| With the development of industrialization in the world,the content of CO2 in the atmosphere is increasing year by year.It is found that the CO2 underground storage technology,represented by CO2 enhanced geothermal systems(EGS)and enhanced oil recovery systems(EOR),has great potential for CO2 storage as well as heat extraction and oil displacement.It can not only utilize CO2 effectively,but also reduce the content of CO2 in the atmosphere.But,the research of EGS and EOR systems were mainly focused on the evaluation of heat extraction and oil displacement,few literatures had been studied on the synergetic mechanisms and optimization methods of heat extraction/CO2 storage and oil displacement/CO2 storage.In view of this,the synergistic mechanisms and comprehensive optimization methods considering the CO2 storage of CO2-EGS and CO2-EOR systems are respectively studied in this paper.Because the formation thermal property around the CO2 injection well is the basic data for analyzing the flow and heat transfer of CO2 in the injection well and it is difficult to measure directly and accurately,a method for predicting the formation thermal property is proposed and its distribution is studied in this paper.The existing literatures ignore the difference of formation thermal properties in vertical direction,and assume that thermal properties of formation do not change with well depth.This assumption has great limitations when injection wells are deep.In this paper,the heat transfer model between the CO2 injection well and surrounding formation considering heat losses was established.According to the correlation between thermal properties of formation and CO2 temperature,a prediction method for calculating formation thermal conductivity and volumetric heat capacity based on measured CO2 temperature was proposed.Furthermore,the vertical distribution of formation thermal conductivity and volumetric heat capacity was predicted.Secondly,in view of the performance of heat extraction and CO2 storage in EGS systems,the wellbore-thermal reservoir comprehensive heat transfer model of EGS including injection wells and production wells was established considering CO2 heat losses in this paper.Based on the established model,the synergetic mechanisms and comprehensive optimizations of heat extraction/CO2 storage were studied.It was found that the lower injection temperature of CO2 could not only increase the heat extraction,but also store a higher proportion of CO2.In addition,the double-objective optimization method for heat extraction and CO2 storage of CO2-EGS was studied by using genetic algorithm.The optimization results showed that the maximum heat extraction rates could reach 8.0 MW and the maximum storage ratio of CO2 was 30.0%.Besides,the sensitivity analysis of CO2 injection parameters and reservoir structure parameters showed that the heat extraction of EGS mainly depended on CO2 injection flow rates and injection pressure,and the storage amount of CO2 was mainly determined by reservoir porosity.Finally,in view of the two enhanced oil recovery modes of continuous CO2 injection and water alternating gas(WAG)injection,the synergistic mechanisms of oil displacement and CO2 storage was studied,and the influencing factors of oil displacement and CO2 storage under different injection conditions were studied.It was found that the CO2 storage capacity reached the maximum when the water injection rates were 0.3 kg·s-1 in WAG injection,and the oil recovery reached the maximum when the ratio of water-CO2 was 1:2.Furthermore,the oil recovery and CO2 storage capacity of two enhanced oil recovery modes under different injection flow rates were compared.It was found that larger amount of CO2 was stored when the CO2 injection rates and water injection rates were high in continuous CO2 injection.On the other hand,oil recovery was higher in WAG inj ection with the same injected amount of CO2 due to additional water injection. |
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