Importance of mineral sequestration during CO2 gas migration: A case study from the Greater Gorgon area.

Abstract: High- CO₂ gas fields serve as important analogues for understanding various processes related to CO₂ injection and storage. The chemical signatures, both within the fluids and the solid phases, are especially useful for elucidating preferred gas migration pathways and also for assessing the relative importance of mineral precipitation and/or solution trapping efficiency. In this paper, we present a high resolution study focused on the Gorgon gas field and associated Rankin Trend gases on Australia’s North West Shelf. The gas data we present here display clear trends for CO₂ abundance (mole %) and δ¹³C CO₂ both areally and vertically. The strong spatial variation of CO₂ content and δ¹³C and the interrelationship between the two suggests that processes were active to alter the two in tandem. We propose that these variations were driven by the precipitation of a carbonate phase, namely siderite, which is observed as a common late stage mineral. This conclusion is based on Rayleigh distillation modeling together with bulk rock isotopic analyses of core, which indicates that the late stage carbonate cements are related to the CO₂ in the natural gases. The results suggest that a certain amount of CO₂ may be sequestered in mineral form over short migration distances of the plume. [Copyright &y& Elsevier]