Enhancing geothermal assessment: Coupled BHT and hydrogeochemical approach in north dakota's Deadwood Formation

Abstract

The Williston Basin, a vast intracratonic sedimentary basin extending across eastern Montana, western North Dakota, South Dakota, and southern Saskatchewan, holds significant potential for geothermal energy exploration. Within this basin lies the Deadwood Formation, a sedimentary layer of the Sauk Sequence, dating from the Upper Cambrian to Lower Ordovician epochs. The Deadwood Formation's substantial thickness, complex lithology, elevated temperatures, and unique geochemical properties make it a promising target for Enhanced Geothermal Systems (EGS). This study addresses critical challenges in EGS design by refining bottom-hole temperature (BHT) correction methods and conducting comprehensive geochemical analyses specific to the Deadwood Formation.

We developed new BHT correction models tailored to the Formation's unique thermal characteristics using polynomial regression on well-log data. Our results show that traditional BHT correction methods, developed for other sedimentary basins, lack accuracy when applied to the Williston Basin. The new correction framework significantly improves temperature estimations, allowing for a more reliable geothermal assessment. Additionally, the geochemical analysis of Deadwood Formation brines revealed high total dissolved solids (TDS) and a Na-Cl-dominated ionic composition, with varying pH and redox conditions that present challenges for geothermal energy production, such as scaling and corrosion. Mineral saturation indices and Geothermometry techniques further indicate reservoir temperatures ranging from 150 °C to 225 °C, suggesting favorable conditions for geothermal extraction.

This study's novel integration of refined BHT corrections with in-depth geochemical characterization provides a robust foundation for optimizing EGS design in the Deadwood Formation. It also offers a reference framework for geothermal resource development in similar sedimentary basins.