This paper is the result of the geothermal geological survey engineering.
[Objective]The CO₂- plume geothermal system (CPGS) can achieve geological CO₂ storage during heat extraction. Under the background of carbon peaking and carbon neutralization, the economics of CPGS carbon storage attracts much attention. [Methods] Taking the Quantou Formation in the Songliao Basin as example, the influence of injection pressure, well spacing and reinjection temperature on the heat extraction rate were analyzed by numerical simulation in this paper. In addition, the benefit of CPGS and the cost of carbon storage were calculated and compared with conventional hydrothermal geothermal systems. [Results]Results show that the temperature of mining wells in CPGS exhibits a trend of "decrease-stabilization-decrease" due to the transformation of heat-carrying medium and thermal breakthrough. Typically, the well spacing has a significant impact on the temperature drop of the mining well. Smaller the well spacing contributes to larger temperature drop of the mining well. The heat extraction rate has a positive correlation with the reinjection pressure and a negative correlation with the reinjection temperature. The influence of well spacing on the heat extraction rate is limited. Compared with the conventional hydrothermal geothermal system, CPGS has three stages of heat recovery, namely, high, low and high stages successively. A low reinjection pressure and a close reinjection temperature with the reservoir temperature helps to shorten the time required for the CPGS to recover a similar heat energy with the water medium. [Conclusions]Taking the price of CO₂ and the benefits of heat extraction into account only, the well spacing has a dominating impact on the unit cost of CO₂ storage after the heating revenue offsets part of the cost of carbon storage. Small well spacing contributes to quick decrease of the unit cost of CO₂ storage. The unit cost of CO₂ storage can be reduced to 160 yuan/ton after 30 years of continuous mining when the well spacing is 300 m.