Coupling Smart Seawater Flooding and CO_2 Flooding for Sandstone Reservoirs: Smart Seawater Alternating CO_2 Flooding (SMSW-AGF)

摘要

Petroleum engineers continue to seek cost-effective improved oil recovery (IOR) methods to increase recovery efficiency, especially in heavy oil accumulations. Currently, smart water, low-salinity (LS) water, and CO2 are the most economically viable IOR methods according to the abundance of resources. The purpose of this work is to flood Bartlesville sandstone cores saturated with heavy oil successively with seawater, "smart" seawater, and finally CO2, with the aim of obtaining an optimum combination of these relatively low-cost methods. The core-flood experiments achieved promising results that could inform traditional enhanced oil recovery (EOR) methods for heavy oil. Several core-flooding scenarios were run, but the optimum scenario was 8 PV of seawater, 8 PV of smart seawater with depleted Ca2+, and 10 PV of miscible CO2. The seawater alone produced only similar to 20% of original oil in place (OOIP); the smart seawater produced an additional 12.9% of OOIP; and the final miscible CO2 step produced 64.52% of OOIP, for a total of 96.77% of OOIP. There appears to be a synergistic effect of these methods. Other cases investigated also incorporated one LS water and three "smart" seawater cases. When LS water was injected instead of smart seawater, the total oil recovery was slightly lower than that of the smart seawater case. We found that the significant oil recovery was due to the LS water effect and not from the synergic effect of LS water and CO2. This conclusion is based on the solubility of CO2 in LS water being higher than that in smart seawater, which redirects CO2 to dissolve in heavy crude oil and results in increased oil recovery. Using the same compositions of brines that were used in the core-flood experiments, contact angle measurements and spontaneous imbibition tests on the same core materials were performed. The results of contact angle and spontaneous imbibition confirmed a wettability alteration of the rock surface toward more water wetness using our new EOR process. This combination technology can mitigate the CO2 flooding problems (gravity override, viscous channeling, and early breakthrough) and improve CO2 sweep efficiency by incorporating smart seawater, which itself has the ability to increase oil recovery by altering the wettability toward more water wetness and reducing the solubility of CO2 in the injected water, which redirects it to heavy crude oil.