| It is urgent to find replacement fields for oil and gas exploration around Ya’nan Sag in the west of Qiong dongnan Basin. In view of the three geological problems existing in the exploration and research, the characteristics of Red River fault activity and its influence on the structure-sedimentation and hydrocarbon accumulation around Ya’nan Sag are analyzed by using abundant drilling and seismic data. It is considered that the strike slip activity of Red River fault transfers shear stress to the west of Qiongdongnan Basin through Fault F1, and its evolution has a good space-time coupling relationship with the structure-sedimentation around Ya’nan Sag, and controls the oil and gas migration around Ya’nan Sag. In Late Oligocene, the sinistral strike slip activity of Red River fault induced EW trending compressive stress and SN trending tensile stress in the west of Qiongdongnan Basin through Fault F1, resulting in the intense activity of NEE trending strike slip faults and the formation of two sedimentary centers, Yabei Sag and Ya’nan Sag. During the Middle and Late Miocene, the Red River fault was inactive, and under the control of regional dextral tension and torsion stress and the decrease of sedimentary source in Hainan Island, carbonate platform developed at the local uplift around Ya’nan Sag, and the Meishan Formation and Huangliu Formation were absent in wide. Since Pliocene, the dextral strike slip activity of Red River fault has induced SN trending compressive stress and EW trending tensile stress in the west of Qiongdongnan Basin through Fault F1, which has constrained the tension in the west of Qiongdongnan Basin and caused NEE and NE trending faults to be closed by compressive stress and NW trending faults to be open by tensile and torsional stress. The Pliocene is the peak period of hydrocarbon generation and expulsion in the basin. NW trending faults can effectively transport oil and gas, while NEE and NE trending faults have poor oil and gas transportation ability, which reasonably explains the oil and gas discovery in drilled structures. The next step of oil and gas exploration around Ya’nan Sag should focus on NW trending fault zones. |
