Damage evolution and fluid flow in poroelastic rock |
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| Authors: | V Lyakhovsky Ya Hamiel |
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| Institution: | (1) Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem, 95501, Israel;(2) IGPP, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA |
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| Abstract: | We present a formulation for mechanical modeling of the interaction between fracture and fluid flow. Our model combines the
classic Biot poroelastic theory and a damage rheology model. The model provides an internally consistent framework for simulating
coupled evolution of fractures and fluid flow together with gradual transition from brittle fracture to cataclastic flow in
high-porosity rocks. The theoretical analysis, based on thermodynamic principles, leads to a system of coupled kinetic equations
for the evolution of damage and porosity. A significant advantage of the model is the ability to reproduce the entire yield
curve, including positive and negative slopes, in high-porosity rocks by a unified formulation. A transition from positive
to negative values in the yield curve, referred to as a yield cap, is determined by the competition between the two thermodynamic
forces associated with damage and porosity evolution. Numerical simulations of triaxial compression tests reproduce the gradual
transition from localized brittle failure to distributed cataclastic flow with increasing pressure in high-porosity rocks
and fit well experimentally measured yield stress for Berea sandstone samples. We modified a widely used permeability porosity
relation by accounting for the effect of damage intensity on the connectivity. The new damage-permeability relation, together
with the coupled kinetics of damage and porosity evolution, reproduces a wide range of realistic features of rock behavior.
We constrain the model variables by comparisons of the theoretical predictions with laboratory results reporting porosity
and permeability variation in rock samples during isotropic and anisotropic loading. The new damage-porosity-permeability
relation enables simulation of coupled evolution of fractures and fluid flow and provides a possible explanation for permeability
measurements in high-porosity rocks, referred to as the “apparent permeability paradox.”
The text was submitted by the authors in English. |
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