Abstract：

In order to obtain the actual change characteristics of the gas-water relative permeability in coalbed methane (CBM) reservoirs and to further deepen the understanding of the gas-water production process of CBM reservoirs, a relative permeability dynamic calculation method of CBM reservoirs combined with the real-time production situation of the reservoir was constructed. Firstly, the production history match of the target single coal seam or multiple coal seams is carried out using the multiple coal seam whole process coupling flow model, which is to obtain the basic physical parameters of the reservoir and fluid. Then, based on the obtained basic physical parameters, the full production cycle productivity prediction of the CBM well is carried out. At the same time, the reservoir parameters are averaged according to the real-time expansion behavior of the reservoir pressure drop, and the gas-water permeability curve of the CBM reservoir is calculated based on the averaged reservoir parameters and the actual fluid migration. The results show that the relative permeability dynamic calculation method of CBM reservoirs proposed in this paper can dynamically calculate the actual gas-water relative permeability of the CBM reservoir on the basis of real-time quantitative analysis of the internal production situation of the CBM reservoir. There is a reversal point on the gas relative permeability curve calculated by the method proposed in this paper. The reversal point characterizes the stable and continuous supply of desorption gas in CBM reservoirs. If the actual expansion of the CBM reservoir pressure drop is not considered and the reservoir parameters are averaged in the whole area, the calculated gas-water relative permeability of the CBM reservoir will be low. For multiple coal seam reservoirs, the interlayer mass exchange of fluids and the decrease in the reservoir pressure caused by the crossflow cannot be ignored. The ratio of the crossflow of gas to gas production can reach 0.57, and the ratio of the crossflow of water to water production can reach 0.69 after 3 years of production. The calculated gas-water relative permeability of the CBM reservoir under the condition of ignoring the crossflow is low, which is only 42.9% and 24.4% respectively of the calculated gas-water relative permeability under the condition of considering the crossflow. In the actual production process of CBM wells, the water saturation remains at a high value, more than 40%. Restricted by the high water saturation, the gas relative permeability of CBM reservoirs is low, less than 0.2.

Key words：coalbed methane; relative permeability; productivity prediction; commingled production; crossflow

Received： 2023-08-21

Corresponding Authors：wangzm@cup.edu.cn

Cite this article：黄天昊, 汪志明, 曾泉树, 蔡先璐, 戴安娜. 煤层气藏相对渗透率动态计算方法研究. 石油科学通报, 2024, 03: 525-534 HUANG Tianhao, WANG Zhiming, ZENG Quanshu, CAI Xianlu, DAI Anna. Research into relative permeability dynamic calculation methods for coalbed methane reservoirs. Petroleum Science Bulletin, 2024, 03: 525-534.

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