珠江口盆地白云-荔湾深水区幔源CO2充注的黏土矿物成岩响应

珠江口盆地白云-荔湾深水区油气勘探中钻遇大量高含量CO₂气层，使得如何规避高CO₂风险成为当前面临的挑战。通过工区充注CO₂的储层砂岩黏土矿物X射线衍射（XRD）、流体包裹体显微测温和稀有气体同位素组成等分析，明确了幔源无机CO₂的成因，并运用黏土矿物特征讨论高温幔源无机CO₂充注的黏土矿物成岩响应:有序带倒转和大量自生高岭石的生成。依据CO₂气井的XRD全定量分析数据剖面图将幔源无机CO₂气层段的黏土矿物组合分为3类:Ⅰ类为I/S混层黏土矿物中S体积分数介于10%~25%之间，有序度处于R₂~R₃带，高岭石体积分数高；Ⅱ类为I/S混层黏土矿物中S体积分数介于10%~15%，有序度为R₂~R₃带，自生高岭石体积分数低；Ⅲ类为I/S混层黏土矿物中S体积分数介于50%~60%，有序度为R₀带，高岭石体积分数低。总结出幔源CO₂在珠江组和珠海组中存在2种运聚模式:一是幔源CO₂通过与基性岩浆连通的深大断裂垂直向上运聚；二是垂直向上运移后通过连通砂体侧向长距离运聚。研究结果对珠江口盆地白云-荔湾深水区下一步油气勘探规避高含量CO₂风险具有指导作用。 

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

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.