Carbon dioxide has been used commercially to recover oil from reservoirs for more than 40 years. Currently, CO2 flooding is the second most applied enhanced oil recovery (EOR) process in the world behind steam flooding. Water alternating gas (WAG) injection has been a popular method to control mobility and improve volumetric sweep efficiency for CO2 flooding. Average EOR is about 9.7% with a range between 6 and 20% for miscible WAG injection. Despite all the success of WAG injection, sweep efficiency during CO2 flooding is a typical challenge to reach higher oil recovery.

We applied polymer-alternating-gas (PAG), in which polymer flooding is combined with miscible CO2 injection, to improve the volumetric sweep efficiency of the WAG process in TR78 of the North Burbank Unit. High heterogeneity and high permeability at the top layers are the two main challenges of the North Burbank Unit. Then, we compared PAG performance with WAG and continuous gas injection (CGI). Polymer concentration and injection slug patterns were optimized during the PAG process. Simulation results show that PAG would increase oil recovery about 14.3% compared with 7.3% for WAG in TR78.

This study can not only be used to guide the development of the North Burbank Unit, but also to demonstrate that encouraging recovery can be obtained in high-heterogeneity reservoirs by using PAG.

You can access this article if you purchase or spend a download.