车西洼陷油气“倒灌”运移机理及最大距离预测

Hydrocarbon “Downward Migration” mechanism and Maximum Migration Distance Estimation in Chexi Sag

车西洼陷是济阳坳陷西北部次级构造单元,勘探实践发现,在源储不对接的情况下,在Es3烃源岩之下的沙四段储层中发现了规模油气藏。基于"倒灌"油藏储盖沉积体系配置关系、源储动力构成、输导体系岩心观察等研究,提出了"厚泥封盖、隐蔽输导、超压启动、源储压差下排"的油气"倒灌"运移成藏机理,认为在输导体系存在的条件下,当Es3烃源岩中的压力大于下伏Es4地层压力时,烃源岩生成的油气可以向下充注到Es4的储层中并运移成藏,向下充注的距离取决于源岩剩余压力(源动力)的大小及衰减程度。基于当源动力衰减到与常压系统中静水柱压力平衡时油气不再"倒灌"运移的动力学原理,建立了油气"倒灌"运移最大距离的定量预测方法。该项研究对拓展深层勘探空间,深化油气成藏认识有较好的指导作用。

Chexi Sag is a secondary structural unit in the northwest of Jiyang Depression and field exploration practice indicates that considerable hydrocarbon reservoirs are discovered in Shahejie-4 reservoir under Es3source-rock without favorable source-reservoir configuration. A'thick mud sealing,subtle conduction,overpressure activation,downward expulsion by source-reservoir pressure difference'hydrocarbon'downward migration'migration-accumulation mechanism is developed based on the researches of'downward migration'deposition system configuration of reservoir-caprock,source-reservoir dynamic properties,core observation of conduction system and other aspects. When the pressure in Es3source-rock exceeds that in Es4 formation,the hydrocarbon Es3 in source-rock will migrate and accumulate in Es4 reservoir under active conduction system. The corresponding migration distance depends on the residual pressure of source-rock( source dynamic) and its attenuation level. A quantitative estimation of maximum hydrocarbon'downward migration'distance is proposed according to the dynamic principle that hydrocarbon'downward migration'continues until the source dynamic decreasing to the hydrostatic pressure of normal pressure system. This research could provide certain guidance for deep exploration space expansion and further understanding of hydrocarbon accumulation.