Challenge Problem Statements for a Code Comparison on the Fenton Hill Reservoir - an Invitation to the Geothermal Modeling Community

Abstract

The U.S. Department of Energy, Geothermal Technologies Office is supporting a code comparison study of numerical simulators for enhanced geothermal systems to test, diagnose differences, and demonstrate modeling capabilities of these modeling tools. By design, this study comprises two stages: benchmark problems and challenge problems. During the now completed benchmark problem stage, numerical simulators were exercised on a series of seven problems that considered various double and triple couplings of thermal, hydraulic, geomechanical, and geochemical (THMC) processes. Problems were selected and designed to isolate selected coupled processes, to be executed on workstation class computers, and have simple but illustrative metrics for result comparison. Simulation results and comparisons between the participating simulation groups for the benchmark problems have been published. Whereas the concepts for the seven benchmark problems selected for this study were the outcome of a single workshop, defining the objectives and nature of challenge problems required a longer-term effort. This paper describes the steps taken by the study to create two challenge problems and provides full problem statements to encourage international participation in providing solutions. Both challenge problems are based on the enhanced geothermal systems research conducted in hot dry rock at Fenton Hill, near Los Alamos, New Mexico, between 1974 and 1995, covering two research stimulation, development and circulation phases in two separate reservoirs. Both challenge problems address specific questions via numerical simulation in three topical areas: 1) reservoir creation/stimulation, 2) reactive and passive transport, and 3) thermal recovery. Challenge Problem #1 considers the Phase II Reservoir at Fenton Hill, located at true-vertical depths between 3,283 and 3,940 m, between wells EE-3A and EE-2A. Challenge Problem #2 considers the shallower Phase I Reservoir at Fenton Hill, located at true-vertical depths between 2,615 and 2,758 m, between wells EE-1 and GT-2B. The series of benchmark problems devised for this study were designed to test capabilities for modeling coupled processes under specified conditions. In contrast, the challenge problems seek to demonstrate what new understanding of enhanced geothermal systems can be generated via numerical simulation by the scientists and engineers that develop and apply these analytical tools.