Experimental Investigation of the Effectiveness of Cement Expansion Additives for Improved Abandonment of High Rate Gas Wells

Abstract Cement expansion tests performed on slurries used in cementing and abandoning of Oil and Gas Wells are done to ensure no micro-annuli develop post cement setting which leads to gas bubbles (seepage) on surface post abandonment – this was the case in one abandoned Well from few decades back. Industry use API ring mold testing to ensure cement expands post setting to overcome cement shrinkage issue. To ensure best in class, industry leading abandonments, Operator performed – in additional to API Test – additional extensive cement expansion testing in the Operator lab. Testing utilized novel advanced cement expansion measurement setups which simulate cement setting at downhole conditions of pressure and temperature using small and large cement plug sizes. This study calculated permeabilities of various cement abandonment plugs recipes with different expansion additives. Results were then compared to API ring mold testing for same slurries at surface and downhole conditions. Comparison concluded that expansion results obtained from API ring tests didn't match testing performed at STCA. In another words, Cement Expansion Additives which showed acceptable expansion percentage with API ring mold test, proved to result in permeability below NORSOK abandonment thresholds, and not to always yield the required expansion pressures when tested in the large-scale downhole conditions’ setup. Hence API ring mold tests which are widely utilized by the Oil and Gas industry are not fully representative of downhole conditions and give inaccurate representation of cement expansion and sealing ability.