Challenges in Controlling CO2 Foam Generation and Propagation

Summary CO2 injection in subterranean reservoirs for storage, for oil recovery, or for both, is challenging because of its very high mobility. CO2 foam or emulsion is a way to remedy this problem by increasing CO2 apparent viscosity. However, the generation of foam and its propagation in porous media present several issues which have to be overcome for this process to be economically realistic in practice. For example, it may take time, i.e., a number of pore volumes to be injected, before foam is created. It is the objective of this study to investigate these issues thoroughly, and to identify the mechanisms underlying them by looking at the effect of various parameters. It is found that surfactant adsorption on the surface of the rock is an important factor intervening in the delay of foam formation, but it may not explain all the results [ 1 ]. Surfactant adsorption and nature of porous media have been studied on two limestone materials coming from different sources. Despite same type of mineralogy, they yield very different behaviors: in one case, the foam is formed at the inlet of the core with a delay due to surfactant adsorption, while in the other case it is generated at the outlet of the core by end-effect probably due to elevated Minimum Pressure Gradient (MPG). Thus, the nature and morphology of the porous medium may be in some cases the dominant factor for foam generation and propagation. On the other hand, the effect of various parameters (CO2 volume fraction, temperature, presence of oil) on transient and steady-state characteristics of foam/emulsion transport has been investigated on quartz sandpack of high permeability, in conditions such that the pressure gradient is above the MPG. Steady state emulsion strength increases with CO2 fraction but is accompanied by a delay in foam generation and propagation, which is a drawback to overcome. From the understanding of the origin of the encountered problem, relevant mitigation strategies are envisioned and evaluated. The mitigation strategy will vary according to which factor is most relevant to the desired objective. This study highlights also the importance of porous media not only for steady-state conditions but also for transition behavior of foam as well. [1] Klimenko, A., Cui, L., Ding, L., & Bourrel, M. (2024). CO2 Geostorage and Enhanced Oil Recovery: Challenges in Controlling Foam/Emulsion Generation and Propagation. ACS omega.