Low Salinity Waterflooding in North Sea Reservoir Rocks:: An Experimental Investigation with emphasis on Wettability Effects

Abstract

For the last decades several laboratory tests and field tests on low salinity waterflooding have been done on oil bearing reservoirs. Overall the tests have shown an increased oil recovery with use of low salinity water. In this project a laboratory experiment on core samples from the Frøy field in the North Sea has been performed along with a literature review on low salinity waterflooding with focus on problems with waterflooding. Mechanisms in order to understand why low salinity waterflooding has an effect are reviewed.

The waterflood experiments were performed at a temperature of 60°C. The core samples were cleaned, porosity and permeability was measured and it was saturated with formation brine. Mineral oil was used to establish irreducible water saturation. Then it was aged with crude oil to restore in-situ wettability. 100% seawater brine, 10% diluted seawater brine and 1% diluted seawater were used in the flooding experiments for testing the low salinity effect in secondary and tertiary mode. The results found in this study shows that oil recovery increases as the salinity of the injecting water decreases. And low salinity water gives a higher oil recovery in secondary mode than high salinity water. Two cores did not show any effect of low salinity flooding, but all cores showed an overall increment in differential pressure which may indicate a reduction of permeability as an effect of salinity decrease.

A wettability test was also conducted on a core sample from the reservoir, which implies a neutral wet behavior of the reservoir. More experiments on several cores are recommended to get a better indication on the effect of wettability on low salinity waterflood recovery.