珠江口盆地西江南半地堑浅层油气成藏特征及成藏模式

Reservoir Characteristics and Reservoir-forming Patterns of Shallow Strata in Southern Xijiang Half-graben of Pearl River Mouth Basin

西江南半地堑一直以上构造层渐新统的珠海组和中新统下段的珠江组为主要勘探目的层,已获重大油气储量发现。近年来在"复式油气藏、立体勘探"思维指导下,加大了珠江组之上的浅层(中新统中段的韩江组、中新统上段的粤海组)的油气勘探,并探明有规模性的商业油藏,累计探明石油地质储量约2051万m3。浅层油藏具有以边水油藏为主、油藏数量多、储量规模大、充满度高和储层物性好等特征。通过对浅层油气分布规律、油气来源以及断裂活动性的研究,建立了西江南半地堑三类浅层油气运聚模式:源内断裂带—垂向运移模式、源外陡坡带—二次调整运移模式和源外边缘带—侧向运移模式。源内断裂带—垂向运移模式的浅层油藏分布在活动性强的油源断裂附近,断裂在主成藏期时活动的强弱与时间长短决定了浅层油气的富集程度及富集层系。源外陡坡带—二次调整运移模式的浅层油藏远离供烃半地堑,为控圈断裂在主成藏期后的再次活动对早期油藏进行再次调整和分配的结果。源外边缘带—侧向运移模式明显受成藏期时优势构造脊控制,油气靠断面、不整合面和横向疏导的砂体空间有效配置进行阶梯式侧向运移。

The ZhuJiang ＆ ZhuHai Formation are the main traditional exploration targets in southern XiJiang half-graben, ZhuⅠdepression, Pearl River Mouth Basin. According to the “compound reservoir” and “stereoscopic exploration” theories, more studies focused on the shallow strata （HanJiang ＆ YueHai Formation）. A large amount of commercial reservoirs have been discovered in the shallow strata in southern XiJiang half-graben, the total reserves are about 2051？04m3. Reservoir quantities, reserves, fullness and reservoir physical properties of shallow strata are better than those of the underlying formation. Based on the studies of reservoir distributional rules, sources of shallow strata hydrocarbons, characters of fault activities and fault sealing properties, we recognized three kinds of migration and accumulation modes for shallow strata in southern XiJiang half-graben, namely a inner-source vertical migration pattern in fault terrace belts, a far-source hydrocarbon readjustment migration pattern in steep belts and a far-source lateral migration pattern in edge belts. The shallow strata reservoirs are determined by the intensity and duration of fault activities during the main hydrocarbon accumulation period about vertical migration pattern. The hydrocarbon readjustment migration pattern are depended on late-stage faults re-activities and hydrocarbon readjustment after the main hydrocarbon accumulation period. While the lateral migration pattern dominates the shallow strata hydrocarbon occurrence in the edge belts, and it depended on the advantage structure ridges, and the oil accumulation of shallow strata are determined by the faults, unconformities and connected sand bodies.