Simulation study of multilayer coalbed methane production in steeply inclined reservoirs in the southern edge of Junggar Basin

In order to promote the efficient development of coalbed methane (CBM) with extremely thick, multi-layered and steeply inclined coal reservoirs in the southern margin of the Junggar Basin, based on the geological data of CS18 well in Fukang west area, the production characteristics of three-layer steeply inclined CBM reservoir under different interlayer spacing, different drainage intensity and different physical parameters were simulated and studied by using Eclipse software. The simulation results show that the shape of the total gas production curves of steeply inclined reservoirs with different layer spacings are basically the same, and they all show a trend of increasing first and then decreasing daily gas production. With the increase of interlayer spacing, the gas production of the first layer increases gradually due to the higher permeability, while the third layer is opposite. However, the increase in the production of the first layer of reservoir and the decrease of the production of the third layer of the reservoir mostly offset, and the gas content in the updip direction of the reservoir increases slightly faster than that in the downdip direction with the increase of interval. Therefore, in the process of three-layer commingled production, the closer the first layer and the third layer are to the main production layer (the first layer), the higher the gas production, the larger the layer spacing, the lower the gas production. There is also a difference between the updip direction and the downdip direction of multi-layer commingled reservoirs for steeply inclined reservoirs. With the increase of drainage intensity, the reservoir pressure in the updip direction decreases rapidly, which accelerates the process of three-layer commingled production. However, the drainage intensity is low, and the desorption and production of CBM are restrained due to the high reservoir pressure in the updip direction, but with the progress of drainage, the inhibition gradually disappears. The effect of gas content and permeability physical parameters on multi-layer commingled production is also different. The simulation results show that the high gas content in the middle reservoir can make use of the upper and lower CBM production, while the high permeability will inhibit the production of CBM in the upper and lower reservoirs. © 2022 China Coal Society. All Rights Reserved.