ORIGIN, MIGRATION AND ACCUMULATION OF CO₂ IN SANSHUI BASIN AT NORTHERN SOUTH CHINA SEA CONTINENTAL MARGIN AND MAIN CONTROLLING FACTORS

Geological and geochemical characteristics suggest that the CO₂ of the Sanshui Basin is mainly of a volcanic mantle type. The rest is from the thermal alteration of limestone crust, with a small amount formed by the mixing of gases from both of the mantle and crust. The CO₂ was mainly supplied by the degassing of magma in the volcanic mantle. However, the CO₂ released from limestone under the affect of thermal alteration by igneous intrusion could be an important supplement to it. The formation and distribution of the carbon dioxide of volcanic mantle-type mainly depended on the space-time configuration of the degassing of the volcanic mantle, the deep fault pattern, which provided the path for gas migration, and the availability of effective traps. There are two main controlling factors, namely the source and gas supply system (gas source contents and transport framework), and the accumulation and trap system (reservoir-seal combination and effective trap). According to the origin, the characteristics of gas source composition and the migration and accumulation pattern of the carbon dioxide of volcanic mantle type and limestone thermal alteration type in this area, we could make an evaluation of resource potential and prediction of favorable exploration targets to provide a reference for decision making in exploration and deployment of the resources.