针对水基增强型地热系统在地热开采过程中易损失流量,造成资源浪费等问题,选取CO2作为CO2羽流地热系统的传热工质,通过热交换实验、溶蚀实验和CO2驱后气水相渗曲线评价实验等手段,定量评估超临界CO2在不同条件下的换热性能和CO2-水溶液对岩石的溶蚀效果,并对CO2和水的携热能力及采热速率进行评价。研究表明:在传热工质的质量流量相同的条件下,当注入温度为24 ℃时,CO2换热效率比水高27%以上,当注入温度为35 ℃时,CO2换热效率比水高8%以上,CO2的换热效率和携热能力均高于水;当储层压力升至25 MPa时,CO2热容值为水热容值的0.45倍,流动能力为水的2.5倍,CO2的采热优势更强;CO2与绿泥石反应的溶蚀作用较强,导致岩心孔隙空间和渗流通道增大,有效提高了储层渗透率,增强了流体在孔隙中的对流,提高了热传递效率。该研究为CO2羽流地热资源开采技术的应用推广提供了基础理论依据。
To address the issues of flow loss and resource waste during geothermal extraction in water-based enhanced geothermal systems,CO2 was selected as the heat transfer fluid for the CO2-plume geothermal system. Through methods such as heat transfer experiments,dissolution experiments,and post-CO2 flooding gas-water relative permeability curve evaluation experiments,the heat transfer performance of supercritical CO2 under different conditions and the dissolution effect of CO2 aqueous solution on rocks were quantitatively assessed. Additionally,the heat-carrying capacity and heat extraction rate of CO2 and water were evaluated. The study shows that under the condition of the same mass flow rate of the heat transfer fluid,when the injection temperature is 24 ℃,the heat transfer efficiency of CO2 is over 27% higher than that of water;when the injection temperature is 35 ℃,the heat transfer efficiency of CO2 is over 8% higher than that of water,indicating that CO2 has higher heat transfer efficiency and heat-carrying capacity than water. When the formation pressure of the gas reservoir rises to 25 MPa,the heat capacity value of CO2 is 0.45 times that of water,and its mobility is 2.5 times that of water,making CO2′s heat extraction advantage more pronounced. The dissolution reaction of CO2 with chlorite is strong,leading to an increase in the pore space and permeation channels of the core,effectively enhancing the reservoir permeability,strengthening the convection of fluids in the pores,and improving the heat transfer efficiency. This study provides a fundamental theoretical basis for the application and promotion of CO2-plume geothermal resource extraction technology.
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