An experimental investigation into quantifying CO2 leakage in aqueous environments using chemical tracers

Abstract

Chemical tracers can be an effective means of detecting, attributing and quantifying any leaks to the surface from geological CO 2 stores. CO 2 release experiments have found it difficult to ascertain the fate, or quantify the volume of CO 2 without the application of tracers. However, a significant proportion of global CO 2 storage capacity is located offshore, and the marine environment poses constraints that could limit the success of using tracers. These constraints include uncertainties in the behaviour of tracers in marine sediments and the water column and sampling challenges. However, to date there have been few experimental investigations to address these uncertainties. Here, we used a benchtop experimental setup to explore how effectively methane, a common constituent of captured CO 2 and of reservoir fluids, can aid the quantitation of CO 2 leakage in aqueous environments. The experiment simulated gas leakage into sediments that mimic the seabed, and we measured the partitioning of co-released gases under different environmental conditions and injection rates. We find that the style of seepage and the fate of the CO 2 are affected by the presence of a sand layer and the injection rate. We discuss the implications for leak monitoring approaches, including how tracers may be used to quantify the leak rates and fate of CO 2 in aqueous environments. Our work contributes to ongoing efforts to develop robust offshore monitoring system that will assure operators, regulatory bodies and the public of CO 2 storage integrity.

Efficient marine environmental characterisation to support monitoring of geological CO2 storage

“…The resulting fuzzy quality of stoichiometric relationships in aquatic systems can degrade the precision of derived anomaly criteria, without additional observations. • Comparing the isotopic composition of sequestered CO 2 with aquatic CO 2 , or further the deliberate dosing of sequestered CO 2 with inert tracers has been proposed as a method to aid the attribution of detected CO 2 (Myers et al, 2019;Roberts et al, 2017). Isotope analysis was used in the QICS release experiment to demonstrate that injected and seeping CO 2 was identical (Blackford et al, 2014;Lichtschlag et al, 2015).…”