A Conceptual Geologic Model for the Newberry Volcano EGS Site in Central Oregon: Constraining Heat Capacity and Permeability Through Interpretation of Multicomponent Geosystems Data

Abstract

Newberry Volcano, a voluminous (500 km3) basaltic/andesitic/rhyolitic shield volcano located near the intersection of the Cascade volcanic arc, the Oregon High Lava Plains and Brothers Fault Zone, and the northern Basin and Range Province, has been the site of geothermal exploration for more than 40 years. This has resulted in a unique resource: an extensive set of surficial and subsurface information appropriate to constrain the baseline structure of, and conditions within a high heat capacity magmatically hosted geothermal system. During EGS stimulation efforts carried out by AltaRock Energy in 2012, a collaboration between NETL, Oregon State University and Zonge International carried out an extensive program of magnetotelluric, InSAR, ground-based interferometric radar, and microgravity observations within and surrounding the planned EGS stimulation zone on the western flank of Newberry Volcano. This group repeated magnetotelluric, InSAR and ground-based radar observations during AltaRock’s successful 2014 EGS stimulation. These observations as well as borehole and microseismic stress field and location solutions provided by AltaRock and its collaborators, in combination with well logs, petrologic and geochemical data sets, LIDAR mapping of fault traces and extrusive volcanics, surficial geologic mapping and seismic tomography, have led to the development of a conceptual geologic model for Newberry Volcano. A three-dimensional digital model has been constructed in EarthVision™ that enables lithology, directly and remotely measured material properties, and derived properties such as permeability, porosity and temperature, to be co-registered. This provides a powerful tool for characterizing the sustainability of the site for EGS production and testing, particularly within the more data-dense western portion of the volcano. The model and its implications for EGS research and production will be discussed. A portion of this area has been selected as a candidate site for the DOE FORGE (Frontier Observatory for Research in Geothermal Energy) Program as a collaboration between Pacific Northwest National Laboratory, Oregon State University, AltaRock Energy and additional partners, and the conceptual geologic model is being further developed within that target area, under the support of that program.