7 kt, of the injected CO2 has dissolved into formation water. The CO2/3He and δ13CCO2 values imply that dissolution is occurring at pH = 5.8, consistent with the previous determinations. δ13CCO2 measurements and geochemical modelling rule out significant carbonate precipitation and we determine that the undissolved CO2 after 18 months of injection (1.5 Mt) is stored by stratigraphic or residual trapping. After 45 months of CO2 injection, the noble gas concentrations appear to be affected by CO2-oil interaction, overprinting the signature of the formation water