Waterflooding of carbonate reservoirs - Optimization and improved oil recovery

Oil recovery from carbonate reservoirs is more or less dictated by the wetting condition of the reservoir. Opposite to sandstone reservoirs, about 90% of the carbonate reservoirs are believed to be neutral to oil-wet. The oil properties described by the a cid and base number appeared to play an important role in determining the wetting state and the wetting mechanism. We have previously demostrated that it is possible to modify the wetting conditions of various carbonates where the wetting conditions are dictated by the AN, and improved oil recovery by sponatneous water injection was obtained. This was done by adding surface active chemicals to injection water, or adjusting the the injected fluid for potential determining ions towards the carbonate surfa ce. In the present project, we will work with basic crude oils and crude oils of varying AN/BN ratios. The wetting mechanism is different for basic crude oils compared to acidic crude oil, and the chemical modification of the injected water must be diffe rent from an acidic crude oil/brine/carbonate system. The present project is divided into three tasks, and the content of the different tasks is shortly described below: (1) Wetting characterisation - Different AN/BN ratios of crude oils - D ifferent carbonate rocks (Chalk, limestone and dolomite) - Effects of brine salinity/composition - Effect of temperature (2) IOR related to spontaneous imbibition of water - Study the influence of added potential determining ions - Chemical modification of injection water. (3) Field case study - Core materials and crude oil samples from actual fields with various AN/BN ratios are selected.