Experimental Investigation on the Use of Water Soluble Polyacrylamides as Thickeners During CO_(2) WAG EOR

CO_(2) flooding often results in poor sweep efficiency due to the high mobility ratio caused by its low viscosity. To mitigate this problem, alternate injection of water and CO_(2) slugs (WAG) is widely applied. Recently, numerical simulation and core flood experiments in heavy oil indicate that the use of chemicals in the water slug may improve mobility control during WAG. Therefore, stability studies of common polymers used for EOR applications in CO_(2) saturated environments becomes necessary. Also, the possibility to extrapolate the benefits observed in heavy oil to light and medium oil reservoirs needs to be assessed as they gather the majority of the existing CO_(2) applications.

This thesis presents an evaluation of the use of polymers as water thickeners during CO_(2). The work has been divided into three stages: An investigation on the stability of acrylamide based polymers exposed to CO_(2) for 328 days at 122 ?F. The determination of the MMP for the system crude oil ? CO_(2) using the slim tubing technique in a fast approach that employs a short column of 20 ft in length. And the execution of 12 core flooding experiments under miscible and immiscible conditions, in homogeneous and heterogeneous rock.

We conclude that polyacrylamide based polymers can resist the presence of CO_(2). HPAM was able to retain 54% of its original viscosity after 215 days at 122 ?F. PAM - ATBS increased its viscosity to 104% of its original viscosity after 328 days. A MMP of 1563 psia was calculated, which has a good correlation to previous laboratory measurements and EOS predictions for live oil. The core flooding experiments gave insights regarding the role of miscibility, frontal advance rate, heterogeneity and water viscosity on the viscous fingering of CO_(2) into the oil and suggested that thickening the water during WAG could be beneficial in highly heterogeneous formations. The limitations to scale reservoir heterogeneity prevented us to reach a fully understanding of the process. An approach combining numerical simulation with experimental work is recommended.