Research on abnormal pressure of dark shale in the Tiemulike formation of the Yining Sag, Ili basin

The study of abnormal pressure in the dark shale of the Tiemulike Formation in the Yining Sag of the Ili Basin holds significant importance for its oil and gas exploration. Based on the Acoustic time difference data of shale, the overexposure development interval in the Tiemulike Formation was of the Yining Sag determined. The equilibrium depth method had been adopted to quantitatively calculate the excess pressure and pressure coefficient of dark shale in the Tiemulike Formation for the first time. The distribution map of abnormal excess pressure in single well profiles and well-tie comparison profile had been drawn, and the abnormal excess pressure characteristics of the shale had been fully Analyzed. The results show that the pressure coefficient of the dark shale in Tiemulike Formation is 1.21–1.95, belonging to the weak-high pressure to Ultra-high pressure layers. The excess pressure gradually increased from the top to the deeper layers in the Tiemulike Formation, with three abnormal pressure significantly increased layers. The abnormal excess pressure in Tiemulike Formation is about 5–10 MPa higher than that in the overlying Upper Permian Basiergan Formation, indicating high abnormal pressure characteristics. The horizontal distribution characteristics of abnormal excess pressure in Tiemulike Formation show that the abnormal excess pressure is mostly above 10 MPa, with a highest reaching 29.4 MPa. The Higher abnormal excess pressure has good continuity in the horizontal direction, several high abnormal fluid pressure compartments were formed in the central low-laying area of Yining Sag. The formation of abnormal excess pressure in the shale of the Tiemulike Formation in the Yining Sag was mainly controlled by the hydrocarbon generation expansion of dark shale, as well as the influence of clay mineral diagenesis.