Numerical simulation on the heat extraction from the porous medium-low temperature geothermal reservoirs by self-circulation wellbore and its enhanced methods

Abstract

Benefiting from the closed wellbore space for heat-carrying fluid circulation, the wellbore self-circulation technology can effectively avoid the problems of wellbore scaling, corrosion, formation deficit, and reinjection capacity decline in the traditional geothermal mining technology. However, its applicability and how to enhance the heat extraction rate still need to be further clarified, especially in the medium-low temperature geothermal reservoirs. In this study, a comprehensive simulation model on the heat extraction from a porous medium-low temperature geothermal reservoir in Xining Basin, China by self-circulation wellbore was established to study the heat extraction capacity and influencing factors. Different methods to improve the heat extraction rate of self-circulation wellbore were investigated, compared and discussed. The results show that the heat extraction rate of the self-circulation wellbore is relatively low. Under reasonable cycling, wellbore and reservoir conditions, the heat extraction rate can reach 20–100 kW, and the heat extraction range is mainly within 50 m around the well. The injection temperature, geothermal water seepage, and formation lithology have significant effects on heat extraction rate. The horizontal well, intermittent self-circulation, open self-circulation, and cross-layer pumping and reinjection can all enhance the heat extraction capacity of the self-circulation wellbore but with different disadvantages. Comprehensively considering the low capital cost, slight scaling and corrosion risk and good heat extraction performance, the self-circulation of open wellbore is the best way to enhance the heat extraction rate in a medium-low temperature geothermal reservoir.