Mechanical and hydraulic coupling of injection-induced slip along pre-existing fractures

Nemoto, Katsumi; Moriya, Hideshige; Niitsuma, Hiroaki; Tsuchiya, Noriyoshi

doi:10.1016/j.geothermics.2007.11.001

Cited by 38 publications

(29 citation statements)

References 55 publications

(58 reference statements)

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“…Using injection‐induced shear tests on saw cut fractures, Nemoto et al () used the term quasi‐static slip to represent fracture slip with a low velocity (less than 5 × 10 −5 m/s) and used dynamic slip to indicate fracture slip with a fast velocity (higher than 5 × 10 −5 m/s). However, the corresponding stress drop during fracture slip was not characterized in their tests.…”

Section: Discussionmentioning

confidence: 99%

“…As shown in Figure c, the effective normal stress and shear stress on the local n ‐ s coordinates of the fracture plane are as follows:

σ_{n}^{'} = ((), σ_{3} - P_{p}) + ((), σ_{1} - σ_{3}) {sin}^{2} θ

τ = ((), σ_{1} - σ_{3}) sin θ cos θ

where

σ_{n}^{'}

and τ are the effective normal stress and shear stress on the facture plane, respectively, θ is the fracture inclination angle with respect to the vertical axis of the sample, σ 1 is axial stress, σ 3 is confining pressure, and P p is pore pressure which can be estimated as the average of the injection pressure ( P i ) and the production pressure ( P o ):

P_{p} = 0.5 \times ((), P_{i} + P_{o})

For a given stress condition with a constant confining pressure ( σ 3 ) and an initial axial stress ( σ 1 ), constant axial stress (Bauer et al, ; Nemoto et al, ; Rutter & Hackston, ; Ye, Janis, & Ghassemi, ; Ye, Janis, Ghassemi, & Bauer, ) and constant piston displacement (Ye, Janis, & Ghassemi, ; Ye, Janis, Ghassemi, & Bauer, ) are two different experimental control modes that can be used to induce fracture slip by increasing injection pressure. These two control modes provide two different boundary conditions when running a triaxial shear test.…”

Section: Methodsmentioning

confidence: 99%

“…A few researchers have conducted triaxial‐injection shear tests on saw cut fractures (Bauer et al, ; French et al, ; Nemoto et al, ; Rutter & Hackston, ). French et al () conducted saw cut fracture slip tests on dry or saturated sandstones (permeable Berea and Darley Dale sandstones) to investigate the effects of stress path and fluid pressurization rate on fracture slip characteristics (slip velocity, shear stress drop, etc.).…”

Section: Introductionmentioning

confidence: 99%

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Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

2018

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Shear stimulation, so‐called hydroshearing, is believed to reactivate critical or near‐critical preexisting fractures by pressurized fluid injection, causing them to slip and dilate for economic production from geothermal and unconventional petroleum reservoirs. However, little or no experiments have been conducted to directly probe the coupled hydromechanical responses and permeability evolution during fracture shearing. In this paper, we present the results of novel injection‐induced shear tests on cylindrical granite samples each containing a single tensile or saw cut fracture. The shear test on rough fractures demonstrates that retainable permeability enhancement can be achieved through dilatant shear slip. The characteristic stick‐slip behavior of the fracture during shearing is also observed. Fracture aperture controlled by effective normal stress dominates the fluid flow in stick state, while in slip state, the major contributor to production increase is the irreversible normal dilation caused by fracture shear slip. The experimental data show that depending on the fracture roughness, the fracture slip process includes two quasi‐static slip intervals with a slip velocity of ~10−9 to ~10−6 m/s and a dynamic slip interval with a slip velocity of ~10−7 to ~10−5 m/s. The fracture slip correlates well with the associated stress relaxation: a faster fracture slip induces a quicker stress relaxation, and vice versa. The influence of surface roughness on the hydromechanical responses during fracture shearing and the shear‐induced asperity degradation are also studied. The various experimental observations on rough and smooth fractures clearly indicate that the key component to shear stimulation is fracture self‐propping by asperities.

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Section: Discussionmentioning

confidence: 99%

“…As shown in Figure c, the effective normal stress and shear stress on the local n ‐ s coordinates of the fracture plane are as follows:

σ_{n}^{'} = ((), σ_{3} - P_{p}) + ((), σ_{1} - σ_{3}) {sin}^{2} θ

τ = ((), σ_{1} - σ_{3}) sin θ cos θ

where

σ_{n}^{'}

P_{p} = 0.5 \times ((), P_{i} + P_{o})

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

2018

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“…A limited number of experimental studies were conducted to investigate fault sliding behavior induced by controlled fluid overpressure. Injection-induced slip experiments on granite with rough saw-cut fractures show that the occurrence of stepwise slip and temporal drops in pore pressure is associated with shear dilation (Nemoto et al, 2008). From triaxial shear experiments on permeable and impermeable sandstones with saw-cut fractures, Rutter and Hackston (2017) demonstrated that dynamic slip may be easily generated by fluid pressurization in the case of a less permeable rock matrix.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Study on Fluid‐Induced Fault Slip Behavior: The Role of Fluid Pressurization Rate

Wang

Kwiatek

Rybacki

et al. 2020

Geophysical Research Letters

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Understanding the physical mechanisms governing fluid‐induced fault slip is important for improved mitigation of seismic risks associated with large‐scale fluid injection. We conducted fluid‐induced fault slip experiments in the laboratory on critically stressed saw‐cut sandstone samples with high permeability using different fluid pressurization rates. Our experimental results demonstrate that fault slip behavior is governed by fluid pressurization rate rather than injection pressure. Slow stick‐slip episodes (peak slip velocity < 4 μm/s) are induced by fast fluid injection rate, whereas fault creep with slip velocity < 0.4 μm/s mainly occurs in response to slow fluid injection rate. Fluid‐induced fault slip may remain mechanically stable for loading stiffness larger than fault stiffness. Independent of fault slip mode, we observed dynamic frictional weakening of the artificial fault at elevated pore pressure. Our observations highlight that varying fluid injection rates may assist in reducing potential seismic hazards of field‐scale fluid injection projects.

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“…Experiments performed by Nemoto [52] show how a wet joint can transition between the modes depending on the roughness of the joint, as shown in the figure to the right. Thus, gouge formation [40] is not the only mechanism for inducing slow slip events.…”

Section: Fracture Monitoring (Dynamic Mechanical)mentioning

confidence: 99%

Creating the link between micro-seismic observations and hydro-mechanical changes in the reservoir

Johnson¹

2012

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Mechanical and hydraulic coupling of injection-induced slip along pre-existing fractures

Cited by 38 publications

References 55 publications

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

Laboratory Study on Fluid‐Induced Fault Slip Behavior: The Role of Fluid Pressurization Rate

Creating the link between micro-seismic observations and hydro-mechanical changes in the reservoir

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