| Autor: |
McLean, Matthew L., Espinoza, D. Nicolas |
| Předmět: |
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| Zdroj: |
Rock Mechanics & Rock Engineering; Oct2024, Vol. 57 Issue 10, p8759-8775, 17p |
| Abstrakt: |
Deep closed-loop geothermal systems are a potential technology to provide heating and power generation. Although these systems are not new, they have recently regained interest because the design avoids reservoir stimulation (and potential fluid injection induced seismicity) and thermal short-circuiting of the working fluid. However, the poromechanical response to long-term heat depletion of closed-loop wells at large depths is largely unexplored. This paper investigates the response of rock around closed-loop geothermal system over 30-years of heat depletion through numerical simulation. The numerical solution is based on the theory of thermo-poroelastoplasticity and is solved through the Fenicsx finite element computing platform. The formulation takes effective poroelastoplastic properties of the bulk rock mass to indirectly account for strength and permeability of a rock mass with pre-existing fractures. Results for a normal faulting scenario show that the reservoir response to heat depletion causes vertical and horizontal stress redistribution far around the wellbores. Moreover, the rock mass may respond with partially undrained behavior in deep locations with a sparse fracture network. Shear failure may occur within a fraction -up to 30%- of the geothermal reservoir volume (limited by the thermal diffusion length) mostly driven by increase of effective stress anisotropy between vertical and horizontal stresses. The potential of induced microseismicity in deep closed-loop geothermal systems depends on the shear reactivated reservoir volume and effective rock stiffness. Energy dissipation depends case by case and can extend over the entire operation period, likely a consequence of the elastic perfectly-plastic model. Heat-drainage induced microseismicity is most likely expected to occur for closed-loop wells in geothermal reservoirs under normal faulting regime where small changes of horizontal effective stress may reactivate pre-existing fractures. Furthermore, heat depletion may increase stress intensities around the wellbore and facilitate tensile fracturing. Highlights: Heat depletion around wells changes effective stresses Effective rock stiffness has a first-order impact on mechanical response to cooling Shear reactivated reservoir volume due to heat depletion can be up to 30% in our simulation case Likelihood of thermally induced tensile fracturing of the wellbore increases with operation time [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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