东海西湖凹陷大中型油气田形成条件及勘探方向

为了解决东海西湖凹陷保俶斜坡带勘探成效差以及中央背斜带勘探效果南北差异大的问题,通过盆地分析理论体系对西湖凹陷石油地质条件进行了系统研究和重新认识,认为保俶斜坡带和中央背斜带由于构造格局及构造演化的差异形成了不同的油气成藏体系,有利成藏要素的叠合区为大中型油气田的发育区。保俶斜坡带以断陷构造层为主,晚期挤压弱,构造定型早,具有"紧邻富生烃洼陷、发育多期叠置的规模储集体、形成多类型构造-岩性复合圈闭、具有良好的垂向封盖条件以及发育网毯式高效输导体系"的有利成藏条件。近生烃洼陷的断层坡折带及地貌坡折带处形成的大型潮控三角洲砂体上倾尖灭带为大中型油气田发育区。中央背斜带经历了拗陷期强烈挤压,形成了大型反转背斜,具有"先存古构造背景、发育大型构造-岩性复合圈闭、断砂配置条件好以及具备高效储盖组合"四元控藏的特征,成藏条件叠合较好的龙井、古珍珠、湖心亭等地区是大中型气田发育区。

Formation conditions and exploration direction of large and medium oil and gas reservoirs in Xihu Sag,East China Sea

A low exploration success ratio on the Baochu Slope of Xihu Sag of East China Sea has been inferred, and the ratio in the Central Anticline Belt varies significantly in different sub structures. To solve this issue, the petroleum geologic conditions of the sag were systematically reviewed in light of new basin analysis methodologies, and new understanding have been achieved. Due to the differences in tectonic features and evolution histories, the Baochu Slope and Central Anticline Belt developed different petroleum systems and play types. Only those areas with overlapping favorable fairways of all petroleum system elements promise the formation of large oil and gas fields. The Baochu Slope is featured by tectonic rifting, with weak later compression and early structure formation. Its favorable conditions for hydrocarbon accumulation include: short distance to the main source kitchen; multiple, overlapping, large-scale reservoirs; multiple structural-stratigraphic trap types; good vertical sealing zones; and effective lattice pattern migration pathways. The large to medium structural-stratigraphic fields are concentrated in fairways with a large scale source kitchen and updip pinchout of tide-dominated delta sands controlled by paleo slope break which in turn were induced by either faulting or paleo morphology. The Central Anticline Belt has experienced strong inversion and compression during the late depression stage, and developed inverted compressional slip faults and large scale anticlines. Hydrocarbon accumulation is controlled by four major factors: preexisting structural highs before the compressional event, large scale structural-lithological traps, excellent timing of hydrocarbon charging during deformation, and highly effective reservoir-seal combinations. The areas with good congruence of these contro-lling factors promise the occurrence of large-scale deposits such Longjing, Guzhenzhu, Huxinting fields.