鄂尔多斯盆地上古生界低压气藏成因

鄂尔多斯盆地上古生界气藏具有明显的低压特征,其流体压力梯度东高西低,与现今构造形态基本一致。研究表明,剥蚀期间的温度下降和后期埋深的增加是造成上古生界气藏低压形成的主要原因。对苏里格气田的实例研究表明,在150℃成藏时,流体压力梯度约为1.22MPa/100m;温度下降时,压力梯度下降14.9%,到白垩纪末压力梯度约为1.06MPa/100m。在新生代,随着埋深增加,压力梯度再下降21.4%,从而形成典型的低压气藏。

Genesis of low-pressure gas reservoir of the Upper Paleozoic in Ordos Basin

The fluid pressure is obviously lower than the static pressure in gas reservoir of the Upper Paleozoic in Ordos Basin. The fluid pressure gradient of the reservoir is high in the east part and low in the west part. Its change is accordant with the current structural gradient. It is suggested that the low pressure gradient of gas reservoir in the Upper Paleozoic was resulted from the increase in depth of the later sedimentation and the decrease of temperature during erosion. The fluid pressure gradient of Sulig Gas Field was 1.22 MPa per a hundred meters of formation, when the temperature of reservoir formation was 150℃. The pressure gradient decreased about 14.9 percent with temperature decreasing during erosion. The pressure gradient was about 1.06 MPa per a hundred meters of formation at the end of the Cretaceous and decreased about 21.4 percent with the depth increasing in the Cenozoic. Thus, the representative low pressure gas reservoir could be formed in Sulig Gas Field.