大尺寸真三轴煤岩水力压裂模拟试验与裂缝扩展分析  

Hydraulic fracturing simulation test and fracture propagation analysis of large-scale coal rock under true triaxial conditions

作　　者：张帆[1] 马耕[1,2,3] 冯丹 ZHANG Fan;MA Geng;FENG Dan(School of Energy Science and Engineering,Henan Polytechnic University,Jiaozuo,Henan 454003,China;Research Institute of Henan Energy Resource and Chemical Industry Group Co.Ltd.,Zhengzhou,Henan 450046,China;Henan Engineering Research Center of Simultaneous Extraction of Coal and Gas with Low Permeability & Outburst Coal Seam,Zhengzhou,Henan 450046,China;State Key Laboratory for Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing 400044.China)

机构地区：[1]河南理工大学能源科学与工程学院,河南焦作454003 [2]河南能源化工集团研究院有限公司,河南郑州450046 [3]河南省低渗突出煤层煤与瓦斯共采工程技术研究中心,河南郑州450046 [4]重庆大学煤矿灾害动力学与控制国家重点实验室,重庆400044

出　　处：《岩土力学》2019年第5期1890-1897,共8页Rock and Soil Mechanics

基　　金：2016年国家科技部创新方法工作专项(No.2016IM010400);2015年河南省科技攻关项目(No.152102310095);河南省创新型科技人才队伍建设工程(No.164100510024)~~

摘　　要：水力压裂是一项广泛应用于低渗煤层的卸压增透技术。为了深入研究煤岩受力、天然裂缝、泵注排量对水力裂缝扩展规律及空间结构的影响,采用大尺寸真三轴水力压裂试验系统、压裂液中添加示踪剂等方式,在真三轴条件下对大尺寸煤岩进行了水力压裂试验。通过剖切压裂试样描述了水力裂缝扩展和空间展布规律,分析了裂缝宽度与应力之间的关系,并初步探讨了煤岩水力裂缝网络的形成机制。结果表明:(1)水力裂缝自割理处起裂并沿割理扩展、连接割理,进而形成复杂的裂缝网络结构;(2)水力裂缝受应力条件作用明显,当最大水平主应力和垂向应力相近,且远大于最小水平主应力时,易形成复杂的裂缝形态;(3)煤岩天然裂隙的存在是形成裂缝网络结构的前提,泵注排量对裂缝网络的形成也有重要影响;(4)煤岩裂隙在局部区域影响水力裂缝转向、分叉,但最终水力裂缝在扩展过程中逐渐转向至最大主应力方向;(5)水力压裂过程中,裂缝宽度的变化不仅与煤岩所受应力有关,还受到压裂液排量、天然裂缝等因素的影响。研究结果可以为煤岩裂缝网络的形成机制、现场施工参数的选取提供技术支持。Hydraulic fracturing is a pressure relief and permeability enhancement technology widely applied in low permeable coal seam. To study the impacts of in-situ stress, natural fractures and flow rates on fracture propagation and fracture network, the true triaxial hydraulic fracturing experiments of large-scale coal seam were conducted on large-scale true triaxial hydraulic fracturing experimental system and tracer technique in hydraulic fluid. The propagation and geometry of hydraulic fractures were described by cutting the fractured specimen. The relationship between fracture width and in-situ stress was analyzed and fracture network mechanism in coal rock was studied. The experimental results indicate that: 1) Fracture network forms when hydraulic fractures propagate along cleats after initiation. 2) Hydraulic fracture is greatly affected by in-situ stress. Complex fracture morphology easily forms when maximum horizontal stress is close to vertical stress and both of them are much bigger than minimum horizontal stress.3) Natural fractures in coal rock are the foundation of fracture network, which is also affected by flow rate. 4) Hydraulic fractures may steer and branch under the impacts of natural fractures at local, but they finally adjust the propagation to the direction of maximum horizontal stress. 5) During hydraulic fracturing process, the changes of fracture width are affected by factors include in-situ stress, flow rates, natural fractures in coal rock, etc. The results could provide technical support for understanding fracture network mechanism and determination of field fracturing parameters in CBM reservoir.

关 键 词：煤层气 水力压裂 裂缝扩展 裂缝网络 裂缝宽度 

分 类 号：TD712[矿业工程—矿井通风与安全]