水力裂缝周围应力场解析模型及应力扰动分析

Stress Field Analytic Model and Stress Perturbation Analysis around Hydraulic Cracks

运用势理论建立了无限大地层Ⅰ-Ⅱ复合型裂缝周围应力场解析模型,得到地应力和流体压力双重作用下Ⅰ-Ⅱ复合型裂缝应力场函数和复合裂缝应力场解析表达式。计算并分析了裂缝倾角为0°、30°、45°和60°等4种倾斜裂缝周围的有效应力分布。研究中发现:当垂直于裂纹面方向距离超过4倍半缝长时,诱导应力几乎可以忽略不计;垂直于裂纹面方向的应力扰动范围比平行于裂纹面方向的扰动范围大57.7%~61.5%;平行于最大水平主应力的裂缝在垂直于裂纹面方向中心区域的应力诱导范围比端部高7.9%~10.8%,不平行于最大水平主应力的裂缝垂直于裂纹面方向中心区域应力诱导范围比端部低23.8%~26.4%;在裂缝周围存在应力增强区和应力屏蔽区,且范围和形态与射孔方向和最大水平主应力夹角存在关系。研究结果可为水平井射孔角优选以及分段压裂的裂缝优化布置提供一定的理论指导。

An analytic model of stress field around I - II mixed m o d e fracture in an infinite plate based on the Potential theory has been established. The function of the stress field of the I - II composite fracture and the analyt-ical expression of the stress field of the composite fracture have been obtained under both ground stress and fluid pressure. The effective stress distributions around the four kinds of inclined fractures with the inclination angle of 0o,300,450 and 60o have been calculated and analyzed. The study found that the induced stress is almost negli-gible when the distance to the fracture plane is more than 4 times the half fracture length. The range of stress dis-turbance perpendicular to the fracture plane is 5 7 . 7 %？61.5 % larger than that of the stress disturbance parallel to the fracture plane. The central stress-induced area perpendicular to the fracture surface by the fracture parallel to the maximum horizontal principal stress is7.9%~10. 8 % higher than that of the fracture end. While for the frac-ture not perpendicular to the maximum horizontal principal stress, the central stress-induced area perpendicular to the fracture surface is 23. 8%~26. 4% lower than that of the fracture end. There exist stress-enhanced regions and stress-shielded regions around the fracture, whose range and morphology are related to the angle between the perfo-ration direction and the maximum horizontal principal stress . The study results can provide theoretical guidance for optimization of the horizontal well perforating angle and the fracturing layout in the multistage fracturing.