射孔对地层破裂压力的影响

射孔孔眼是沟通井筒和地层的通道,压裂施工中射孔参数的选择影响到施工效果。采用三维有限元模型和岩石的抗拉破坏准则,系统研究了垂直井中射孔对地层破裂压裂的影响,考虑的射孔参数包括射孔密度、射孔方位、射孔孔眼直径和射孔孔眼长度。计算结果表明,射孔方位角是影响地层破裂压力的主要因素,孔眼长度和射孔孔眼直径的影响不大。随着射孔密度的增加,地层破裂压力减小;当射孔方位角小于45°时,地层破裂压力随射孔方位角的增大而增加。这对实际的射孔参数优化设计和压裂施工具有重要的参考意义。

A Study of the Influence of Perforation on Formation Fracturing Pressure

Hydraulic fracturing treatments of oil wells are greatly affected by the perforation parameters selected. The three-dimensional finite element model together with the tensile criterion of rock materials is employed to systematically investigate the influence of perforation parameters, such as perforation density, perforation orientation, perforation diameter, and perforation length as well as wellbore ellipticity, in vertical wells on the formation fracturing pressure. Based on a six-month simulation research in the University of Petroleum, China, several conclusions are drawn for the first time. Perforation density and perforation orientation angle are the most important parameters controlling the formation fracturing pressure. As the perforation density increases, the fracturing pressure decreases, not linearly but progressively. The fracturing pressure increases with the perforation orientation angle only when the angle is less than 45 degrees, and the relationship becomes very flat when the angle is 45 degrees. However, with regards to the perforation diameter and perforation length, their influences are much slighter. The wellbore ellipticity has a significant effect on the formation fracturing pressure. It is obvious that fracturing pressure increases linearly with the ellipticity of the wellbore.