Diagenetic effect of mantle-derived CO2 charge to clay minerals in the Baiyun-Liwan deepwater area of the Pearl River Mouth Basin in South China Sea

Abstract

During petroleum exploration in the Baiyun-Liwan deep-water area of the Pearl River Mouth Basin (PRMB), South China Sea, a huge number of CO2 gas reservoirs has been met. Therefore, how to avoid the high CO2 risk has become a big challenge now. In this paper, the X-Ray diffraction (XRD) of clay minerals in the sandstone filled with CO2, microthermometry of fluid inclusions and isotopes of noble gas were used for analysis. The results show that the origin of inorganic CO2 is magmatic. The effects of mantle-derived CO2 on clay minerals are the inversion of clay mineral order degree and the formation of a largeamount of authigenic kaolinite. Moreover, the clay mineral assemblage was divided into three types based on the of XRD analysis data in CO2 wells. Finally, two patterns of CO2 migration and accumulation in the Zhujiang and Zhuhai Formations were summarized: (1) the mantle-derived CO2 migrates vertically upward through the deep faults which connected with the mafic igneous rocks, and (2) lateral long-distance migration through connecting sand bodies after vertical upward migration. These results have certain guiding significance for avoiding the risk of high CO2 in the future exploration in the deep-water area of PRMB, South China Sea.

Keywords

• the mantle-derived co2
• clay minerals
• diagenetic response
• the deepwater area
• pearl river mouth basin(prmb)