Viability of carbonated water injection (CWI) as a means of secondary oil recovery in heavy oil systems in presence and absence of wormholes: Microfluidic experiments

Abstract

In this study, the performance of carbonated water injection (CWI) as a means of secondary oil recovery process was investigated. A series of flooding experiments were carefully designed and conducted in two state-of-the-art micromodels representing single and dual permeability porous media. The dual permeability micromodel is referring to a model with 17 high permeability channels mainly to mimic wormholes generated in unconsolidated sandstone reservoirs during sand production. Prior to CWI tests, waterflooding (WF) tests were carried out in both single and dual permeability micromodels saturated with two heavy crude oils (Type-I, °API = 20.44 and Type-II, °API = 15.49) to investigate the displacement performance of conventional and well known waterflooding technique. Next, through a series of flooding experiments performed at constant injection rate of qinj = 0.05 cm3/min and temperature of Texp = 21 °C, the effect of oil °API gravity on efficiency of CWI was examined. Results obtained for Type-I crude oil from a single permeability micromodel showed that the ultimate oil recovery of CWI can be increased by about 9% as compared to that of conventional WF. Furthermore, the analysis of the images taken during the displacement process of CWI showed wider distribution of frontal advancement compared to that of conventional WF when conducted in the same heavy oil saturated micromodel. It was also observed that for Type-II crude oil (°API = 15.49), the recovery factor was improved by 2.2% under the same conditions with that of conventional WF when performed in a single permeability micromodel. Therefore, the comparative evaluation of the performance of CWI conducted in two heavy oil systems to a single permeability micromodel showed 4.8% of improvement per one degree increase in oil °API gravity under the conditions of this study. Similarly, a series of experiments were conducted with both heavy oil samples in a dual-permeability micromodel where 17 high permeability channels representing dilated regions (or wormholes) were included in the model. The carbonated water injection implemented in the dual permeability micromodel saturated with heavy oil Type-II (°API = 15.49) resulted in 23.5% improvements in the recovery factor over single permeability case at nearly 1.6 PVs of injection at aforementioned experimental conditions and operations. Results of this study showed that CWI is a viable option for enhanced oil recovery in heavy oil reservoirs. Additionally, CWI has additional benefits through CO2 storage and carbon tax credits, though less than immiscible and miscible CO2 injection processes. Therefore, it is crucial to consider this relatively easier to implement alternate option prior to other costly enhanced oil recovery (EOR) methods.