Analysis of the Deadwood Formation in North Dakota: Applying Rock Physics

The geothermal potential within North Dakota's Deep Sedimentary Basin formations, particularly the Deadwood Formation, holds promise. Viability of developing unconventional geothermal reservoirs in these complex lithologies depends on thorough subsurface characterization and modeling before injection. Advanced rock physics modeling techniques become essential to unravel the fundamental petrophysical properties and architectures to pinpoint optimal zones. This research uses rock physics methodologies to accurately classify lithofacies and characterize the reservoir rocks in the Deadwood Formation. The methodology integrates theory, analysis, and data for subsurface understanding. Additionally, incorporating composition and modulus data adds precision. This integrated approach is crucial given the complexities. Various analytical techniques are deployed, enabling determination of responses. Diverse scenarios are explored, acknowledging variability and heterogeneity. Results reveal nuanced coexistence of intraparticle and interparticle porosity associated with depositional facies. This suggests intraparticle nanoporosity likely enhances permeability by increasing interconnectivity. Larger pores may store fluids, influencing productivity. In summary, this research significantly advances understanding of fundamental parameters, relationships, and motifs. Findings facilitate identifying prospective units across the basin. Results should reduce uncertainties around potential, providing development guidance. This opens avenues for geothermal exploration and contributes to the energy conversation. 1. INTRODUCTION 1.1. Background The Deadwood Formation is a deep sedimentary unit in the Williston Basin, spanning parts of North Dakota, South Dakota, and Montana in the United States and in parts of Alberta, Saskatchewan, and the southwestern corner of Manitoba in Canada. This predominantly sandstone formation (Fig.1) with interbedded shales was deposited in a continental fluvial environment during the Late Cambrian to Early Ordovician periods (Lochman-Balk & Wilson, 1967). Deep Earth Energy Production Corporation (DEEP) has drilled five geothermal wells aimed at the Deadwood Formation at depths of approximately 11,500 feet and temperatures approaching 250°F (Fig.2) (Murphy, 2021). However, the intricacy of its depositional architecture, coupled with likely facies variability at both regional and local scales, poses challenges for geothermal reservoir characterization and development (Goldstein et al., 2011). A thorough analysis of fundamental petrophysical properties and internal lithofacies relationships across the Deadwood Formation is required to reduce subsurface uncertainties and enable the identification of optimal zones for sustainable geothermal energy production. Advanced subsurface modeling techniques integrating geology, geophysics, petrography, and rock physics will play a crucial role in unraveling the stratigraphic complexity and inherent heterogeneities of potential geothermal reservoir units within the Deadwood Formation.