Discussion on the coal measure gas co-mining method by the stratified pressure relief in surface wells

In order to further understand the restrictive factors of coal measure gas co-mining, and to improve the gas production contribution of each production layer of coal measure gas co-mining, based on power, passage and gas source conditions, the necessary factors of coal measure gas co-mining were analyzed. Based on the principle of changing the crustal stress state to improve the reservoir conductivity and changing the reservoir fluid pressure in different layers to meet the dynamic conditions of multi-layer co-mining, the coal measure gas development method by stratified pressure relief in surface wells was proposed. Through directional drilling on the surface, high-pressure water jet operation is carried out in the target reservoir, pressure relief spaces (slots, grooves, holes) are artificially created, the stress state is changed, with the effective stress damage the being reduced, and then the number and opening of reservoir diversion channels are increased, and the fluid pressure drop of the target reservoir is finally induced. When the reservoir pressure drops to meet the dynamic conditions of coal measure gas combined production, the combined layer drainage will be carried out, realize the coordinated multi-layer gas combined production, and improve the gas production contribution of each production layer of coal measure gas combined production. Compared with conventional reconstruction technologies, the method can reduce the damage of coal measure gas reservoirs under the effective stress action, improve the efficiency of inducing the pressure to promote the desorption and diffusion of coal measure gas, and reduce interlayer interference. On the basis of the above research, it is considered that the development mode of surface well delamination relief is mainly suitable for the coal measure gas reservoir with large in-situ stress and small spacing between production layers, and it is expected to be applied in the field of thin interlayer gas reservoir stimulation and the development of symbiotic coal measure reservoir with serious interlayer interference.