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Modeling fluid injection induced microseismicity in shales
Language
English
Obiettivo Specifico
1TR. Studi per le Georisorse
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/15 (2018)
Pages (printed)
234
Issued date
2018
Abstract
Hydraulic fracturing in shales generates a cloud of seismic—tensile and shear—events that can
be used to evaluate the extent of the fracturing (event clouds) and obtain the hydraulic properties
of the medium, such as the degree of anisotropy and the permeability. Firstly, we investigate the
suitability of novel semi-analytical reference solutions for pore-pressure evolution around a well
after fluid injection in anisotropic media. To do so, we use cylindrical coordinates in the presence
of a formation (a layer) and spherical coordinates for a homogeneous and unbounded medium.
The involved differential equations are transformed to an isotropic diffusion equation by means
of pseudo-spatial coordinates obtained from the spatial variables re-scaled by the permeability
components. We consider pressure-dependent permeability components, which are independent
of the spatial direction. The analytical solutions are compared to numerical solutions to verify
their applicability. The comparison shows that the solutions are suitable for a limited
permeability range and moderate to minor pressure dependences of the permeability. Once the
pressure evolution around the well has been established, we can model the microseismic events.
Induced seismicity by failure due to fluid injection in a porous rock depends on the properties of
the hydraulic and elastic medium and in situ stress conditions. Here, we define a tensile threshold
pressure above which there is tensile emission, while the shear threshold is obtained by using the
octahedral stress criterion and the in situ rock properties and conditions. Subsequently, we
generate event clouds for both cases and study the spatio-temporal features. The model considers
anisotropic permeability and the results are spatially re-scaled to obtain an effective isotropic
medium representation. For a 3D diffusion in spherical coordinates and exponential pressure
dependence of the permeability, the results differ from those of the classical diffusion equation.
Use of the classical front to fit cloud events spatially, provides good results but with a re-scaled
value of these components. Modeling is required to evaluate the scaling constant in real cases.
be used to evaluate the extent of the fracturing (event clouds) and obtain the hydraulic properties
of the medium, such as the degree of anisotropy and the permeability. Firstly, we investigate the
suitability of novel semi-analytical reference solutions for pore-pressure evolution around a well
after fluid injection in anisotropic media. To do so, we use cylindrical coordinates in the presence
of a formation (a layer) and spherical coordinates for a homogeneous and unbounded medium.
The involved differential equations are transformed to an isotropic diffusion equation by means
of pseudo-spatial coordinates obtained from the spatial variables re-scaled by the permeability
components. We consider pressure-dependent permeability components, which are independent
of the spatial direction. The analytical solutions are compared to numerical solutions to verify
their applicability. The comparison shows that the solutions are suitable for a limited
permeability range and moderate to minor pressure dependences of the permeability. Once the
pressure evolution around the well has been established, we can model the microseismic events.
Induced seismicity by failure due to fluid injection in a porous rock depends on the properties of
the hydraulic and elastic medium and in situ stress conditions. Here, we define a tensile threshold
pressure above which there is tensile emission, while the shear threshold is obtained by using the
octahedral stress criterion and the in situ rock properties and conditions. Subsequently, we
generate event clouds for both cases and study the spatio-temporal features. The model considers
anisotropic permeability and the results are spatially re-scaled to obtain an effective isotropic
medium representation. For a 3D diffusion in spherical coordinates and exponential pressure
dependence of the permeability, the results differ from those of the classical diffusion equation.
Use of the classical front to fit cloud events spatially, provides good results but with a re-scaled
value of these components. Modeling is required to evaluate the scaling constant in real cases.
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