Transport of CO2 foam stabilized with engineered nanoparticles

Abstract:

Foam injection into the subsurface is performed to improve gas control mobility for residual oil extraction in, e.g., enhanced oil recovery and contaminated site remediation. Foam improves the gas mobility control as the gas viscosity is increased through its dispersion into a liquid phase. Finer the bubbles the lower the gas apparent viscosity (or foam viscosity) and the better is the sweep efficiency of the residual oil. A chemical surfactant adsorbed at the gas-liquid interface is generally used to maintain an optimal foam texture (number of bubbles for unit volume) however it can be desorbed making the foam coarser.

Here, we present an experimental and modeling study on the effect of nanoparticles on foam stability. Nanoparticles are adsorbed onto the bubble interface irreversibly and therefore they are expected to keep the desired texture of the foam for the entire time of its application. In this study, we use silica nanoparticles in conjunction with a surfactant to study the transport behavior of a CO₂ foam in a porous medium. Experiments were performed using a glass-bead pack and Boise sandstone with foam quality (f_g) 0.1-0.9 until steady-state. Foam flow was described by a mechanistic population balance model coupled with the fractional flow equation and constitutive equations for foam generation and destruction based on lamella division and bubble coalescence mechanisms, respectively. In order to minimize the uncertainty, model parameters were estimated by combining experimental data of pressure gradient during steady-state and transient.

Experiments and theory agree very well and the overall results show a significant increase in foam texture and stability when nanoparticles and surfactant are added to a foam flow in a low permeability porous medium. Data from tests with various nanoparticle concentrations (c_n) show that gas apparent viscosity changes with f_g and c_n. But its optimal value does not vary with c_n and it is already attained at f_g equal to 0.8 when 0.1 wt.% of nanoparticles are added together with 0.04 wt.% of surfactant. Employing 0.04 wt.% of surfactant under conditions of temperature, salinity, and permeability comparable to a deep formation, foam viscosity is approximately 4·10^-2 Pa·s, and increases of one order of magnitude when only 0.1 wt.% of nanoparticle is also added.