The growing interest in geothermal energy applications is part of the national transition to renewable and decarbonized energy sources. Due to the geologic settings of the state of Nevada, geothermal energy is an economically important area of interest (that also aligns with national reduced carbon emissions goals). The primary challenge in many geothermal fields is how to enhance the permeability of the field, primarily via small aperture fractures for improved heat exchange. In this proposal, however, we seek to address an important and different situation where the geothermal field is dominated by a few large fractures that reduce fluid residence time and limit heat exchange with the geothermal rock surfaces. Proposed permeability reduction methods have relied on injection of silicate gels or heat responsive polymer microbeads, both have shown certain promise for modifying small fracture apertures but are not suitable for large and dominant fractures we seek to block in this project. The primary objectives of the proposal are to synthesize and test heat resistance and closed-cell epoxy resin foam that will be transported, foam and cure in target high permeability fractures to block short-circuiting fluid pathway towards improving geothermal heat extraction efficiency.

The proposal outlines a multidisciplinary effort that involve synthesis of resin and chemical foaming agent (CO₂) and its rheological characterization in simple geometries and parallel-plate rheometer under different thermal regimes. In parallel, we will implement extensive modifications of a leading fracture network transport model (dfnWorks and PFLOTRAN) to consider the special physics of foam with its non-Newtonian transport with special attention to proposed resin and polymer foam behavior within in fracture networks under thermal regimes expected in geothermal fields. The project will construct and use laboratory benchtop 2-D glass fracture networks with built-in temperature control to test in-situ foaming and curing within the visualizable fractured network under a range of temperatures (within low enthalpy scenarios). Information from resin and foam characterization and benchtop transport experiments will be used to tune the modified model (Foam-dfn) towards applications at the Enhanced Geothermal System (EGS) scale for scenario generation under realistic boundary conditions.