Hydrocarbon accumulation conditions and exploration direction of Baiyun–Liwan deep water areas in the Pearl River Mouth Basin

An integrated geologic study was performed in the Baiyun–Liwan deep water areas, Pearl River Mouth Basin, based on the achievements obtained during the past five exploration stages. The following understandings were obtained. (1) The Baiyun Sag has superior source rock conditions and has experienced three tectonic evaluation stages like rifting, rifting-depression and depression. The Wenchang–Enping Fms deposited during the rifting stage have large hydrocarbon generation potentials. During the rifting-depression and depression stages, the deposition in the study area was controlled by the Oligocene and Miocene shelf slope break zones. The Oligocene Zhuhai Fm shallow marine delta-longshore depositional system and the Miocene Zhujiang–Hanjiang Fms deep fan depositional system were formed, and they are the most favorable reservoir-caprock assemblages in the study area. (2) The Hydrocarbon accumulation pattern in the deep waters is different from that in the northern shallow waters. Shelf slope break zone, composite conduction system consisting of structural ridge, fault, sandbody, unconformity and fluid diapir as well as late tectonic movement are the three major factors controlling hydrocarbon migration and accumulation in the study area. (3) The Liwan 3-1 gas field is a typical example. The superior trapping conditions, high-quality reservoirs of delta distributary channel controlled by shelf slope break zone, vertical conduction system consisting of fault and diapir, as well as the overlying massive marine mudstone caprock provide favorable geologic conditions for the formation of large gas fields. Four areas were identified as the targets of gas exploration in the near future: the deep water fan system in the central sag, the structural-stratigraphic traps in the uplifted areas on both sides of the main sag of Baiyun, a series of large structural traps on the fault terrace to the southwest of the main sag, and the ultra-deep frontiers in sags such as Liwan to the south of the main sag.