On one of the ways of geothermal energy production
This paper reviews the state of geothermal energy sector in the world. Today, geothermal heat generated at geothermal stations is used in many countries as electric or thermal energy. Huge potential of geothermal heat provides prospects for further development of this kind of energy in many industries. This entails the necessity in theoretical studies. One of the ways of geothermal energy production discussed in this paper is heating of liquid in a two-string well. Water is injected into the tubing-casing annulus. When moving downward, water is heated by the casing string walls due to convection and conduction. Heat from the earth depths is transferred to the surrounding rock. Average heat stream is 50 mW/m<sup>2</sup> varying from region to region. Heated water goes to the surface via the tubing string. The tubing string should be heat-insulated to minimize heat losses. This paper presents mathematical model of water heating in a wellbore due to conductive transfer of heat from the surrounding rock. Various well depths, rock temperature gradients and rates of flow are discussed. Based on diagrams of outlet liquid temperature vs time, injection rate, and temperature gradient, application of this technology in a certain region has been analyzed. This paper also presents temperature patterns near the wellbore at various time points, which can be used to analyze rock cooling due to conductive transfer of heat to the wellbore. Conclusions have been drawn concerning the possibility of using this method to capture geothermal energy in various regions.