ScCO2 Foams for Geothermal Reservoirs’ Stimulation: Impact of Fracture Roughness and Temperature on Rheology

Abstract Applications of foams as fracturing fluids have gained a significant interest over the past few decades. Foams possess several advantages over regular fracturing fluids, such as flexible rheology, better mobility control, and reduced water utilization. While the flow of foams in porous media has been extensively studied, their performance in fractures remains partially unclear. This research aims to expand this knowledge and discuss potential applications of foams for the controlled stimulation of geothermal reservoirs. The experimental work for this study involved utilizing granite rock samples, saw-cut into halves to mimic fractures. A spacer was used to keep smooth fractures open during experiments, while rough fractures were generated by modifying the rock surface using a sandblasting technique. The performance of the supercritical CO2 (scCO2) foam (65-90% quality), represented by its viscosity, was tested in rough and smooth fractures at 1200 psi pressure and temperatures ranging from 90°C to 150°C via multiple core flood experiments. The study revealed that foam viscosity drops considerably as temperature rises, with a reduction of over 2-fold observed beyond 90°C. Additionally, foamability decreased at higher temperatures, resulting in less and weaker foam at the same flow rates compared to lower temperatures. However, injecting foam at higher flow rates improved foamability at elevated temperatures. Moreover, the roughness of fractures had a positive, though less significant, impact on foam rheology than anticipated. In some cases, roughness improved foam generation, while in others, smooth fractures yielded better results. The outcomes of this study provide more detailed insights into the performance of foam under high-temperature conditions. A better understanding of foam behavior in rough and smooth granite fractures at high temperatures further expands its potential applications in geothermal reservoirs for controlled stimulation.