Heat extraction from abandoned petroleum wells utilizing coaxial borehole heat exchanger in Ordos basin, China

To extract geothermal energy from abandoned petroleum wells in Ordos basin, China, a coaxial deep borehole heat exchanger (DBHE) is studied through a 3D numerical model. Factors, such as thermophysical properties, geological characteristics and operational conditions, are considered. Given the geothermal gradients and rock/soil properties, numerical results suggest that a sustainable heat extraction rate can be achieved for building heating purpose in long term; after 20 years’ operation, with an injection rate of 30 m3/h at 20 °C and wellbore length being 2350 m, the outlet temperature is around 24 °C, the heat load per unit depth ranges from 89.2 W/m to 67.7 W/m. Through comparison between on-site tests and numerical modeling, it is suggested that factors like well integrity, operational conditions and insulation between the inflow and outflow pipe should be taken into account. Numerical modeling on variation of well depth is performed; results show that both the wellbore length of 1800 m and 2350 m could satisfy a heat extraction load of 80 W/m, and the greater the wellbore length, the larger the outlet temperature. According to results from a DBHE array model, the general 200 m–300 m wellbore interval would not cause thermal interaction.