基于瓦斯渗透异性的煤层抽采钻孔合理布置

基于煤层瓦斯渗透各向异性特征,在九里山煤矿煤层进行了180d井下瓦斯抽采有效影响半径测试,同时,建立煤层瓦斯各向渗透异性的气-固耦合渗流模型,数值模拟了瓦斯抽采有效半径的时变规律,分析了抽采钻孔的合理布置方式。研究结果表明:煤层平行层理方向的渗透率是垂直层理方向的渗透率的2.6倍左右。煤层钻孔不同方向有效抽采半径均随抽采时间增加而增大,且与预抽时间满足幂指数关系,数值模拟结果与井下现场测量一致。有效抽采距离在平行层理方向最大,垂直层理方向最小,有效抽采区域为椭圆形。据此确定了不同预抽时间煤层抽采钻孔的合理间距,并针对九里山煤矿二1煤层计算分析了预抽时间与百米钻孔数的关系。

Reasonable layout of drainage boreholes based on anisotropic permeability in coal seam

Coal seam degasification by in-seam drilling borehole is one of the popular techniques for coal mine methane (CMM) control. Generally, the more borehole numbers for a specific drainage area, the shorter drainage time but the higher drainage cost. In order to resolve the contradiction between borehole numbers and drainage duration, in-situ tests of effective gas drainage radius were conducted continuously in an anisotropic coal seam for 180 days at Jiulishan coal mine in China, and coal permeability was measured associated with bedding and cleat structures, and then gas-solid coupled seepage model was built to simulate the change rules of effective drainage radius in an anisotropy coal seam using finite-element based Comsol package. The results indicate that the coal permeability parallel to the bedding plane in butt cleat direction is 2.6 times as high as that perpendicular to the bedding plane. And effective drainage radius parallel to the bedding plane in butt cleat direction will get much larger than that perpendicular to the bedding plane with the increase of drainage duration and shows exponential relationship with gas pre-extraction time. The numerical results of simulated tests are consistent with those of field tests. Based on numerical results, the ellipse influence area of borehole in an anisotropic coal seam is proposed, and the relativity of effective drainage radius with drainage time is found. On the basis of these findings the proper in-seam borehole arrangements for a specific mining panel at different drainage duration are determined.