ALBERT

Description: In the course of the submission, revision and publication of the research paper, author affiliations changed to some extent. The authors regret that these affiliation changes are not reflected in the final publication and would like to apologise for any inconvenience and confusion caused thereby. The corrected affected affiliations are as follows: Felix Kögler, RWS IP Services, Chalfont St. Peter, UK; formerly Wintershall, Ante Borovina, OMV AG, Austria; formerly Wintershall, Foppe Visser, retired; formerly Wintershall

Description: As a dynamic screening tool for a high-salinity oilfield (186 g/L), anaerobic sandpacks were established to simulate Microbial Enhanced Oil Recovery (MEOR) under defined laboratory conditions. Glass beads, quartz sand or crushed reservoir rock were used to produce porous media which varied in permeability, wettability, homogeneity and geochemistry. In total, 14 sandpacks were flooded with oil and inoculated with indigenous fermentative bacteria of the order Halanaerobiales. After waterflooding, these were treated with nutrients in different injection scenarios during which incremental oil recovery, permeability, microbial activity and produced metabolites were measured. Our results indicate that the efficiency of MEOR is dependent on the type of porous medium used: Both glass beads and outcrop quartz sand were found to be no suitable analogue to reservoir material because not all potential MEOR effects were accounted for. MEOR was least efficient in quartz sandpacks with a recovery factor of 7.0 ± 1.7% with respect to the original oil in place (IRFOOIP), attributed mainly to fluid-fluid interactions. In sandpacks with reservoir rock, wettability alteration, matrix dissolution and bioplugging were additional MEOR mechanisms and resulted in an incremental recovery which was almost three-fold higher compared to pure quartz sandpacks (IRFOOIP = 23.2 ± 6.4%). Bioplugging was not detected in sandpacks with a permeability of 8–10 D, although cell retention was observed. Mean pore sizes of these sandpacks were calculated to be in the range of 100 μm, thus considered to be too large to allow for significant plugging. Our findings support the use of MEOR as potential tertiary recovery method but also emphasize the importance of carefully designing laboratory experiments. We argue that porous medium properties such as permeability, pore size, wettability and mineralogy play a crucial role during dynamic MEOR feasibility studies, because they directly influence incremental recovery.