体积压裂过程中岩性界面对套管应力影响研究

Effect of Lithology Interface on Casing Stress during Stimulated Reservoir Volume Fracturing

页岩气井压裂过程中套管变形问题显著,岩性界面是导致套管变形的重要影响因素。基于页岩气井压裂工程实际,建立了套管-水泥环-地层有限元模型,采用解析法和数值法结合的方式,计算了页岩储层各向异性、瞬态温度-压力耦合作用以及岩性界面对套管应力的影响。研究结果表明:相比各向同性储层,页岩储层各向异性提高了套管应力,弹性模量各向异性相比泊松比各向异性更为敏感;瞬态温度-压力耦合作用下套管应力先增大后减小,压裂液排量越大,套管应力越高;岩性界面大幅提高了套管应力,是导致套管产生变形的重要原因。研究结果可为页岩气井压裂过程中套管完整性设计和控制提供参考。

Casing deformation issue during shale gas well fracturing is outstanding. The lithology interface is an important factor that causes casing deformation. Based on the practice of shale gas well fracturing,a casing-cement sheath-formation finite element model is established. Using the combination of analytical method and numerical method,the shale reservoir anisotropy,the transient temperature-pressure coupling effect and the lithology interface effects on casing stress are calculated. The results show that compared to isotropic reservoir,the shale reservoir anisotropy increases the casing stress,in which the elastic modulus anisotropy is more sensitive than the Poisson＇s ratio anisotropy. Under the transient temperature-pressure coupling effect,the casing stress increases first and then decreases. The larger the displacement of the fracturing fluid,the higher the casing stress. The lithology interface greatly increases the casing stress and is an important cause of casing deformation. The study results can provide references for casing integrity design and control in shale gas well fracturing.