Investigation of spontaneous imbibition induced by wettability alteration as a recovery mechanism in microbial enhanced oil recovery

This paper explores the potential of spontaneous imbibition (SI) induced by wettability alteration to improve incremental oil recovery during microbial enhanced oil recovery (MEOR). A laboratory work is presented that consists of SI and contact angle (CA) tests on reservoir and outcrop sandstone cores. The SI and CA measurements were conducted with aqueous phases with/without MEOR to assess the incremental recovery mechanism triggered by the wettability alteration during MEOR. It was observed that the oil recovery in the SI experiments with the MEOR nutrient solution reached a plateau at 0.62 ± 0.05% of original oil in place (OOIP) while it was 0.32 ± 0.02% of OOIP with the non-MEOR reference SI experiment conducted in outcrop sandstone cores. The CA of the oil droplet measured on polished reservoir rock sample decreased from 120° to 60° when exposed to the MEOR nutrient solutions. The observed changes occurred in parallel to the growth process of the bacteria in both SI and CA tests. The experimental data shows that the wettability alteration needs cell growth because SI experiments performed only with metabolites and without microbial cells exhibited negligible incremental recovery. Numerical models calibrated with SI experiments demonstrated the wettability alteration as one of the potential MEOR mechanisms. The bacterial network that forms a biofilm at the oil-water interface, and hence, creates a viscoelastic layer is thought to be the main cause of wettability alteration, which is supported by the oscillating pendant drop measurements.