Induced microseismicity and reservoir growth at the Fjällbacka hot dry rocks project, Sweden

Jupe, A.; Green, A.S.P.; Wallroth, Thomas

doi:10.1016/0148-9062(92)90511-w

Cited by 36 publications

(19 citation statements)

References 7 publications

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“…3a and 3b) coincides approximately with a strong reflection band in the migrated images presented by Dyer and Wallroth [1997]. However, earthquakes observed during the high-pressure injection of viscous gel [Jupe et al, 1992] are located consistently above the low-velocity zone (Figs. 3a and 3b) (Fig.…”

Section: Introductionmentioning

confidence: 93%

Anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization

Vécsey

Holliger

Pratt

et al. 1998

Geophysical Research Letters

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Abstract. To assess the effects of changing fluid pressure in a potential hot dry rock reservoir, two crosshole seismic surveys were conducted: one at ambient pressures and one with the investigated volume hydraulically overpressured by ~3.3 MPa. Sources and receivers were located in two straight subvertical boreholes ~100 m apart. Traveltime data were inverted for velocity information in two phases. During the first phase the seismic velocities were constrained to be isotropic, and during the second they were allowed to be anisotropic. Accounting for anisotropy enhanced greatly the interpretability of the tomograms. Before pressurization, a low-velocity anomaly at 455-475 m depth correlated with a subhorizontal zone of hydraulically permeable fractures connecting the two boreholes. Although the absolute magnitude of anisotropy is not well constrained, the dominant orientation of the TIaxes is consistent with the local stress field. Hydraulic over-pressurization resulted in a pronounced extension of the low-velocity zone, but had no significant effects on the velocity structure elsewhere. The results of this study suggest that anisotropic seismic tomography may be a key method for characterizing hot dry rock reservoirs.

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Section: Introductionmentioning

confidence: 93%

Anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization

Vécsey

Holliger

Pratt

et al. 1998

Geophysical Research Letters

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“…Two different "end-member" mechanisms commonly appear in discussions of permeability creation processes through hydraulic injections: (1) hydraulic fracturing as the initiation and propagation of new tensile fractures and (2) hydraulic shearing, i.e., the reactivation of existing discontinuities in shear with associated irreversible dilation that is often referred to as the self-propping mechanism. Hydraulic shearing is of particular relevance for EGS as it has been shown that slip along fractures can generate a permeability increase by up to 2-3 orders of magnitude (Jupe et al, 1992;Evans et al, 2005a;Häring et al, 2008). If the rock mass in the reservoir is stressed to a critical level (e.g., Byerlee, 1978), then a relatively small reduction in effective normal stress would be sufficient to cause shearing along preexisting discontinuities that are optimally oriented for failure (Hubbert and Rubey, 1959;Raleigh et al, 1976;Zoback and Harjes, 1997;Evans et al, 1999;Evans, 2005).…”

Section: Stimulation By Hydraulic Shearingmentioning

confidence: 99%

“…Welldocumented hydraulic stimulation datasets generally include microseismic observations as well as injection pressures and flow rates and, occasionally, tilt monitoring (Evans, 1983;Warpinski and Teufel, 1997). Although much information can be gained from these datasets, including imaging of microseismic structures (Niitsuma et al, 1999;Maxwell, 2014), energy balance between injected fluids and seismic energy release (Boroumand and Eaton 2012;Zoback et al, 2012;Warpinski, 2013), and source mechanisms (Jupe et al, 1992;Deichmann and Ernst, 2009;Warpinski and Du, 2010;Horálek et al, 2010), the constraints placed on the processes are insufficient to resolve details of the hydromechanical processes that underpin permeability enhancement, flow-path linkage, channeling or the interaction with natural fractures. Many of these processes possibly also depend on rock type.…”

Section: Stimulation By Hydraulic Shearingmentioning

confidence: 99%

“…At Soultz-sous-forêt, it was possible to estimate stimulation-induced slip and the normal opening of fractures that cut the borehole by comparing pre-and post-stimulation acoustic televiewer logs (Cornet et al, 1997;Evans, 2005). Shearing of fractures was also proposed as the predominant mechanism of permeability enhancement in granite at the Fjällbacka site in Sweden, by Jupe et al (1992), based upon focal mechanism analysis. The above observations provide evidence of a link between shearing and permeability changes.…”

Section: Stimulation By Hydraulic Shearingmentioning

confidence: 99%

“…In the geothermal domain, such projects constitute expensive experiments and thus are relatively few in number, whereas, in the oil and gas domain, where hydro-fracture operations are frequent and routine, the data tend to be proprietary. Nevertheless, some notable datasets have been acquired for deep brine injection projects (Ake et al, 2005;Block et al, 2015), deep scientific drilling projects such as the German KTB project (Zoback and Harjes, 1997;Emmermann and Lauterjung, 1997;Jost et al, 1998;Baisch and Harjes, 2003), and hydraulic fracturing for oil and gas production enhancement (Warpinski, 2009;Das and Zoback, 2011;Dusseault et al, 2011;Pettitt et al, 2011;Vermylen and Zoback, 2011;Boroumand and Eaton, 2012;Bao and Eaton, 2016) and during the stimulation of deep geothermal boreholes (Parker, 1989;Jupe et al, 1992;Cornet and Scotti, 1993;Tezuka and Niitsuma, 2000;Asanuma et al, 2005;Evans et al, 2005a;Häring et al, 2008;Brown et al, 2012;Baisch et al, 2015). Welldocumented hydraulic stimulation datasets generally include microseismic observations as well as injection pressures and flow rates and, occasionally, tilt monitoring (Evans, 1983;Warpinski and Teufel, 1997).…”

Section: Stimulation By Hydraulic Shearingmentioning

confidence: 99%

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The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

et al. 2018

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Abstract. In this contribution, we present a review of scientific research results that address seismo-hydromechanically coupled processes relevant for the development of a sustainable heat exchanger in low-permeability crystalline rock and introduce the design of the In situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to studying such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydromechanical processes that would enhance process understanding in a way that aids future stimulation design. Small-scale laboratory experiments provide fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from (1) difficulties and uncertainties in upscaling the results to the field scale and (2) relatively homogeneous material and stress conditions that lead to an oversimplistic fracture flow and/or hydraulic fracture propagation behavior that is not representative of a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales and for which access to the target rock mass with a comprehensive monitoring system is possible. The ISC experiment is designed to address open research questions in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland). Two hydraulic injection phases were executed to enhance the permeability of the rock mass. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation, and the microseismic response were monitored at a high spatial and temporal resolution.

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Consistent treatment of shear failure in embedded discrete fracture models using XFVM

Conti,

Deb,

Matthäi

et al. 2023

Num Anal Meth Geomechanics

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Understanding deformations and fluid flow in fractured rocks is of central importance for many subsurface flow applications. Thus, numerical frameworks are needed that capture the coupled mechanical and hydraulic behaviour, including scenarios with complex fracture networks. This paper employs the extended finite volume method to represent fracture manifolds in a poroelastic matrix domain and to compute shear and tensile displacements of fracture segments. However, using embedded fractures with non‐conforming grids can lead to severe convergence issues while computing shear slip and tensile opening of intersecting and parallel fractures, particularly if they have similar slopes. Our proposed solution of this problem is to slightly deform the fracture geometry by merging critical segments. We discuss and show examples of which attributes the merged segment has to adopt to ensure the correct slip behaviour at an intersection. Thereby it is crucial that the flow topology remains unaltered. Analysing failures of kinked fractures and fracture intersections show the flexibility of the devised algorithm. Moreover, it is demonstrated that deformation and opening patterns of a natural network with more than 200 fractures are qualitatively predicted very well. This method is a simple solution to treat multiple fracture segments in a grid cell, hence it can be used for any model embedding fractures in non‐conforming grids.

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Induced microseismicity and reservoir growth at the Fjällbacka hot dry rocks project, Sweden

Cited by 36 publications

References 7 publications

Anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization

Anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

Consistent treatment of shear failure in embedded discrete fracture models using XFVM

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