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REFEREED PUBLICATIONS IN JOURNALS
Beckers, K. F. , N. Rangel Jurado, H. Chandrasekar, A. J. Hawkins, P. M. Fulton, and J. W. Tester, Techno-Economic Performance of Closed-Loop Geothermal Systems for Heat Production and Electricity Generation, Geothermics, 2022. https://doi.org/https://doi.org/10.1016/j.geothermics.2021.102318 [View Abstract]Closed-loop geothermal systems, recently referred to as advanced geothermal systems (AGS), have received renewed interest for geothermal heat and power production. These systems consist of a co-axial, U-loop, or other configuration in which the heat transfer or working fluid does not permeate the reservoir but remains within a closed-loop subsurface heat exchanger. Advocates indicate its potential for developing geothermal energy anywhere, independent of site-specific geologic uncertainties, and with limited risk of induced seismicity. Here, we present a technical and economic analysis of closed-loop geothermal systems using a Slender-Body Theory (SBT) model, COMSOL Multiphysics simulator, and the GEOPHIRES analysis tool. We consider a number of different scenarios and evaluate the influence of variations in reservoir temperature (100 to 500℃), well termination depth (2 to 4 km), mass flow rate (10 to 40 kg/s), injection temperature (10 to 40℃), fluid type (liquid water vs. supercritical carbon dioxide), design configuration (co-axial vs. U-loop), and degree of reservoir convection (natural, forced or conduction-only). The resulting average heat production rates range from about 2 to 15 GWh per year for cases considering a co-axial design and from 9 to 67 GWh per year for cases with a U-loop design. Assuming generous economic and operating conditions, estimates of levelized cost of heat range from ∼$20 – $110 per MWh (∼$6 – 32/MMBtu) and ∼$10 – $70 per MWh (∼$3 – $20/MMBtu) for greenfield co-axial and U-loop cases, respectively. In the scenarios in which electricity generation is considered, annual electricity production ranged between 0.12 and 7.5 GWh per year at a levelized cost of electricity from roughly $83 to $2,200 per MWh. In all scenarios, the results exhibit a large rapid drop in production temperature after initiation of operations that levels off to a steady value significantly below the initial reservoir temperature. Operating at lower flow rates increases the production temperature but also lowers the total heat production. The consistently low production temperatures hinder efficient electricity generation in most cases considered. Natural or forced convection can increase thermal output but requires sufficiently high reservoir permeability or formation fluid flow. As expected, overall system costs are heavily dependent on drilling costs; hence, repurposing existing wells could significantly lower capital and levelized costs. In comparison with other types of geothermal systems, our results for closed-loop geothermal systems predict long-term production temperatures considerably below the initial reservoir temperature, and relatively high levelized costs for greenfield closed-loop geothermal systems, particularly for electricity production, unless significant reductions in drilling costs are obtained.
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Beckers, K. F. , C. R. Galantino, N. Rangel Jurado, N. Kassem, A. J. Hawkins, S. M. Beyers, O. J. Gustafson, T. E. Jordan, P. M. Fulton, and J. W. Tester, Geothermal District Heating Using Centralized Heat Pumps and Biomass Peakers: Case-Study at Cornell University, GRC Transactions, 44, 2020. [View Abstract]As part of the university’s commitment to become carbon-neutral by 2035, Cornell University is researching and developing a geothermal deep direct-use system to provide baseload heating for its main campus in Ithaca, NY. The term Earth-Source Heat (ESH) was adopted to distinguish Cornell’s approach to extract thermal energy from rock formations 2.5 to 5 km deep at low temperatures. Over the last several years, the ESH team has characterized the local and regional subsurface, using well log analysis and bottom hole temperature interpretation of regional wells, and tools such as gravity and aeromagnetic surveys and active and passive seismic campaigns. We investigated optimal integration of ESH into the existing district heating network. Promising sedimentary (Trenton-Black River, Galway and Potsdam) formations have been identified with temperatures in the range 70–90°C, and a fractured basement target (3.0–3.5 km, ~90–100°C) has been considered. Reservoir simulations indicate acceptable thermal drawdown over a 30-year lifetime. Enhanced Geothermal System technology may be applied to increase formation permeability. Techno-economic modeling results show hybridizing the ESH with centralized heat pumps enhances the overall performance and results in an attractive levelized cost of heat (LCOH) on the order of $5/MMBTU. Biomass is considered to produce continuously renewable natural gas that on an annual basis covers the campus peaking heating load. Currently, a borehole is being designed to obtain cores from target formations and in-situ measurements of critical parameters (e.g., temperature, stress field). The ESH project at Cornell — a mid-sized community with 30,000 staff, students and faculty — serves as a regional demonstration site. If successful, demonstrating ESH at Cornell could accelerate the development of geothermal district heating in other communities in the northeastern U.S., where subsurface temperatures in the range 50–100°C are widely available. In the northern tier of the U.S., heating loads are high and dominated by fossil fuel combustion, and contribute significantly to statewide total greenhouse gas emissions. Geothermal district heating could be key to decarbonize heat supplies and meet the enacted greenhouse gas reduction targets in these states.
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Rangel Jurado, N., Thermal Performance Evaluations of Fractured and Closed-Loop Geothermal Reservoirs. , MSc Thesis, 88 pp., 2021. [View Abstract]Earth’s interior contains an enormous amount of heat that can be exploited for carbon- free direct-use or electricity generation. Even though numerous studies have predicted that geothermal power will become an important contributor to the world’s energy mix, the use of these resources is still growing at a notably slow speed compared to other renewable energy alternatives. This thesis uses computational models to explore the technical challenges that two kinds of geothermal resources face to reach full commercialization. In particular, the temporal evolution of heat production of several fractured and closed-loop geothermal reservoirs is investigated. Thermal-hydraulic simulations are conducted for a fractured meso-scale geothermal reservoir in northern New York, USA. The modeling parameters considered here are constrained by empirical data related to lithology, hydrogeology, and thermal behavior measurements collected on site. This work shows how the addition of realistic complexities, that are well-constrained by field data and often disregarded, can significantly improve the thermal performance predictions compared to overly simplified models. Additionally, the results presented here highlight the importance of characterizing subsurface permeability distributions in order to optimize thermal efficiency and devise appropriate reservoir management strategies that extend the lifespan of geothermal reservoirs. To evaluate how closed-loop or advanced geothermal systems (AGS) compare to alternative ways of extracting geothermal energy, several AGS designs displaying varying reservoir and operating conditions are evaluated to estimate their heat and temperature generating potential. Our findings indicate that the thermal efficiency of AGS is characterized by a considerable exergy loss. Sensitivity analyses show that varying different parameters have slight and moderate improvements on thermal performance, however, AGS designs appear to present multiple technical challenges making them less cost-competitive than both conventional hydrothermal systems and enhanced geothermal systems (EGS). The following key findings summarize the results of these two studies: 1) if well- constrained, computational models are a good tool to assess, manage and intervene geothermal reservoirs to ensure their long-term sustainability, 2) non-uniform permeability can drastically modify fluid flow and heat transport processes in geothermal reservoirs compared to theoretical models that consider homogenous reservoir properties, 3) prospecting adequate subsurface properties is of critical importance to develop geothermal reservoirs, and 4) despite their recent popularity, closed-loop systems are expected to be considerably less productive than other types of geothermal resources at a similar scale.