南海西部油田高温高压气井套管磨损预测

为避免南海西部油田高温高压气井套管磨穿问题的发生,对套管磨损进行了预测。采用滑台式套管磨损试验机,在模拟工况下开展了系列磨损试验,得到了接触力、转速、钻井液密度等参数与套管磨损量之间的关系,求取了套管壁厚损失、抗内压强度、抗外挤强度及安全系数等参数。试验结果显示,接触力越大,转速越高,钻井液密度越大,则套管累计磨损量越大;不同耐磨带对应的套管磨损不同且差别较大,在设计工况下套管磨损系数小于2.0×10-14 Pa-1。以A7H井为例,造斜率为3°/30m,φ339.7 mm和φ244.5 mm套管磨损后壁厚分别减小8.5%和13.1%,抗内压强度分别降低8.0%和13.0%,抗外挤强度分别降低8.0%和13.0%,抗内压最小安全系数分别为1.41和1.47,抗外挤强度最小安全系数分别为1.22和1.20,强度满足相关标准的要求,现场作业中未出现套管磨损失效现象。研究表明,接触力、转速、钻井液密度相同的条件下,磨损量与磨损时间之间呈多项式关系;该预测方法可较为准确地预测套管磨损程度,从而决定是否采取防磨减磨措施,避免井下故障发生。 

Casing Wear Prediction for HTHP Gas Wells in West of South China Sea Oilfield

Casing wear prediction is conducted to avoid casing wear at the HPHT gas wells west of South China Sea Oilfield.The relation of casing wear loss vs. contact force, rotary speed and drilling fluid density was obtained after casing wear tests were performed with slide-platform tester under simulated conditions. The casing wall thickness loss, burst strength, collapse strength and safety factors were calculated. The tests demonstrated that cumulative casing wear loss increases with the increase of contact force, rotary speed and drilling fluid density. Casing wear magnitude varies greatly in different hardbandings, but the casing wear coefficient is less than 2.0×10-14 Pa-1 under the designed operation conditions.Taking the Well A7H as an example, its build-up rate is 3°/30m, the losses of wall thickness for φ339.7 mm and φ244.5 mm casings are 8.5% and 13.1% respectively after wearing, the burst strength dropped by 8.0% and 13.0%, the collapse strength was reduced by 8.0% and 13.0%. The minimum safety factors of burst strength are 1.41 and 1.47, and the minimum safety factors of collapse strength are 1.22 and 1.20 respectively, which can still meet the requirements of related standards, and no casing worn out and failed at site operation. A study shows that the polynomial linear relationship between casing wear magnitude and wear time existed when the contact force, rotary speed and drilling fluid density are kept in constant. The method can predict the casing wear magnitude accurately, so as to decide whether the corresponding measures to be taken against casing wear, and to avoid drilling problems.