四川盆地PT1井区海相地层工程地质特征研究

Study on Engineering Geological Characteristics of Marine Formation in PT1 Well Area of Sichuan Basin

PT1井区超深海相地层钻井过程中气侵和井漏频发,严重制约该区块的安全高效开发。文章基于有效应力法,利用最优化方法开展了海相地层孔隙压力评价;结合断层和裂缝发育程度探讨了PT1井区气侵和井漏纵横向分布特征。结果表明,受异常高压和裂缝发育程度的双重影响,气侵主要发生在龙潭组,占比达40%;井漏主要发生在筇竹寺组和灯影组,占总漏失量的80%以上。气侵与异常压力、裂缝发育程度、断裂情况等因素有关,异常高压是气侵内在的原因,而断裂带和发育的构造裂缝为气侵提供了必要条件。井漏层位和漏失量主要受一、二级大型断裂带控制,不同断裂带的影响具有显著的叠加效应,断裂带附近发育的构造裂缝为漏失提供了通道,距离F I7断裂越近越易出现漏失,且漏失量越大。研究成果为PT1井区钻井过程井下复杂预防和处理提供了科学支撑。

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 Formation and Dengying Formation,accounting for more than 80%of the total leakage.Gas invasion is related to abnormal 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 developed near the fault zone provide channels for leakage,and the closer the FⅠ7 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.