Study On The Capacity Of Crude Oil Injection With Transcritical CO₂ Injector

The ejector is an important process unit.With a simple structure,lacking in motion parts and stable performance,it's widely used in the field of petrochemical,energy and power and refrigeration etc.During crude oil lifting,ejector is employed increasingly wide that it proves to exhibit more prominent advantages than the traditional sucker-rod pump.Current researches on working fluid of ejector mostly focus on water,steam and air,while carbon dioxide is rarely mentioned in the relevant research and application.In order to determine the geometric model of the transcritical CO₂ injector for crude oil injection,according to the gas dynamic function method proposed by Sokolov of the former Soviet Union,combined with the physical properties of carbon dioxide,the design method of carbon dioxide as the working fluid injector is deduced.The geometry of the transcritical CO₂injector was calculated to determine the injector model that is basically suitable for field operations.Because the internal flow field of the injector is very complicated,in order to analyze the injection performance of the transcritical CO₂ injector,the computational fluid dynamics software is used to simulate the flow process of the internal working fluid of the injector.Because the change of the CO₂ density near the phase transition point is huge,the actual gas state equation cannot obtain accurate values.Therefore,according to the physical property data of the REFPROP software,the curve of carbon dioxide density with temperature under various pressures is fitted,and UDF programming will be adopted.Embed the calculations into the boundary condition custom settings through UDF programming.By simulating and comparing the changes of the working performance of the injector caused by air and carbon dioxide as working fluids,it is concluded that the injection performance of carbon dioxide is better.On the operating conditions,I analysis performance influence to ejector by researching working pressure,injection pressure as well as outlet pressure.The simulation shows,the change trend of the injection coefficient with the working pressure is first increased and then decreased,and the optimal working pressure is 15 MPa;The injection coefficient increases linearly with the increase of the pressure of the ejector liquid,and the effect of the ejector pressure can be used to determine the effect of formation pressure on the efficiency of the injector.Changing the outlet pressure,the injection coefficient does not substantially change when it is below the critical pressure,and causes a sudden drop above the critical pressure.Therefore,the optimum outlet pressure is 2.4 MPa.In terms of its structural size,through numerical simulation analysis was made of the influence of nozzle distance,diameter and length of mixing chamber as well as length of diffuser of the ejector on its performance.The results show that with the increase of nozzle distance,the working efficiency of the injector increases slowly and then decreases sharply.When the nozzle distance is 12mm,the injection performance is optimal.With the increase of the mixing chamber size,the injection coefficient first increases and then decreases.The optimum diameter is 10.84mm,and the corresponding area ratio is 16.05.If the length of the mixing chamber is too long,the resistance loss will increase.If the mixing time is too short,the mixing process will be insufficient.Therefore,there is an optimal value,that is,the length is75.88mm.The aspect ratio is 7,which makes the ejector performance the best;the unreasonable matching between the parameters of the diffusion chamber will make the ratio of the inlet and outlet area imbalance,resulting in additional energy dissipation,so when the expansion angle is 12°,the diameter ratio is 2.4.At the time,the size of the diffusion chamber is the most reasonable,and the efficiency of the injector is optimal.The simulation results show that carbon dioxide is more efficient than air,and it has a good working condition after optimization of its operating parameters and geometry.Therefore,carbon dioxide can replace the air as the working medium of the injector to illuminate the crude oil.