Engineered Geothermal Systems (EGS) can be developed in reservoirs otherwise lacking sufficient permeability by hydraulic fracturing. Proppants can be used to hold the fractures open when the fracture job is complete. Although the use of proppants is commonplace in the oil and gas industry, their use in geothermal reservoirs has been far more limited. In geothermal systems, proppants may be exposed to temperatures higher than those observed in oil and gas reservoirs. Proppants may dissolve or act as nucleation sites for mineral precipitation. In either case, fracture conductivity may be affected.

Experiments were conducted on sintered bauxite and quartz sand proppants and on mixtures of proppant and granite at temperatures up to 230°C. Deionized water, deionized water spiked with silica and geothermal water from the Raft River geothermal reservoir were used.

Scanning electron microscopy (SEM) was used to image the proppant and granite surfaces. Energy dispersive X-ray spectroscopy (EDS) was employed to determine the composition of the solids. Dissolution of sintered bauxite proppant was observed.

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