Researches On Flow And Heat Transfer Involved In Enhanced Geothermal System And Carbon Dioxide Utilization

The exploitation of renewable energy and the reduction of the carbon emission hasbecome an important global issue recently. On the background of the enhancedgeothermal system and the utilization of carbon dioxide, this paper investigates the flowand heat transfer involved in these issues at both channel scale and field scale byexperimental measurements, theoretical analyses and numerical simulations.In the aspect of channel scale, this paper experimentally and numericallyinvestigates the convection heat transfer of supercritical CO2in a straight vertical minitube and a serpentine mini tube both with inner diameter of0.953mm. For theinvestigation on the straight tube, the results show that for low inlet Reynolds turbulentflow and high heat fluxes, the heat transfer is impaired with the existence of two localwall temperature peak regions for upward flow and improved with the existence of onelocal wall temperature valley region for downward flow due to buoyancy effect. For theinvestigation on the serpentine tube with bend diameter of8.01mm, the experimentalresults show that for upward turbulent flow, the wall temperature distribution generallyexist the monotonous growing trend without the existence of the local temperature peakregion, and the heat transfer deterioration is strongly repaired due to the centrifugalforce and the periodic change of the bend direction, and the minimum local Nu numberreach up to20even for low inlet Reynolds number which is much larger than that in thestraight tube experiments. For laminar flow in the serpentine tube, the heat transfercoefficient reaches the maximum value as the fluid temperature is near thepseudocritical point and the centrifugal force is fully developed. Some empiricalcorrelations are developed to predict the laminar heat transfer of fluid of constantproperties or supercritical pressure CO2in the serpentine tube.In the aspect of field scale, this paper carries out the field scale simulations on theenhanced geothermal system (EGS) and the carbon dioxide storage with gas recovery(CSEGR). For the simulation on EGS, the influence of the permeability of the inducedfractures near the wellbores, the working fluid, the wellbore perforation location, theheat transfer between the wellbores and the surrounding reservoirs and the local thermalnon-equilibrium are analyzed. The main results show that the pressure drop through thereservoir can be significantly reduced by creating relatively small size of fractures with large permeability in the reservoir around the wellbores, and that the local thermalnon-equilibrium model should be used while the fluid flow paths in the reservoir arelimited. For the simulation on CSEGR, the theoretical analyses present that that thechoice of fluid flow path in the vertically heterogeneous reservoir gives rise to a highereffective permeability which accelerates the CO2transport to the production well,resulting in earlier CO2breakthrough and less CO2storage amount and CH4recoveryrate than in the homogeneous reservoir. Further, the simulation results show that fordifferent reservoir with various kh/kvratios, the optimum option of the wellboreperforation locations is different.