A Rock Physics Feasibility Study of the Geothermal Lodgepole Reservoir, North Dakota

ABSTRACT Geothermal energy extraction from the Earth's crust requires a thorough understanding of the mechanisms that enhance fluid flow in rocks. Geoscientists must evaluate the elements that regulate the development of permeability networks and the parameters that control rocks’ responses to stimulation procedures across various spatial and time scales. The Williston Basin is a major geological depression with complex stratigraphic sequences, and its rocks’ complex microstructures and mineral compositions make it challenging to assess effective moduli accurately. In addition, the Lodgepole Formation in the Williston Basin is a primary geothermal aquifer with low-salinity waters co-produced with oil and gas, which are often discarded as waste. This study aimed to develop a rock physics model of the Lodgepole formation, emphasizing its geomechanics and petrophysical features, and explore the connections to locate additional geothermal energy sources in the future. The study used several methods to estimate rock physics characteristics, including elastic modulus of minerals and rock pore shape and found that the intra-particle model matches the available data. INTRODUCTION The Lodgepole Formation, is the second deepest (Fig. 1) of the Williston Basin's four principal geothermal aquifers. The Formation has been identified as a potential source of low-salinity geothermal fluids co-produced with oil and gas. These fluids are often considered waste and are discarded by reinjection into the ground. However, North Dakota is now exploring harnessing geothermal waters to produce power. To evaluate the geothermal potential of the Lodgepole Formation, it is essential to understand the geomechanical and petrophysical features of the rocks in the Formation. Non-typical reservoir rocks, such as tight sandstones and shales, are known for their complex microstructures and mineral compositions, making it challenging to assess their effective moduli. Additionally, data from the literature may only sometimes be accurate since XRD data is only continuous at some levels, and the elastic modulus information for minerals can vary based on the study location.