Improvement of Spontaneous Imbibition in Carbonate Rocks by CO2-saturated Brine

摘要

Carbon dioxide (CO2) can improve the oil recovery from oil reservoirs. When CO2 is mixed with water, CO2 saturated water (carbonated water, CW) can be formed. CW can be formed in tertiary CO2-floods after water injection and if water is injected to reduce CO2-mobility, e.g. CO2-WAG and CO2-foam. The potential for CW to improve the spontaneous imbibition of water in fracture chalk has been studied. Spontaneous imbibition experiments have been carried out at reservoir conditions using brines with and without CO2. Core plugs with different wettability conditions were prepared. The wettability of chalk plugs was before and after viscous floods with CW, also characterised by the water-wet area. CW was found to improve the spontaneous imbibition of water into chalk and thereby improve the oil production. The water-wet area was increased during viscous flooding of chalk plugs with CW. CW has been shown to alter the wettability of chalk to more water-wet conditions. The potential for CW to improve the spontaneous imbibition and thereby improve the oil recovery in fractured carbonate fields is therefore promising. The results show that CO2 dissolved in water is not lost in these reservoirs, because CW can improve the oil recovery.