| Abstract |
In this presentation, a new PFLOTRAN process model which simulates variable density, multiphase fluid flow and reactive transport with energy through an equivalent continuum porous media (ECPM) representation of a discrete fracture network, is introduced. PFLOTRAN is a well-established subsurface simulator that has been used previously to study problems in subsurface flow and transport, including CO2 sequestration, geothermal processes, radioactive waste repositories, and other hydrogeological systems (Hammond et al. 2014). Because it is open-source software, with active developer and user communities, PFLOTRAN is an ideal platform in which to develop advanced simulation capabilities for modeling enhanced geothermal systems, while ensuring broad benefits to future researchers interested in using or expanding on the current development work. Moreover, its reactive transport and geochemistry capabilities are unmatched by any other community-based, research-class simulator, and thus PFLOTRAN provides a wealth of modeling capabilities for treating the complex geochemistry inherent in geothermal systems. The new PFLOTRAN Geothermal Fracture Model, developed at Sandia National Laboratories, allows users to define an ECPM representation of discrete fracture networks, directly in the PFLOTRAN input file, consisting of any combination of individually defined fractures with specified fracture parameters (i.e., deterministic) or fracture families defined by sampling from statistical distributions of key fracture parameters (i.e., stochastic). Key fracture parameters include: (1) the fracture spatial orientation, in terms of the fracture center location and fracture plane normal vector, (2) fracture spatial extent, in terms of the maximum lengths along all 3 dimensions, and (3) fracture aperture size. Once an initial ECPM representation of the discrete fracture network is defined, fracture permeability can evolve in time throughout the simulation as a result of two key processes: (1) changes in fracture aperture due to thermal expansion and/or contraction of the host rock matrix, and (2) geochemical processes such as mineral dissolution and precipitation. Changes in fracture permeability are sequentially coupled to both the flow and reactive transport process models at every time-step. More information and documentation on PFLOTRAN is available at https://www.pflotran.org, and the software can be downloaded for free at https://bitbucket.org/pflotran/pflotran. PFLOTRAN is an open-source software which can be distributed and/or modified under the terms of the GNU Lesser General Public License (version 2.1 or later) as published by the Free Software Foundation. Sandia National Laboratories is a multimission laboratory operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration. SAND2024-11989A. |