Dawsonite and ankerite formation in the LDX-1 structure, Yinggehai basin, South China sea: An analogy for carbon mineralization in subsurface sandstone aquifers

International audienceThe geochemistry and petrology of the LDX-1 structure of the Yinggehai basin, a natural analog of a sedimentary carbon storage site, was investigated to understand the consequences of the charging of CO 2 gas in this system. The rocks in this structure are dominated by subarkose and sublitharenite sandstones. The authigenic minerals formed after CO 2 injection are dawsonite, microcrystalline quartz, kaolinite and ankerite. Dawsonite and ankerite are formed just beneath a CO 2 bearing anticlinal structure due to the reactions between silicate minerals (feldspars and clay minerals) and the fluid phase. Carbon and oxygen isotopic analyses indicate that the main carbon source for dawsonite and ankerite formation was mantle magmatic CO 2. The aqueous activities of sodium and calcium, the partial pressure of CO 2 , pH and temperature are the key factors influencing the stability of the dawsonite and ankerite. The presence of the anticlinal structure maintaining a locally high CO 2 partial pressure in the waters beneath this structure is likely responsible for the observed long-term persistence of dawsonite and ankerite in this system