Numerical Simulation of Low Salinity Water Flooding: Wettability Alteration for Enhanced Oil Recovery

Abstract

Injection of low salinity water into the reservoir has been observed and tested in laboratories to have increased the oil recovery up to a maximum of 40 percent. Chemical and physical mechanism that modifies reservoir fluid properties attributes to this recovery which does not occur in conventional waterflooding. Wettability is the key reservoir parameter that has been recognized to have affected the rock-fluid properties such as residual oil saturation,relative permeability and capillary pressure. This alteration can lead to mobilization of stranded oil inside pore spaces.

The objective of this study is to evaluate the effects of low salinity water flooding in a segment of the Frøy field located in the North Sea. The field is located in blocks 25/2 and25/5 in the central North Sea. It is approximately 32 km southeast of the Frigg field and 25km northeast of the Heimdal field. The field was discovered in 1987 by drilling well 25/5-1,which found a 76-m thick oil-bearing Brent sequence. Production started in 1995 and stopped in 2001 due to production related problems and oil price decline. A total gross production of 5.9 MSm3 of oil and 1.7 Gm3 of gas was reported produced during this period. The field currently operated by Det Norske and with Premier oil as a stakeholder is planned to be reactivated.

Using Eclipse 100 as the reservoir simulator, the concept of wettability alteration has been applied to affect the local contact angle by changing the brine composition. This altered the distribution of fluids in the reservoir which in turn affected the relative permeability.Relative permeability functions were expressed by Corey functions. Corey parameters were assumed to be dependent on water salinity. The result showed that there is a 15% increase inoil recovery. In this study the simulation analysis has been limited to a segment in there servoir to limit the simulation time.