Numerical Modeling of 3D Transient Thermal Groundwater Flow and Heat Transport of Geothermal Fields of Low to Moderate Temperature

Abstract

Understanding of the changes in hydraulic heads and temperatures under the exploitation condition is important for the development and utilization of geothermal resources in a geothermal field. Mathematical models related to a geothermal system of low to moderate temperature are needed to simultaneously describe the 3D transient thermal groundwater flow and heat transport. On the basis of previous work, the governing equation of thermal groundwater flow is established, assuming that the density of water is a function of temperature and pressure. By assuming the geodynamic equilibrium between porous media and water is instantaneous, the energy equation of the geothermal system is developed, and is solved using the standard Galerkin finite element method. Fortran 90 is employed to compile the code FEMFH 1.0 for the numerical implementation of the mathematical models describing the thermal groundwater flow and heat transport. The code is composed of five parts, including grid discretization, input of data, solving for the hydraulic head, solving for temperature, and output of calculation results. The code is run for the numerical simulation of the bedrock carbonate reservoir in the Dongli area of the Tianjin geothermal field in northeastern North China Plain. The results show that the models and code enable description of the changes in hydraulic heads and temperatures with reasonable accuracy under the condition of a 6-month period of exploitation and injection followed by a 6-month period of non-pumping in each year.