斜井井筒附近水力裂缝空间转向模型研究

Three-dimensional model for space reorientation of hydraulic fractures near deflecting well bore

在斜井井筒附近应力场分布复杂,往往造成水力裂缝转向。基于最大拉伸应力准则和拉格朗日极值法,建立了斜井井筒附近水力裂缝空间转向模型,用于分析三向地应力和井筒内压作用下斜井井筒水力裂缝的起裂位置和扩展形状。根据此模型,编制了数值计算程序。对长、宽、厚均为300mm的岩石试样在真三轴水力压裂模拟装置上进行了物理模拟,模型计算结果与物理模拟结果基本一致。模拟计算和物理试验结果表明,斜井井筒附近确实存在水力压裂裂缝空间转向的现象。斜井井筒附近水力裂缝的空间转向大致发生在3倍于井筒直径的范围内。

The complicated stress distribution around deflecting well bore always results in the reorientation of hydraulic fractures. A three-dimensional model for reorientation of hydraulic fracture near well bore was presented using the maximum tensile stress criterion and the Lagrange multiplier method. The model can be used to analyze the initiation position and propagation shape of hydraulic fractures under the action of the three-dimensional underground stresses and well-bore pressure. Some numerical calculation procedures were made for simulation. According to the model, laboratory experiments on rock samples with three-dimensional size of 300 mm were performed on the true tri-axis simulation equipment of hydraulic fracturing. The calculated results are basically in agreement with the experimental results. The fundamental patterns of the three-dimensional reorientation of hydraulic fractures near well bore were drawn. The results show that the three-dimensional reorientation of hydraulic fractures near deflecting well bore exists indeed and occurs generally within the range of three times of the well bore diameter.