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.