Surfactant Prefloods During Carbon Dioxide Foam Injection for Integrated Enhanced Oil Recovery in Fractured Oil-Wet Carbonates

Abstract

Summary An integrated enhanced-oil-recovery (EOR) (IEOR) approach is used in fractured oil-wet carbonate core plugs where surfactant prefloods reduce interfacial tension (IFT), alter wettability, and establish conditions for capillary continuity to improve tertiary carbon dioxide (CO2) foam injections. Surfactant prefloods can alter the wettability of oil-wet fractures toward neutral/weakly-water-wet conditions that in turn reduce the capillary threshold pressure for foam generation in matrix and create capillary contact between matrix blocks. The capillary connectivity can transmit differential pressure across fractures and increase both mobility control and viscous displacement during CO2-foam injections. Outcrop core plugs were aged to reflect conditions of an ongoing CO2-foam injection field pilot in west Texas. Surfactants were screened for their ability to change the wetting state from oil-wet using the Darcy-scale Amott-Harvey index. A cationic surfactant was the most effective in shifting wettability from an Amott-Harvey index of –0.56 to 0.09. Second waterfloods after surfactant treatments and before tertiary CO2-foam injections recovered an additional 4 to 11% of original oil in place (OIP) (OOIP), verifying the favorable effects of a surfactant preflood to mobilize oil. Tertiary CO2-foam injections revealed the significance of a critical oil-saturation value below which CO2 and surfactant solution were able to enter the oil-wet matrix and generate foam for EOR. The results reveal that a surfactant preflood can reverse the wettability of oil-wet fracture surfaces, lower IFT, and lower capillary threshold pressure to reduce oil saturation to less than a critical value to generate stable CO2 foam.

Core-scale sensitivity study of CO2 foam injection strategies for mobility control, enhanced oil recovery, and CO2 storage

“…A shift to oil-wet can cause the lamellas to detach from the pore walls and foam may be destabilized. Schramm and Mannhardt (1996) confirmed reduced foam effectiveness at intermediate to oil-wet conditions [13] and Fredriksen et al (2019) induced surfactant wettability alteration in oil-wet fractures to generate CO2 foam in matrix below a critical oil saturation [14]. The impacts of wettability and the presence of oil on foam stability are areas under active investigation.…”

“…The North Sea crude oil has an API of 33.6° (calculated from specific gravity), a little above the API gravity of the Permian Basin crude of 31° at standard conditions. Compositions of brine and crude oil are reported elsewhere [14,24]. The North Sea crude oil is considered MCM with CO2 at 60°C and 180 bar, with a minimum miscibility pressure (MMP) of 125 bar [25].…”

“…Huntsman L24-22) was previously selected for the CO2 foam field pilot from a surfactant screening study that quantified adsorption on reservoir rock with and without CO2 present [26]. The non-ionic surfactant was also screened for its ability to alter wettability of oil-wet carbonate rocks to weakly oilwet conditions in favor of foam generation [14]. The nonionic surfactant was used at a 1.0 wt% concentration in Permian Basin Brine.…”

“…However, during multi-cycle SAG, the step-wise increase in differential pressure and significantly increased apparent viscosity compared to single-cycle SAG suggest that the alternating injection scheme did improve conditions for foam generation and stability. Figure 2 shows co-injection foam quality scans, D1 and D2-D3 (orange and green curves), which have previously been published [14,31] and are shown here for comparison. Peak apparent foam viscosities at steady state for fg = 0.70 was 34.9 ± 1.0 cP (D1), and 56.0 ± 1.6 cP (D2-D3), higher than single-cycle SAG (18.2 ± 2.7 cP), but lower than multi-cycle SAG (120.2 ± 0.3 cP) in Figure 1.…”

Modeling Near-Miscible Gas Foam Injection in Fractured Tight Rocks and Its Challenges

“…A weakness of this technique is that strong foam and ultra-low IFT are usually found to be incompatible during the chemical formulation development, thus a compromise between the two counterparts is needed [17,18]. The alternative foam, i.e., the miscible or near-miscible foam is considered when the reservoir pressure is high enough and the resource of miscible gas such as CO 2 or ethane is available [19][20][21][22][23][24]. Miscible gas foam not only reduces the gas-oil IFT to allow injected gas to enter the rock matrix, but also benefits from the advantages of miscible gas flooding including oil swelling, viscosity reduction, and molecular diffusion.…”