Characterization of Rock Pore Features in Geothermal Systems Using Small Angle Neutron Scattering (sans)

Enhanced Geothermal Systems (EGS) are engineered reservoirs created to economically extract heat from low permeability and/or porosity geothermal resources. Existing geochemical reactive transport models for such systems lack essential data on the structure of the pore systems in geothermal reservoirs, and how they evolve in the relevant ranges of temperature, pressure, composition, and length scale. Small angle and ultra-small angle neutron scattering (SANS/USANS) are powerful tools to characterize the pore systems in geothermal rocks from the nanoto the micron scale. In this communication, we provide a brief summary of neutron scattering techniques, and discuss the utility of neutron scattering (NS) for EGS reservoir characterization and present example analyses of the pore systems of representative rocks from the Geysers, CA geothermal system. Future communications will address natural and experimental samples from Fenton Hill, N Mex.; Long Valley, CA, Desert Peak, NV, Yellowstone, WY and Awibengkok, Java. The results obtained by include the pore size, pore size distribution, pore number, and surface and mass fractal nature of the pore structures. Comparison of samples from the vapordominated and liquid dominated parts of the system show that the former has smoother, Figure 1. Schematic representation of the relationship between macroscopic flow channels and nanoenvironments (grain boundaries, pore networks) in a geothermal system (DOE,