水平井压裂水泥环应力分析

Stress analysis of cement sheath of horizontal well during hydraulic fracturing

为获取准确的井筒应力分布,根据弹性平面应变力学理论,考虑套管-水泥环-地层系统各部分的应力加载过程和水力裂缝产生的诱导应力场,建立了水平井压裂时套管-水泥环-地层系统应力分布的计算模型。利用该模型,分析了水力裂缝形成前后的系统应力分布,以及裂缝诱导应力场、水泥石杨氏模量、套管壁厚对水泥环内壁应力分布的影响。分析结果表明:随着与裂缝的距离增大,水泥环内壁受到的径向压缩应力逐渐降低,环向应力逐渐由压缩应力变为拉伸应力;优化裂缝间距、降低水泥石杨氏模量、增加套管壁厚可以降低水泥环内壁受力,缓解水泥环内壁的应力集中程度。本文所建模型可为水力压裂水平井的固井设计以及裂缝间距设计提供理论指导。

In order to obtain the accurate stress distribution of wellbore, according to the plane theory of elasticity, considering the stress loading process of casing-cement sheath-formation system and the stress field induced by hydraulic fractures, a calculation model of stress distribution in casing-cement sheath-formation system is established. Using this model, the stress distribution of the system before and after the formation of fractures, and the influences of the induced stress field, the Young's modulus of cement stone and the casing thickness on the stress distribution of cement sheath are analyzed. The results show that the radial compressive stress of the inner wall of the cement sheath decreases gradually with the distance from the fracture, and the circumferential stress gradually changes from the compressive stress to the tensile stress. Optimizing the fracture spacing, reducing the Young's modulus of cement stone and increasing the casing thickness can reduce the stress and relieve the stress concentration on the inner wall of the cement sheath. The model provided in this paper supplies a theoretical guidance for cementing design and fracture spacing design of horizontal well that will conduct hydraulic fracturing.