The Research About CO₂ Enhanced Geothermal Systems Dynamic Characteristic

With the change of the world’s energy structure,we continually develop more high quality,less impact on the environment of new energy sources,including is currently being developed hot dry rock.The concrete engineering technology of hot dry rock development,called Enhanced Geothermal systems（EGS）.Specific refers to use the methods which similar to hydraulic crack,build a thermal reservoir which can make the fluid from the middle through and at the same time to extract rock in heat in deep rock density,after will be used to adopt hot after cold fluid conveying to the system to produce underground rock in range of 3¹0 km in the great heat.As for the quality of resources,hot dry rock resources can use to generate electricity or regional heating,solve the root of the national energy demand.As for the environmental protection,enhanced geothermal systems using carbon dioxide as with medium heat and CO₂ geological storage could be reached and solve the environmental problems to better.In this paper,choose to carbon dioxide as the whole process of heat transfer working medium,using the method of numerical simulation calculation and analysis of underground heat exchanger parts.The first is the involves the basic characteristic of the system,mainly includes:as in the thermal properties of carbon dioxide,which thermodynamic properties;compared with water as heat transfer medium,carbon dioxide have what advantage;hot dry rock of reservoir as the key technology ofenhanced geothermal systems,its key steps,principle and advantage of the characteristics of carbon dioxide for fracturing is what,and so on.After,in songliao basin geology model design as an example,and choose to double well heated model for numerical simulation,mainly studied what circumstance should consider injection wells and production wells wellbore heat transfer with the surrounding rock 、different circulation velocity of heat transfer fluid carbon dioxide on the stability of the geothermal reservoir operation cycle and the influence of heat extraction rate、using different heat transfer working medium such as water and carbon dioxide,which has more hot mining economy.Results show that when the injection well or well within the wellbore carbon dioxide output by small circulation flow rate of fluid flow,the heat transfer between the surrounding rock with wellbore should not be neglected.But when the carbon dioxide in the wellbore with larger circulation flow velocity of fluid flow,can not consider shaft and output shaft of the surrounding rock heat transfer;with the increase of the flow of carbon dioxide fluid velocity of reservoir,during the system running smoothly carbon dioxide extract heat from the reservoir has said,but,large circulation flow rate will make the system running smoothly cycle shortened,from the system of the whole economy,large circulation flow rate is unfavorable for geothermal exploitation;compared with water analysis shows that when the system is stable operation cycle is roughly same,carbon circulation flow rate is double that of water,but in this case,which after the flow through the reservoir,water pressure drop loss about carbon dioxide yes twice,the water from the reservoir absorption net heat than carbon dioxide absorption net heat raised less than one over ten.