Thermal and Structural Analysis of the Casing in a High Temperature Geothermal Well During Discharge

Abstract

During the discharge of high temperature geothermal wells, the temperature difference in the well from non-flowing to flowing conditions is in the range of couple of hundreds of degrees centigrade and the pressure fluctuation is also large. The wellhead rises due to thermal expansion of the casing and the wellbore pressure, in some cases excessively because of concrete damage or poor cementing job. Measurements of a particular high temperature well were performed during discharge. Temperature and pressure changes were measured at the wellhead as well as the wellhead rise. A model was constructed using the finite element method (FEM) and computational results from the model were compared to the measurements. The results from the transient thermal FEM analysis show a rapid temperature response in the concrete layers of the well. In the concrete surrounding the production casing the temperature rises to roughly 95% of thermal equilibrium in only few hours. The coupling-concrete interactions in the FEM model indicate that the concrete has a weak spot and is most likely to get damaged at the coupling ends. The results show that the rise of the wellhead is exclusive to the uppermost 500 meters of the well but displacements are negligible beneath.