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运用自主研发的多场耦合煤层气开采物理模拟试验系统,开展三维应力状态下煤层气开采物理模拟试验,分析不同抽采长度条件下煤储层内气体压力参数的动态演化规律。研究表明:不同抽采长度条件下,气体压力都是从钻孔中心周围开始下降的;抽采前期气体压力下降显著,随着抽采时间的延伸,各测点气体压力值变化速率减小;随着抽采长度的增加,气体压力梯度较大的区域明显扩大,同时会提高瓦斯的解吸速率,抽采效率提高。抽采断面上的等压线则以钻孔为中心,呈圆环状分布,气体主要是汇流至抽采钻孔,层面流场中等压线则以钻孔为对称轴呈漏斗形分布。抽采长度对突出危险消除区域出现时间影响不大,但随抽采长度增加,消除突出危险性所需时间减少;由于应力集中区应力大、解吸速率慢,消除突出危险性抽采所需时间较其他区长。研究成果可为现场合理布置抽采钻孔,提高抽采效率以及确定合理的抽采时间提供一定的理论依据。
The physical simulation test system of coalbed methane exploitation under three-dimensional stress state is carried out by using the self-developed multi-field coupled physical simulation test system for coalbed methane exploitation. The dynamic evolution of gas pressure parameters in coal reservoir under different pumping lengths is analyzed. The results show that the gas pressure drops from around the center of the borehole under different pumping lengths. The gas pressure drops significantly in the early stage of gas drainage. With the extension of pumping time, the rate of gas pressure changes at each measuring point decreases. With the increase of pumping length, the area with larger gas pressure gradient obviously expands, meanwhile, the gas desorption rate will be increased and the pumping efficiency will increase. The isobaric line on the pumping section is centered on the borehole and distributed in an annular shape. The gas is mainly converged to the drainage borehole. The isobaric line in the flow field is distributed in a funnel shape with the borehole as the symmetry axis. As the length of extraction increases, the time needed to eliminate the prominent danger decreases. Due to the large stress in the stress concentration zone and the slow desorption rate, the time required to remove the outburst danger is eliminated More than other mayors. The research results can provide a theoretical basis for the rational arrangement of drilling holes on site, improvement of pumping efficiency and determination of reasonable extraction time.