具有腐蚀坑缺陷的套管强度评估

Assessing the Strength of Casing Pipes that Contain Corrosion Pit Defects

近年来,油田套管腐蚀越来越严重,据统计,大港油田某区块套管腐蚀达到34.4%,造成了严重的套损、套漏等问题。基于上述问题,以弹性力学理论和球形腐蚀坑套管力学模型为基础,分别建立了具有两个腐蚀坑缺陷和一个腐蚀坑缺陷的套管-水泥环-地层三维有限元模型,通过具有两个腐蚀坑缺陷的模型对套管上的应力分布规律的研究,发现腐蚀坑之间的距离大于0.65 mm时,可以用具有单个腐蚀坑缺陷模型来评价套管的强度。基于单个腐蚀坑缺陷的模型,研究了腐蚀坑的半径、深度对套管强度的影响及其应力集中系数的变化规律,且研究了不同钢级在地层水化条件下对具有腐蚀坑的套管的受力影响。结果发现,有腐蚀坑缺陷的套管,其最大应力和应力集中系数随腐蚀坑深的增加而增大,且腐蚀坑半径越小,应力集中系数越大,最大达到2.0以上;其次,地层水化后加快具有腐蚀坑的套管的损坏。

The corrosion of oilfield casing pipes has become increasingly severe in recent years.According to statistical data,the corrosion of the casing pipes in each block of the Dagang Oilfield has reached 34.4%,leading to problems such as severe casing damage and leakage.To address this problem,this study constructed three-dimensional finite element models for casing pipe-concrete sheath-ground strata systems with casings that contain either one or two corrosion pit defects based on elasticity theory and mechanical models of casing pipes with spherical corrosion pits.By studying the patterns of stress distribution in casing pipes using the model with two corrosion pit defects,it was found that the model with a single corrosion pit defect could be used to evaluate the casing strength if the gap between the corrosion pits exceeds 0.65 mm.The effects of the corrosion pit radius and depth on the strength of the casing pipes and the variational patterns of a casing pipe’s stress concentration factors were studied herein using the single-corrosion pit defect model.The effects of steel grade on the loading of casing pipes with corrosion pitting in hydrated strata were also investigated.Consequently,the maximum stress and stress concentration factors in the casing pipes with corrosion pitting both increased with the increasing corrosion pit depth.The stress concentration factor also increased as the radius of the corrosion pit decreased.The stress concentration factor may exceed 2.0 in certain cases.Furthermore,the strata hydration accelerated the damage of casing pipes that contained corrosion pits.