Assessing Geothermal Potential in Abandoned Oil and Gas Wells of the Deadwood Formation: Impacts of Thermal Shock on Sandstone Properties.

ABSTRACT: Recent investigations of subsurface temperature maps across North Dakota's basins have identified the Deadwood Formation as a promising unit for geothermal exploration. To assess the feasibility of using this formation, this study examined the physical and mechanical properties of sandstone core samples under simulated geothermal conditions. Sandstone core samples from the Deadwood Formation were obtained from an abandoned well in Slope County, North Dakota. The samples were thermally treated to 100 and 150°C to mimic the geothermal reservoir conditions. After thermal treatment, the cores samples were rapidly cooled using water and the process is repeated for four (4) cycles. The effect of successive heating and cooling on key petrophysical properties of the sandstone cores were examined using Nuclear Magnetic Resonance (NMR), Ultrasonic Velocity Measurements, and X-ray Diffraction (XRD). The results showed that as the number of cycles increased, the cores became more porous and permeable, but their strength decreased. The increase in permeability is attributed to the micro-cracks that were initiated within the crystal structures, making the rocks more suitable for geothermal energy extraction. These findings emphasize the role of thermal shock fatigue in sandstone durability, illustrating how repeated heating and cooling affect the material's structural integrity under geothermal conditions.