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.

Hydrocarbon-miscible gas flooding typically involves injection of an associated gas (AG) mixture containing mainly methane (CH 4 ) enriched with light hydrocarbon fractions and possibly acid gases. The AG mixture has been recognized as an excellent candidate for miscible gas injection (MGI). However, in general, the viscosity of the AG at reservoir conditions is significantly lower than that of crude oil leading to an unfavorable mobility ratio and low volumetric sweep efficiency during flooding. This study assesses the suitability of a library of commercially available polymers to thicken AG as a means of mobility control. The focus of the study is on the Field A located in the Harweel cluster in southern Oman. First, soluble polymeric thickeners for an AG mixture (CH 4 60%, C 2 H 6 9%, C 3 H 8 6%, and CO 2 25%) were identified using a parallel gravimetric extraction technique combined with cloud point measurements. Then, the viscosity of the identified soluble polymeric candidates in AG mixture was measured in a capillary viscometer at reservoir conditions. Three polymers were found to be completely or partially soluble in the AG mixture at 377 K and 55 MPa including poly(1-decene) (P-1-D), poly(methyl hydro siloxane) (PMHS), and poly(dimethylsiloxane) (PDMS). P-1-D found to be an effective thickener in AG mixture under conditions relevant to Field A, i.e., high temperatures and pressures. The polymer is soluble in the concentration range of 1.5−9 wt%. The viscosity of the P-1-D-thickened AG mixture increased by 2.2−7.4 times greater than AG mixture viscosity at 358−377 K. Furthermore, reservoir condition core flooding experiments were performed to examine the effectiveness of P-1-D-thickened AG gas mixture flooding to enhance oil recovery. The thickened-AG mixture flooding resulted in delayed gas breakthrough and subsequently 10−12% additional oil recovery.

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