柴达木盆地狮子沟油田古近系异常高压成因

GENESIS OF PALEOGENE ABNORMAL HIGH PRESSURE OF SHIZIGOU OILFIELD IN QAIDAM BASIN

实测地层压力资料显示，柴达木盆地狮子沟油田古近系异常高压明显，压力系数最高可达2．07。研究认为，异常高压的主要成因为不均衡压实、有机质生烃和构造挤压作用，3种因素产生的异常压力占现今剩余压力的比例分别为20％-30％，30％-40％和35％-50％。此外，依据地质历史时期异常压力产生的主控因素和时间顺序，提出了研究区异常高压形成过程的概念模式：地层先因不均衡压实而出现弱超压，由于厚度较大的泥质岩、上覆膏岩层和断层在时空上的有效组合，在深部形成较好的封闭体系；随着地层的快速埋深，有机质逐渐成熟生烃，成为内部增压的主要来源；持续并且逐渐加强的构造挤压作用进一步提高了异常压力幅度。

The actually measured data of the formation pressure show that the abnormal high pressure is obvious for Paleogene system of Shizigou Oilfield in Qaidam Basin and the pressure coefficient can reach 2.07 at most. The studies prove that the main causes of abnormal high pressure are due to disequilibrium compaction, hydrocarbon generation from organic matters and tectonic compression. The contributions of the abnormal pressure induced by these three factors are 20%-30% , 30%-40% and 35% -50% respectively of the present remained pressure. In addition, based on the main controlling factors and time order of the abnormal pressure generated in the geological history, the conceptual model of abnormal high pressure in the study area can be established as followings： （ 1 ） low overpressure initially appears in the formations resulted from the disequilibrium compaction, and later a much better closed system generated in the deep part just because of the effective combination of pretty thicker pelite, overlying gypsolyte and faults in time and space ; （2 ） with the rise of fast buried depth of the formations, the organic maters gradually mature and generate hydrocarbon, and finally these conditions become the main source for inner supercharging; （3 ） the continuously increased and gradually strengthened tectonic compression have further enhanced the degree of lhe almurmal pressure.