Casing Optimization for CO2 Corrosion Resistance in the Xushen Gas Field

Currently, HP13Cr-110 casing is extensively used in the Xushen Gas Field, its performance can meet all the needs, but the cost is higher. To avoid the use of a single material of casing and lower the cost, the tensile strengths, hardness, toughness and carbon dioxide corrosion resistance of three kinds of casing materials, including 13Cr-95, HP13Cr-110 and 11Cr-110, were tested in lab. Tests obtained the variation curve of corrosion rates with time by fitting test, and the calculation formula to determine the corrosion rates and corrosion indexes for various casing materials. Indoor testing showed that 11Cr-110 possesses good mechanical properties equivalent to HP13Cr-110, and has outstanding resistance to CO2 corrosion. Since the cost of the 11Cr-110 casing is much lower than that of HP13Cr-110 casing, the 11Cr-110 casing has been selected in cementing three wells in Xushen Gasfield. Field tests indicated that the 11Cr-110 casing has excellent anti-corrosion performances, with average corrosion rate of 0.019 6 mm/a only, which can fully meet the demand of Xushen Gas Field, and save 550 000 RMB Yuan in each well on average, playing the role of lowering cost and raising the efficiency.