Fundamental investigation of underlying mechanisms behind improved oil recovery by low salinity water injection in carbonate rocks

When low salinity water (below 10,000 ppm) was injected in tertiary mode, the crude oil with a positive tendency to form micro-dispersions demonstrated a significant additional oil recovery of 6.3%. In contrast, no additional oil recovery was observed from LSWI with the crude oil sample that had reacted poorly to low salinity water (i.e. not formed micro-dispersion) nor with the treated sample. Using a novel method, the mineralogy of the rock was identified, which indicated the presence of anhydrite minerals. A series of spontaneous imbibition tests were also performed, which indicated similar mixed-wet conditions for the systems, which would make the systems comparable. The results of this fundamental work have demonstrated that despite the occurrence of geochemical processes, micro-dispersion formation appears to be the more dominant mechanism behind the IOR obtained by LSWI in carbonate rocks.