Reducing the CO2-Oil Minimum Miscibility Pressure Using Gas-Soluble Polymers

Minimum miscibility pressure (MMP) is one of the main technical challenges during carbon dioxide (CO2) flooding. Therefore, in this work, we explore the effect of small-molecule CO2-soluble polymers, including poly(dimethyl siloxane) (PDMS), poly(fluoroacrylate) (PFA), poly(1-decane) (P-1-D), and poly(vinyl ethyl ether) (PVEE), on MMP during gasflooding. Different concentrations of polymers (1,000–50,000 ppm) were considered to dissolve in CO2 at 60°C and 80°C. According to the cloudpoint pressure (CPP) results, the small-molecule CO2-soluble polymers dissolved in CO2 at pressure commensurate with CO2-enhanced oil recovery (EOR) (less than 2,500 psi) at both 60°C and 80°C. Also, the dissolution of the small-molecule gas-soluble polymers in CO2 results in increasing the CO2/polymer solutions’ densities and led to extremely reduced (CO2/polymers)-oil interfacial tensions (IFTs). Moreover, the MMPs decreased significantly by 19.4% for CO2/PFA, 17% for CO2/PDMS, 13.6% for CO2/PVEE, and 10% for CO2/P-1-D scenarios compared with pure CO2 scenario. In addition, the tertiary oil recovery factors were 88.7% (at stabilized pressure gradient of 80.3 psi/ft) and 62.2% (at stabilized pressure gradient of 72 psi/ft) of original oil in place (OOIP) during the miscible CO2/PDMS and pure CO2 injection scenarios, respectively. Therefore, the small-molecule CO2-soluble polymers containing functional groups with oxygen can be one of the most promising candidates for miscible CO2 displacement on the field scale, but the economic concerns, long-term sustainment of miscibility, and field-relevant flux rate (for both low and high permeability) need to be further investigated.