水平井体积改造应力干扰计算模型及其应用

Stress interference calculation model and its application in volume stimulation of horizontal wells

基于位移不连续边界元法,引入应力校正因子,建立裂缝介质应力场计算模型。模型计算精度与三维位移不连续模型接近,并显著减小了计算复杂度。在此基础上,基于断裂准则和扩展速度模型,建立了多裂缝扩展形态算法,对多裂缝应力干扰及应力干扰下裂缝扩展形态进行了计算研究。结果表明：应力干扰作用范围由缝高或缝长的最小尺寸决定,对缝长大于缝高的裂缝,应力干扰作用范围为1.2～1.5倍缝高,对缝长小于缝高的裂缝其范围为1.2～1.5倍缝长;缝间距相对缝高越大或净压力相对原场主应力差越小,裂缝偏转位置距离井筒越远,裂缝偏转角度越小。3簇等间距布缝时,中间裂缝沿直线路径扩展,而非等间距布缝时,中间裂缝会向间距远的裂缝一侧偏转,且存在单一主扩展裂缝。

A new model for calculating stress fields of fractured media was established by incorporating stress correction factor based on displacement discontinuity boundary element method.The accuracy of the new model is close to 3D displacement discontinuity model,and its calculation is significantly simplified.An algorithm for multi-fracture propagation geometry was proposed based on fracture criterion and fracture growth rate law,which was used to investigate multi-fracture stress interference and propagation geometry.The results show that the size of stress interference is determined by the shortest dimension of fracture face,which is 1.2？1.5 times fracture height when fracture length is longer than fracture height,and 1.2？1.5 times fracture length when fracture length is shorter than fracture height.The larger the ratio of fracture spacing to fracture height,or the smaller the ratio of net pressure to the differential principle stress,the more close to well-bores the deviation position is,and the larger the deviation angle is.The middle fracture propagates to the fracture at a further distance and one dominating fracture propagates longest when three-cluster fractures are not equally spaced,while the middle fracture propagates straightly when three-cluster fractures are equally spaced.