页岩气井多簇压裂套管应力影响因素分析

Influential Factors of Multi-Cluster Fracturing Casing Stress in Shale Gas Wells

页岩气井储层改造多采用多簇压裂技术实现增产目的,同时也引发了套管失效问题。为研究多簇压裂对套管应力的影响,基于理论公式和有限元分析方法,建立套管应力力学计算模型和多簇裂缝-地层-水泥环-套管三维有限元模型,借助力学模型验证有限元模型的可行性,模拟裂缝簇数、岩石弹性模量、水泥环弹性模量、套管内壁压力和地应力变化对套管应力的影响,并针对威荣区块某井压裂段进行实例分析。研究结果表明:套管应力随着裂缝倾角θ的增大而减小,θ=15°为套管应力风险值;套管应力随着压裂簇数的增加整体呈现先小幅增大后减小的趋势;套管应力随着岩石弹性模量的增大而减小,当岩石弹性模量低于45 GPa时,套管应力随着水泥环的硬度增强而增大;套管应力随着水泥环弹性模量的增大而增大,变内压不会改变套管应力变化趋势;套管应力随套管内壁压力的增大而增大,地应力差值的变化不改变套管应力变化趋势;随着地应力差值的增大,套管应力呈现增大的趋势。研究成果对多簇压裂套管的损坏防治具有一定的指导意义。

Multi-cluster fracturing technology is often used in shale gas reservoir reconstruction to increase production,which also leads to casing failure.To study the influence of multi-cluster fracturing on casing stress,based on theoretical formulas and finite element analysis method,a casing stress mechanics calculation model and a multi-cluster fracture-formation-cement sheath-casing 3D finite element model were built;then,the mechanical model was used to verify the feasibility of the finite element model,and simulate the influence of fracture cluster number,rock elastic modulus,cement sheath elastic modulus,inner wall pressure of casing and in-situ stress variation on casing stress;and finally,a case analysis was conducted on a fracturing section in a well of the Weirong block.The results show that the casing stress decreases with the increase ofθ,andθ=15°is the risk value of casing stress;as the number of fracturing clusters increases,the casing stress shows a trend of first slightly increasing and then decreasing as a whole;the casing stress decreases with the increase of rock elastic modulus,when the rock elastic modulus is below 45 GPa,the casing stress increases with the increase of cement sheath hardness;the casing stress increases with the increase of the elastic modulus of cement sheath,while the change in internal pressure does not change the trend of the casing stress change;the casing stress increases with the increase of the inner wall pressure of casing,and the change in in-situ stress difference does not change the trend of the casing stress change;and as the in-situ stress difference increases,the casing stress shows an increasing trend.The study results have certain guiding significance for the prevention and control of damage of multi-cluster fracturing casings.