Modeling Study of Single-Well EGS Configurations


Zhe Wang, Mark W. McClure and Roland N. Horne

Key Words:

downhole heat exchanger, thermosiphon, EGS, CO2


World Geothermal Congress




31. EGS - Enhanced Geothermal Systems (Hot Dry Rock)



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From the perspective of reducing EGS cost, a single wellbore configuration could be cost-efficient compared to a traditional doublet system because fewer wells would be required. The applicability of a single wellbore configuration depends on its thermal output capacity. In this work, a numerical model was built to investigate the thermal output capacity of several single-well EGS configurations. The parameters that affect the output were also studied.

A single-well downhole heat exchanger (DHE) with connection to artificial fracture intervals was investigated. In this configuration, the working fluid is circulated directly through the wellbore, taking advantage of the resulting thermosiphon effect. CO2 as a working fluid was compared with other common binary working fluids, e.g. isopentane.

However, the simulation results show limited thermal production capacity of the downhole heat exchanger configuration. Hence, several other alternative single wellbore configurations were studied, in an attempt to improve the thermal production capacity. The numerical study showed that a key factor determining the thermal production is the flowrate in the fractures.

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