BASIN ANALYSIS AND RESERVOIR CHARACTERIZATION FOR GEOTHERMAL DEEP DIRECT USE THERMAL ENERGY STORAGE (DDU-TES) IN PORTLAND, OREGON

Deep Direct Use Thermal Energy Storage (DDU-TES) is an emerging technology where summer heat and waste heat are stored in brackish or saline, slow-flowing aquifers for later extraction during the winter. The Portland Basin is a prime location to assess the feasibility of DDU-TES because natural geologic conditions provide thermal and hydraulic separation from overlying aquifers that would otherwise sweep away stored heat. Under the Portland Basin, the lower Columbia River Basalt Group (CRBG) aquifers contain brackish water (1,000-10,000 mg/L TDS), indicating low groundwater flow rates and poor connection with the overlying regional aquifer. Further, CRBG lavas tend to have comparatively low thermal conductivity, indicating that the 400-1,000 ft thick CRBG may be an effective thermal barrier to the overlying aquifer. A temporally and spatially limited previous study of a Portland Basin CRBG aquifer demonstrated that the injection of waste heat resulted in an increase in temperature by more than a factor of two, indicating a high potential for storing heat. As part of a larger U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) directive, we are constraining the geometry, stratigraphy, rock properties (permeability and porosity), and relevant structures of the Portland Basin to create a 3D basin model. The basin model will be the foundation of groundwater and heat flow simulations that will be used to evaluate the effects of geologic variability on the potential of DDU-TES. In addition to providing the critical information necessary to determine DDU-TES feasibility, this effort may also provide refined insights into the tectonic evolution of the Portland Basin with implications for seismic activity in the Portland metropolitan area.