Noble and major gases released from rock core materials as intrinsic tracers for detecting carbon dioxide leakage – Laboratory evaluation

Abstract

Acidification of pore water in geological formations by carbon dioxide (CO2) results in the release of trapped gases, the detection of which can potentially be used to signal leakage of CO2 from storage reservoirs at carbon sequestration sites. In a set of laboratory tests, core materials from a stratigraphic borehole at the proposed FutureGen 2.0 carbon storage site (Jacksonville, IL, USA) were reacted with phosphoric acid to simulate contact with aqueous CO2. Gas released by the reaction was collected and analysed for the composition of the major and noble gases (including isotopes). These experiments yielded several promising tracer candidates for intrinsic monitoring of CO2 leakage at the proposed FutureGen 2.0 site. The most robust signals are the CH4 and 4He released by carbonates in the dolomite and siltstone formations that comprise the proposed primary containment zone. Xenon released from the primary-containment zone also showed promise as a tracer, but a more robust analysis requires a different experimental set up. A general enrichment of CH4, N2 and light noble-gas isotopes with respect to Ar abundance was observed and is consistent with the addition of major gases (CO2, CH4, and to a lesser extent, N2) released by decomposition of carbonate mineral phases and/or organic matter in the dolomite and siltstone formations. No useful signal was obtained from the sandstone formation (representing the proposed injection zone) due to its very low yield of gas when acidified.