A semi-analytical model to calculate energy production in single fracture geothermal reservoirs

The ultimate goal of geothermal reservoir management is to mine as much energy as possible from the reservoir. Since most of geothermal reservoirs are fractured, the development of improved techniques for monitoring, prediction, and control of two-phase mass and energy transport in the fractures are needed. Tracer testing is a powerful tool for characterizing fractures properties such as swept pore volume. By incorporating the pore volume of the fracture estimated from tracer data with a semi-analytical model of mass and energy transport in the fracture and matrix, the energy production rate can be calculated. Previous models to predict energy production assumed single-phase flow and semi-infinite matrix blocks and thus overestimate the energy that can be usefully produced from the reservoir. In this paper, a semi-analytical solution to the mass and energy balance equations is derived for two-phase flow in a fracture with heat conduction from a finite matrix. Calculations using the semi-analytical model are shown to be in good agreement with numerical simulations using the TETRAD simulator.