煤岩层水力致裂的应力扰动效应研究

发布时间：2018-04-11 21:43

本文选题：水力致裂 + 骨架应力　；参考：《中国矿业大学》2017年硕士论文

【摘要】：煤岩体水力致裂技术已广泛应用于煤炭行业,利用水力致裂技术防治煤与瓦斯突出以及冲击矿压等方面已取得初步成效。目前,水力致裂期间引起煤岩体应力的变化规律还不清楚,对于利用水力致裂技术进行煤矿动力灾害防治而引起的应力扰动是否会诱导突出和冲击仍具有争议。因此,研究煤岩体水力致裂期间及致裂之后的应力扰动规律是一项非常迫切且必要的基础性研究。本文采用物理模拟实验、数值模拟、理论分析和现场分析等方法对煤岩体水力致裂期间及之后的应力扰动规律进行研究。通过在试块内部埋设骨架应力传感器和孔隙水压力传感器,运用大尺寸真三轴水力致裂实验系统进行了物理模拟实验,实时监控了水力致裂过程中水压力的动态变化,监测了试块内骨架应力的动态变化,研究了水力致裂过程中裂缝周边的应力及其梯度变化规律,实验结果表明:在三个主应力方向上,排量越大,应力扰动现象越明显;距离致裂钻孔越近,其应力扰动现象越明显;在垂直于主破裂面方向的应力扰动最为明显,其他方向的应力扰动相对较小。运用RFPA2D-FLOW数值模拟软件对水力致裂的应力扰动规律进行研究,模拟结果表明:钻孔开裂前,在钻孔周围形成压应力集中,并且随着钻孔水压力的增大,垂直于最小主应力方向上的应力集中系数逐渐增大,最大主应力方向上的应力集中系数逐渐减小,并且应力扰动的影响范围逐渐增大;钻孔开裂后,随着水压裂缝的张开及扩展,垂直于最小主应力方向的应力集中系数及应力升高区的范围逐渐增大,并且在水压裂缝尖端形成明显的拉应力集中,使裂尖发生张拉破坏;距离钻孔越远,水压力对主应力的影响越小,同时应力梯度的变化也越小。运用弹性力学、水力学、渗流力学及断裂力学进行理论分析,分别从钻孔未注水时、钻孔注水未开裂时及钻孔注水开裂后三个阶段计算了钻孔周边和裂缝周边应力场。结合燕子山煤矿8403工作面水力致裂现场实测数据,选取了2个致裂孔数据进行分析,结果表明:在致裂的过程中,在工作面听见多次顶板破裂声,说明由于水压裂缝的产生及扩展使得工作面内的应力扰动较为明显,在某个局部形成较大的应力集中,使煤岩体处于塑性变形范围内,当应力集中超过煤岩体的塑性极限时,应变能释放,进而煤岩体内的应力向深部转移。
[Abstract]:Hydraulic fracturing technology of coal and rock mass has been widely used in coal industry. Preliminary results have been obtained in preventing coal and gas outburst and impacting rock pressure by hydraulic fracturing technology.At present, it is not clear how the stress of coal and rock mass changes during hydraulic fracturing, and whether the stress disturbance caused by hydraulic fracturing technology can induce outburst and impact is still controversial.Therefore, it is an urgent and necessary basic study to study the stress disturbance during and after hydraulic fracturing of coal and rock mass.In this paper, physical simulation, numerical simulation, theoretical analysis and field analysis are used to study the stress disturbance during and after hydraulic fracturing of coal and rock mass.By embedding skeleton stress sensor and pore water pressure sensor inside the specimen, the physical simulation experiment was carried out by using the large size true triaxial hydraulic fracturing experimental system, and the dynamic change of water pressure during hydraulic fracturing was monitored in real time.The dynamic change of skeleton stress in the specimen is monitored, and the stress and its gradient change around the crack during hydraulic fracture are studied. The experimental results show that the larger the displacement of the three principal stresses is, the more obvious the stress disturbance is.The closer the borehole is to the fracture, the more obvious the stress disturbance is, the more obvious the stress disturbance is in the direction perpendicular to the main fracture plane, the smaller the stress disturbance is in the other directions.The RFPA2D-FLOW numerical simulation software is used to study the stress disturbance law of hydraulic cracking. The simulation results show that the compressive stress concentration is formed around the borehole before the borehole cracks, and with the increase of the borehole water pressure,The stress concentration factor perpendicular to the direction of the minimum principal stress increases gradually, the stress concentration factor in the direction of the maximum principal stress decreases gradually, and the influence range of stress disturbance increases gradually.The stress concentration factor perpendicular to the direction of the minimum principal stress and the range of the stress increasing zone gradually increase with the opening and expansion of the hydraulic crack, and the tensile stress concentration forms at the tip of the hydraulic crack, which leads to the tensile failure of the crack tip.The farther away from the borehole, the smaller the influence of water pressure on principal stress and the smaller the change of stress gradient.Based on the theoretical analysis of elasticity, hydraulics, seepage mechanics and fracture mechanics, the stress fields around the borehole and around the fracture were calculated from the three stages of the borehole without water injection, the borehole water injection cracking and the drilling water injection cracking.Combined with the measured data of hydraulic cracking in 8403 working face of Yanzishan Coal Mine, the data of two cracked holes are selected for analysis. The results show that: in the process of cracking, the sound of roof cracking is heard many times in the working face.It is shown that the stress disturbance in the working face is obvious due to the production and expansion of the hydraulic crack, and a large stress concentration is formed in a certain area, which makes the coal and rock mass within the plastic deformation range, and when the stress concentration exceeds the plastic limit of the coal and rock mass,The strain energy is released and the stress in the coal and rock is transferred to the deep.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD712.6

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