Comprehensive geological dataset describing a crystalline rock mass for hydraulic stimulation experiments

Krietsch, Hannes; Doetsch, Joseph; Dutler, Nathan; Jalali, Mohammadreza; Gischig, Valentin; Loew, Simon; Amann, Florian

doi:10.1038/sdata.2018.269

Cited by 46 publications

(98 citation statements)

References 34 publications

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“…Krietsch et al () created a 3‐D model providing a deterministic description of the local geology. Discontinuities spanning multiple scales are included, from borehole fracture traces to shear zones mapped across tunnels over distances up to 50 m. Key attributes for 590 traces identified from optical televiewer logs were determined, including depth, azimuth, dip, thickness, and geologic type (fracture, vein, or shear zone).…”

Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

“…However, the spatial arrangement and topology of shear zones have been constrained through cross‐hole image log correlation and tunnel mapping. Shear zones are thus integrated explicitly as nonplanar surfaces (Figure b) based on specific interpolation procedures (see Krietsch et al, ).…”

Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

“…Unlike the S1 faults, S3 faults accommodated two sets of fractures (Figure c): (i) a NE‐SW fracture set and (ii) a set striking toward the dykes at large angles, identified as the extension fractures commonly seen with dykes at the Grimsel Test Site (Keusen et al, , Figure 4b). The contact with metabasic dykes is clear and discrete, with evidence of dextral shear (Krietsch et al, ), and foliation remains above background up to 0.5 m from fault cores (Wenning et al, ).…”

Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

“…In the present paper, we first map spatial variations in transmissivity ( T ) from single‐hole tests at high resolution (<2.5 m) to investigate near‐wellbore heterogeneity (Part 1) and identify permeable structures for cross‐hole testing (Part 2). We integrate our results into a 3‐D geological model (Krietsch et al, ) compiled from extensive geological characterization and available as an open data set (https://doi.org/10.3929/ethz-b-000243199). Finally, we also assess potential stress‐permeability coupling and use results from stress measurement campaigns to examine if rock stresses have any detectable impact on fracture transmissivity in the shallow crustal faults studied.…”

Section: Introductionmentioning

confidence: 99%

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Tracking Fluid Flow in Shallow Crustal Fault Zones: 1. Insights From Single‐Hole Permeability Estimates

et al. 2020

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New in situ measurements to constrain the range, distribution, and spatial (meter-scale) variations of permeability in shallow crustal fault zones are reported based on systematic downhole tests at 0.5-km depth in crystalline rock. Single and cross-hole hydraulic packer tests were performed at a new dedicated test facility hosted in the Grimsel Test Site, in the Swiss Alps, following the technical instrumentation and isolation of discrete fault zones accessed by an array of boreholes. Single-hole test results are presented in this paper, while cross-hole experiments are reported in the companion paper. Our results reveal a sharp spatial falloff in permeability, from 10 -13 to 10 -21 m 2 , with off-fault distances of 1-5 m and characterized by a power-law relation with fracture density. Fractures linking subparallel faults were detected as high-permeability discrete spots several meters away from off-fault damage. Due to the narrow (centimeter-wide) thickness of fault cores, the hydraulic tests presented in this study do not characterize the permeability of fault core materials. The transmissivity of single fractures spans six orders of magnitude (10 -12 to 10 -6 m 2 /s) and is systematically higher in damage zones. In situ stresses appear to have a minor effect on natural, present-day fracture transmissivity at the borehole scale. We suggest that the geometrical and topological properties of fracture systems instead tend to control the permeability of the shallow crustal faults studied.Characterizing the structural properties of exhumed fault is key to understand their geometrical complexity at depth, and field studies have described how brittle damage around faults develops both along-strike and off-fault (i.e., off-plane) as fractures in damage zones organize themselves in response to off-fault stresses. Consequently, their spatial arrangement is not random (Kim et al., 2004;Peacock et al., 2017). Previous

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Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

Section: Field Setting and Subsurface Test Facility Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Tracking Fluid Flow in Shallow Crustal Fault Zones: 1. Insights From Single‐Hole Permeability Estimates

et al. 2020

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“…In this study, we consider a 20-m-long subsection, between 17 and 37 m depth, of this hydrophone VSP dataset consisting of 41 receiver positions. This part of the borehole features three fractures at 23.5, 23.9 and 25 m depth, as evidenced from optical and acoustic televiewer data (Krietsch et al, 2018).…”

Section: Resultsmentioning

confidence: 72%

Bayesian full-waveform inversion of tube waves to estimate fracture aperture and compliance

Hunziker¹,

Greenwood²,

Minato³

et al. 2019

Preprint

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Abstract. The hydraulic and mechanical characterization of fractures is crucial for a wide range of pertinent applications, such as, for example, geothermal energy production, hydrocarbon exploration, CO2-sequestration, and nuclear waste disposal. Direct hydraulic and mechanical testing of individual fractures along boreholes does, however, tend to be slow and cumbersome. To alleviate this problem, we propose to estimate the effective hydraulic aperture and the mechanical compliance of isolated fractures intersecting a borehole through a Bayesian Markov chain Monte Carlo (MCMC) inversion of full-waveform tube-wave data recorded in a vertical seismic profiling (VSP) setting. The solution of the corresponding forward problem is based on a recently developed semi-analytical solution. This inversion approach has been tested for and verified on a wide range of synthetic scenarios. Here, we present the results of its application to observed hydrophone VSP data acquired along a borehole in the underground Grimsel Test Site in the Central Swiss Alps. While the results are consistent with the corresponding evidence from televiewer data and exemplarily illustrate the advantages of using a computationally expensive stochastic, instead of a deterministic, inversion approach, they also reveal the inherent limitation of the underlying semi-analytical forward solver.

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Poroelasticity contributes to hydraulic-stimulation induced pressure changes

Dutler

Valley

Amann

et al. 2020

Preprint

Self Cite

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Hydraulic stimulation operations for enhanced geothermal systems (EGSs), petroleum applications, and wastewater disposal wells are potential sources of seismic hazards. In many places, the high-pressure and/ or massive volume of injections has led to an increase in the frequency and magnitude of earthquakes (Bao & Eaton, 2016;Ellsworth, 2013;Frohlich, 2012). Presently, predictions of seismic hazards from injections remain difficult, and determinations of the causality of earthquakes located at a large distance (>10 km) from injection locations are particularly arduous (Goebel et al., 2017;Keranen et al., 2014).The possible underpinning mechanisms remain under debate. Injection-induced seismicity is frequently explained by the pore pressure increase within the rock mass connected with the injection well. This zone can be referred to as the "pressurized zone," and it can be illuminated by active seismic measurements during high-pressure fluid injections (Calò et al., 2011;Schopper et al., 2020), as the relative change in p-wave velocity is directly linked to pore pressure changes. These pore pressure changes can lead to fault ruptures, and if the energy at the fracture tip overcomes the tensile strength of the rock, new fractures can be created.Within the pressurized zone, in the near-field of the injection site, the pore pressure distribution is dominated by fluid flow along a pressure gradient, that is, pressure diffusion. However, the time scale for diffusion-induced pore pressure changes is too slow to explain rapid far-field pressure changes and remotely induced seismic events. One hypothesis explaining remote seismicity is that such activity might be associated with aseismic slip processes. Aseismic slip has been observed in-situ in response to fluid injection (Guglielmi et al., 2015) and can potentially extend beyond the pressurized zone (Bhattacharya & Viesca, 2019). An alternative hypothesis involves poroelastic processes, which can be used to explain pressure changes caused by rock deformation and associated pore space variations reaching beyond the pressurized zone (Jacqey Abstract High-pressure fluid injections cause transient pore pressure changes over large distances, which may induce seismicity. The zone of influence for such an injection was studied at high spatial resolutions in six decameter-scaled fluid injection experiments in crystalline rock. Pore pressure time series revealed two distinct responses based on the lag time and magnitude of pressure change, namely, a near-and far-field response. The near-field response is due to pressure diffusion. In the far-field, the fast response time and decay of pressure changes are produced by effective stress changes in the anisotropic stress field. Our experiments confirm that fracture fluid pressure perturbations around the injection point are not limited to the near field and can extend beyond the pressurized zone. Plain Language SummaryThe far-field pore pressure response in geological reservoirs due to high pressure fluid injection is not clarified y...

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Comprehensive geological dataset describing a crystalline rock mass for hydraulic stimulation experiments

Cited by 46 publications

References 34 publications

Tracking Fluid Flow in Shallow Crustal Fault Zones: 1. Insights From Single‐Hole Permeability Estimates

Tracking Fluid Flow in Shallow Crustal Fault Zones: 1. Insights From Single‐Hole Permeability Estimates

Bayesian full-waveform inversion of tube waves to estimate fracture aperture and compliance

Poroelasticity contributes to hydraulic-stimulation induced pressure changes

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