页岩夹煤层弱面水平井段定面射孔优化分析

Optimized Analysis on Surface Perforation with Weak-plane Horizontal Well Section of Shale and Coal Seam

在水平井压裂施工过程中,射孔参数的优化是降低储层破裂压力,提高油田经济效益最直接有效的方法。在地下储层中,弱面的存在增强了储层的非均质性,同时改变了射孔时的起裂压力。应用单一弱面强度理论,结合射孔完井下单孔眼最大主应力公式,推导出含弱面水平井段单孔眼最大主应力与弱面倾角的关系。并使用有限元分析软件ABAQUS,对9组不同角度弱面倾角水平井段进行定面射孔模拟分析,得到弱面倾角对孔眼最大主应力和最佳射孔密度的影响规律,对理论模型结果进行验证。结果表明:孔眼处最大主应力受弱面倾角控制,当弱面倾角β<φ/2+45°时,孔眼处最大主应力随弱面倾角增大而减小,此时最佳射孔密度选用13孔/m;当弱面倾角β>φ/2+45°时,随弱面倾角增大,孔眼处最大主应力先减小后增大,最佳射孔密度选用16孔/m;当弱面倾角β=φ/2+45°时,井筒将会沿着弱面发生破裂。对于含弱面水平井段的射孔提出优化方案,最大限度地降低地层破裂压力,该方法对实际生产具有一定的理论指导意义。

In the process of horizontal well fracturing,the optimization of perforation parameters was the most direct and effective method to reduce the fracture pressure of the reservoir and improved the economic benefit of the oilfield.In underground reservoirs,the presence of weak planes enhanced reservoir heterogeneity,changed the perforation fracture pressure at the same time.The single weak plane strength theory and the maximum principal stress formula of perforation under perforation completion were used to deduce the relation between the maximum principal stress of single hole and the inclination of weak plane in horizontal well with weak plane.The finite element analysis software ABAQUS was used to simulate the flattened perforations of 9 groups of horizontal facets with different angles and the influence of the weak planes inclination on the maximum principal stress and the optimum perforation density was obtained.The results show that the maximum principal stress at the perforation was controlled by the inclination of the weaker plane,and the maximum principal stress at the perforation decreases with the inclination of the weak face at a weak face inclination ofβ<φ/2+45°.The perforation density is 13 holes/m.When the weak face inclination angle is granter thanφ/2+45°,the maximum principal stress decreases first and then increases with the increase of the inclination angle of the weak face.The optimal perforation density is 16 holes/m.When the weak face inclination angle isφ/2+45°,the wellbore will crack along the weak plane.For the perforation with weak-plane horizontal well sections,an optimization scheme is proposed to minimize the fracture pressure of the formation.This method has certain theoretical guiding significance for actual production.