Geothermal energy plays a growing role in the transition to renewable and carbon free energy sources. A challenge for many geothermal operations is how to enhance water-rock heat exchange either by creation of new fractures in a tight rock, or by blocking short-circuiting large conduits. Here we report a novel approach for blocking large aperture (cm scale) fractures using heat-activated epoxy resin foam. The foam is injected as discrete inert resin droplets that are transported to regions of the geothermal field and activated upon reaching sufficiently high temperatures, where they undergo foaming and curing, thereby locally reducing permeability. In contrast to alternative methods for reducing rock permeability such as silicate gels or heat responsive polymer microbeads that target fractures of small apertures (< 0.1 mm), the epoxy foam can reduce permeability of fractures with large apertures (about 10 mm) while attaining mechanical strength and thermal stability. Results from laboratory aluminum-glass fracture models provide insights by visualizing the transport phase of resin droplets and their subsequent temperature-induced foaming and curing transformations with associated flow pathway blocking. Modeling results for transport and foaming in a simple fracture considering rheological properties and foaming (volume expansion) behavior are compared with measurements of permeability changes. Challenges associated with upscaling to fracture networks and large transport distances of resin droplets are discussed.
Or et al. (Tue,) studied this question.