Fault characteristics and its significances on hydrocarbon accumulation in northeastern Baiyun Sag, Pearl River Mouth Basin

The distribution of oil and gas fields in the northeastern Baiyun Sag of the Pearl River Mouth Basin is characterized by the “inner gas, outer oil” pattern, and faults play important roles on hydrocarbon migration and accumulation. Based on seismic interpretation and borehole data, fault characteristics and its significances on hydrocarbon accumulation in the northeastern part of the Baiyun Sag are analyzed in this paper. NWW- and EW-trending faults are predominant in the study area, which are listric and planar shapes in cross section. According to their significances on hydrocarbon accumulation, the faults in the northeastern Baiyun Sag can be divided into oil-source faults and trap-controlled faults. The oil-source faults dipping into source kitchen have an activity rate of 20~40 m/Ma in the key accumulation stage, and a value of shale gouge ratio more than 50% in the lower Zhujiang Formation. Also, the normal stress on oil-source fault surface is larger than the ultimate compressive strength of mudstone. These are helpful for hydrocarbon migration along the oil-source faults. In contrast, the trap-controlled faults have perfect lateral sealing ability, because of activity rate less than 20 m/Ma and value of shale gouge ratio more than 95% in the lower Zhujiang Formation, as well as normal stress on fault surface less than the ultimate compressive strength of mudstone. The feature of differential accumulation of hydrocarbon in the northeastern Baiyun Sag is obvious. Oil is accumulated in the footwall of the far-source antithetic trap- controlled faults, and gas is in the near-source traps.