The mechanism of differential enrichment of deep oil reservoirs in the southern part of the Panyu 4 depression in the Pearl River Mouth Basin

In recent years, deep-seated hydrocarbon reservoirs have gradually become the focus of exploration and development. The distribution of deep-seated oil reservoirs in the southern part of the Panyu 4 depression in the Pearl River Mouth Basin shows the characteristics of more in the north and less in the south, and uneven in the east and west. The unclear causes of oil differentiation have constrained its exploration. This paper uses a combination of logging, seismic, and physical property data to analyze the reasons for oil enrichment differences from the perspectives of source-reservoir matching, dominant migration channels, and fault activity, and establishes an oil accumulation model.

Research findings indicate that: (1) Based on the matching relationship between hydrocarbon source rocks and reservoirs, the area can be divided three types of well areas: "near-source poor in sand", "near-source rich in sand", and "far-source rich in sand". The northern sand bodies close to the hydrocarbon source rocks and have a large scale, so the oil enrichment degree is relatively high. (2) The fault structure ridges are the preferred channels for lateral oil migration. The oil is more enriched in the well areas near the structure ridge, leading to differences in oil reservoir between adjacent well areas in the east-west direction. (3) The strength of fault activity controls the stratum of oil enrichment in different well areas. In the northern area, the fault activity is strong, and oil is distributed in multiple stratum. In the southern area, the fault activity is weak, and the oil is transported over long distances through the oil source fracture and the sand body of the Wenchang Formation to the high structural parts in the south, where they are trapped in the Wenchang Formation. (4) Based on the aforementioned research, two types of oil accumulation models were established: the "proximal fault multi-layer accumulation model" near the source and the "long-distance stepwise migration and accumulation model" far from the source, along the dominant migration channels. This study has significant guiding implications for the further exploration and development of the Panyu 4 depression oil reservoir.

Key words: Differential enrichment of oil; Source-reservoir matching; Dominant migration channel; Fault activity; Oil accumulation model.