Abstract: Injection of CO2 and water in saline aquifers or oil reservoirs causes changes of pressure, saturation and concentrations that affect the state of stress and promote chemical reactions in the host rock, resulting in porosity and permeability variations. It is therefore a coupled hydro-mechanical and chemical (HMC) problem. The fault reactivation problem considers that shear (with dilation), tension or compression of filling material may cause changes in hydraulic properties. Important aspects related to the fault reactivation problem are the huge range of variation of hydraulic and mechanical parameters in the damage zones (with fracture networks) and core zones (with deformation bands) and the lack of reliable experimental data associated with the materials in these highly heterogeneous zones.
To circumvent these limitations, models that predict permeability by considering analogues have been used to enhance the understanding of the relative contribution of deformation bands and fracture networks to reservoir quality. The analogue data can overcome scale limitations (sub-seismic to mm) and/or lack of consistency in subsurface datasets (e.g., seismic data, well logs, and cores). Fluid flow modeling of naturally fractured reservoirs remains a challenge because of the complex nature of fracture systems controlled by various chemical and physical phenomena. A discrete fracture network (DFN) model represents an approach to capturing the relationship of fractures in a fracture system and topology represents the connectivity aspect of the fracture planes, which have a fundamental role in flow simulation in geomaterials involving fractures and the rock matrix. On the other hand, deformation bands are subseismic brittle structures with tabular geometries that accommodate small shear offsets, occurring as either single structures or cluster zones (where slip surfaces can initiate), associated with the process of faulting in porous rocks and sediments (>15% porosity) due to grain rearrangement and strain softening, affecting the petrophysical properties of host rocks. Deformation bands can influence fluid flow within reservoirs, mainly acting as flow barriers. We used the finite element method for modeling the fracture system, with the incorporation of discontinuities for the representation of fractures in the medium. It has been shown the influence of fractures interconnection degree (topological patterns) on the equivalent permeability of the fractured medium. Our petrophysical analysis showed that samples affected by deformation bands have lower porosity (by up to two orders of magnitude) and permeability (by up to four orders of magnitude) values than samples collected in the host rocks. Numerical fluid flow simulation allowed us to conclude that the deformation bands act as partial flow barriers where the hydraulic head can indicate the barrier effect intensity.
Numerical simulation of multiphase and multicomponent flow of CO2, oil and water with mechanical coupling allows realistic modeling of fault reactivation. Whether the fault is activated or not is governed by the boundary conditions of the problem and by the modeling of the constitutive behavior of involved materials.
Bio: Professor Leonardo Guimaraes is a Full Professor in the Department of Civil Engineering at the Federal University of Pernambuco, Brazil. His research interests and areas are Computational Geomechanics, Reservoir Simulation, and Numerical Methods, with main applications in environmental geotechnics, reservoir engineering, and coupled thermo-hydro-mechanical and chemical modeling via finite element method.
Professor Guimaraes is a holder of the Industrial Research Chair in Reservoir Simulation of Energi, a non-profit foundation based in Calgary (Alberta, Canada), with a focus on Reservoir Modelling and Robust Optimization.
He is also a Principal Investigator and consultant for research projects funded by Petrobras (Brazilian State Oil Company) in multi-physics simulation of oil reservoirs and CO2 injection.
Professor Guimaraes is a frequent reviewer for top journals and research proposals in geomechanics and coupled Thermo-Hydro-Mechanical and Geochemical problems in porous media.