Carbonated Water for Acceleration of Oil Production, Reduction of Water Production and Improvement of CO2-Storage Capacity
Authors: Fjelde I. , Omekeh A. 
Published: September 2024

Carbon Dioxide (CO2) capture, storage and its utilization can be used to decrease Greenhouse Gas (GHG) emissions (Hong 2022). Alteration of the wettability of oil reservoirs has the potential to improve the oil recovery (Sheng, 2010). Wettability is defined the tendency of a fluid to adhere to a solid surface in the presence of other immiscible fluids (Craig, 1971). In multiphase flow in oil reservoirs, wettability is important for phase distribution and flow properties. In fractured reservoirs, wettability alteration will improve the spontaneous imbibition of water and thereby improve the oil recovery (Sheng, 2010; Fjelde and Asen, 2009). In spontaneous imbibition experiments, carbonated water (CW, water saturated with CO2) at oil reservoir conditions has been found to improve the spontaneous imbibition of water in fractured chalk models and improve the oil production (Fjelde et al., 2011).
Sandstone rocks can also contain carbonate minerals (e.g. Pan et al., 2016). In addition, clay minerals in sandstone rocks are often more oil-wet than the other non-carbonate minerals. The surface area of clay minerals can be high in sandstone rocks, and these surfaces are very important for the wettability on core scale and reservoir scale. The flow properties in oil reservoirs depends on the saturation functions (relative permeability and capillary pressure) (Dake, 1978). Mineral composition and mineral distribution will together with the fluid compositions and conditions (temperature, pressure) determine these functions. Alteration of wettability for non-fractured oil reservoirs to more water-wet has also the potential to accelerate the oil production due to improvement of the relative permeability of oil (Collins and Melrose, 1983; Clementz 1976; 1977; 1982; Lager et al., 2007). Alteration of the wettability to more water-wet may have the potential to reduce the mobility ratio and thereby improve the volumetric sweep of the reservoir. The water production will be less at more water-wet conditions, because the relative permeability of water is low and higher volumetric sweep efficiency will the delay the water breakthrough. Alteration of wettability to more water-wet will therefore reduce the water production. Increase in relative permeability for oil and decrease in the relative permeability for water will give a shorter production period. Shorter production period and less water production will also reduce the environmental impact.
Surface Complexation Modeling (SCM) with the geochemistry solver, PHREEQC has been used to estimate the wettability preferences of the minerals and rocks (Mehdiyev et al. 2022). The wettability preferences were estimated by calculating Bond Products defined as the product of the mole fraction of oppositely charged oil and mineral surfaces. It was shown that the SCM technique can predict the tendency for wettability alteration of the individual minerals and reservoir rocks during injection of CW using the different rock, brine and Stock Tank Oil (STO) compositions.