Caractérisation microsismique des massifs rocheux fracturés - Modélisation thermo-hydraulique - Application au concept géothermique de Soultz

Pascal Audigane. ( 2000 )
Institut National Polytechnique de Lorraine, Nancy

Abstract

The Hot Dry Rock (HDR) site at Soultz-sous-Forets is constituted by a geothermal doublet (one injection weIl and one production weIl) which are hydraulically connected by a fracture network approximatively situated at a depth of 3500 m. The bottom hole temperature has been measured at 162 oC at a depth of 3800 m. This project aims to recover the heat contained in the fractured reservoir by circulating fiuid between wells. When percolating through the fracture network, the cool fiuid injected from the surface is warmed in contact with the rocks. Then, it is pumped at the surface where its carried heat is transformed into electricity. In order to increase the permeability of the reservoir and to improve the connectivity between the wells, hydrofracturing experiments were conducted on two wells. The injections are performed at high pressure (several tenth of MPa). They induced low magnitude seismic events (lower than 4) called microseismicity. The induced microseismicity is used for solving two types of problems: - Firstly: to estimate an equivalent permeability tensor of the stimulated area. During the fiuid injection, the pore pressure perturbation propagates through the granitic fractured reservoir. Using the spatio-temporal distribution of the micro-earthquakes, the velo city of the pore pressure perturbation can be quantified. The poroelasticity theory can be used to obtain a relationship between the hydraulic diffusivity and the effective permeability of the equivalent porous medium. Studying the variation in the 3D space of such estimates, a permeability tensor is calculated. This method is also applied on two other sets of data collected from the Fenton Hill (USA) and Ogachi (Japan) geothermal sites. - Secondly: to build a 3D model of the geothermal doublet at the Soultzsous-Forets area. This model will try to integrate hydraulic, geologic and thermal data which were observed and measured in situ. Once a consistent hydraulic model is built, the associated Darcy velocity field is used to simulate the cooling of the granitic reservoir versus time using a streamline approach. Such a calculation can provide an estimate of the "life time" of the geothermal exchanger. A similar approach has been used to estimated the cooling time of the future geothermal exchanger situated at 5000m depth. These technical parameters are important to determine the economical viability of such a project.

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    BibTeX Reference

    @PHDTHESIS{Audigane2000,
        author = { Audigane, Pascal },
         title = { Caractérisation microsismique des massifs rocheux fracturés - Modélisation thermo-hydraulique - Application au concept géothermique de Soultz },
          year = { 2000 },
        school = { Institut National Polytechnique de Lorraine, Nancy },
      abstract = { The Hot Dry Rock (HDR) site at Soultz-sous-Forets is constituted by a geothermal
    doublet (one injection weIl and one production weIl) which are hydraulically
    connected by a fracture network approximatively situated at a depth of
    3500 m. The bottom hole temperature has been measured at 162 oC at a
    depth of 3800 m. This project aims to recover the heat contained in the fractured
    reservoir by circulating fiuid between wells. When percolating through the
    fracture network, the cool fiuid injected from the surface is warmed in contact
    with the rocks. Then, it is pumped at the surface where its carried heat is
    transformed into electricity.
    In order to increase the permeability of the reservoir and to improve the
    connectivity between the wells, hydrofracturing experiments were conducted
    on two wells. The injections are performed at high pressure (several tenth
    of MPa). They induced low magnitude seismic events (lower than 4) called
    microseismicity. The induced microseismicity is used for solving two types of
    problems:
    - Firstly: to estimate an equivalent permeability tensor of the stimulated
    area. During the fiuid injection, the pore pressure perturbation propagates
    through the granitic fractured reservoir. Using the spatio-temporal distribution
    of the micro-earthquakes, the velo city of the pore pressure perturbation
    can be quantified. The poroelasticity theory can be used to obtain a relationship
    between the hydraulic diffusivity and the effective permeability of the
    equivalent porous medium. Studying the variation in the 3D space of such estimates,
    a permeability tensor is calculated. This method is also applied on two
    other sets of data collected from the Fenton Hill (USA) and Ogachi (Japan)
    geothermal sites.
    - Secondly: to build a 3D model of the geothermal doublet at the Soultzsous-Forets
    area. This model will try to integrate hydraulic, geologic and thermal
    data which were observed and measured in situ. Once a consistent hydraulic
    model is built, the associated Darcy velocity field is used to simulate
    the cooling of the granitic reservoir versus time using a streamline approach.
    Such a calculation can provide an estimate of the "life time" of the geothermal exchanger. A similar approach has been used to estimated the cooling time
    of the future geothermal exchanger situated at 5000m depth. These technical
    parameters are important to determine the economical viability of such a
    project. }
    }