煤层水力压裂裂缝的微震震源参数反演及动态表征方法研究

Hydraulic fracturing (HF) of coal seam has achieved good results in controlling the gas disasters and gas extraction in coal mines. But there has been no effective monitoring tool for the hydraulic fractures of coal seam. Lack of available monitoring method has become one of the challenges that restrict the development of HF technique in coal mines. Recent research shows that a mass of microseismic (MS) signals occur during the coal seam HF process in coal mines. Therefore, the MS location and focal mechanism are introduced to study the expanding process, distribution and fracture mechanism of hydraulic fractures of coal seam in this proposal. Firstly, based on instantaneous frequency and envelope function, the automatic picking method of arrival time for weak MS waves induced by the coal seam HF is studied and proposed. And a layered wave velocity model considering the travel path is constructed. And then, using both of the arrival time and the azimuth angle information as constraints, a new double-difference MS location and wave velocity tomography joint inversion method that suits the coal seam HF is developed. Under the P-wave amplitudes and initial motion polarity constraints, a new moment tensor inversion method based on the waveform matching is developed to determine the MS focal mechanism of hydraulic fractures for coal seam. Based on the above study, the source location and mechanism parameters of MS events induced by the hydraulic fractures expanding process are obtained, and furtherly the source parameters evolution rules are investigated. Based on the MS source parameters, a dynamic characterization method of the coal seam hydraulic fractures is established to infer the distribution and fracture mechanism of hydraulic fractures. The impact scope of coal seam HF can be confirmed by the dynamic characterization method of the coal seam hydraulic fractures, which will be verified through field tests. The research results have important theoretical and practical significance for further understanding the HF mechanism of coal seam, and driving the research of monitoring and effect evaluation for coal seam HF in underground coal mines.

煤层水力压裂在煤矿瓦斯治理和抽采中取得了较好效果，然而煤层水压裂缝监测一直缺少有效手段，是制约该技术发展的难题之一。煤层水力压裂会产生大量的微弱微震信号，本项目利用微震定位及震源机制对煤层水压裂缝扩展过程、形态和破裂机制进行研究。提出基于瞬时频率和包络函数的煤层水力压裂诱发微弱微震波形到时自动拾取方法，构建基于传播路径的煤岩分层波速模型；建立基于到时和方位角共同约束的煤层水压裂缝双差微震定位与波速成像联合反演方法；将P波振幅和初动极性作为约束条件，建立基于波形匹配的煤层水压裂缝微震震源机制矩张量反演方法。得到煤层水压裂缝的微震定位和震源机制参数，并研究震源参数的演化规律；建立基于微震震源参数的煤层水压裂缝动态表征方法，揭示水压裂缝分布形态和破裂机制，确定压裂影响范围，并进行现场试验验证。该研究对进一步认识煤层水力压裂机理，促进煤层水力压裂监测和效果评价技术发展具有重要的理论意义和应用价值。

近年来，水力压裂技术在煤矿煤与瓦斯突出、煤层卸压增透及煤层气（瓦斯）抽采中得到了广泛应用，然而煤矿井下煤岩体水压裂缝监测一直缺少有效技术手段，是煤矿水力压裂面临的研究难题之一。本项目研究改进了实验室煤岩体真三轴水力压裂声发射监测实验系统，研发了钻孔可回收式微震传感器安装装置及方法；分别在实验室和煤矿井下开展了煤岩体真三轴水力压裂声发射定位监测实验和煤层穿层钻孔水力压裂微震监测试验研究；研究提出了基于瞬时频率和包络函数的微震/声发射波形到时自动识别方法和基于AIC的改进微震/声发射波形到时自动识别方法，为水压裂缝震源定位提供了高质量的波形到时数据；研究发展了基于单纯形和双差的煤岩体水压裂缝联合震源定位方法，研究建立了煤岩张-剪破裂位移不连续震源模型，提出了张-剪破裂震源机制定量反演方法，开发了煤岩破裂震源定位及震源机制定量反演程序，实现了煤岩体破裂诱发微震/声发射事件自动识别和波形到时自动拾取、震源定位及震源机制反演；研究揭示了煤岩体水力压裂过程中的震源定位、震源机制等震源参数时空变化规律，研究提出了基于波形特征及震源参数的煤岩体水力压裂裂缝动态表征方法，揭示了基于微震监测的水压裂缝分布形态和破裂机制，确定了压裂影响范围。项目研究成果对进一步认识煤岩体水力压裂机理，促进煤岩体水力压裂监测和效果评价技术发展具有重要的理论意义和应用价值。通过项目研究，共发表论文11篇，其中被SCI收录9篇；申请且授权国家发明专利9项，申请且授权软件著作权2项；培养3名博士研究生，5名硕士研究生；项目组成员参加国内外学术会议10余次，其中做学术报告9次。