Exploring the principle and method for commingled production of coal-measure gas through layered pressure relief in surface wells

This study aims to gain an in-depth understanding of factors restricting the commingled production of coal-measure gas and boost the contributions of various pay zones to gas production. To this end, it analyzed the essential factors of the dynamic, channel, and gas source conditions in the commingled production. The dynamic conditions for the commingled exploitation of multiple reservoirs can be met by (1) enhancing the flow conductivity of reservoirs by altering the crustal stress state and (2) changing reservoir fluid pressure by layers. Following this principle, this study proposed a method for the commingled production of coal-measure gas through layered pressure relief in surface wells. This method involves directional drilling on the surface and then high-pressure water jet in target reservoirs to artificially create pressure-relief spaces (e.g., fractures, slots, and cavities) and alter the crustal stress state. This can reduce the damage caused by effective stress, increase the number and aperture of diversion channels in reservoirs, and accelerate pressure drop transfer in target reservoirs. Afterward, commingled production can be conducted after the reservoir pressure decreases to the dynamic conditions for the commingled production of coal-measure gas, thus enhancing the contributions of pay zones to gas production. Compared to conventional reservoir stimulation, this method can reduce the damage of effective stress to coal-measure gas reservoirs, improve the transfer efficiency of pressure drop, enhance the desorption and diffusion of coal-measure gas, and decrease the interlayer interference during the commingled production of multiple coal-measure gas reservoirs. Based on these findings, this study proposed that the commingled production of coal-measure gas through layered pressure relief in surface wells is primarily applicable to coal-measure gas reservoirs with high crustal stress and small spacings between pay zones. Furthermore, this method is expected to be widely applied to the stimulation of coal-measure gas reservoirs with thin interbeds for production growth and to the exploitation of superimposed paragenetic coal-measure reservoirs with severe interlayer interference.