Experimental analysis on the characteristics of gas migration extracted by parallel boreholes under different stress conditions
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Abstract:
With using the independently developed "multi-field coupling coalbed methane recovery physical simulation test system", physical simulation tests by parallel borehole gas drainage under different stress levels are carried out. The results are as follows:1) In parallel borehole gas extraction, the pressure drop curve slope in the early stage was large, while in the middle and late stage it was relatively small. The gas desorption rate between adjacent extraction pipes was faster than that of the boundary extraction pipe, and was parallel at any time. The change of pressure in the direction of vertical pumping pipe was symmetrical about the pumping pipe. The closer to the pumping stage of the pumping pipe, the faster the gas desorption rate, which was not related to the distance between the connection sections of the pumping pipe; 2) In the process of gas drainage, with stress increasing, gas desorption rate slowed down, pressure drop funnel shrank, and gas desorption area became smaller. Stress influenced the elimination of outburst hazardous areas, and the difference it brought about was not obvious at first, but with the increase of it, the scope of eliminating the conflict gradually decreased; 3) In the process of gas drainage, instantaneous flow rate evolution over time can be divided into three stages:rapid increase, rapid decay and limit extraction, and with the increase of stress, instantaneous flow peak value decreased, and its attenuation rate slowed down. The cumulative flow of gas was reduced, and its growth rate slowed down, resulting in reduction of extraction efficiency.
