A prospect analysis of the Upper Oligocene sandstone reservoirs of the Wenchang 9 block, Pearl River Mouth Basin, northern South China Sea margin

Abstract

Faults can act as a migration pathway and/or a lateral seal in structural traps in the Wenchang 9 block (WC9B) oil field, affecting the potential for enhanced hydrocarbon recovery in the field. In this study, three-dimensional (3D) seismic survey and well data are used to characterize Upper Oligocene fan delta - tidal flat heterogeneous reservoirs and investigate fault seal potential in two new structural traps interpreted in the WC9B oil field. Five lithofacies are identified in the Upper Oligocene Zhuhai Formation based on the well log analysis and core description. The fan delta front and sand-rich tidal flat sandstone of facies F1 in reservoir unit A of the middle Zhuhai member is characterized by the best porosity and permeability. The RMS amplitude attribute analysis and facies modeling help to predict gradual upward progression of the F1 fan delta deposits from the proximity of the Shenhu Uplift to the NW into the basin for ∼ 7–8 km during accumulation of the middle member. The NE-dipping conjugate normal faults of lower throw in the hanging wall of the NW-dipping main normal basement faults contributed to the formation of hydrocarbon-bearing structural traps and side seals. Two new structural traps in the middle member of Zhuhai Formation interpreted in the WC9B oil field. The traps are 3-way dip closure bounded by the NE-dipping normal faults of the conjugate set that are characterized by good sealing potential in the interval of the middle member. The results of this study contribute to the optimization of the enhanced hydrocarbon recovery of the WC9B oil field.