PRE-ASSESSMENT OF RESERVOIR THERMAL ENERGY STORAGE FOR THE UNITED STATES

Storing thermal energy underground for later use in electricity production or direct-use heating/cooling is a promising green energy option. Reservoir thermal energy storage (RTES) is one such approach that stores energy in underutilized permeable strata with low ambient groundwater flow rates and more geochemically evolved waters relative to overlying aquifers. The U.S. Geological Survey has begun assessing RTES potential nationally by focusing on five generalized geologic regions (Basin & Range, Coastal Plain, Illinois Basin, Michigan Basin, Pacific Northwest) in the United States. Reservoir models are developed for the following eight metropolitan areas to evaluate RTES performance across different climates and subsurface conditions: Albuquerque, New Mexico; Charleston, South Carolina; Chicago and Decatur, Illinois; Lansing, Michigan; Memphis, Tennessee; Phoenix, Arizona; and Portland, Oregon. Evaluated metrics include required well spacing, thermal storage capacity, and thermal recovery efficiency through time. Potential complicating factors considered for each reservoir include reservoir depth, free convection, and groundwater salinity. This work focuses on direct-use cooling because it has been shown that office space cooling needs greatly exceed those for heating in most parts of the country; however, the evaluated metrics are also relevant to heating and electricity applications. Results indicate that favorable RTES conditions exist in each region, with the Coastal Plain and Basin & Range being particularly favorable for thermal storage capacity, while the Pacific Northwest and Michigan Basin excel at energy recovery for the evaluated cooling application. The results underscore the utility of developing maps of thermal storage capacity, subsurface temperature models, and volumetric estimates of thermal storage capacity by integrating corresponding maps to serve as potential key RTES resource classification standards. Overall, this pre-assessment provides a basic understanding of RTES potential in several cities and geologic regions throughout the country and could aid further evaluation of national RTES efficacy.