油气穿越未成岩断裂运移富集成藏模式与主控因素 ——以珠江口盆地恩平凹陷为例

恩平凹陷隆起带远离洼陷生烃中心,油气以侧向运移为主。基于浅层断裂埋藏浅、活动晚、封闭性弱的特征,提出穿断成藏模式成功地指导了隆起带勘探,发现一批商业性油田。对恩平凹陷南、北隆起带浅层主要油田成藏特征进行剖析,阐述了浅层油气穿越未成岩断裂运移富集成藏模式及其成因机制。断层岩弱成岩导致有限油柱封闭高度与油气强充注是其形成机制,弱成岩是关键。断裂-输导砂体-构造脊构成多次穿断运移的地层格架,油气充注强度与圈闭汇聚能力的平衡控制穿断运移路径上圈闭的富集程度,断-储排替压差控制穿断过程中油气垂向侧向分流。穿断运移成藏模式对浅层油气成藏具有一定借鉴意义。

Accumulation and Key Controls of Lateral Cross-fault Hydrocarbon Migration: A Case Study of the Enping Sag in the Pearl River Mouth Basin

The uplift area of the Enping Sag is far away from the center of hydrocarbon-generation where the hydrocarbon is mainly accumulated via lateral migration.The model of cross-fault accumulation was proposed based on the characteristics of shallow faults,such as shallow burial depth,late activity and weak sealing ability,which has been used as guide for the exploration in the uplift areas and led to the discovery of a number of commercial oil fields.In this paper,the major accumulation features of the shallow subsurface of the northern and southern Enping Uplift areas have been analyzed.The model and genetic mechanism of hydrocarbon in shallow lateral migration across undiagenetic faults also have been elaborated.It is concluded that weak diagenesis is the key factor which limits oil column height and strong hydrocarbon injection.Fault-channel sand body-structural ridge form the stratigraphic framework.The balance between hydrocarbon charging intensity and trap convergence ability controls the enrichment of the traps on the oil migration path,while the difference of displacement pressure between faults and the reservoir controls the distribution of hydrocarbon in the process of its migration.The accumulation model of lateral cross-fault migration is a useful guideline for shallow petroleum exploration.