深水浅部地层水泥环应力分布规律研究

The Cement Sheath Stress Distribution Research in Shallow Formation of the Deep Water Area

位于深水浅部地层的固井水泥环面临十分复杂的环境,目前针对深水浅层水泥环力学分布规律的研究较少。研究深水浅层水泥环应力分布规律,对于预测水泥环的完整性,防止安全事故的发生具有十分重要的意义。以弹塑性力学理论为基础,运用ABAQUS有限元软件,建立套管-水泥环-深水浅层组合体模型,分析不同因素对水泥环应力分布规律的影响;并得出以下结论:水泥环内壁为危险界面;随套管内压的增加,水泥环径向压应力逐渐增大,水泥环周向应力由压应力状态向拉应力状态过渡,水泥环的失效形式主要是周向拉伸破坏;水泥环弹性模量越大,其周向拉应力和径向压应力越大,而水泥环泊松比对应力分布规律的影响规律相反;深水浅部地层弹性模量和泊松比越大,水泥环越安全;水泥石在硬化过程中传递深水浅部地层孔隙压力在一、二界面产生初始应力,该力能减小水泥环周向拉伸破坏风险,有利于维持水泥环完整性。

Located in the shallow strata of in deep water,the cement sheath suffers more complex environment,and there are few people research this theory,therefore,it is significant to study the rule of cement sheath stress distribution,to predict the integrity of the cement sheath and prevent the occurrence of safety accidents. This paper is based on the theory of elastic-plastic mechanics and the casing-cement sheath-formation assembly is established,using the finite element software ABAQUS to analysis the stress distribution of cement sheath and draw the following conclusion: with the increase of the casing pressure,cement sheath radial compressive stress increases gradually and the cement sheath circumferential stress transits from compressive stress to tensile stress state,thus,the radial cracks caused by the circumferential tensile is the failure forms of cement sheath; the circumferential tensile stress and radial compressive stress are greater with the elastic modulus increasing,and the effect of cement sheath poisson's ratio is the opposite; with the increase of the formation elastic modulus and poisson's ratio,the cement sheath becomes more safer; the inner concrete sheath wall is the dangerous interface; the first and second interface initial stress can reduce the risk of damage of the cement sheath,which is beneficial to maintain the integrity of cement sheath.