Modeling of fractures with a continuum-based approach for process understanding of induced seismicity
Geo-energy and geo-engineering applications are becoming widespread due to their contribution to achieve net-zero emissions within the next decades. These applications, which include geothermal energy production, geologic carbon storage and hydrogen storage, involve fluid injection into and production from deep geological formation. Discontinuities, i.e., joints, fractures and faults, are ubiquitous in these deep formations, which poses challenges on achieving accurate predictive modeling. We have developed an equivalent fracture layer in a continuum-based approach that yields identical results to the ones of a model that represents a discontinuity with its actual aperture (Zareidarmiyan et al., 2018; 2020). The equivalent fracture layer can have a thickness in the cm scale, upscaling fracture thickness by several orders of magnitude. Such upscaling facilitates discretization of discontinuities while preserving accuracy. Including discontinuities in models is necessary when their spacing is in the order of the reservoir size to capture all the relevant thermo-hydro-mechanical processes induced by fluid injection and/or production (Zareidarmiyan et al., 2021). Equivalent porous media can be calibrated to reproduce fairly well the pressure evolution at the injection and production wells. However, pore pressure and temperature distribution within the fractured media significantly differs from the actual one, which is controlled by discontinuities. Such differences occur at all-time scales. In the short term, pressure diffusion has not enough time to propagate into the rock matrix and thus, pressure changes concentrate along the high-permeable discontinuities. In the long term, pressure diffuses into the rock matrix, equilibrating with the pore pressure in discontinuities, but the pressure distribution still differs from the one of an equivalent porous media because pressure distribution is controlled by the high-permeable network of discontinuities rather than distributing homogeneously as occurs in equivalent porous media. Furthermore, the cooling front due to cold fluid injection also presents differences between fractured media and equivalent porous media. Consequently, accounting for fractures into numerical models is essential to properly assess the changes in the stability of discontinuities, and thus, potential induced seismicity. We have applied our equivalent fracture layer model to geologic carbon storage (Vilarrasa et al., 2019) and superhot geothermal systems (Parisio et al., 2019). In the latter, we simulated a doublet in which water is produced at 450 ºC and reinjected at 150 ºC. A steep high-permeable fault is located between the two wells. Pore pressure changes are moderate and barely affect fault stability. However, as the cooling front advances, the cooling-induced contraction within the cooled region generates a stress redistribution around it that, in a normal faulting stress regime, destabilizes the sides of the cooled region and increases stability above and below it (Figure 1). After 25 years of water circulation, a large portion of the fault is destabilized despite the cooling front has not reach the fault yet. Thus, modeling of discontinuities in physics-based models is a useful tool for process understanding of induced seismicity, a necessary step to achieve a successful forecasting of injection-induced seismicity
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | comunicación de congreso biblioteca |
| Language: | English |
| Published: |
2021-09
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| Subjects: | Equivalent fracture layer, Geomechanics, Geoenergies, Superhot geothermal system, Discontinuity instability, |
| Online Access: | http://hdl.handle.net/10261/261487 |
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| Summary: | Geo-energy and geo-engineering applications are becoming widespread due to their contribution to
achieve net-zero emissions within the next decades. These applications, which include geothermal
energy production, geologic carbon storage and hydrogen storage, involve fluid injection into and
production from deep geological formation. Discontinuities, i.e., joints, fractures and faults, are
ubiquitous in these deep formations, which poses challenges on achieving accurate predictive modeling.
We have developed an equivalent fracture layer in a continuum-based approach that yields identical
results to the ones of a model that represents a discontinuity with its actual aperture (Zareidarmiyan et
al., 2018; 2020). The equivalent fracture layer can have a thickness in the cm scale, upscaling fracture
thickness by several orders of magnitude. Such upscaling facilitates discretization of discontinuities
while preserving accuracy.
Including discontinuities in models is necessary when their spacing is in the order of the reservoir
size to capture all the relevant thermo-hydro-mechanical processes induced by fluid injection and/or
production (Zareidarmiyan et al., 2021). Equivalent porous media can be calibrated to reproduce fairly
well the pressure evolution at the injection and production wells. However, pore pressure and
temperature distribution within the fractured media significantly differs from the actual one, which is
controlled by discontinuities. Such differences occur at all-time scales. In the short term, pressure
diffusion has not enough time to propagate into the rock matrix and thus, pressure changes concentrate
along the high-permeable discontinuities. In the long term, pressure diffuses into the rock matrix,
equilibrating with the pore pressure in discontinuities, but the pressure distribution still differs from the
one of an equivalent porous media because pressure distribution is controlled by the high-permeable
network of discontinuities rather than distributing homogeneously as occurs in equivalent porous media.
Furthermore, the cooling front due to cold fluid injection also presents differences between fractured
media and equivalent porous media. Consequently, accounting for fractures into numerical models is
essential to properly assess the changes in the stability of discontinuities, and thus, potential induced
seismicity.
We have applied our equivalent fracture layer model to geologic carbon storage (Vilarrasa et al.,
2019) and superhot geothermal systems (Parisio et al., 2019). In the latter, we simulated a doublet in
which water is produced at 450 ºC and reinjected at 150 ºC. A steep high-permeable fault is located
between the two wells. Pore pressure changes are moderate and barely affect fault stability. However,
as the cooling front advances, the cooling-induced contraction within the cooled region generates a stress
redistribution around it that, in a normal faulting stress regime, destabilizes the sides of the cooled region
and increases stability above and below it (Figure 1). After 25 years of water circulation, a large portion
of the fault is destabilized despite the cooling front has not reach the fault yet. Thus, modeling of
discontinuities in physics-based models is a useful tool for process understanding of induced seismicity,
a necessary step to achieve a successful forecasting of injection-induced seismicity |
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