古压力恢复与天然气成藏关系——以昌潍坳陷潍北凹陷为例

RECONSTRUCTION OF PALEOPRESSURE AND ITS RELATION TO GAS RESERVOIRING:TAKING WEIBEI SAG IN CHANGWEI DEPRESSION AS AN EXAMPLE

利用埋藏压实方法计算了昌潍坳陷潍北凹陷在古压力状况，尽管目前该地区的压力基卒处丁骨水压力或弱低压状况，但在地质历史中曾经存在超压状态。其压力演化过程可以划分为3个阶段：①由欠压实引起的超压一释放阶段（距今52～51Ma）；②超压再聚集阶段（距今50Ma沙河街构造运动前）；③压力释放阶段（沙河街构造运动一现今）。发生在古近纪晚期的沙河街构造运动造成的巨大剥蚀，导致了原存异常高压的卸压，在沙河街构造运动之后，压力就处于静水压力或弱低压状态。由于异常压力的出现与油气充注密切相关，卸压作用对于潍北凹陷深部的天然气资源有重要的影响。

Paleopressure in Weibei sag of Changwei depression was calculated by using burial and compaction methods. Though the current formation pressures in the study area are dominated by hydrostatic pressure or weak low pressure, overpressure had occurred in geologic history. The evolution of formation pressure can be divided into 3 stages: overpressure resulted from uncompaction and pressure release (52 to 51 Ma); ② overpressure re-accumulation (50 Ma to the beginning of Shahejie structural movement); and ③ pressure release (Shahejie structural movement to present). The large amount of erosion resulted from Shahejie structural movement in Late Paleogene caused the release of the previous overpressure. The formation pressure has been kept to be hydrostatic or weak low pressure since the ending of Shahejie structural movement. As abnormal pressure is closely related with hydrocarbon charging, pressure release has important influences on gas resources in deep Weibei sag.