水力压裂近井裂缝转向延伸轨迹模拟

Simulation of the fracture extension trajectory near the hydraulically fractured wellbore

室内实验和现场实践已经证明射孔方位对水力致裂裂缝延伸转向有极其重要影响,但尚无定量化的理论预测模型。针对均匀各向同性线弹性多孔材料,考虑射孔井水力裂缝起裂的原地应力场和孔隙压力、孔眼内压、压裂液向地层渗滤附加应力等多种机理,基于弹性力学和孔隙介质流体渗流理论,建立了孔眼深度任意位置的应力分布计算模型;基于孔眼末端最大周向拉应力判据,首次建立了压裂裂缝转向模拟的理论计算模型。结合长庆某气田参数进行模拟分析,揭示了垂直井射孔方位对压裂裂缝转向规律:水平主应力差是影响水力裂缝转向半径最主要因素,且随水平主应力差增加,射孔深度减小;射孔方位小于30°时对裂缝转向半径影响较小。

Indoor experiment and field practice have proved that the perforation orientation plays an important role in the hydraulic fracture propagation and re-orientation. But so far, there is no quantitative theoretical predicting model. In the light of the porous material of uniform isotropic linear elastic state, considering a variety of mechanisms such as the in-situ stress field, pore pressure, inner pressure in the hole and the seepage additional stress of the fracturing fluid into the formation for the hydraulic crack fracturing of the perforated well, based on the theory of the elastic mechanics and the theory of the fluid seepage in the porous media, the calculating model of the stress distribution was established for any position of the hole depth;based on the maximal circumferential tensile stress criterion at the end of the hole, the theoretical simulating model was built for the first time for the fracture orientation. Integrated with the simulation analysis with the help of the parameters in a gas field of Changqing, the fracture orienting law for the fracture orientation of the vertical well is revealed: the horizontal principal stress difference is the most important factor affecting the orientation radius of the hydraulic fracture, with the rise of the the horizontal principal stress difference, the depth of the perforation reduces;when the perforation azimuth is smaller than the 30°, the effect on the radius is less.