| The Wenchang A Sag in Zhu Ⅲ Depression of the Pearl River Mouth Basin is an important natural gas
exploration area, with a major crude oil breakthrough in Oligocene Zhuhai Formation of Wenchang 9-7 zone recently. In
order to better understand its reservoir-forming rules, based on fault geometry analysis, activity rate and displacementdistance
analysis, biomarker composition and inclusion analysis by making full use of pre-stack 3D seismic, drilling and
geochemical data, the deformation characteristics and evolution rules of Wenchang 9-7 syndromic superimposed transfer
slope zone in the Zhu ⅢDepression are clarified, and the reservoir-controlling mechanism of the transfer slope zone is
analyzed in combination with the reservoir characteristics. The results show that: (1) Wenchang 9-7 transfer slope zone is
characterized by large polygonal fault slope. Due to early extension and transformation, late oblique extension and strikeslip
pull-apart, its tectonic evolution has gone through three stages: isolated fault, formation of transfer zone and late
complication with more derived branch faults. (2) According to the local oil-oil correlation and oil-source correlation
results and the regional oil-source study, the crude oil of Wenchang 9-7 reservoir mainly comes from the source rock of
Wenchang Formation in the 9th sub-sag, and partially from the source rock of Enping Formation. (3) Wenchang 9-7
transfer slope zone has three stages of crude oil accumulation process. In the early Miocene (21-18.5 Ma), the transform
fault controlled the migration and accumulation of crude oil generated by the source rocks of Wenchang Formation in the
9th sub-sag. In the middle Miocene (16-12 Ma), the adjustment fault caused the damage and adjustment of the early oil
reservoirs, and controlled the migration and accumulation of crude oil generated by the source rocks of the Enping
Formation in the 9th sub-sag. In the late Miocene-Pliocene (9-4.5 Ma), the crude oil generated by the source rock of the
Enping Formation in the transfer slope zone was migrated and accumulated into reservoirs. The syndromic superimposed
transfer zone has excellent reservoir forming conditions and is a key exploration area. |
