煤层注水促抽瓦斯及其影响因素的数值模拟

为有效预防煤矿瓦斯灾害,获取煤层注水促抽瓦斯的合理参数,以常村煤矿2103工作面为例,依据多相渗流理论,采用Fluent软件的VOF模型及多孔介质模型耦合求解,对煤层注水促抽瓦斯技术及其影响因素进行数值模拟,并将模拟结果应用于现场,对比分析数值模拟与现场实测数据,二者基本吻合.研究结果表明:煤层瓦斯含量以注水孔为中心径向逐步降低,以抽采孔为中心径向逐步升高;注水前抽采阶段,随着抽采时间的增加,抽采范围逐渐增大,抽采孔瓦斯流量先快速下降,后逐步缓慢降低;注水促抽阶段,随着注水时间的增加,注水范围逐渐增大,注水流量逐步降低,煤层瓦斯含量缓慢升高,抽采孔瓦斯流量逐渐增加;注水后抽采阶段,随着抽采时间的增加,压力水覆盖范围持续增大,煤层瓦斯含量逐渐降低,抽采孔瓦斯流量逐渐减小.注水时机、注水时间、注水压力、注水方式、布置方式及钻孔间距是影响煤层注水促抽瓦斯效果的6个主要因素.瓦斯正常抽采20 d后,按照一注一抽方式及5 m间距布置注抽钻孔,在8 MPa煤层注水压力下间歇注水10 d,煤层注水促抽瓦斯效果较好.

Numericalsimulation of coal seam water infusion promoting methane drainage and its influence factors

In order to prevent the methane disaster in coal mine effectively and obtain the reasonable parameters of promoting methane extraction by coal seam water infusion, the 2103 working face of Changcun coal mine was investigated as an example. Using the coupling of VOF model of Fluent software and porous medium model, promoting methane drainage by coal seam water infusion and its influence factors was simulated based on the multi-phase porous flow theory. The comparison shows that the simulation results were basically consistent with the measured data. The results are detailed as follow. The gas content in coal seam gradually decreased with the increase of the radial distance from centerline of water injection hole and it increased with the increase of the radial distance from centerline of gas drainage hole. During drainage period before water injection, the scope of drainage increased gradually and gas flow in drainage hole decreased quickly at first, and then decreased slowly. During the stage of water injection, the scope of drainage increased and water injection flow decreased gradually, while gas flow in coal seam and gas flow in drainage hole also increased gradually over time. And after water injection, the coverage area of pressure water continued to increase, while gas content in coal seam and gas flow in drainage hole both declined little by little over time. The opportunity, time, pressure, layout, pressure, space between boreholes and the way of water injection are the 6 main factors which influence the effect of promoting methane extraction by coal seam water infusion. It can achieve the best effect when intermittent water injection was carried out for 10 days under the pressure of 8 MPa water injection according to the way of one injection and one pumping and arranging the drilling holes spacing at 5 m after 20 days of the methane drainage.