The effects of wettability and permeability on hydrocarbon foam performance in unconsolidated porous media: An experimental investigation at elevated pressure and temperature conditions

Abstract

Propped fractures in hydraulically fractured reservoirs function as unconsolidated porous media with permeability orders of magnitude greater than the matrix. This disparity in permeabilities leads to poor conformance control and sweep efficiency. The foam generated inside the fractures can be effective in addressing such challenges. It can reduce the gas mobility and enhancing the fracture-matrix interactions. However, the foam performance is influenced by the wetting conditions and pore space properties of the porous medium. In this work, for the first time, the effect of a complex interplay between permeability and wettability on hydrocarbon foam performance was investigated in unconsolidated porous media. To this end, methane foam experiments were conducted on sandpacks of varying wettability and permeability at high-pressure and high-temperature conditions. Additionally, interdependence between permeability and key foam parameters, including surfactant concentration and foam quality, were probed. Foam performance was evaluated based on the steady-state pressure drops across the medium and the foam’s apparent viscosity. The results showed a non-monotonic dependency of foam strength on the permeability of porous media, irrespective of their wetting conditions. We observed that foamability and foam stability were significantly enhanced at ascending permeability due to enlarged pores and pore-to-throat ratios, leading to reduced gas mobility. However, excessively large pore bodies adversely affected the bubble generation and downgraded the foam performance. Furthermore, foam quality significantly influenced the foam performance at all permeabilities. Distinct foam behavior was observed vis-à-vis variations in foam quality and separated by the low- and high-quality regimes. The results showed a modulated correlation between steady-state foam strength and permeability throughout the low-quality regime; however, no common trends were observed in the high-quality counterpart. Additionally, the transition foam quality was higher in oil-wet media than in water-wet systems. This shift broadened with ascending permeability and can be attributed to the wettability of porous media. Interestingly, variations in surfactant concentration produced similar trends in all wettability cases and displayed insensitivity to permeability. The results indicate that an increase in concentration improved the viscoelastic properties of the aqueous films, improving the foam strength in water- and oil-wet media of all permeabilities.