关键词: 瓦斯, 煤层气, 水力割缝, 注气, 多过程, 渗流

Abstract: In order to improve the ability of gas extraction in low permeability coal seam, different kinds of gas extraction methods are applied in engineering practice, including relief to increasing permeability by high pressure water jet slotting, strengthening pre-extraction method, displacing and driving gas method by air injection, and inhibiting gas desorption method by water injection. To increase the permeability of coal seam, the high pressure water jet slotting method is applied through boreholes in the rock under the floor of coal seam. Then the high pressure gas is extracted by pre-extraction method. After reaching the limit time of pre-extraction method does not work, the air injection method is taken. When the air injection method becomes invalid, the new method that inhibiting gas desorption by water injection is applied to increase the moisture of coal seam and inhibit desorption of residual gas in coal seam. Field tests show that the permeability of coal seam increases more than 100 times after taking the multiple gas strengthening extraction methods and the gas extraction efficiency is increased from 16.4% to 58.6%. The flow ability of gas-injected air-water has a succession of theses multiple processes. In other words, the later sub-process seepage commences just when the former sub-process seepage comes to an end. The new conception of multi-process seepage is introduced to study the whole process for the first time. The multi-process seepage equations are also built taking the seepage pressure distribution in the former sub-process as the initial condition of the following seepage sub-process. Then these equations are solved. These numerical solutions are more practical and reasonable, especially for the multi-process and multi-fluid seepage. The results show that the gas pressure curve is a parabola form in the first sub-process and the final state of this stage can be expressed by power function; in the following sub-process, the injecting air pressure curve decreases first and then increases in a trough form at initial state and decreases in a power function form; in the last sub-process, the injecting water pressure curve decreases in a power function form. All these results will provide theoretical and engineering references for multiple process gas strengthening extraction practices.