Application of noble gas tracers to identify the retention mechanisms of CO2 migrated from a deep reservoir into shallow groundwater

Abstract

Carbon Capture and Storage (CCS) is a valuable climate-mitigation technology, which offers the potential to costeffectively reduce the emissions associated with the burning of fossil fuels. However, there is a potential risk of a small portion of the stored CO2 unintentionally migrating from a storage site to a shallow groundwater aquifer which is the final retaining zone for any migrated CO2 before it escapes to the atmosphere. Hence, it is imperative to identify the physical retention mechanisms of CO2 within a shallow aquifer. In this study 1.70x102 kg of CO2 and noble gas tracers (He, Ar and Kr) were continuously injected into a groundwater aquifer over 28 days with the aim of identifying the mechanisms and amount of CO2 retention. Among the tracers, Kr was found to be the earliest indicator of CO2 migration. The other tracers -He and Ar -arrived later and exhibited diluted signals. The diluted signals were attributed to degassing of the plume mass (1.6% of CO2) during the early stages of CO2 migration. Diffusion accelerated the dilution of the lighter elements at the plume boundaries. Consequently, the clear relation of the noble gases with the CO2 proved that degassing and mixing primarily control the mass retention of CO2 in shallow groundwater, and the relative importance of these processes varies along the evolving path of migrating CO2.

Hydrochemical Parameters to Assess the Evolutionary Process of CO2-Rich Spring Water: A Suggestion for Evaluating CO2 Leakage Stages in Silicate Rocks

“…Therefore, monitoring and verification (M&V) operations are a key process to gain public acceptance and to sequester CO 2 safely into deep geologic formations. M&V techniques have been proposed to evaluate the response of soil, water, and living resources to injected CO 2 in the shallow subsurface environment at different scales (e.g., laboratory, pilot, or full) and formations (e.g., sedimentary or crystalline) [7][8][9][10][11][12]. However, the artificial CO 2 injection tests provide limited information about the long-term CO 2 -water-rock interaction and the related changes in the subsurface environment (e.g., groundwater quality, porosity, permeability).…”

Estimating reservoir parameters and gas storage volume available in the DU6 gas field, Northeast China

“…18,19 Therefore, geological foundation reconstruction and gas storage space determination is a very necessary work, in order to establish a safe and efficient underground gas storage. [20][21][22] Research on underground gas storage reconstruction is more comprehensive and detailed than that of conventional oil and gas reservoirs, therefore, the results of gas reservoir geological research cannot be directly applied to the geological evaluation of gas storage reconstruction. [23][24][25] The evaluation objective of underground gas storage is the trap and its basic conditions, such as scale, seal capacity, storage, and operating conditions, which are used to optimize the goal of building good gas storage.…”