Abstract
Alternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths.
Highlights
Geothermal energy is an ideal candidate to dominate the energy industry in the foreseeable low-carbon future
Icelandic Deep Drilling Project (IDDP)-1 drilling was abandoned after hitting a magma intrusion at 900 ◦C at 2100 m and the first flow test of IDDP-2, conducted in December 2019, encountered delays (DEEPEGS 2018, 2019)
Overcoming the challenges posed by these unique resources could potentially unlock a five times greater energy content and a factor of ten times electricity generation potential associated with supercritical fluids at 400 ◦C compared with Enhanced Geothermal System (EGS) technology at 200 ◦C (Cladouhos et al 2018)
Summary
Geothermal energy is an ideal candidate to dominate the energy industry in the foreseeable low-carbon future. Conventional deep geothermal methods have been utilised to provide power production from natural hydrothermal reservoirs with these desired characteristics: a large heat source, highly permeable, sufficient supply of injected water, impermeable layer of cap rock, and a reliable recharge system (DiPippo 2015). Doran et al Geotherm Energy (2021) 9:4 are unique and restricted by location, severely limiting the true potential of geothermal energy—according to the International Energy Agency, this resource could generate 1400 TWh per year by 2050 while avoiding 800 Mt of C O2 (IEA 2011) This largely untapped resource demands alternative solutions to compete in the renewable energy market, exploiting unconventional methods to extract heat, notably from petrothermal sources where permeability and/or porosity are lacking (Falcone et al 2018). Overcoming the challenges posed by these unique resources could potentially unlock a five times greater energy content and a factor of ten times electricity generation potential associated with supercritical fluids at 400 ◦C compared with EGS technology at 200 ◦C (Cladouhos et al 2018)
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