裂缝性储层水力裂缝扩展规律数值模拟研究

Numerical Simulation Study on Propagation Regularity of Hydraulic Fracture in Naturally Fractured Reservoirs

天然裂缝与水力裂缝的相互作用形成复杂裂缝的关键,采用耦合孔隙水压力的内聚力单元,模拟了天然裂缝存在下水力裂缝的扩展情况,探讨了逼近角及天然裂缝起裂应力对水力裂缝扩展及天然裂缝开启范围的影响。为保证缝内压力的连续性,在预置天然裂缝与水力裂缝的相交处耦合孔隙压力,裂缝位置采用变密度进行网格划分以提高收敛性。数值分析结果表明:水力裂缝的诱导应力场使得天然裂缝提前开启,天然裂缝的破坏形式以剪切破坏为主导;水平主应力差一定时,逼近角越小天然裂缝越易开启且开启长度越长;天然裂缝起裂应力增加,水力裂缝最大缝宽增加天然裂缝开启范围缩小。

The cohesive zone method coupling stress-seepage-damage field was used to simulate the interaction between hydraulic fracture and natural fracture. The effect of approaching angle and natural fracture fracturing initiation pressure on expansion of hydraulic fracture and the open range of natural fracture was investigated. In order to maintain the fluid flow continuity in the fracture, the pore pressure at the intersection of natural fracture and hydraulic fracture was coupled. To improve the convergence, variable density grid was used at the position of fracture. The results show that the induced stress field of the hydraulic fracture causes the natural fracture to be opened earlier. The failure mode of natural fracture is dominated by shear failure. The open length of the natural fractures increases with the decreasing of the approaching angle. The maximum crack width of hydraulic fracture increases while the open range of natural fracture decreases with increase of natural fracture fracturing initiation pressure.