| Wenchang G block in the western part of the Pearl River Mouth Basin is adjacent to Shenhu uplift. During the early Oligocene Enping period, affected by the continuous activity of Zhusannan fault, multi-stage fan delta sedimentation with multiple sediment sources developed. This set of sedimentation has the characteristics of frequent vertical superposition and strong horizontal heterogeneity. Starting from the evolution of structure-sedimentary filling, this paper analyzes the influence of fault system on each stage of fan delta, and analyzes the vertical facies sequence change and plane reservoir distribution law considering the complexity of sedimentary inner. Vertically, Enping formation is divided into two sequences(upper and lower) and five subsequence sets. On the plane, a series of NEE faults developed in the early stage of upper sequence form a group of fault terraces developed from south to north, which changed the structure-sedimentary pattern at that time to a certain extent, and affected the distribution of delta in the lowstand stage, making it the most widely distributed. The sedimentary mechanism and hydrodynamic conditions are the important factors that affect the differences of reservoirs. Firstly, the sedimentary facies belt is the prerequisite to affect the physical properties of the reservoirs. The physical properties of the underwater distributary channel and mouth bar sandbody in fan delta front are obviously better than those in fan root of fan delta, with dominant primary intergranular pores supplementing by secondary pores. Secondly, the overpressure due to the thick mudstone of upper sequence would be helpful to the deep buried reservoir. It is indicated that the lowstand fan delta sealed by mudstone in Enping Member-1 would be the favorable exploration target. |
