体积压裂改造非对称性对套管损坏影响机理

Study on the Mechanism of the Asymmetry Effect of SRV Fracturing on Casing Damage

针对致密油气藏体积压裂改造过程中的套管损坏问题,根据弹塑性力学、接触力学理论,结合体积压裂改造施工实际情况,建立全三维尺寸的套管-水泥环-地层耦合有限元分析模型,以不同椭圆柱形表征体积压裂改造的非对称区域,采用Fortran子程序对ABAQUS求解器进行干预和二次开发,模拟了体积压裂改造区域水化膨胀的物性动态演化和力学性质。结果表明:随着椭圆形改造区域长短轴之比增加,井筒周围外载荷的非均匀性增强,通过水泥环传递到套管上的非均匀程度先增加后趋于稳定;随体积膨胀率增加,套管外载荷的非均匀程度增加;套管外载荷非均匀性的增强极大地增加了套管的应力水平,容易造成套管失效问题。该研究可为体积压裂参数优化设计提供理论依据,对预防套管及水泥环失效具有指导意义。

To address the problem of casing damage in the SRV fracturing of tight oil and gas reservoirs,a full-sized three-dimensional casing-cement sheath-formation coupled finite element analysis model was established according to the theories of elastoplastic mechanics and contact mechanics and the actual construction conditions of SRV fracturing,with SRV fracturing asymmetric zones characterized by different elliptic cylinders and ABAQUS solver intervened and secondly developed with Fortran subroutine,in order to simulate the dynamic evolution of physical properties and the analysis of mechanical properties of hydration-induced swelling in the SRV fracturing zones.The results showed that the loads outsides the perimeter of the wellbore were more nonuniform with the increase of the ratio of the long and short axes in the elliptical stimulated zone,and the non-uniformity transmitted to the casing through the cement sheath increased first and then tended to be stable;the non-uniformity of the external load on the casing increased with the increase of the volume expansion rate;the increase of the non-uniformity of the external load on the casing exerted more stress on the casing,easily leading to casing failure.This study provides a theoretical basis for the optimal design of SRV fracturing parameters,and plays a guiding role in the prevention against casing and cement sheath failure.