水泥环弹性参数对套管—水泥环—地层固结体结构完整性的影响

Impact of elastic parameters of cement ring on structural integrity of casing-cement ring-strata cementing combination

油气井套管试压、压裂等施工作业过程中,套管—水泥环—地层固结体将产生应力与变形响应。过高的载荷作用下,可能会造成水泥环本体破坏、胶结界面撕开等结构破坏形式,危及水泥环的封固效果。应用力学原理及有限元理论,建立了套管—水泥环—地层固结体力学模型,分析了水泥环弹性常数对固结体结构完整性的影响。研究结果表明,水泥环弹性模量较小时,变形能力强,载荷作用下不易于产生结构破坏,卸载后抗撕裂能力较好;高地应力地层条件下,泊松比越小水泥环抗破坏能力越强;低地应力地层,泊松比越大胶结界面抗撕开能力越好。工程中应根据封固井深等具体情况综合考虑加载、卸载两种载荷作用方式对水泥环弹性参数进行优选。

In the process of the oil and gas well operations such as casing pressure test, fracturing, etc., casing-cement ring-strata cementing combination will have stress and deformation response. Under the condition of high load, the cement ring body damage, cementing interface tear, and other forms of structural failure may occur, which may make the effect of cement ring sealing worsen. The casing-cement ring-strata cementing combination ifnite element mechanics model was established by using the mechanics theory and ifnite element theory in the paper. The impact of elastic parameters of cement on the casing-cement ring-strata cementing combina-tion structural integrity was analyzed. The results showed that, when the elastic modulus of cement ring was smaller, the deformability was better, and cement stone was more dififcult to be hardness crushed after load, while the tear resistance was better after unload;The smaller the poisson ratio was, the harder the cement was to be crushed under the geological conditions of high in-situ stress. The larger the poisson ratio was, the harder the cementation interface was to be tore under the geological conditions of low in-situ stress. The opti-mization of cement ring elastic perameters should be based on speciifc circumstances such as cementing well depth in the comprehensive consideration of loading and unloading methods in engineering designing.