A New Design of Low Salinity-CO2-Different Chemical Matters

摘要

In this study, we proposed a new EOR method by combining low salinity (LS) water, alkaline, Surfactant, and CO2. Generally, injecting CO2 into oil reservoirs is a fruitful EOR technique that improves oil recovery, but injecting CO2 accompanied with technical in situ problems such as early breakthrough, viscous fingering, and gravity override. This prompted to find a solution to improve the gas sweep efficiency to prevent the mentioned problems from happening. Water was proposed to be alternated with CO2 for this purpose, and the outcome was promising. LS water was used instead of the regular water, which resulted in higher oil recoveries than the regular water. We proposed to inject surfactant-CO2 and LS water with foam which provided the most top results (28.35% OOIP). In this work, we presented a new method to inject Alkaline-Surfactant-CO2-LS water successively. The tertiary oil recovery can reach ~34% of the OOIP for all the cores in this study. The new process can improve the sweep efficiency as well as increasing oil recovery up to 20.1% OOIP. The oil recovery due to this new method is higher than mixing alkaline and foam together by a factor of 2 and more than this factor for WAG and CO2 injection. Coupling LS water with alkaline, Surfactant, and CO2 is a novel idea which takes advantage of the relative strengths of all processes and prevents the precipitation that could affect the performance of alkaline-foam EOR process. We proposed a new procedure to avoid this surfactant precipitation by injecting an LS water slug in between alkaline and foam flooding.