Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Uçar, Eren; Berre, Inga; Keilegavlen, Eirik

doi:10.1002/2017gl074282

Cited by 31 publications

(24 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The finite volume scheme has previously been extended to fracture deformation by adding additional displacement unknowns on the fracture faces [45]. This formulation was successfully used to implement a fixed-point type iteration to approximate the friction bound [43]; however, this formulation suffers from the fact that a step length parameter needs to be tuned and that it might require many iterations to converge [6]. An advantage of the scheme used in this work, where the Lagrange multiplier of the hybrid formulation is coupled with the surface traction obtained from the finite volume scheme, is that it gives a natural formulation of the contact condition per subface.…”

Section: Introductionmentioning

confidence: 99%

Finite volume discretization for poroelastic media with fractures modeled by contact mechanics

Berge

Berre

Keilegavlen

et al. 2019

Numerical Meth Engineering

Self Cite

View full text Add to dashboard Cite

A fractured poroelastic body is considered where the opening of the fractures is governed by a nonpenetration law while slip is described by a Coulomb-type friction law. This physical model results in a nonlinear variational inequality problem. The variational inequality is rewritten as a complementary function, and a semismooth Newton method is used to solve the system of equations. For the discretization, we use a hybrid scheme where the displacements are given in terms of degrees of freedom per element, and an additional Lagrange multiplier representing the traction is added on the fracture faces. The novelty of our method comes from combining the Lagrange multiplier from the hybrid scheme with a finite volume discretization of the poroelastic Biot equation, which allows us to directly impose the inequality constraints on each subface. The convergence of the method is studied for several challenging geometries in 2d and 3d, showing that the convergence rates of the finite volume scheme do not deteriorate when it is coupled to the Lagrange multipliers. Our method is especially attractive for the poroelastic problem because it allows for a straightforward coupling between the matrix deformation, contact conditions, and fluid pressure.

show abstract

Section: Introductionmentioning

confidence: 99%

Finite volume discretization for poroelastic media with fractures modeled by contact mechanics

Berge

Berre

Keilegavlen

et al. 2019

Numerical Meth Engineering

Self Cite

View full text Add to dashboard Cite

show abstract

“…The fluid injection causes elevated pressures inside the fractures and reduces contact forces facilitating shear slip on favorably oriented faults (Kohl & Mégel, ). Crack closure after fluid injection may also trigger seismicity by enhancing pressure propagation related to the abrupt decrease of porosity and fluid expulsion (Ucar et al, ). Heinicke et al () highlight the role of hydrothermal alteration in filling preexisting fractures and the consequent increase in the fluid pressure into the reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Seismic and Geodetic Evidences of a Hydrothermal Source in the Md 4.0, 2017, Ischia Earthquake (Italy)

et al. 2019

View full text Add to dashboard Cite

Seismic events characterize active hydrothermal and volcanic areas and may be due to magma/fluid migration, hydrothermal pressurization, gravitational instability, and local tectonics. On 21 August 2017, an M d 4.0 earthquake occurred at Ischia volcanic island (Italy), within an active hydrothermal system. We analyze seismic, Global Positioning System, and interferometric synthetic aperture radar data to shed light on the source mechanism of such an event. The low-frequency content (2 Hz), the low stress drop (0.01 MPa), and a low S/P spectral ratio suggest the involvement of fluids in the source mechanism. The focal mechanism suggests a mixed shear-tensile (opening) rupture with the P first arrivals showing up movements in the nearest stations. Geodetic data describe an E-W elongated area of coseismic subsidence overlapping a WSW-ENE fault bounding the hydrothermal reservoir at depth. The modeled deformation field is consistent with a two-source model consisting of a WSW-ESE striking, north dipping normal fault, and a closing subhorizontal crack. This closure immediately followed an initial opening related to a fluid pressurization event responsible for the earthquake. We show that moderate magnitude earthquakes in active hydrothermal areas may be associated with the pressurization/depressurization cycles of a hydrothermal reservoir due to self-sealing processes and not to the arrival of new fluids from depth. Other events like that recorded at Ischia, which have affected the island in historical times, are not necessarily associated with 'volcanic unrest' episodes and imply the occurrence of fault-valve mechanisms. Therefore, the dynamics of hydrothermal systems must be taken into account in the seismic hazard evaluation.

show abstract

“…We believe that the capabilities of the presented methodology will be valuable in understanding governing mechanisms for permeability enhancement and induced seismicity in stimulation of fractured geothermal reservoir. The methodology has already been applied in investigating the effects of the normal closure of fractures on postinjection seismicity (Ucar et al, ). Herein, we have investigated the effect of rock matrix permeability in reservoir stimulation.…”

Section: Discussionmentioning

confidence: 99%

Three‐Dimensional Numerical Modeling of Shear Stimulation of Fractured Reservoirs

2018

Self Cite

View full text Add to dashboard Cite

Shear-dilation-based hydraulic stimulations can enable commercial exploitation of geothermal energy from reservoirs with inadequate initial permeability. While contributing to enhancing the reservoir's permeability, hydraulic stimulation processes may also lead to undesired seismic activity. Here we present a three-dimensional numerical model aiming to aid increased understanding of shear-dilation based hydraulic stimulation and its consequences. The fractured reservoir is modeled as a network of explicitly represented large-scale fractures immersed in a permeable rock matrix. The numerical formulation is constructed by coupling three physical processes: fluid flow, fracture deformation, and rock matrix deformation. For flow simulations, the discrete fracture-matrix model is used, which allows fluid transport from high-permeable conductive fractures to rock matrix and vice versa. The mechanical behavior of the fractures is modeled with reversible and irreversible deformations corresponding to elastic deformation and slip. Linear elasticity is assumed for mechanical deformation and stress alteration of the rock matrix. Fractures are modeled as lower-dimensional surfaces embodied in the domain, subjected to specific governing equations for their deformation along the tangential and normal directions. Both the fluid flow and momentum balance equations are approximated by finite volume discretizations. The new numerical model is demonstrated considering a three-dimensional fractured formation with a network of 20 explicitly represented fractures. The effects of fluid exchange between fractures and rock matrix on the permeability evolution and the generated seismicity are examined for test cases resembling realistic reservoir conditions. Numerical modeling of the shear stimulation can be a powerful tool for estimating the potential performance of the stimulated reservoir, for understanding governing mechanisms, and/or for forecasting possible undesired by-products of the stimulation process. However, due to the complex structure of the fractured rock and the number of coupled physical processes involved in the stimulation process, many modeling aspects remain unresolved. Challenges include the description of the mechanical and hydraulic behavior of the UCAR ET AL. 3891

show abstract

Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Cited by 31 publications

References 35 publications

Finite volume discretization for poroelastic media with fractures modeled by contact mechanics

Finite volume discretization for poroelastic media with fractures modeled by contact mechanics

Seismic and Geodetic Evidences of a Hydrothermal Source in the Md 4.0, 2017, Ischia Earthquake (Italy)

Three‐Dimensional Numerical Modeling of Shear Stimulation of Fractured Reservoirs

Contact Info

Product

Resources

About