Nanoparticle-Surfactant Stabilized Strong Foam for Enhanced Oil Recovery in High-Salinity Fractured Carbonate Reservoirs

Abstract

Summary Foam flooding can minimize bypassing in gasfloods in fractured reservoirs. Finding a foam formulation effective in high-salinity brine is challenging, especially with divalent cations, e.g., American Petroleum Institute (API) brine (8% NaCl with 2% CaCl2). When formulating with nanoparticles, the colloidal dispersion stability is difficult due to the dramatic reduction in zeta potential and the Debye length at high salinity. The aim of this work was to develop a strong foam in API brine at the ambient temperature, using a nonionic surfactant and ethyl cellulose nanoparticles (ECNP), for gasflooding in fractured carbonate reservoirs. ECNPs was synthesized and dispersed in API brine using a nonionic surfactant (also denoted as SF). SF and SF/ECNP foams were generated, and their stability was studied at atmospheric pressure and 950 psi. Foam mobility was measured in a sandpack at high pressure. Foam flood experiments were conducted in oil-saturated fractured carbonate cores. The nonionic surfactant proved to be a good dispersion agent for ECNP in API brine. The SF/ECNP mixture stabilized foam in API brine, even in the presence of oil. Injecting a partially miscible gas (below its minimum miscibility pressure) as an SF foam into a fractured core more than doubles the oil recovery over injection of the gas alone. The injection of the strong foam (SF/ECNP) further improves the oil recovery over that of the SF foam, indicating the synergy between ECNP and surfactant. ECNP accumulates in the foam lamella and induces larger pressure gradients in the fracture to divert more gas into the matrix for oil displacement.

Nanofluid-Based Foam for Enhanced Oil Recovery in Fractured Carbonates

“…Fractured tight reservoirs pose several challenges due to the differences in density and viscosity between injected fluids such as the gas and the resident oil, combined with the high matrix/fracture permeability contrasts, which reduce the sweep efficiency and limit matrix/fracture interactions. − Therefore, improved mobility control is required between the injected fluids (e.g., gas and brine) and the original oil in place (OOIP) . Techniques such as foam-based enhanced oil recovery (EOR) can be used to reduce gas mobility and increase the viscous pressure gradient in high-permeability streaks. ,− Foam EOR is particularly suited for such reservoirs because the large pressure drop across the fracture can divert injected fluids into the tight matrix instead of the fracture. ,− Consequently, very stable foams are needed to block high-permeability streaks (i.e., fractures) and divert the gas flow into the oil-bearing matrix.…”

“…Improved conformance control by foam was also reported with organic NPs such as ethyl cellulose (EC), carbon nanodots (CND), graphene oxides (GOs), and multiwalled carbon nanotube (MWCNT) . For instance, EC/nonionic surfactant blends generated robust foams in a fractured carbonate sample .…”

“…Improved conformance control by foam was also reported with organic NPs such as ethyl cellulose (EC), carbon nanodots (CND), graphene oxides (GOs), and multiwalled carbon nanotube (MWCNT) . For instance, EC/nonionic surfactant blends generated robust foams in a fractured carbonate sample . The accumulation of EC within the foam lamellae induced a high-pressure drop across the fracture and diverted more gas into the matrix, resulting in improved oil recovery .…”

“…39−45 Aluminum oxide or alumina demonstrated high foam stability by increasing the apparent foam viscosity with both CO 2 and methane gases. 39,40,42,45 Improved conformance control by foam was also reported with organic NPs such as ethyl cellulose (EC), 27 carbon nanodots (CND), 46 graphene oxides (GOs), 47 and multiwalled carbon nanotube (MWCNT). 48 For instance, EC/ nonionic surfactant blends generated robust foams in a fractured carbonate sample.…”

“…48 For instance, EC/ nonionic surfactant blends generated robust foams in a fractured carbonate sample. 27 The accumulation of EC within the foam lamellae induced a high-pressure drop across the fracture and diverted more gas into the matrix, resulting in improved oil recovery. 27 In another study, a remarkable increase in the mobility reduction factor (MRF) was observed during core flooding experiments with MWCNT-based foam with no formation damage, compared to silica-based foam.…”