低渗煤层多脉冲压裂激励煤层气解吸的地应力松弛技术与理论研究

Choosing the low permeability coal seam blocks, collecting and making the coal sample for the test, the mechanical properties of the coal seam are tested by the triaxial rock mechanics experiment, the physical properties and the critical desorption pressure of CBM, are tested by the property simulation experiment of the coal core, meanwhile selecting and confirming the applicable scope of these parameters, the multi-pulse fracturing performance parameter, as well as the matching condition by combining with the characteristics of the multi-pulse fracturing; After proceeding the experimental test by the experimental system device of HEGF which could fully simulating the formation, we have researched the optimized design method which generates and forms the favorable fracture network, in the meantime, relaxes the ground stress; At the same time, we have analyzed the several action mechanisms, such as the falling of the fracture network, the matrix pore pressure, heat energy, gunpowder gas composition and explosive pulse vibration wave, to stimulate the desorption-seepage of CBM；Analyzing a series of coupled relation between the multi-pulse pressure, action time, crack length，non-closed condition and some parameters of the coal seam such as the mechanical properties, ground stress and its physical properties, etc.；By studying the experimental data and numerical simulation method, we have studied the suitable technological principle and theoretical model named multi-pulse fracturing and ground stress relaxation; Combined with the condition of the low permeability coal seam blocks, the systemic theoretical model and technology, which regard to the multi-pulse fracturing applied in the whole block network arrangement, have been built, then perfected through the checking. Finally, this paper provides a theoretical direction and technological approaches for the application and development of the reservoir reform technique on the low coal seam.

初选低渗煤层区块分类采集制作试验煤样，通过三轴岩石力学实验测试煤层力学特性参数，煤心物性模拟实验测试煤层物性及临界解吸压力等相关参数，结合多脉冲压裂技术特点筛选煤层力学特性及物性相关参数的适应范围，确定多脉冲压裂性能参数及匹配条件，建立分类组合模拟实验体系；通过全模拟地层高能气体压裂实验系统装置实验测试，研究其诱生煤层产生和形成有利裂缝网络的地应力松弛优化方法；分析其多裂缝网络及基质孔隙压力降低、热效应、燃气产物、脉冲振动等激励煤层气解吸-渗流的作用机理；分析脉冲压力、作用时间、裂缝长度及不闭合条件等与煤层力学特性、地应力及物性等相关参数一系列耦合关系；研究实验数据信息和数值模拟方法，研究适用于低渗煤层多脉冲压裂的地应力松弛技术原理与理论模型；结合低渗煤层区块条件，建立区块整体网络布局多脉冲压裂的地应力松弛技术与理论模型。并验证完善。为低渗煤层气储层改造技术应用研发提供理论指导及技术途径。

国内外研究表明,煤储层的渗透性对地应力的变化非常敏感,地应力对煤储层渗透性的影响,其实质是通过对煤储层的孔隙结构产生变形引起煤层渗透性发生变化。提高煤储层的渗透性是煤层气有效开发的关键。因此，基于高能气体压裂原理，开展低渗煤层多脉冲压裂激励煤层气解吸的地应力松弛技术与理论研究具有重要意义。.通过对低渗煤层气煤层物性及力学特性参数实验分析，结合多脉冲压裂原理与作用特点试验研究，确定了适用于煤层多脉冲压裂的技术性能参数及匹配条件、试验模型设计与实验方法；分析了多脉冲压裂裂缝扩展规律，建立煤层多脉冲压裂多裂缝物理模型,确定了启裂裂缝及延伸裂缝的产生机理与形成条件；建立了全封闭煤层多脉冲压裂的能量利用率计算模型，分析了多脉冲压裂产生的高能气体能量作用分布特征、有效作用于煤层的能量利用率计算方法；研究确定了适用于低渗煤气层多脉冲压裂的地应力松弛技术原理与设计方法，研发了浅层煤层气全封闭多脉冲压裂开发的工艺与技术，设计了相应的多脉冲压裂装置与工艺，增加了总装药量（总能量），提高了能量利用率，有利于使煤层产生更长的多裂缝缝网；开展了煤层液体火药/液体炸药压裂技术的试验研究，分析了煤层多脉冲压裂/爆炸压裂的作用机理，以达到松弛煤层地应力提高煤层渗透性的目的。.在技术成果与转化方面，把研究所得出的理论与方法用于指导工艺设计与优化，已初步形成浅层煤层气全封闭多脉冲压裂开发技术、煤层气井强脉冲射孔压裂复合工艺等多项工艺技术，并分别在沁水、柳林等地区煤层气现场进行放大化试验应用取得了初步效果，并经在现场通井规通井实际检测符合工艺要求；开展了液体火药技术、中低速液体炸药技术在煤层气压裂开发的作用机理试验研究，并在水平井进行试验应用取得初步进展，为实现厚层、多薄层组合及长井段水平井地层压裂改造的一次性处理提供新技术与研究方法。本项研究为低渗煤层气储层压裂开发提供新的技术途径，具有重要的研究价值与应用前景。