Monetizing Low-Moderate Enthalpy Geothermal Reservoirs: Lessons Learned

Physicists Richard Thomson, James Joule, and William Rankine theorized thermodynamic heat engines to transform thermal energy into mechanical work in the 1840s and 1850s (Smith, 1977). Tabor and Bronicki (e.g., 1964) developed organic Rankine cycle (ORC) engines and opened the market for the use of ORC engines in heat waste power generation. ORC engines use a refrigerant with a boiling point below that of water to generate electricity for waste heat down to 65°C. Power generation at temperatures in the 65°-150°C range is of specific interest to well owners in sedimentary basins, particularly those in oil and gas where wells access similar reservoir temperatures (Johnson et al., 2020). Paired with geofluid flow rates that provide adequate thermal mass for power generation, the concept of geothermal power generation coproduced alongside oil and gas has been modeled and tested in several locations across the United States (e.g., ElectraTherm, 2012; Gosnold et al., 2017; Akhmadullin, 2017). This paper discusses the role of geothermal energy in our future energy mix and specifically how ORC's have enabled lower temperature resources to be used for electricity generation. This paper discusses the results of the first phase of feasibility from a pilot project at the Blackburn oil and gas field in northeast Nevada. The location and history of the Blackburn field also prefaces the specific challenges and opportunities examined by the project in examining thermal energy loss throughout the geofluid gathering system and in optimizing the process flow of the fluids at the central facility to maximize power generation from both load and cumulative energy standpoints. The pilot project resulted in several important learnings throughout the duration of this pilot project preparing the way. While the growth of geothermal energy will undoubtedly accelerate, several important economic considerations are presented herein and some successful strategies to overcome some of these hurdles discussed. The confluence of evolving technologies in the ORC space as well as utilizing some of the lessons of a highly optimized drilling process from the oil and gas industry in the geothermal space will likely drive a pretty steep reduction in the cost curve for new geothermal projects. In the meantime, prudently utilizing existing operations, whether in the secondary recovery of mature oil fields or in the new lithium mining space, allows geothermal projects to leverage much of the early investment in infrastructure as well as collapse the geothermal permitting process delay associated with new projects.