川中地区中二叠统断溶体发育特征及形成机制

Development characteristics and forming mechanism of Middle Permian fault-karst carbonate reservoirs in the central Sichuan Basin

川中地区中二叠统碳酸盐岩经历了多期构造变形和岩溶作用,并沿溶蚀断裂带形成了各种不规则的断溶体。为了明确断溶体形成及发育特征,预测断溶体发育区,对断溶体类型及形成机制进行研究。根据岩心、薄片、测井和地震资料,在川中地区识别出溶洞—裂缝型、裂缝型和裂缝—溶洞型3种类型的断溶体,断溶体类型受断裂和岩溶储层发育规模和期次控制。溶洞—裂缝型断溶体主要是同沉积断裂带叠加茅口组暴露剥蚀的岩溶洞而形成的;裂缝型断溶体是加里东期及海西期形成的深大断裂在后期复活后受到大气淡水溶蚀、热液溶蚀以及有机酸溶蚀共同作用下形成的;而裂缝—溶洞型断溶体是加里东期和海西运动产生的次生断裂在大气淡水和有机酸溶蚀中二叠统颗粒滩形成的断控复合面状溶蚀体。断溶体作为一个复合的储集体为油气提供了良好的储集空间,其主要分布于深大断裂带及其伴生的次生断裂带溶蚀面,且叠加颗粒滩的裂缝—溶洞型断溶体为最有利的储集体。

The Middle Permian carbonate rocks in the central Sichuan Basin have experienced multi-stage tectonic deformation and karstification, and accordingly various irregular fault-karst carbonate rocks have been formed along the dissolved fault zone. In order to clarify the forming and development characteristics, and predict where fault-karst carbonate rocks are developed, the type and forming mechanism of fault-karst carbonate rocks have been studied. According to core, thin section, logging and seismic data, three types of fault-karst carbonate rocks were identified, including vug-fracture type, fracture type and fracture-vug type, which depend on the development scales and periods of karst reservoirs and faults. The vug-fracture type is based on the karst vugs from the superposition of syn-depositional fault belts and the exposure of the Maokou Formation. The fracture type is the result of the joint dissolution action among meteoric water, thermal fluids and organic acid on the resurrecting deep and large faults formed in the Caledonian and Hercynian periods. The fracture-vug type is the fault controlling composite formed in the Caledonian and Hercynian Movements, which are formed by the secondary faults and plane faultkarst carbonate rocks as the result of meteoric water and organic acid dissolving the Middle Permian granular beach. As a type of composite reservoir, fault-karst carbonate rocks provide good spaces for oil and gas, and are mainly distributed in the dissolution planes of large and deep faults and its associated secondary fault belts. The fracture-vug type is the most favorable reservoir.