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Stress Profiling in Enhanced Geothermal Systems (SPINE)

Titre du projet
Stress Profiling in Enhanced Geothermal Systems (SPINE)
Description
This project is about developing a new tool and test protocols to conduct stress profiling in crystalline rock for a better estimation of stimulation efficiency and induced seismicity related to the creation of subsurface heat exchangers. It is organized into four inter-related work packages aiming to develop instrumentation and test protocols at the laboratory, the intermediate field-laboratory and the geothermal project scales: (1) borehole instrument testing and upgrading at relevant geothermal temperatures and pressures, (2) field-scale demonstration of stress profiling in the highly controlled environments of two major underground research laboratories, SURF (USA) and BULG (Switzerland), (3) laboratory-scale testing of protocols in fully controlled 3D stress regimes, and (4) forward and inverse 3D stress analyses using fully coupled Thermo-Hydro-Mechanical (THM) numerical modeling conducted at different scales.
Chercheur principal
Williams, Molly
Zabihian, Farid
Statut
Ongoing
Date de début
1 Janvier 2021
Date de fin
1 Janvier 2023
Organisations
Identifiant interne
46481
identifiant
https://libra.unine.ch/handle/123456789/2197
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  • Publication
    Accès libre
    Characterization, Hydraulic Stimulation, and Fluid Circulation Experiments in the Bedretto Underground Laboratory for Geosciences and Geoenergies
    (: ARMA, 2021-6-18)
    Hertrich, Marian
    ;
    Brixel, Bernard
    ;
    Broeker, Kai
    ;
    Driesner, Thomas
    ;
    Gholizadeh, Nima
    ;
    Giardini, Domenico
    ;
    Jordan, D.
    ;
    Krietsch, Hannes
    ;
    Loew, Simon
    ;
    Ma, Xiadong
    ;
    Maurer, Hansruedi
    ;
    Nejati, M.
    ;
    Plenkers, K.
    ;
    Rast, M.
    ;
    Saar, Martin O.
    ;
    Shakas, A.
    ;
    van Limborgh, R.
    ;
    Villiger, Linus
    ;
    Wenning, Q. C.
    ;
    Ciardo, F.
    ;
    Kaestli, P.
    ;
    Obermann, A.
    ;
    Rinaldi, P.
    ;
    Wiemer, Stefan
    ;
    Zappone, Alba
    ;
    Bethmann, Falco
    ;
    Christe, Fabien
    ;
    Castilla, Raymi
    ;
    Dyer, Ben
    ;
    Karvounis, Dimitrios
    ;
    Meier, Peter
    ;
    Serbeto, Francisco
    ;
    Amann, Florian
    ;
    Gischig, Valentin
    ;
    Valley, Benoît 
    Reservoir stimulation and hydraulic fracturing in oil-and-gas reservoirs has become common practice and the techniques are continuously improved. However, directly applying the same techniques to extract geothermal energy from low permeability crystalline rocks (i.e., Enhanced Geothermal Systems, EGS) continues to present operational challenges. The research community and industry have shown great interest in addressing the unresolved problems using down-scaled in-situ hydraulic stimulation experiments. Focus has been on the 1–10 m field scale, but in comparison to a realistic EGS operations (1000s m) the scale is two orders too small, the depth and associate stress field differ, and the hydraulic conditions are not perfectly representative. To study the processes in-situ and to bridge the scale between in-situ labs and actual EGS projects, the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) was built in a tunnel in the Swiss Alps so that hydraulic stimulation experiments could be performed with dense monitoring systems at the 100 m scale. This effort enables process-oriented research and testing of field scale techniques at conditions that are closer to target reservoir depths and scale. This study gives in-sight on the initial geologic, hydraulic, and stress characterization of the BULGG related to on-going stimulation and circulation experiments
  • Publication
    Accès libre
    Depth-Dependent Scaling of Fracture Patterns Inferred from Borehole Images in GPK3 and GPK4 Wells at Soultz-sous-Forêts Geothermal Site
    (2021-4-19)
    Moein, M. J. A.
    ;
    Bär, Kristian
    ;
    Valley, Benoît 
    ;
    Genter, Albert
    ;
    Sass, Ingo
    Engineering an Enhanced Geothermal System (EGS) requires a proper understanding of the fracture network properties from small to large scales in order to create a reliable geological model for reservoir simulations. As deterministic identification of all fractures in a reservoir is practically impossible, stochastic approaches known as Discrete Fracture Networks (DFN) are used. This consists of parametrizing a statistical realization of fracture networks constrained by direct observations from borehole images and/or outcrop data, if available. DFN models can be used to study the thermo-hydro-mechanical (THM) properties of fractured rocks and to simulate the processes associated within: I) fluid circulation, II) flow and heat production as well as III) seismic response to hydraulic stimulations. Fractal DFNs are based on multiscale fracture network characteristics and are constrained by the scaling properties of fracture network attributes such as length (or size) and spatial distribution. The dual power-law model is a mathematical representation of fractures that parametrize fractal DFNs with two scaling exponents: 1) scaling of spatial distribution using two-point correlation dimension of fracture centers in three dimensions and 2) power-law exponent of fracture length distribution. Direct measurements of fracture length exponents from borehole images or cores are an unresolved challenge and the resolution of geophysical investigations is not sufficient to image the natural fracture networks. In contrast, the spatial distribution of fractures may be precisely characterized using borehole image logs and cores. Currently, the depth-dependence of spatial clustering of fracture patterns in the earth’s crust is not fully understood, although it may be required to anticipate deep reservoir conditions from shallower datasets. Here, we study such a depth dependency by using the two-point correlation dimension of fractures along the boreholes as a reliable estimate of the fractal dimension. We investigate the data stemming from two deep boreholes, GPK3 and GPK4, drilled into the crystalline basement rocks at the Soultz-sous-Forêts geothermal site. Recent analyses unraveled no systematic variation of fractal dimension with depth in any of the boreholes at the one standard deviation level of uncertainty. This conclusion may support the hypothesis of generating fracture network models with only a single correlation dimension using the stereological relationships in reservoirs up to 5 km depth in crystalline basements.
  • Publication
    Accès libre
    Transient inverse analyses of overcoring data for improved stress estimation
    (: ARMA, 2022-6-26)
    Valley, Benoît 
    Overcoring is a common technique for measuring stresses in mining projects. Knowledge of the in-situ stress state is essential to ensure the stability of underground infrastructures as well as to assess the induced microseismic risk associated with deep mining operations. There are different types of overcoring probes. Some are bonded in the pilot hole with an epoxy resin and allow for 3D stress measurement (e.g. CSIRO-HI), and others are based solely on a mechanical coupling of the probe, but are limited to biaxial stress measurement (e.g. USBM). The need to glue the probe to obtain a 3D measurement limits the applicability of this technique to short boreholes because it is technically difficult to glue probes in deep boreholes. In any case, traditionally the data analysis is done only based on the final deformation obtained after overcoring. In this paper we propose to use the transient deformation response during overcoring to: (1) allow to evaluate the 3D stress field from a single biaxial overcoring measurement, and (2) add a quality control component by reproducing the entire overcoring response. The general principle of our approach is to simulate the transient response of overcoring by numerical elastic simulation. The principle of superposition is used to derive the responses for any set of parameters from a limited number of basic models and thus allows to limit the total number of model runs. Such approach allows for a systematic inversion procedure to be applied for determining the optimal parameter sets that best capture the transient response of the overcoring. This allows the estimation of a 3D stress tensor from biaxial measurements. It also allows to have a quality control on the measurements evaluating the quality of the fit between the model and the data. In this paper, we evaluate the robustness of the proposed approach by performing a systematic sensitivity analysis on the stress estimation from the inversion of transient overcoring data. We demonstrate the advantages of the approach but also its limitations. The preliminary results obtained in this study suggest that the transient overcoring response contains sufficient information for constraining efficiently the 3D stress tensor. The inversion must be performed using multiple starting point, and the mode of the obtained calibrated parameters is in close adequacy with expected values, while some outliers can be present in the calibrated set. Further work is required for confirming these encouraging results by testing of broader range of stress configurations and applying the method to actual field measurements.