西湖凹陷中部西斜坡地区超压成因机制

沉积盆地超压成因研究已取得了重要进展，关于超压主要成因的认识也发生了重要变化，以往一些被普遍认为属于典型不均衡压实成因的超压已被部分或完全否定，生烃作用作为超压成因的普遍性得到愈来愈多的证实。西湖凹陷多个构造带的不同层位均发育超压，目前认为超压的形成仍然离不开不均衡压实（欠压实作用）的贡献。根据异常压力形成的基本地质条件和异常压力产生的地质、地球物理效应两方面因素，利用测井曲线组合分析法、鲍尔斯法（加载-卸载曲线法）、声波速度-密度交会图法、孔隙度对比法、压力计算反推法以及综合分析法系统解剖分析了西湖凹陷中部西斜坡地区平湖组不同岩性异常压力成因。研究结果表明：西湖凹陷中部西斜坡泥岩中烃源岩超压主要为自源生烃增压，非烃源岩超压为邻源压力传导成因。储层中至少存在常压-超压型和常压-超压-常压型两种压力结构类型，异常压力自南向北顶界面逐渐变深，主要为油气在生烃增压驱动下向储层运移过程中的压力传导所致。

Genetic mechanism of overpressures in the west slope of central Xihu sag

Many important progresses have been made in studying the genesis of overpressure in sedimentary basins, and there are significant changes in the understanding of major causes for overpressure. The general conclusion that some overpressure is caused by typical unbalanced compaction has been completely or partially negated. It has been increasingly demonstrated that the overpressure generally results from hydrocarbon generation. Overpressure is formed in different layers of several structural belts in Xihu sag. It is believed that unbalanced compaction (under-compaction) is still essential for the formation of overpressure According to the basic geological conditions formed by abnormal pressure and the geological and geophysical effects generated by abnormal pressure, the causes of different lithologic abnormal pressure in the Pinghu Formation in the west slope of central Xihu sag are systematically analyzed using the logging curves combination method, Bowers method (loading-unloading curve method), the acoustic velocity-density crossplot method, porosity comparison method, pressure calculation inverse method and comprehensive analysis method. The results show that the overpressure in source rocks in mudstones from the west slope of central Xihu sag is mainly generated by self-sourced hydrocarbon generation, and the overpressure in non-source rocks is caused by pressure transfer between adjacent sources. There are at least two types of pressure structures in the reservoir:atmospheric pressure-overpressure and atmospheric pressure-overpressure-atmospheric pressure. The top surface of abnormal pressure gradually declines from south to north, which is mainly caused by the pressure transfer during the hydrocarbon migration and transport towards reservoirs under the drive of hydrocarbon generation.