松软煤层井下造缝导向压裂瓦斯运移机理及富集规律

Nowadays, hydraulic fracturing technology has been preliminarily tried to improve the extraction of gas in soft and low-permeability coal seams in underground coal mine. The results show that hydraulic fracturing technology can improve gas permeability of coal seams and increase output of coal-bed gas. However ,when the water is injected into the coal seams, the characteristics of coal, the effect of gas-water surface ,the stress field of coal seams and fracture field will be changed, which leads to the mechanism of gas migration and enrichment regularity are undefined. The key factor to decide gas extraction efficiency is space between boreholes and put those boreholes in the enrichment area. Hence, this project will investigate coal-bed gas migration mechanism and enrichment regularity affected by forming fissure and hydraulic fracturing in soft coal seams. Therefore, based on the research of the physical and mechanical property of coal-rock mass with fracturing fluid and gas ,the project will build constitutive equation and failure criteria; reveal the mechanism of fracturing fluid to promote desorption and seepage; gain the effect law of crustal stress field and fracture filed variation characteristic’s impact on coal gas desorption and seepage in hydraulic fracturing process; build gas migration governing equation affected by hydraulic fracturing in soft coal seams; calculate the contour maps of permeability after hydraulic fracturing and predicts gas accumulation area ,which provides theoretical support to optimize space between extraction boreholes and improve coal-bed gas extraction rate during the hydraulic fracture process .

煤矿井下水力造缝导向压裂抽采煤层气（瓦斯）技术初期实验结果表明该技术能够大幅增加煤层透气性，提高煤层气产量，但压裂过程中由于压裂液注入引起煤体物性变化、气-液界面作用及煤层应力场、裂隙场变化，导致瓦斯运移机理及富集规律尚不明确，能否合理设计压裂孔间距并将抽采钻孔布置在瓦斯富集区是决定瓦斯抽采效率的关键。因此，松软煤层井下造缝导向压裂瓦斯运移机理及富集规律是本项目研究的关键科学问题，本项目拟在研究含压裂液与瓦斯的煤体结构和物性变化的基础上，建立含压裂液、瓦斯煤体本构方程和破坏准则；揭示压裂液促进煤体瓦斯解吸渗流机理；研究水力造缝导向压裂周围煤体应力场、裂隙场变化规律；建立压裂过程中煤层瓦斯渗流运移控制方程并通过试验进行校正；计算松软煤层水力造缝导向压裂完成时及卸压后煤层瓦斯真实渗透率的等值线分布图，预测瓦斯富集区，为优化压裂孔、抽采孔布孔工艺，提高煤层气抽采率提供理论支撑。

针对松软煤层导向压裂过程中由于压裂液注入引起煤体物性变化、气-水界面作用及煤层应力场、裂隙场变化，瓦斯运移机理及富集规律尚不明确，导致抽采钻孔布置困难等问题。项目组采用理论分析、数值模拟、室内及现场试验相结合的方法，建立了含压裂液、瓦斯煤体本构方程和破坏准则；开展瓦斯吸附解吸与渗流试验，揭示了压裂液促进煤体瓦斯解吸渗流机理；基于COMSOL Multiphysics计算方法，研究了阐明了松软煤层水力压裂裂缝周围煤体应力场、裂隙场变化规律。综合考虑压裂液、地应力场、瓦斯压力场等因素影响，建立了压裂过程气-液界面作用下煤层瓦斯渗流运移模型；该模型能计算松软煤层水力造缝导向压裂完成时及卸压后煤层瓦斯真实渗透率的等值线分布图，预测瓦斯富集区；并在重庆松藻矿区进行了水力造缝导向压裂现场试验。与传统煤层增透方法相比，煤层气平均抽采量提高到3~5倍，预抽钻孔数量减少26%以上。该研究成果能为水力造缝导向压裂高效增透技术及工艺提供有力的基础理论支撑。发表学术论文5篇，其中SCI检索5篇（2区1篇，3区2篇，4区2篇）；授权发明专利2项；协助培养博士研究生1人，硕士研究生2人。申请人在国际国内会议上做大会报告3次。