彭水及邻区龙马溪组页岩气藏在地质历史时期存在过超压现象,但现今为常压,发生了由超压向常压的转变。通过抬升过程中地层压力演化模拟,揭示龙马溪组泥页岩在抬升过程中发生了超压破裂,产生裂缝,导致页岩气散失和超压释放。依据泥页岩覆压渗透率测试分析数据,认为当龙马溪组泥页岩裂缝面上所受的正应力大于15 MPa,即埋深大于1 000 m时裂缝将发生闭合。但裂缝闭合程度受泥页岩超固结比（OCR）影响,处于脆性带之下的泥页岩,OCR相对小,裂缝闭合程度相对高,超压可能未完全释放,现今仍然维持一定程度的超压;处于脆性带之上的泥页岩,OCR越大,裂缝闭合程度越差,对页岩气保存不利,容易导致超压完全释放,变为常压。泥页岩的OCR与地层流体压力系数之间具有显著的相关性,OCR比越大,越趋于常压。

The shale gas reservoirs in Longmaxi formation in Pengshui and its adjacent areas were overpressured in geological history, but nowadays they transformed into normal pressure. Through the simulation of formation pressure evolution in the uplifting process, it is revealed that Longmaxi shale was fractured under excessive pressure in this process, resulting in shale gas loss and therefore overpressure release. By overburden pressure permeability test, it is found that when the normal stress on the mudstone fracture surface of Longmaxi formation is more than 15 MPa, that is to say, when the buried depth is more than 1 000 m, the cracks will be closed, but the degree of fracture closure is affected by overconsolidation ratio（OCR） of shale. For the mudstone or shale under the brittle zones, OCR is relatively small, the closure degree of fracture is relatively high, the overpressure may not be completely released, and a certain degree of overpressure is still maintain. But for those above the brittle zones, the lager the OCR, the worse the fracture closure degree, and it is apt to cause the overpressure released completely, finally transit to normal pressure state. There is a significant correlation between OCR and the pressure coefficient of the formation fluid, that is, the higher the OCR ratio, the more normal the pressure will tend to be.