Effective permeability of deformation bands in fault damage zones – Can deformation bands reduce the risk of fault leakage?

Abstract

Faults are major geological structures that can dominate the flow paths in subsurface reservoirs by, e.g., connecting otherwise unconnected layers. In CO2 storage sites where the faults act as the main structural trap, the sealing properties of the faults must be fully understood, thus, requiring an accurate representation of the fluid flow close to the faults on all scales. This paper study the effects low permeable deformation bands have on the fluid flow in the near fault region. Deformation bands are generated stochastically, and numerical simulations that include the deformation bands explicitly in the simulation domain are performed to obtain an upscaled effective permeability. The numerical examples show that using a simple harmonic average to calculate the effective permeability may overestimate the effective permeability by up to an order of magnitude. A new analytical approximation of the effective permeability based on the deformation band length, density, and rotation is given, and this approximation fits the numerical simulations better than the harmonic average. The results confirm that deformation bands significantly alter the fluid flow close to faults and may decrease the potential leakage of CO2 through faults.