滨里海盆地下二叠统盐上盐下构造特征与油气成藏主控因素

Structural Characteristics and Main Controlling Factors of Hydrocarbon Accumulation of the Lower Permian Post-salt and Pre-salt Sequences in the Pre-caspian Basin

滨里海盆地以下二叠统空谷阶盐岩为界,发育了极具特色的盐上和盐下2套成藏体系。为加深对区域成藏规律的认识,为进一步勘探提供参考,从区域构造沉积演化入手,利用最新钻井资料、地震剖面解释和构造编图,分析了盐上、盐下层系的构造特征与油气成藏主控因素。结果表明,盐下古生界构造层以发育大型古隆起和斜坡带为特征,海西期风化淋滤作用改善了碳酸盐岩储集层的储集性能,礁滩和岩溶控制着油气的富集。相比而言,盐上层系受空谷阶盐构造运动的影响明显,可形成盐刺穿遮挡型、盐檐、地层尖灭型、砂岩透镜体等不同类型的圈闭,高效盐窗和盐边/断裂等运移通道是成藏的关键,盐构造活动期与盐下烃源岩排烃高峰期相匹配是油气成藏的必要条件。

The Pre-caspian Basin is typically characterized by hydrocarbon accumulation in two salt-related sequences, i.e., thepost-salt and pre-salt sequences divided by the Lower Permian Kungurian Group. To improve the understanding of the regularities ofhydrocarbon accumulation and provide exploration stratedy data, this paper studies the structural characteristics and controlling factorsof hydrocarbon accumulation in the two post- and pre-salt sequences by using the latest data of drilling, seismic section interpretationand structural mapping. Results show that large-scale paleo-uplift and slope were developed in the Paleozoic pre-salt sequence and theHercynian weathering and leaching greatly improved carbonate reservoir properties. Reef, shoal and karst controlled hydrocarbonaccumulation. In contrast, the Lower Permian post-salt sequence was significantly controlled by the lower Permian Kungurian tectonicmovement, leading to the formation of different types of traps, such as salt diapir, salt eave, stratigraphic pinchout and sandstone lensbody. The highly-efficient salt windows, salt flanks and fractures are the key factors controlling hydrocarbon migration. Favorable match between salt tectonic activity and peak hydrocarbon expulsion of source rock is necessary for hydrocarbon accumulation.