Study on Engineering Geological Characteristics of Marine Formation in PT1 Well Area of Sichuan Basin
The frequent occurrence of gas invasion and well leakage during the drilling process in the ultra-deep marine formation of the PT1 well area seriously restricts the safe and efficient development of the block.Based on effective stress method and optimization method,the pore pressure evaluation of marine formation is carried out in this paper.The article is based on the effective stress method and utilizes optimization methods to evaluate marine formations'pore pressure.The vertical and horizontal distribution characteristics of gas invasion and well leakage in the PT1 well area were explored based on the degree of development of faults and fractures.The results show that due to the dual influence of abnormally high pressure and the degree of fracture development,gas invasion mainly occurs in the Longtan Formation,accounting for 40％;Well leakage mainly occurs in the Qiongzhusi For-mation and Dengying Formation,accounting for more than 80％of the total leakage.Gas invasion is related to ab-normal pressure,degree of fracture development,and fault conditions.Abnormal high pressure is the inherent cause of gas invasion,while fault zones and developed structural fractures provide the necessary conditions for gas invasion.The location and amount of well leakage are mainly controlled by the first and second level large fault zones,and the influence of different fault zones has a significant superposition effect.The structural fractures de-veloped near the fault zone provide channels for leakage,and the closer the F Ⅰ 7 fault is,the more likely leakage occurs and the more significant the leakage amount.The research results provide scientific support for preventing and treating downhole complications during the drilling process in the PT1 well area.
PT 1 well areagas invasionwell leakagepore pressurefracture development degreefault zone
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