Bridging the Gap between Complex Numerical Modeling and Rapid Scenario Assessment: A Dimensionless Parameter Approach for Enhanced Geothermal Systems

Abstract

Assessing the timing, cost, and market competitiveness of geothermal energy production requires understanding the thermal performance of the reservoir, but numerical models of reservoir performance can be complex and time consuming to execute. The computational overhead and numerical complexity runs counter to the needs of real-time scenario analysis and the propagation of uncertainties in the physical, technological, and economical parameters. The ability of existing analytical solutions to simulate realistic heat transfer in a reservoir is limited by the complexity of the system. Here, we develop an approach for utilizing output from complex numerical models in a rapidly deployable systems based assessment model. The approach generates a series of dimensionless temperature drawdown curves based on the numerical modeling of a number of reservoir conditions that are specific to enhanced geothermal systems (EGS). This approach allows for substituting a complicated numerical solution with lookup tables that can be used in system dynamic assessment models. We considered a homogeneous 3-dimensional reservoir. A series of simulations were run by varying the distance between the injection and production wells, the permeability, the reservoir thickness, the mass injection rate, the injection temperature, the initial reservoir temperature, the porosity and the reservoir depth. These simulations were done using FEHM (finite element multi-phase flow and heat and mass transport computer code, Los Alamos National Laboratories) to compute the temperature drawdown T(t) in the production well. The T(t) curves were converted into dimensionless Td(td) curves. Dimensionless temperature (Td) and time (td) were defined similarly to the corresponding dimensionless parameters in Gringarten et al. solution. The approach was verified by using the dimensionless curves to predict temperature drawdown and comparing the predicted curves with the FEHM simulations.