珠江口盆地西江主洼油气运聚主控因素及运聚模式

Main control factors and models of hydrocarbon migration-accumulation in Xijiang major sag,Pearl River Mouth basin

珠江口盆地西江主洼是一个典型的古近纪"北断南超"箕状断陷,具有"下断上坳"的二元结构。西江主洼古近纪经历了两幕裂陷作用,形成了2个完整的沉积旋回,其中裂陷I幕(文昌组沉积期)发育了洼陷内最重要的烃源岩,裂陷II幕(恩平组沉积期)发育了洼陷深层关键的地区性泥岩盖层。受"势"、"路"、"梯"三大主控因素的控制,西江主洼生成的油气主要向洼陷长轴以南运聚。三大主控因素的空间配置关系不同,导致该洼陷发育3种油气运聚模式,即"势-路"二元主控模式——中央隆起模式、"势-路-梯"三元主控模式——东南隆起模式和"势-梯"二元主控模式——南部隆起模式。综合分析认为,西江主洼中央隆起的深层、东南隆起的中—深层以及南部隆起的中层均具有很好的油气勘探潜力。

Xijiang major sag in Pearl River Mouth basin is a typical Paleogene half-graben-like rift with “south faulting and north overlapping”, in which there is a binary configuration with “lower faulting and upper sagging”. In this major sag, two rifting episodes developed in Paleogene, form- ing two complete sedimentary cycles. The most important source rock in the major sag deposited during Rifting Episode I （the deposition period of Wenchang Formation）, and a seal of regional mud- stone formed during Rifting Episode II （the deposi- tion period of Enpinng Formation）, with the latter being crucial for the deep zones. Due to the impacts of three main control factors, i. e. “ potential”, “pathway” and “ladder”, the generated hydrocarbon tends to migrate and accumulate towards the south of the long axis of Xijiang major sag. Different spa- tial combination modes of the three factors have re- sulted in three types of hydrocarbon migration-accu- mulation models, the central uplift model predomi- nated by binary controls of “potential” and “path- way”; the southeast uplift model predominated by ternary controls of “potential”, “road” and “lad- der” ; and the south uplift model predominated by bi nary controls of “potential” and “ladder”. A com- prehensive analysis indicates that the deep zone in the central uplift, the middle-deep zone in the southeast uplift and the middle zone in the south uplift are good in hydrocarbon exploration potential.