现场工况条件下含点蚀缺陷套管抗外挤强度分析

Analysis of Collapse Strength of Casing with Pitting Defects under Field Operating Conditions

套管一旦发生点蚀,其表面可能出现孔洞,甚至穿孔现象,这严重削弱了套管的剩余强度,对井场的生产和安全构成了重大威胁。为了评估点蚀后套管的抗外挤强度,提出了一种模拟现场工况对套管抗外挤强度进行分析的方法。首先模拟现场工况下压力和温度条件,严格配比井下腐蚀液体作为介质对套管全尺寸试样和挂片样件进行腐蚀;然后对腐蚀后套管进行抗外挤试验,测量出其被挤毁时的失效压力;接着观察腐蚀后挂片的表面点蚀规律,并计算和测出其平均腐蚀速率、最大点蚀深度和点蚀密度,为有限元分析提供数据支撑;最后使用ABAQUS对不同条件下套管的抗外挤强度进行分析。结果表明:在一定温度和压力范围内,温度和压力越高,套管失效压力越高;平均腐蚀速率、最大点蚀深度和点蚀密度随温度和压力升高而增大,其中平均腐蚀速率增长率为112.5%,增长最为显著;套管的抗外挤强度随腐蚀时间增长而降低;点蚀密度会影响套管的应力分布情况和承载能力。

Once pitting occurs in the casing,it can lead to the formation of holes or even perforations on the surface,severely compromising the casing’s residual strength,and posing a significant threat to production and safety in the wellfield.To assess the extrusion resistance of the casing after pitting,a method is presented for analyzing the extrusion resistance of the casing under simulated field conditions.Firstly,the pressure and temperature conditions under field conditions are simulated,strictly matching downhole corrosive fluids as the medium to corrode full-scale casing specimens and coupon samples.Subsequently,extrusion resistance tests are conducted on the corroded casing to measure its failure pressure.The pitting patterns on the corroded coupons is observed,the average corrosion rate,maximum pitting depth and pitting density are calculated and measured,providing data support for finite element analysis.Finally,ABAQUS is used to analyze the extrusion resistance of the casing under different conditions.The results indicate that within a certain range of temperature and pressure,as temperature and pressure increase,the casing’s failure pressure also increases.The average corrosion rate,maximum pitting depth,and pitting density increase with higher temperature and pressure,with the average corrosion rate showing the most significant increase at 112.5%.The casing’s extrusion resistance decreases as the corrosion time increases,and pitting density affects the stress distribution and load-bearing capacity of the casing.