Evaluation of First-Ever Foam Assisted Conformance Control for a Middle Eastern Carbonate Reservoir Offshore Qatar

Summary Gas injection has been evaluated and implemented in a middle-eastern oil field as water alternating gas or WAG. It has been seen that WAG is economically viable and a robust EOR method for areas of the field which are homogenous and do not pose conformance issues. However, the application of WAG in heterogeneous parts of the field has not been widely attempted due to issues like an early gas breakthrough and unfavorable sweep efficiency that are typically associated with WAG in heterogeneous reservoirs. Hence it was decided to design a foam assisted WAG system that can provide the required conformance control to mitigate those issues and expand the use of WAG to the entirety of the field. There are numerous references in literature to ‘aqueous foam’ as an attractive option to reduce the conformance issue of injected gases like hydrocarbon gas or carbon dioxide. There have been many field implementations of foam assisted WAG in CO2 flooded reservoirs in the United States. There is one example of foam-assisted hydrocarbon gas injection in the Snorre field. However, Foam as an EOR or IOR method remains untested and unproven in middle eastern reservoirs. In this study, we have carried out a comprehensive experimental program to design an effective foam system, that evaluates foam performance under specifically field conditions. A complete laboratory program has been carried out to screen the best foaming surfactant formulation that resulted in selection of Alkyl Polyglucoside surfactant. The criteria’s used in selection of surfactant involves having low adsorption on rock, good aqueous stability at reservoir conditions, and strong foam stability in presence of oil. The surfactant screening also involved foamability tests in porous media under oil-wet and water-wet conditions. The selected surfactant showed good foam strength under both oil-wet and water-wet conditions. The impact of mobile oil was also observed by co-injecting oil during the linear core flood experiments which clearly showed that good foam strength can be achieved in lower flow fraction of mobile oil with foam. Additionally, it was shown that altering wettability using another non-ionic surfactant along with APG resulted in a higher foam strength. The evaluation of surfactant formulation for boosting of foam strength using Lauryl Betaine surfactant was also performed. All the experimental results generated in this detailed evaluation of foam in the lab will be used in a foam modeling during next phase of the project to design a field injection strategy.