Mechanism of CO2 EOR in shale oil reservoirs in the Jimsar Sag,the Junggar Basin
The successful development of shale oil reservoirs plays an important role in alleviating the energy shortage in China,but the depletion development can only realize lower recovery factor,and the conventional enhanced oil recovery(EOR)measures can hardly provide effective production and efficiency improvement,so clarifying the mechanisms of CO2 EOR in shale oil reservoirs is of great significance to exploring the shale oil development technologies.Focusing on the shale oil reservoirs in the Jimsar Sag of the Junggar Basin,this paper carries out a series of CO2 injection experiments.Then,combined with the assessment experiments of fluid injection capacity and oil-CO2 component mass transfer,the mechanisms of CO2 EOR are revealed,and the coupling relationships between the efficiency and form of CO2 sequestration and the production performance are illustrated.And the following research results are obtained.First,the injection capacity of CO2 is 7.77 times that of water and 1.18 times that of N2.Increasing injection pressure facilitates interactions between CO2 and oil,effectively enhancing CO2 injection capacity.Second,the ability of CO2 to improve the physical properties of oil is significantly stronger than that of N2.Under the synergistic effect of CO2-oil component mass transfer,the recovery factor by CO2 EOR is 6.84%higher than that by N2 EOR.Third,oil expansion and viscosity reduction are the main EOR mechanisms in the early stage of CO2 flooding.In the later stage,the further increase of recovery factor is realized through the replacement and extraction of light hydrocarbon components from oil by CO2.Miscible pressure(MMP)is the threshold pressure of CO2.Fourth,in the process of CO2 injection,the sequestration rate decreases continuously from the initial 77.77%to 7.14%.The proportions of different forms of CO2 sequestration change dynamically,but mainly in the form of free state and dissolved state.In conclusion,CO2 injection in the shale oil reservoir of the Jimsar Sag not only enhances the recovery factor but also facilitates CO2 sequestration.The experimental results provide theoretical support and experience insight for CO2 EOR and sequestration efficiency improvement of similar shale oil reservoirs in China.
国家科技期刊平台
NSTL
万方数据
