Minimizing Induced Seismicity in Synthetic Geothermal Reservoirs by Fracture Control in Hydraulic Stimulation

Summary We investigated the induced seismicity, source mechanisms and mechanical responses of a decameter-scale hydraulic stimulation of a pre-existing shear zone in crystalline rock, at the Grimsel Test Site, Switzerland. The analysis reveals the meter-scale complexity of hydraulic stimulation, which remains hidden at the reservoir-scale. High earthquake location accuracy allowed the separation of four distinct clusters, of which three were attributed to the stimulation of fractures in the damage zone of the shear zone. The source mechanism of the larger-magnitude seismicity varied by cluster, and suggests a heterogeneous stress field already prevailing before stimulation, which is further modified during stimulation. In the course of the experiment, stress redistribution led to the aseismic initiation of a tensile-dominated fracture, which induced seismicity in the fourth of the identified seismic clusters. The streaky pattern of seismicity separated by zones without seismicity suggests fluid flow in conduits along existing fracture planes. The observed sub-meter scale complexity questions the forecasting ability of induced seismic hazard at the reservoir scale from small-scale experiments.

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Fault slip in hydraulic stimulation of geothermal reservoirs: Governing mechanisms and process-structure interaction

The Leading Edge ◽

10.1190/tle39120893.1 ◽

2020 ◽

Vol 39 (12) ◽

pp. 893-900

Author(s):

Inga Berre ◽

Ivar Stefansson ◽

Eirik Keilegavlen

Keyword(s):

Fault Reactivation ◽

Fluid Injection ◽

Hydraulic Stimulation ◽

Structure Interaction ◽

Geothermal Reservoirs ◽

Biot Coefficient ◽

Matrix Permeability ◽

Stress Changes ◽

Process Structure ◽

Stimulation Of

Hydraulic stimulation of geothermal reservoirs in low-permeability basement and crystalline igneous rock can enhance permeability by reactivation and shear dilation of existing fractures. The process is characterized by interaction between fluid flow, deformation, and the fractured structure of the formation. The flow is highly affected by the fracture network, which in turn is deformed because of hydromechanical stress changes caused by the fluid injection. This process-structure interaction is decisive for the outcome of hydraulic stimulation, and, in analysis of governing mechanisms, physics-based modeling has potential to complement field and experimental data. Here, we show how recently developed simulation technology is a valuable tool to understand governing mechanisms of hydromechanical coupled processes and the reactivation and deformation of faults. The methodology fully couples flow in faults and matrix with poroelastic matrix deformation and a contact mechanics model for the faults, including dilation because of slip. Key elements are high aspect ratios of faults and strong nonlinearities in highly coupled governing equations. Example simulations using our open-source software illustrate direct and indirect hydraulic fault reactivation and corresponding permeability enhancement. We investigate the effect of the fault and matrix permeability and the Biot coefficient. A higher matrix permeability leads to more leakage from a permeable fault and thus suppresses reactivation and slip of the fault compared to the case with a lower matrix permeability. If a fault is a barrier to flow, increase of pressure because of the fluid injection results in stabilization of the fault; the situation is opposite if the fault is highly permeable compared to the matrix. For the given setup, lowering the Biot coefficient results in more slip than the base case. While conceptually simple, the examples illustrate the strong hydromechanical couplings and the prospects of physics-based numerical models in investigating the dynamics.

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Effect of Ground Vibration on Surface Structures and Human Environments -Application of Blasting Vibration to Induced Seismicity in EGS Hydraulic Stimulation-

Tunnel and Underground Space ◽

10.7474/tus.2013.23.6.521 ◽

2013 ◽

Vol 23 (6) ◽

pp. 521-537 ◽

Cited By ~ 2

Author(s):

Chung-In Lee ◽

Ki-Bok Min

Keyword(s):

Induced Seismicity ◽

Ground Vibration ◽

Surface Structures ◽

Blasting Vibration ◽

Hydraulic Stimulation

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Induced seismicity risk analysis of the hydraulic stimulation of a geothermal well on Geldinganes, Iceland

Natural Hazards and Earth System Science ◽

10.5194/nhess-20-1573-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 1573-1593

Author(s):

Marco Broccardo ◽

Arnaud Mignan ◽

Francesco Grigoli ◽

Dimitrios Karvounis ◽

Antonio Pio Rinaldi ◽

...

Keyword(s):

Risk Assessment ◽

Risk Analysis ◽

Induced Seismicity ◽

Energy Demand ◽

Total Duration ◽

Individual Risk ◽

Hydraulic Stimulation ◽

Starting Point ◽

Damage Risk ◽

Stimulation Of

Abstract. The rapid increase in energy demand in the city of Reykjavik has posed the need for an additional supply of deep geothermal energy. The deep-hydraulic (re-)stimulation of well RV-43 on the peninsula of Geldinganes (north of Reykjavik) is an essential component of the plan implemented by Reykjavik Energy to meet this energy target. Hydraulic stimulation is often associated with fluid-induced seismicity, most of which is not felt on the surface but which, in rare cases, can be a nuisance to the population and even damage the nearby building stock. This study presents a first-of-its-kind pre-drilling probabilistic induced seismic hazard and risk analysis for the site of interest. Specifically, we provide probabilistic estimates of peak ground acceleration, European microseismicity intensity, probability of light damage (damage risk), and individual risk. The results of the risk assessment indicate that the individual risk within a radius of 2 km around the injection point is below 0.1 micromorts, and damage risk is below 10−2, for the total duration of the project. However, these results are affected by several orders of magnitude of variability due to the deep uncertainties present at all levels of the analysis, indicating a critical need in updating this risk assessment with in situ data collected during the stimulation. Therefore, it is important to stress that this a priori study represents a baseline model and starting point to be updated and refined after the start of the project.

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Induced seismicity risk analysis of the hydraulic stimulation of a geothermal well on Geldinganes, Iceland

10.5194/nhess-2019-331 ◽

2019 ◽

Author(s):

Marco Broccardo ◽

Arnaud Mignan ◽

Francesco Grigoli ◽

Dimitrios Karvounis ◽

Antonio Pio Rinaldi ◽

...

Keyword(s):

Risk Assessment ◽

Risk Analysis ◽

Induced Seismicity ◽

Energy Demand ◽

Total Duration ◽

Hot Water ◽

Individual Risk ◽

Hydraulic Stimulation ◽

Damage Risk ◽

Stimulation Of

Abstract. The rapid increase in energy demand in the city of Reykjavik has posed the need for an additional supply of hot water from deep geothermal energy. The deep hydraulic (re-)stimulation of well RV-43 on the peninsula of Geldinganes (north of Reykjavik) is an essential component of the plan implemented by Reykjavik Energy to meet this energy target. Hydraulic stimulation is often associated with fluid-induced seismicity, most of which is not felt on the surface, but which, in rare cases, can cause nuisance to the population and even damage to the nearby building stock. This study presents a first of its kind pre-drilling probabilistic induced-seismic hazard and risk analysis for the site of interest. Specifically, we provide probabilistic estimates of peak ground acceleration, European microseismicity intensity, probability of light damage (damage risk), and individual risk. The results of the risk assessment indicate that the individual risk within a radius of 2 km around the injection point is below 0.1 micromorts, and damage risk is below 10−2, for the total duration of the project. However, these results are affected by several orders of magnitude of variability due to the deep uncertainties present at all levels of the analysis, indicating a critical need in updating this a-priory risk assessment with in-situ data collected during the stimulation.

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