地质科技通报 (Jul 2022)
Distribution characteristics and accumulation mechanism of carbon dioxide gas reservoirs in the Pearl River Mouth Basin
Abstract
Exploration practice has revealed abundant carbon dioxide gas reservoirs in many depressions of the Pearl River Mouth Basin, South China Sea with a CO2 content as high as 90%. These CO2 reservoirscan either directly displace the early oil reservoirs or affect the oil and gas charging scale, which further increases exploration risk. Based on the comprehensive analysis of drilling data, geochemical analysis data, gravity and magnetic research results, the migration and accumulation conditions of the CO2 reservoirs have been investigated. Our results suggest that CO2 in the Pearl River Mouth Basin is sourced by inorganic mantle, and its distribution locations are controlled by regional caprocks and reservoirs. CO2 is mainly distributed in upper Oligocene to lower Miocene strata and the overlying strata, with its contents gradually decreasing upwards. Meanwhile, the distribution of inorganic mantle source CO2 is greatly controlled by the fault system, and its distribution locations have a close relationship with the ranges of basement faults and igneous rocks. The inorganic CO2 gas is sourced by the degassing of mantle-derived magma. Its vertical migration process is mainly controlled by different scales faults, especially the regional abyssal faults. Therefore, it can be concluded that mantle-derived magma activity and fault systems are the main controlling factors for the accumulation processes of CO2 reservoirs. The mechanisms of mantle-derived CO2 migration and accumulation can be summarized into two types by structural differences. In the northern depression zone, CO2 migrates along deep faults step by step to the upper and middle crust to form a "transfer station". By contrast, the detachment system developed in the Zhu 2 Depression, and CO2 migrates along the detachment plane to upper strata.
Keywords
