A Comprehensive Method for the Optimization of Cement Slurry and to Avoid Air Channeling in High Temperature and High-Pressure Conditions

Air channeling in the annulus between the casing and the cement sheath and/or between the cement sheath and formation is the main factor affecting the safe operation of natural gas wells at high temperatures and pressures. Prevention of this problem requires, in general, excellent anti-channeling performances of the cement sheath. Three methods to predict such anti-channeling performances are proposed here, which use the weightless pressure of cement slurry, the permeability of cement stone and the volume expansion rate of cement sheath as input parameters. Guided by this approach, the anti-channeling performances of the cement slurry are evaluated by means of indoor experiments, and the cement slurry is optimized accordingly. The results show that the dangerous transition time of the cement slurry with optimized dosage of admixture is only 76 min, the permeability of cement stone is 0.005 md, the volume shrinkage at final setting is only 0.72%, and the anti-channeling performances are therefore maximized. The effective utilization of the optimized cement slurry in some representative wells (LD10-1-A1 and LD10-1-A2 in LD10-1 gas field) is also discussed.