实验尺度下的煤岩水力压裂数值模拟研究

Numerical Simulation of Coal Hydraulic Fracturing at the Experimental Scale

为研究煤岩水力压裂的过程,及其受初始破裂单元和流体注入速度的影响,通过实验图像建立了煤层水力压裂的天然裂缝网络模型。再结合现有的牵引分离准则及流体流动模型建立了煤岩水力压裂数值模拟模型,通过ABAQUS进行数值模拟计算。讨论了煤岩水力裂缝的形成以及数值模拟中的初始破裂单元设置和流体注入速度对裂缝扩展的影响。结果表明:①实验尺度的水力压裂实验研究和数值模拟研究的边界效应应该被考虑;②煤岩水力压裂过程中,裂缝发育可能贯穿于整个压裂过程中;③初始破裂单元个数的增加,煤岩水力压裂的流体压力曲线上的起裂压力逐渐降低,甚至可能低于扩展压力;④流体注入速度越大,煤岩水力压裂的起裂压力和破裂压力越大,而流体注入速度对煤岩水力裂缝扩展的影响存在一定的波动性,应综合考虑。

In order to study the process of coal-rock hydraulic fracturing and its influence by initial fracture unit and fluid injection rate,the natural fracture network model of coal-rock hydraulic fracturing was established through experimental images.Combined with the existing traction separation criteria and fluid flow model,the numerical simulation model of coal-rock hydraulic fracturing is established,and the numerical simulation is carried out by ABAQUS.The formation of coal-rock hydraulic fractures and the influence of initial fracture unit setting and fluid injection rate on fracture propagation in numerical simulation are discussed.The results show that:①The boundary effect of experimental scale hydraulic fracturing experimental research and numerical simulation research should be considered.②Fracture development may run through the whole process of hydraulic fracturing in coal rock.③With the increase in the number of initial fracture units,the initiation pressure on the fluid pressure curve of coal-rock hydraulic fracturing gradually decreases,and may even be lower than the expansion pressure.④The greater the fluid injection rate is,the greater the initiation pressure and fracture pressure of coal-rock hydraulic fracturing are,and the influence of fluid injection rate on coal-rock hydraulic fracture propagation has certain volatility,which should be comprehensively considered.