Coupling Magnetotellurics and Hydrothermal Modeling to Further Understand Geothermal Resources

Abstract:

A comprehensive knowledge of the groundwater flow patterns associated with geothermal resources is critical to sustainable resource management and to discovering blind geothermal systems. Magnetotellurics (MT), which provides subsurface electrical conductivity information to substantial depths, has the ability to image geothermal reservoir features, such as conductive clay caps and hot, saline groundwater circulating within geothermal systems. We have used MT data along with 2D hydrothermal modeling, constrained by temperature, salinity and carbon-14 data, to explore possible deep groundwater circulation scenarios near the Sevilleta National Wildlife Refuge, in the Rio Grande Rift, central New Mexico. The area is underlain by a 100 to 150-m thick molten sill emplaced approximately 19 km below the surface. This sill is referred to locally as the Socorro Magma Body (SMB). Previous studies by Mailloux et al. (1999) and Pepin et al. (2015) suggest that the crystalline basement rocks in this region of the Rio Grande Rift can be significantly fractured to depths of 4-8 km and have permeabilities as high as 10^-14 to 10^-12 m². The combination of high permeability conditions and the presence of the SMB makes this particular region a promising candidate for discovering a blind geothermal system at depth. We constructed a 2D hydrothermal model that traverses a 64-km zone of active uplift that is associated with the SMB. We also completed a 12-km long, 9-station MT transect across a portion of this profile, where land access was permitted and electromagnetic noise was minimal. Preliminary results suggest a deep convection-dominated system is a possibility, although further analysis of the MT data is necessary and ongoing. We hypothesize that using hydrothermal modeling in conjunction with MT surveys may prove to be an effective approach to discovering and managing deep regional hydrothermal resources.