SSD - Berre Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Dr. Inga Berre - Three-Dimensional Numerical Modelling of Hydraulic Stimulation of Geothermal Reservoirs: Permeability Enhancement and Induced Seismicity

Department of Mathematics, University of Bergen, Norway

Abstract

Understanding the controlling mechanisms underlying injection‐induced seismicity is important for optimizing reservoir productivity and addressing seismicity‐related concerns related to hydraulic stimulation in Enhanced Geothermal Systems as well as other sub-surface engineering applications. Hydraulic stimulation enhances permeability through elevated pressures, which cause normal deformations and the shear slip of preexisting fractures.

The process involves strongly coupled physical processes, involving reactivation and deformation of fractures, deformation of surrounding rock, and fluid flow in the fractures and their surroundings. The talk presents an approach for modelling of the governing flow and mechanics, where fractures are modelled as surfaces with associated apertures in a three-dimensional domain. Considering both flow and deformation, processes in the fractures are coupled with processes in the surrounding rock. While flow is assumed to be governed by Darcy’s law both in the fractures and the matrix, the model for deformation is inherently different for the fractured and non-fractured parts of the domain. Fracture reactivation is based on a Mohr-Coulomb criterion, and the corresponding irreversible deformation is based on an empirical model for friction.
Furthermore, fractures may continuously deform in the normal direction according to a non-linear model accounting for the normal loading. For the rock surrounding the matrix, we assume a continuous elastic deformation. Numerical results are presented to show how the methodology can be applied to understand important mechanisms affecting permeability and induced seismicity. In particular, we show how normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for postinjection seismicity.