Changes in fluid flux and hydraulic head in a geothermal confined aquifer

Understanding the changes in fluid flux and hydraulic head in a confined aquifer where heat flow from below exists is important in the development of a geothermal field of basin-type. A 3D mathematical model describing thermal groundwater flow and heat transport is established. The partial differential governing equations are solved with the standard Galerkin finite element method and the streamline upwind Petrov–Galerkin method. Two cases of temperature differences between the bottom and upper boundaries are considered and one case of hydraulic gradient difference between the left and right boundaries are also examined. The numerical results show that when the temperature of the aquifer is under normal temperature and the temperatures of the top boundary are 45, 50 and 55 °C with the temperature of the bottom boundary of 60 °C, the values of fluid flux through the vertical flow section are 1000, 2134, 2214 and 2295 m3/d in Case 2, which are mainly affected by the dynamic viscosity \(u\). When the temperature difference between the top and bottom boundaries increases, the hydraulic gradient in x direction slightly increases with the increasing temperature difference. When the temperature differences are 15, 10, 5 and 0 °C, respectively, the hydraulic gradients are 0.01005, 0.01003, 0.01002 and 0.01 in Cases 1 and 2, and almost keep the same value of 0.01 under normal temperature. The hydraulic head in z direction obeys a nonlinear change and can be described with a 2nd order polynomial function.