异常高压与油气的生成

Abnormal high pressure and generation of hydrocarbon

在烃源岩生烃反应中,地层温度和压力起着相当重要的作用,但是以往强调温度和时间因素的重要性,对于压力的作用研究较少。在研究镜质体反射率与地层压力的关系、烃源岩生烃门限深度及石油窗下限深度与地层压力的关系的基础上,结合前人的实验结果研究认为:异常高压不仅影响油气生成的相态,而且降低了烃源岩的成熟度,延缓了烃源岩热演化的进程;当地层压力超过一定的门限时,压力对成烃有明显的抑制作用,表现为压力系数与烃源岩生烃门限深度、石油窗下限深度正相关。在辽河断陷东部凹陷牛青地区,异常高压使石油窗下限深度加深460m左右。依据有机质成烃动力学原理,对压力影响有机质生烃的机理进行了探讨。

Combined with the experimental results of previous workers, the present research on the relationships among vitrinite reflectance, burial pressure coefficient, oil threshold, and top gas window indicates that abnormal high pressure not only controls the generative phases of hydrocarbons but also results in reduced maturity of source rock and retarded processes of source rock evolution. This delaying effect is particularly clear when pressure exceeds a certain value, which can be inferred by the rise of the oil threshold or the upper limit of the gas window as a result of increase in pressure. In the Niuju-Qinglongtai area of the East Sag, Liaohe Depression, the top gas window is retarded for about 460 meters downward due to abnormal high pressure. Similar relationships between pressure and hydrocarbon window have been confirmed during exploration in some parts of the Bohai Bay Basin.