复合作用下煤层瓦斯抽采时空演化及衰减特性研究

针对顺煤层钻孔瓦斯预抽时间无法合理确定的难题，基于煤岩体力学和渗流力学理论分析顺煤层钻孔瓦斯流动特性并确定瓦斯抽采控制因素，对不同抽采时间和复合作用区域的顺煤层钻孔瓦斯浓度和瓦斯流量进行对比。结果表明：单孔瓦斯浓度在上覆煤层采空区-遗留煤柱和断层带复合作用下具有明显的区域差异特性，在不同区域内呈现相似的不稳定升降、大幅度衰减和趋于稳定阶段演化规律|连续钻孔瓦斯流量均呈负指数衰减规律，初始流量和衰减系数在主控因素是透气性系数时不稳定变化，在主控因素是有效应力时趋于稳定，在预抽时间60～120d内抽采效果最优|同时钻孔瓦斯抽采衰减系数可以作为煤层抽放难易程度的一个辅助判断指标。

Time-space Evolution and Attenuation Characteristics of Gas Extraction in Coal Seam under Combined Effect

In view of the difficulty that gas extraction time of borehole along coal seam cannot be reasonably determined,the gas flow characteristics are analyzed based on the theory of coal rock mechanics and seepage mechanics,and then the control factors are determined.The gas density and gas flow in boreholes with different extraction time and combined effect area are compared.The results show that gas density of single-hole has obvious regional difference characteristics under the combined effect of goaf,residual coal pillar in the overlying coal seam and fault zone,and presents similar evolution law of unsteady rise and fall,large attenuation and stabilization stage in different regions.The gas flow of continuous boreholes presents attenuation law of negative exponential.The initial flow and attenuation coefficient are unstable when the main controlling factor is the permeability coefficient,and tend to be stable when the main controlling factor is the effective stress.The best effect is achieved within 60~120 day of extraction time.Meanwhile,the attenuation coefficient of gas extraction can be used as an auxiliary index to judge the difficulty of coal seam drainage.