Potential and Insight: Sealing Potential of Low‐Permeability Basalt Interlayer in Mudstone Caprock for CO 2 Storage in Sandstone Aquifer

Abstract

ABSTRACT When CO 2 is sequestered in deep aquifers of sedimentary basins, mudstone or shale is usually used as a caprock. When the caprock contains low‐permeability basalt interlayers, its sealing potential could be improved. This study utilized geological data from the Jianghan Basin in central China to establish a generalized two‐dimensional reactive transport model to investigate the sealing potential of basalt as an interlayer in the mudstone caprock. The reactions of CO 2 with the minerals in the basalt interlayer are critical to its sealing performance. On the one hand, CO 2 mineralization sequesters a portion of the CO 2 that enters the caprock, thereby reducing the amount of free CO 2 there. On the other hand—and more importantly—mineral precipitation reduces the porosity of the basalt interlayer by up to 48%, triggering a self‐sealing effect impeding upward CO 2 migration in the caprock. Fresh or weakly altered basalt interlayers containing olivine and pyroxene have a strong sealing capability. When the basalt is completely altered (excluding olivine and pyroxene), its sealing performance is significantly compromised. A basalt interlayer with a permeability in the range of 10 −16 –10 −17 m 2 can effectively impede the upward migration of CO 2 . Even when the basalt interlayer is very thin (only 1 m), a mudstone caprock containing it exhibits superior sealing performance relative to one without a basalt interlayer. Furthermore, the closer the basalt interlayer is to the base of the mudstone caprock, the greater its sealing performance.