Reservoir Evaluation and Development ›› 2020, Vol. 10 ›› Issue (1): 9-16.doi: 10.13809/j.cnki.cn32-1825/te.2020.01.002

• Geomechanics of Shale Gas • Previous Articles     Next Articles

Normal pressure formation mechanism of Longmaxi shale gas in Pengshui and its adjacent areas

YUAN Yusong1,FANG Zhixiong2,HE Xipeng2,LI Shuangjian1,PENG Yongmin1,LONG shengxiang1   

  1. 1. Sinopec Petroleum Exploration and Production Research Institute, Beijing 100083, China
    2. Sinopec East China Oil and Gas Company, Nanjing, Jiangsu 210011, China
  • Received:2019-07-31 Online:2020-02-26 Published:2020-02-04


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.

Key words: shale gas, normal pressure, overconsolidation ratio, brittleness, fracture closure

CLC Number: 

  • TE122