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Valley, Benoît
Nom
Valley, Benoît
Affiliation principale
Fonction
Professeur ordinaire
Email
benoit.valley@unine.ch
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Voici les éléments 1 - 10 sur 123
- PublicationAccès libreTransient inverse analyses of overcoring data for improved stress estimationOvercoring 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.
- PublicationAccès libreFractal characteristics of fractures in crystalline basement rocks: Insights from depth-dependent correlation analyses to 5 km depth(2022-5-27)
; - PublicationAccès libreA systematic methodology to calibrate wellbore failure models, estimate the in-situ stress tensor and evaluate wellbore cross-sectional geometry(2022-1-1)
; ; ; Alcolea, AndresDeep geothermal boreholes, often drilled to the crystalline basement, suffer from borehole breakouts that compromise borehole stability and/or lead to low drilling performance. These issues increase the cost of deep geothermal projects and lead to irregular cross-sectional geometries that may entangle well completion (e.g., packer isolation for zonal stimulation, cementing, etc.). Thus, the proper knowledge of rock strength, state of stress and their interactions at the closest vicinity of the borehole is key to the success of deep geothermal drilling. Typically, the magnitudes of the vertical and minimum horizontal principal stresses, 𝑆𝑣 and 𝑆ℎ𝑚𝑖𝑛, respectively, can be estimated while 𝑆𝐻𝑚𝑎𝑥 is difficult to constrain. This paper presents a systematic methodology to jointly evaluate the heterogeneous distributions of the stress tensor principal components and orientations, and the rock strength properties (e.g. cohesion, friction). Model parameters are estimated from measurements available during or shortly after drilling, i.e., breakout width, breakout extent/depth of penetration, breakout orientation and drilling induced tensile fractures. Additionally, measurements of estimated parameters or transformations of them can be considered in the calibration in a generic manner (e.g., 𝑆ℎ𝑚𝑖𝑛 interpreted from XLOT). For illustration purposes, the methodology is applied to the extensive borehole data set along the crystalline section of the borehole BS-1, in Basel (Switzerland). The methodology allows us (1) to derive plausible sets of stress and strength parameters reproducing the complex distribution of breakouts along BS-1, and (2) to unveil the paradox of having no borehole breakouts at sections with high density of natural fractures. - PublicationAccès libreAseismic deformations perturb the stress state and trigger induced seismicity during injection experiments(2021-10)
; - PublicationAccès libreEvaluation of the Diametrical Core Deformation and Discing Analyses for In‑Situ Stress Estimation and Application to the 4.9 km Deep Rock Core from the Basel Geothermal Borehole, Switzerland(2021-9-14)
- PublicationAccès libreCharacterization, Hydraulic Stimulation, and Fluid Circulation Experiments in the Bedretto Underground Laboratory for Geosciences and Geoenergies(: ARMA, 2021-6-18)
- PublicationAccès libreObservation of a Repeated Step-wise Fracture Growth During Hydraulic Fracturing Experiment at the Grimsel Test Site(2021-4-19)
; ; - PublicationAccès libreDepth-Dependent Scaling of Fracture Patterns Inferred from Borehole Images in GPK3 and GPK4 Wells at Soultz-sous-Forêts Geothermal Site(2021-4-19)
; - PublicationAccès librePlay-Fairway Analysis for Deep Geothermal Resources in Switzerland(2021-4-5)
; Switzerland initiated an energy transition plan for a massive development of renewable energy sources in response to climate change challenges and the decision to shut down nuclear power plants. Geothermal energy represents one component of this transition, with energy scenarios planning for more than 5% of the Swiss electricity demand produced from geothermal energy by 2050. Geothermal energy potentially provides base-load electricity supply, while also contributing to direct and indirect heat supply for replacing fossil fuels, and thus reducing greenhouse gas emissions. In response to this initiative, the Swiss Geological Survey (swisstopo) compiles information of the subsurface relevant for deep geothermal energy, including well data, seismic data interpretation of major stratigraphic horizons and faults, heat flux maps, thermal models of the underground, and geothermal potential studies. Access to this database provides opportunities for reviewing the geothermal potential of Switzerland using a quantitative play-fairway approach. In this contribution, we first review the available data sets and propose conceptual classifications of geological and structural settings favorable for deep-seated fluid circulation in Switzerland. We use the available data to determine best-estimate stress models, which are then used to compute slip and dilation tendency on the main faults identified in the database. We also combine all available information to provide quantitative mapping of the fairway score (favorability maps) for geothermal exploration. Model resolution does not yet capture local effects relevant for specific project development, but does identify general trends at the scale of Switzerland. Currently, this approach provides best estimate models for the currently available data, and will be refined and better-resolved with the acquisition and implementation of future data. - PublicationAccès librePoroelasticity Contributes to Hydraulic-Stimulation Induced Pressure Changes(2021-2)
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