辽河油田欢2-16-304C井套管腐蚀分析

Casing Corrosion Analysis of Huan2-16-304C Well in Liaohe Oilfield

欢2-16-304C井准备转为注水井，转注前套管试压结果表明，井下部分套管存在漏失点。对该井进行大修，发现第6～12根套管外壁腐蚀严重，第12根套管在起出过程中断裂，断裂面很薄。现场检测没有发现硫化氢和二氧化碳，可以排除硫化物应力腐蚀开裂和二氧化碳对套管造成腐蚀损坏的可能性。对该区块浅层水质进行分析，发现50～200m处的地层水矿化度为2.68×10^4mg/L,且存在大量氯离子和硫酸根离子，由此判断浅层流体较高的矿化度是造成套管腐蚀的主要原因。J55套管钢级较低，壁厚较薄，抗腐蚀能力较差。建议今后在钻井设计前必须对土壤的腐蚀性做出评价，对此类高矿化度地区的同一类油水井，最好使用同一材质的油套管，如P110油层套管，固井设计也要考虑到土壤对套管的腐蚀问题，若地层腐蚀性较强，固井时应将固井水泥返至地面。

Huan 2-16-304C well is to be water injector.Before that,hydrostatic test results of casing show thai leakoff point appears at partial casings of the bottom hole.After workover of this well,we found that ectooecium of sixth to twelfth casing were corroded severely and the twelfth easing fractured during it tripped out with thin fracture plane.It cannot be resulted from hydrogen sulphide and carlton dioxide for they are not tested in the field.Analysis on water quality at shallow layers in this block presents that the salinity of formation water at the depth of 50 to 200m is 2.68×10^4mg/L and large amount of Cl^- and SO4^2- exists in the water.So the high salinity of the shallow layers result in casing corrosion mainly.Corrosion resistance of J55 casing is poor for its lower steel grade and thin wall.It is suggested that corrosiveness of the soil must be evaluated before drilling and the same grade casing such as P110 musl be applied for the same type of oilwater wells at this type of high-salinity area.This issue should also be considered during well cementation.If the corrosiveness of the formations is strong,cement should return to the ground during the well cementation.