钻孔煤体破坏渗流模型及在煤层卸压抽采中的应用研究

Damage-seepage Model of Borehole Coal and Its Application for Pressure Relief in Gas Extraction of Coal Seam

为对比分析顺层钻孔在护孔和未护孔条件下的抽采效果,考虑煤体扩容特性,采用煤体孔隙率和渗透率动态数学模型,结合D-P屈服准则,建立了钻孔煤体破坏—渗流的流固耦合模型。以超化煤矿2煤层相关物理参数为基础,开展了钻孔卸压破坏范围及抽采瓦斯数值模拟,结果表明:钻孔发生卸压破坏后,虽然未护孔钻孔卸压范围是护孔钻孔的1.3倍,其周围煤体渗透率和孔隙率均大于护孔钻孔,但钻孔更易塌孔堵孔,当抽采90 d时,护孔钻孔有效抽采半径为未护孔钻孔的1.3倍。现场瓦斯抽采测定数据表明,护孔钻孔平均抽采瓦斯浓度为未护孔的1.6倍,平均抽采瓦斯纯流量为未护孔的1.4倍,并有效缩短了钻孔抽采时间。

In order to compare and analyze the extraction effect of bedding drilling borehole under the condition of hole protected and unprotected,by considering the dilatancy characteristic of coal,adopting the dynamic mathematic model of porosity and permeability in coal and combining with the Drucker-Prager criterion,the fluid-solid coupling model of borehole coal damage-seepage was established.The damage range of borehole pressure relief and gas extraction was numerical simulated based on the physical parameters of coal seam 2 in Chaohua Coal Mine.The results show that,after the pressure relief damage occurs in the borehole,although the released range of unprotected hole is more than 1.3 times of protected hole,and the porosity and permeability of coal around unprotected hole are bigger than protected hole,but unprotected hole is more likely to collapse and plug.After extracting gas for 90 days,the effective drainage radius of protected hole is more than 1.3 times of unprotected hole.The filed data of gas extraction indicates that the average extraction concentration of protected hole is more than 1.6 times of unprotected hole,the average amount of pure gas extraction of protected hole is more than 1.4 times of unprotected hole,and the borehole extraction time is effectively shortened.