Mechanical Stiffness and Permeability of a Reservoir‐Scale Rough Fracture During Closure
Résumé
We study how the normal stiffness and the permeability of a realistic rough fracture at the field scale are linked and evolve during its closure up to the percolation threshold. We base our approach on a well-established self-affine geometric model for fracture roughness, which has proven to be a relevant proxy from laboratory to multi-kilometer scales. We explore its implications for fracture apertures in reservoir-scale open channels. We build our approach on a finite element model using the MOOSE/GOLEM framework and conduct numerical flow-through experiments in a 256 granite reservoir hosting a single, partially sealed fracture under variable normal loading conditions and undrained conditions. Navier-Stokes flow is solved in the embedded 3-dimensional rough fracture, and Darcy flow is solved in the surrounding poroelastic matrix. We study the evolution of the mechanical stiffness and fluid permeability of the fracture-rock system during fracture closure including mechanisms that impact the contact surface geometry like asperity yield and deposit of fracture-filling material in the open space of the rough fracture. The largely observed stiffness characteristic is shown to be related to the self-affine property of the fracture surface. A strong anisotropy of the fracture permeability is evidenced when the fluid percolation thresholds are exceeded in two orthogonal directions of the imposed pressure gradient. We propose a unifying physically based law for the evolution of stiffness and permeability in the form of an exponential increase in stiffness as permeability decreases.
Domaines
Modélisation et simulation
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JGR Solid Earth - 2024 - Deng - Mechanical Stiffness and Permeability of a Reservoir‐Scale Rough Fracture During Closure.pdf (3.6 Mo)
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