Low-salinity carbonated water injection in sandstone reservoirs: interplay between oil recovery improvement, salinity and fines migration

Abstract

Carbonated water injection (CWI) is described as a chemical-enhanced oil recovery method in which CO2-enriched water is injected into oil reservoirs as a displacing fluid. Although confirmed by many that a considerable amount of recovery improvement is attainable through CWI in both lab and field scales, the interaction of salinity on the performance of CWI and its potential fines migration is not very well understood. This study examines the efficiency of oil recovery improvement during low-salinity carbonated water injection (LSCWI) in a sandstone reservoir, while total dissolved salt concentration varies. To this end, a series of coreflooding experiments were performed on homogeneous sandstone cores at 80°C and 2000psi, and the amount of oil recovery was measured. From the experiments, it was observed that CWI could extract more crude oil than conventional water flooding in all salinities. In particular, the highest oil recovery was observed in the lowest salinity (61.2% in CWI and 42% during water flooding), indicating that by carbonating low-salinity water, oil recovery is enhanced by 20%. Moreover, the influence of salinity reduction on recovery enhancement was such that 9% of recovery improvement observed during conventional water flooding when salinity decreased from 40000 to 1000ppm. At the same time, this improvement was around 15% for CWI, suggesting that salinity reduction can be more effective in CWI rather than water flooding in recovery improvement. It was also found out that while recovery improvement and fines migration are both highly affected by water salinity, there is a synergy between the efficiency of CWI and onset of fines migration, which is one of the underlying mechanisms in oil recovery improvement during LSCWI into clay-containing sandstone reservoirs.