射孔完井条件下地层破裂压力修正公式

在重新考察垂直井射孔完井条件下孔眼的应力状态后,利用替代方法给出了某一射孔深度处的孔眼壁面出现破裂所需要注入压力的计算公式.但分析公式,发现人工裂缝将会在射孔根部位置出现,于是给出了相应的地层破裂压力计算修正公式.研究结果袁明,计算修正公式与原公式对比,更能反映射孔完井条件下地层的应力状态和实际情况,可供油田的钻井和压裂设计作参考.

Modified Formula of Formation Breakdown Pressure for Perforation Completions of Vertical Wells

The stress state of perforation holes was re-inspected in this paper, and it is found that the horizon-tal principal stresses should be substituted by the vertical and radial normal stresses. Utilizing the substituting method, the breakdown pressure for one certain position of perforation depth was derived. According to it, the artificial vertical fracture will appear at the base of the perforation,and the corresponding modified formula of formation breakdown pressure for arbitrary perforation completions was given. Comparing the formula with the original formula, we find that the original one can be seen as an approximation of formation breakdown pressure. The results show that the stress condition and actual situation of the perforated formation can be bet-ter reflected in the modified formula, which is applicable to guide drilling and fracturing designs of oilfields.