Supercritical CO₂ Flooding Nozzle Flow Characteristics And Split Injection Process Research

In the long-term oil extraction process,the secondary oil recovery stimulation technology has been unable to meet the current oil field high water content,low formation permeability and other working conditions.Traditional water flooding technology not only causes a lot of waste of water resources but also has a low recovery rate under current operating conditions.With its advantages of no liquid phase,large diffusion coefficient and low viscosity,supercritical CO₂will not cause clay expansion and liquid blockage.Its strong dissolving ability can form a mixed fluid with crude oil in the oil layer to achieve a unique oil displacement mechanism:its The powerful extraction ability can separate or gasify the light components in crude oil,reduce interfacial tension to form a miscible phase;at the same time,it can reduce the viscosity of crude oil and make its volume expansion feature become a research hotspot in tertiary oil recovery technology.However,it is difficult to study the nozzle flow characteristics due to the lack of a gas nozzle structure suitable for CO₂throttling in the process of stratified CO₂injection,which reduces the downhole stratified injection effect.Therefore,in order to realize the supercritical CO₂layered injection process,this paper designs a gas nozzle structure for the special properties of supercritical CO₂to meet the adjustment requirements of different layers and study the nozzle flow rules;according to the parameters of each injection layer,combined with the nozzle flow characteristics In combination with the wellbore dynamics,a set of methods for predicting the opening of each layer of gas nozzles and determining the wellhead injection parameters are formed to provide a scientific basis for the development of the CO₂split injection process.The main research contents are:?1?According to the P-R equation and Vesovic model,the CO₂thermophysical parameters were solved and analyzed.?2?Based on heat transfer and fluid properties,a wellbore temperature and pressure coupling model was established,and the influence of injection parameters on downhole temperature,pressure and phase state was analyzed.?3?Carry on the CO₂throttling adaptability simulation of the existing water injection dispenser,and design a gas nozzle structure adapted to the CO₂throttling according to the existing gas nozzle structure.?4?The supercritical CO₂nozzle flow experiment was carried out to verify the reliability of CFD simulation data.And optimized the size parameters of the gas nozzle,the optimized size of the structure of the gas nozzle has a pressure of 10-70MPa and a temperature of 303-393K.It is fitted with the throttle pressure difference,injection temperature,pressure,flow rate and gas nozzle.Multi-parameter mouth flow formula for opening.According to the wellbore model and the gas nozzle structure,the simulation analysis of the whole well is carried out.The main research results are:The thermal physical parameters solved by PR and Vesovic models meet the accuracy requirements of the project.Data analysis shows that the thermal physical parameters are greatly affected by temperature and pressure,and the trends of density,viscosity,and thermal conductivity are similar with the increase of pressure.The pressure heat capacity and the Joule-Thomson coefficient both decrease to a certain value as the pressure increases;analysis based on the wellbore model shows that the injection temperature has a greater influence on the downhole parameters and phase distribution.The annular gap gas nozzle structure satisfies the 2-2.5MPa interlayer pressure difference and is adjustable;according to the simulation analysis of the whole well injection,it shows that the layered injection process developed in this paper satisfies the interlayer pressure difference at 2-2.5MPa downhole layering Equal injection.