Paper: Gas Migration In Cements Evaluation of Additives

Gas migration or "gas cut cement 'I has been an industry problem for many years. This paper discusses the testing of six different cement slurry additives and a saturated saltwater slurry, all designed to prevent gas migration. The slurries were tested for their effectiveness at preventing gas migration at low pressures, such as is experienced offshore in shallow gas sands. Test equipment of a new design was fabricated. The slurries were exposed to gas pressure at the bottom of a 17 foot cement column in 1-1/2" pipe and the volume of invading gas measured. The hardened columns were then cut into sections to observe the channels created by the gas. The study showed that none of the products were able to completely stop the gas migration. Some products did appear to perform better than others but none were completely effective. The testing showed several of the slurry's properties to be associated with the formation of gas channels. In many of the tests, unexpected and as of yet unexplained gaps enveloped in the cement columns as the cement hardened. Based on these results, additional testing is being conducted.