水平井水力裂缝非平面扩展研究

基于最大拉伸应力准则和拉格朗日极值法,建立了水平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水平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。针对所建立的理论模型,在真三轴水力压裂模拟装置上采用300mm×300mm的岩石试样进行了物理模拟,模型计算结果与物理模拟结果基本一致。通过模拟计算和物理试验,得到了井筒附近水力压裂裂缝空间转向的基本规律。研究结果表明,水平井井筒附近水力裂缝确实存在空间转向现象,裂缝在转向前与井筒的距离随井筒方位角增大而增加,但增加幅度不大,大致发生在3倍井筒直径的范围内。

Non-planar propagation of hydraulic fracture near horizontal wellbore

A three-dimensional model for describing hydraulic fracture reorientation near horizontal wellbore was established on the basis of maximum tensile stress criterion and the Lagrange Multiplier method. The model can be used to analyze non-planar shape of hydraulic fracture during propagation under three far-field ground-stresses and wellbore pressure. The numerical codes were developed for simulation. According to the theoretical model，laboratory experiments with rock sample of 300mm×300mm×300mm in size were made on the true tri-axis simulation equipment of hydraulic fracturing. The calculated results by the theoretical model are basically consistent with those of experiments. The fundamental patterns of three-dimensional reorientation of hydraulic fracture near wellbore were obtained. The main results of theoretical model and experimental verification showed that three-dimensional reorientation of hydraulic fracture exists near horizontal wellbore indeed，and the distance away from wellbore before fracture turning increases with increament of wellbore orientation angle. The increasing magnitude is limited.Generally it occurs within three times of wellbore diameter.