An approximation of the relative permeability and discussion on curve shapes in coalbed methane reservoirs
ZHU Suyang1，PENG Xiaolong1，LI Chuanliang1，DENG Peng1，MA Feiying2，PENG Zhaoyang2，3，#br#
SUN Hanshen4，JIA Huimin5
(1. State Key Laboratory of Oil and Gas Geology and Exploitation，Southwest Petroleum University，Chengdu，Sichuan 610500，China；2. Engineering and Technology Center of Unconventional Resource，Guangdong Petroleum and Chemical Engineering Institute，Maoming，Guangdong 525000，China；3. Sichuan Tebake Oil and Gas Ltd.，Company，Chengdu，Sichuan 610500，China；4. Zhonglian CBM Ltd.，Company，Beijing 100000，China；5. PetroChina Huabei Oil field CBM Exploration and Exploitation Company，Jincheng，Shanxi 048000，China)
Abstract：In coalbed methane(CBM) reservoirs，relative permeability curves are commonly obtained using gas-water displacement experiment，and it is commonly concluded that the 2-phase flow area is very narrow and that the critical water saturation is extremely high according to experimental results. However，the fluid flow in coal is a complex process of coupled desorption from matrix and 2-phase flow in cleats. The process that gas desorbs from matrix，enters cleats and displaces water is different from one-direction gas displacement in laboratory，which leads to that the sweeping efficiency in production process is higher than that in experiment. To obtain the appropriate relative permeability in coal，a CBM productivity model was established in pseudo-steady state considering the desorption effect in matrix. Combining the material balance equation，an inversion method of the relative permeability curve in CBM reservoirs was proposed based on production history. The difference between relative permeability curves obtained from experiment and the developed method was discussed，and it is pointed out that the difference contributes to the low sweeping efficiency in experiment. Finally，the effects of two types of relative permeability curves were illustrated using numerical simulation method.
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2019, Vol. 38 
