Coupled modeling of multiphase flow and fault poromechanics during geologic CO2 storage

Coupling between fluid flow and mechanical deformation in porous media plays a critical role in geologic storage of CO2. One of the key issues in simulation of CO2 sequestration is the ability to describe the mechanical and hydraulic behavior of faults, and the influence of the stress tensor and change in pressure on fault slip. Here, we present a new computational approach to model coupled multiphase flow and geomechanics of faulted reservoirs. We represent faults as surfaces embedded in a three-dimensional medium by using zero-thickness interface elements to accurately model fault slip under dynamically evolving fluid pressure and fault strength. We incorporate the effect of fluid pressures from multiphase flow in the mechanical stability of faults by defining a fault pressure. We employ a rigorous formulation of nonlinear multiphase geomechanics based on the increment in mass of fluid phases, instead of the change in porosity. Our nonlinear formulation is required to properly model systems with high compressibility or strong capillarity, as can be the case for geologic CO2 sequestration. To account for the effect of surface stresses along fluid-fluid interfaces, we use the equivalent pore pressure in the definition of multiphase effective stress. We develop a numerical simulation tool by coupling a multiphase flow simulator with a mechanics simulator, using the unconditionally stable fixed-stress scheme for a computationally efficient sequential solution of two-way coupling between flow and geomechanics. We validate our modeling approach using several synthetic test cases that illustrate the onset and evolution of earthquakes from fluid injection. © 2013 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of GHGT. * Corresponding author. Tel.: +1-617-253-7191; fax: +1-617-253-7475. E-mail address: [email protected] © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of GHGT-12 3314 Birendra Jha and Ruben Juanes / Energy Procedia 63 ( 2014 ) 3313 – 3329