Experimental investigation of well integrity: Annular gas migration in cement column

Cementing operations present various difficulties attributed to shallow flows all around the world. Cement ability to seal the annular space, aids in sustaining the well integrity by mitigating and preventing fluid migration to other formations and to surface. Failure of cement to seal the annular space can result in serious problems that might jeopardize the well integrity. In this study, a wellbore model setup was designed and fabricated to mimic the gas migration in cemented annulus. A series of experiments were conducted on this setup to examine the cement sealability of neat Class H and neat Class G cements, and to also evaluate the effect of anti-gas migration additive on the cement sealability. Different additives were used such as bentonite and latex. Experiments conducted revealed that neat Class H, Class G, and any other slurry design with additives (but without anti-gas migration additives) does not have the ability to serve in mitigating gas migration. The wellbore permeability of annular cement using neat Class H and Class G cement was ranging between 10(-3) to 10(-1) mD. In addition, it has been found that the wellbore permeability of annular cement increases as cement age increases. Annular cement should not be considered as the primary barrier when liner-hanger is used.