Grimsel ISC Experiment Description

Doetsch, Joseph; Gischig, Valentin; Krietsch, Hannes; Villiger, Linus; Amann, Florian; Dutler, Nathan; Jalali, Reza; Brixel, Bernard; Klepikova, Maria; Roques, Clément; Giertzuch, Peter-Lasse; Kittilä, Anniina; Hochreutener, Rébecca

doi:10.3929/ethz-b-000310581

Cited by 6 publications

(9 citation statements)

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“…In the following, the main features of the geological settings, the in situ stress state, and the experimental setup are summarized. For more details on the in situ stress state, see Krietsch et al (2018b); for the geological dataset and model, see Krietsch et al (2018a), and for the experimental setup refer to Doetsch et al (2018a).…”

Section: The Study Sitementioning

confidence: 99%

Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock

Villiger¹,

Gischig²,

Doetsch³

et al. 2020

Solid Earth

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Abstract. We performed a series of 12 hydraulic stimulation experiments in a 20m×20m×20m foliated, crystalline rock volume intersected by two distinct fault sets at the Grimsel Test Site, Switzerland. The goal of these experiments was to improve our understanding of stimulation processes associated with high-pressure fluid injection used for reservoir creation in enhanced or engineered geothermal systems. In the first six experiments, pre-existing fractures were stimulated to induce shear dilation and enhance permeability. Two types of shear zones were targeted for these hydroshearing experiments: (i) ductile ones with intense foliation and (ii) brittle–ductile ones associated with a fractured zone. The second series of six stimulations were performed in borehole intervals without natural fractures to initiate and propagate hydraulic fractures that connect the wellbore to the existing fracture network. The same injection protocol was used for all experiments within each stimulation series so that the differences observed will give insights into the effect of geology on the seismo-hydromechanical response rather than differences due to the injection protocols. Deformations and fluid pressure were monitored using a dense sensor network in boreholes surrounding the injection locations. Seismicity was recorded with sensitive in situ acoustic emission sensors both in boreholes and at the tunnel walls. We observed high variability in the seismic response in terms of seismogenic indices, b values, and spatial and temporal evolution during both hydroshearing and hydrofracturing experiments, which we attribute to local geological heterogeneities. Seismicity was most pronounced for injections into the highly conductive brittle–ductile shear zones, while the injectivity increase on these structures was only marginal. No significant differences between the seismic response of hydroshearing and hydrofracturing was identified, possibly because the hydrofractures interact with the same pre-existing fracture network that is reactivated during the hydroshearing experiments. Fault slip during the hydroshearing experiments was predominantly aseismic. The results of our hydraulic stimulations indicate that stimulation of short borehole intervals with limited fluid volumes (i.e., the concept of zonal insulation) may be an effective approach to limit induced seismic hazard if highly seismogenic structures can be avoided.

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Section: The Study Sitementioning

confidence: 99%

Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock

Villiger¹,

Gischig²,

Doetsch³

et al. 2020

Solid Earth

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“…1a. A summary of the experiments conducted during the ISC measurement campaign and their results are given in Amann et al (2018) and Doetsch et al (2018).…”

Section: Test Sitementioning

confidence: 99%

Characterization of the highly fractured zone at the Grimsel test site based on hydraulic tomography

Ringel

Jalali

Bayer

2022

Preprint

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Abstract. In this study, we infer the structural and hydraulic properties of the highly fractured zone at the Grimsel test site in Switzerland by a stochastic inversion method. The fractured rock is modeled directly as a discrete fracture network (DFN) within an impermeable rock matrix. Cross-hole transient pressure signals recorded from constant rate injection tests in different intervals provide the basis for the herein presented first field application of the inversion. The experimental setup is realized by a multi-packer system. The geological mapping of the structures intercepted by boreholes and data from previous studies that were undertaken as part of the in-situ stimulation and circulation (ISC) experiments facilitate the setup of the site-dependent conceptual and forward model. The inversion results show that two preferential flow paths between the two boreholes can be distinguished. One is dominated by fractures with large hydraulic apertures while the other path consists mainly of fractures with a smaller aperture. The probability of fractures linking both flow paths increases the closer we are at the second injection borehole. The results accord with the findings from other studies conducted at the site during the ISC measurement campaign and add new insights about the highly fractured zone at the prominent study site.

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“…The fractures forming the DFN of the base case, as well as the boreholes for simulating a cross-hole hydraulic tomography experiment are presented in Figure 2a. The injection boreholes and the properties of the fractures with the center connected to the boreholes are oriented at observations from optical televiewer tests conducted during the ISC experiment (Doetsch et al, 2019;Krietsch et al, 2018). The position of the fractures connecting the boreholes and the length of all fractures are based on the connectivity matrix given in Jalali et al (2018).…”

Section: Setup Of Test Casesmentioning

confidence: 99%

“…The standard deviation of the noise is approximately 3% of the mean pressure. To refer to a realistic geological formation, a base case (test Case 1) is developed utilizing data from hydraulic characterization campaigns during the in situ stimulation and circulation (ISC) experiment at the Grimsel test site in Switzerland (Amann et al, 2018;Doetsch et al, 2019;Krietsch et al, 2018). Nevertheless, the present analysis is only theoretical and the fractures of the base case are considered to be perfectly known.…”

Section: Setup Of Test Casesmentioning

confidence: 99%

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Stochastic Inversion of Three‐Dimensional Discrete Fracture Network Structure With Hydraulic Tomography

Ringel

Jalali

Bayer

2021

Water Resources Research

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Groundwater flow through rocks with a low-permeability matrix is usually dominated by the presence of fractures, associated with pronounced local permeability contrasts. Multiple connected fractures yield preferential flow paths along a fracture network permeating the rock mass. Implemented in a model, the network is mostly represented either by a single or multiple continuum method that translates the hydraulic properties of the fractures into an upscaled effective permeability tensor or explicitly as a discrete fracture network (DFN). Combinations of both methods are also possible, such as realized by the discrete fracture matrix model (Berre et al., 2019). Dense fracture networks with many interconnections are more appropriate for the representation in a continuum model. In contrast, if a few fractures dominate the hydraulic conditions, resolving the fractures explicitly in flow models allows for a more detailed insight into preferential flow and transport paths, specific processes such as flow focusing, spatial fracture connectivity, and quantification of the individual influence of single fracture pa-

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Grimsel ISC Experiment Description

Cited by 6 publications

References 0 publications

Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock

Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock

Characterization of the highly fractured zone at the Grimsel test site based on hydraulic tomography

Stochastic Inversion of Three‐Dimensional Discrete Fracture Network Structure With Hydraulic Tomography

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