Cementing Technologies with Large-Size Casing in the Kuqa Piedmont

Aiming at solving the problem of sustained casing pressure in large-size casing in the Kuqa Piedmont, the reasons for sustained casing pressure in large-size casing were investigated by using field data analysis and laboratory test evaluation methods. On this basis, the cementing technologies with large-size casing, featuring quick sealing and whole-process stable pressure, were formed by the measures such as strengthening wellbore, improving pipe string centering, increasing slurry friction difference and wall shear stress. Further, it was necessary to institute strict controls over the thickening, transition, and the developing time for strength in cement slurry. More detailed procedures for pressure holding before cement setting were designed as well. It was found that factors such as the limited staged cementing control in handling complex situations, and poor displacement and pressure stabilization measures led to severe channeling in cementing with large-size casing, which failed to stabilize the high-pressure fluids in formations. All of these resulted in poor-quality of primary cementing, which further caused the sustained casing pressure in large-size casing in the Kuqa Piedmont. The developed technologies were successfully applied to six wells in the Kuqa Piedmont, and achieved overall cementing displacement efficiency of more than 95% with a pass rate of more than 90% for the cementing quality in water-bearing sections. The good cementing performance shows that the technologies are worth of promotion and application.