In order to effectively activate the dormant assets of oil fields, the abandoned oil and gas wells are transformed into coaxial cased heat exchangers to extract geothermal energy and realise the successive development of energy, taking a shut-down oil well in Dingbian County, Shaanbei as the study example, the borehole heat exchanger module of the open-source software OpenGeoSys was used to study its heat exchange performance. Effects of different circulation flow rates, inner tube diameters of heat exchanger, power of heat exchanger, and seasonal heat extraction cycles on the performance of the transformed well are analyzed. Results show that when the heat exchange power is fixed, a flow rate of 15 m3/h can both obtain a higher outlet water temperature and ensure a long-term stable operation of the heat exchanger，using different diameters, variation of water temperature at the outlet end of the inner tube is only 0.17 ℃. For every additional 50 W of heat exchange power per meter, the outlet water temperature at the end of the heating season decreases by about 17.55 ℃, with an average decrease of 0.35 ℃/W. When the heat exchange power is constant, for every one additional month of a heating season, the annual minimum outlet temperature decreases by about 1 ℃， when the heating season is 4, 5, 6, 7, 8 months, the time required for the outlet temperature to reach a quasi-steady state during the heating season is 15, 18, 21, 24, 27 years, respectively. In order to improve the heat exchange performance of the geothermal well, it is recommended that a seasonal cycle of 5 months of heat extraction and 7 months of well shutdown in Ordos Basin area should be used, with a circulation flow rate of 15 m3/h and a heat exchange power of 100 W.