Experimental Evaluations of Polymeric Solubility and Thickeners for Supercritical CO₂ at High Temperatures for Enhanced Oil Recovery

Abstract

Supercritical carbon dioxide (scCO2) is considered to be an excellent candidate for miscible gas injection (MGI) because it can reduce oil viscosity, induce in situ swelling of the oil, and reduce the IFT of the in situ fluid system. However, the unfavorable mobility associated with scCO2 flooding poses a major challenge due to the large viscosity contrast between the crude oil and scCO2, resulting in viscous fingering. An effective approach to overcome this challenge is to increase the viscosity of scCO2 (scCO2 thickening) to effectively control gas mobility and improve the sweep efficiency. The primary focus of this study was on an oilfield (Field A) that is located in the Harweel cluster in southern Oman. In this work, we present results in which the suitability of a library of commercially available polymers capable of thickening scCO2 at a high temperature (377 K). Previous studies have focused on the use of polymers as viscosifiers at much lower temperatures. Out of 26 potential polymers, 4 polymers (poly­(1-decene) (P-1-D), poly­(ethyl vinyl ether) (PVEE), poly­(iso-butyl vinyl ether) (Piso-BVE), and poly­(dimethylsiloxane) (PDMS)) were found to be completely soluble in scCO2 at 377 K and 55 MPa. Given the relatively low viscosity of oil in Field A (0.23 cP), P-1-D and PVEE could be considered as effective thickeners under the in situ conditions relevant to this field. In addition, Piso-BVE was found to be less effective because it did not change the CO2 viscosity above 358 K (55 MPa) when used at a concentration of 1.5 wt %. Furthermore, although it was determined that increasing the side chain length of poly alkyl vinyl ethers would enhance the solubility of this polymer in scCO2, it was determined to be ineffective in noticeably changing the CO2 viscosity. In general, increasing temperature resulted in a decrease in the relative viscosity, while increasing the pressure caused a slight increase in relative viscosity at all temperatures and concentrations.

Modeling of Branched Thickening Polymers under Poiseuille Flow Gives Clues as to How to Increase a Solvent’s Viscosity

“…Branched polymers were used because experiments [5,10,17] and simulations [53,61] have shown them to be more effective in raising the viscosity than linear ones, under similar thermodynamic conditions. The viscosity is obtained as a function of polymer concentration, branch length and flexibility and as a function of angular bonding strength.…”

“…Supercritical CO2 is particularly promising as a fracturing fluid because of its liquidlike density, however its viscosity is gaslike, which can be two orders of magnitude lower than the viscosity of water [11]. Low viscosity leads to viscous fingering and low oil mobility [2,10], limiting the applications of CO2 as a fracturing fluid.…”

Direct Gas Thickener

“…Most previous studies, reported that for low/high molecular weight polymers, a concentration of 1.5-7 wt% is required to thicken CO 2 albeit at very high pressure [6]. In recent studies, [16,17] P-1-D has been found to have sufficient solubility in both CO 2 and associated gas (AG) mixtures (at temperatures above 358 K and pressures of 50-55 MPa) to considerably increase gas viscosity. The viscosity enhancement of P-1-D in an AG mixture (25 mol% CO 2 ) and CO 2 was measured in a capillary viscometer at different pressures (50-55 MPa), 377 K, and varying P-1-D concentrations (1.5-9 wt%).…”

Evaluation of CO2‐philicity and thickening capability of multichain poly(ether‐carbonate) with assistance of molecular simulations

“…In this context, a possible solution to reduce the impact of the CO 2 release is to reuse it as green solvent 3–8 . Within this perspective, nowadays, supercritical carbon dioxide flooding technology in which CO 2 is injected into an oil layer to increase the oil recovery rate has obtained a great deal of attention 9–15 . The first report of CO 2 thickening with polymers dates back to 1985 by Heller et al 16 It is worth mentioning that carbon dioxide can be sealed underground in this technology which will help to achieve the goal of reducing emissions incidentally 12 .…”

“…The first report of CO 2 thickening with polymers dates back to 1985 by Heller et al 16 It is worth mentioning that carbon dioxide can be sealed underground in this technology which will help to achieve the goal of reducing emissions incidentally 12 . However, there are some drawbacks in the flooding process, due to the massive difference in viscosity of the supercritical carbon dioxide and the oil, among them the “sticky finger” phenomenon that leads to an edge displacement phase advancing in the form of a dispersed liquid bundle just like a “finger”, which will greatly affect the efficiency of oil displacement 9,10 . This phenomenon could be reduced if the carbon dioxide viscosity would be increased, therefore, efforts on carbon dioxide thickening have been a subject of increasing interest.…”