Performance of geothermal energy extraction in a horizontal well by using CO2 as the working fluid

With the rapid depletion of oil and gas reservoirs, many oil and gas wells become abandoned. These abandoned wells could be recovered if they are drilled in proper geothermal layers. Besides, CO2 is always selected as working fluid due to huge amount of resources, as well as for the purpose of CO2 geological storage. At present, the study on CO2 flow in the horizontal wellbores is quite limited. In this paper, a series of works were done on establishing a model to describe the heat and mass transfer process of CO2 in abandoned horizontal wellbores. The model is solved with numerical method on space. Some meaningful conclusions are listed below: (a). A smaller injection rate is crucial to obtain a higher geothermal production efficiency. Besides, a high injection pressure can exert too much requirement on the equipment; (b). In order to obtain a higher geothermal energy extraction rate, a larger mass flow rate is recommended; (c). a smaller injection temperature is recommended to obtain a higher geothermal energy extraction rate.