A novel technique for extraction of geothermal energy from abandoned oil wells

Abstract

This paper investigates the possibility of design and construction of a geothermal heat exchanger suitable for installation in abandoned oil wells. Based on the in-situ data collected, an amenable heat transfer numerical model is developed with which the performance of the underground geothermal heat exchanger is assessed. Using a finite volume descretization method, the transient three-dimensional temperature and flow fields in the ground and within the fluid flowing through the heat exchanger are assessed. The model is capable of controlling the rate of heat extraction through continuous adjustment of the inlet water temperature. Sustainable rate of heat extraction is calculated under different heat load variations and for various operational life cycles. Effects of geometrical dimensions and the thermal properties of the medium on the performance of the geothermal heat exchanger are examined. It is found that thermal conductivity of ground plays an important role on the performance of the system. The results of the research suggest that effect of natural convection cannot be always neglected and depending on the hydraulic conductivity of the porous ground medium, an estimation of the significance of natural convection is given. The term "sustainable rate of heat extraction" is introduced and a substantial study of how the geometrical and the thermo-physical properties of the geothermal system affect the sustainable rate of heat extraction is carried out. Eventually, this study aims to create the engineering infrastructure required for the design of underground heat exchangers suitable for extraction of geothermal heat from abandoned oil wells.