Zhang Jianzhong, Gao Tianrun
University of Chinese Academy of Sciences, Beijing 100049, China.
Tianjin University, Tianjin 300072, China.
ACS Omega. 2021 Sep 28;6(40):26221-26230. doi: 10.1021/acsomega.1c03228. eCollection 2021 Oct 12.
The compressibility of abnormal pressure gas reservoirs is hard to test, and the interpretation is confusing, leading to many misunderstandings in the current understanding of abnormal pressure gas reservoirs. In this research, a high-pressure experimental system was designed, and a series of high-pressure compressibility tests of pure water, nitrogen, and rocks under different water saturations were carried out. Then, the effective compressibility of gas reservoirs was calculated; the effect of water saturation on abnormal pressure gas reservoirs and the dynamic prediction was studied. The results show that the compressibilities of water and rock are effectively constant values over the range examined, while the compressibility of gas decreases exponentially with the increase in pressure. The effective compressibility of the stratum increases with the rise of water saturation. The theory of stress and strain of rock mechanics also shows that the rock compressibility is determined by Young's modulus, Poisson's ratio, and porosity and has no connection with the formation pressure. With the increase in water saturation, the swelling degree of the production indicator curve of the simulation experiment becomes larger and larger. After introducing the effective compressibility of the stratum into the gas-water material balance equation, the gas reserves predicted by the revised production indicator curve are the same as the original reserves. The research results have important guiding significance for the efficient development of gas reservoirs.
异常压力气藏的压缩性难以测试，解释也很混乱，导致目前对异常压力气藏的认识存在诸多误解。本研究设计了一套高压实验系统，对纯水、氮气以及不同含水饱和度下的岩石进行了一系列高压压缩性测试。然后，计算了气藏的有效压缩性；研究了含水饱和度对异常压力气藏的影响及动态预测。结果表明，在所考察的范围内，水和岩石的压缩性为有效常数，而气体的压缩性随压力升高呈指数下降。地层的有效压缩性随含水饱和度的升高而增大。岩石力学的应力应变理论也表明，岩石压缩性由杨氏模量、泊松比和孔隙度决定，与地层压力无关。随着含水饱和度的增加，模拟实验生产指标曲线的膨胀程度越来越大。将地层有效压缩性引入气水物质平衡方程后，修正后的生产指标曲线预测的气藏储量与原始储量相同。研究成果对气藏的高效开发具有重要指导意义。
