The Experimental And Theoretical Research On CO₂ Flooding Based On The Multi-field Coupling

The reserves of low permeability oil fields in China are abundant,but the recovery rate is very low under the current technical conditions.In order to improve oil recovery and production in low permeability oil field,it is urgent to look for new oil displacement agent and oil displacement method.A large number of domestic and foreign research results show that CO₂ flooding can greatly improve the oil and gas recovery.At the same time,At the same time,CO₂ is one of the major greenhouse gases and easy to cause pollution to the environment.The study of CO₂ flooding is beneficial to environmental protection,and can realize the organic unity of economic profit and social benefit.In order to predict the variation rule of CO₂ flooding under different injection schemes,and to determine the optimal injection scheme,we need to have a very clear understanding of the migration rule and influencing factors in the whole oil displacement process.In the current theory and engineering construction,we mainly use the numerical simulation software to complete the analysis of the effect of CO₂flooding,lack of in-depth knowledge of CO₂ flooding mechanism.We creatively introduce the ultrasonic testing technology,as a means of monitoring the CO₂ flooding process,to study the CO₂ flooding mechanism theoretically and experimentally.According to the basic rule ultrasonic technology,we design an equipment to test the parameter of CO₂ flooding.Then we carry out a series of experiments in this equipment with the actual test data.The results reveal the relationship between oil displacement and ultrasonic wave velocity and the method provides an effective means for monitoring the formation of CO₂ flooding process.At the same time,in order to study CO₂ flooding migration mechanism in the process of the CO₂ flooding in complex geological environment,we build a sophisticated model to describe this phenomenon.This model takes into the consideration of influence of the percolation mechanics,rock mechanics,thermodynamics and diffusion effect.Finally,we provide a solution to the model and implement the mathematical method to a field.The results show that the model and the measured data are in good agreement.The main research results are shown as follows:?1?Based on the basic principle of ultrasonic testing technology,the ultrasonic CO₂ flooding test device is designed and manufactured.A series of experiments of core saturation CO₂ test are carried out.The experimental results show that,with the increase of CO₂ gas saturation and the decrease of oil saturation,the ultrasonic P-wave velocity will decrease,while the ultrasonic shear wave velocity will remain unchanged.?2?Through the comparative analysis of P-wave velocity characteristics in different experimental conditions of multiple cores,the linear regression processing of measurement data is carried out with the least squares method.The fitting curve of the relationship between experience of gas saturation,porosity,external pressure and temperature of ultrasonic longitudinal wave velocity with the core of CO₂.The results show that the core porosity has the most important effect on P-wave.In addition,the second obvious factor is gas saturation.The influence of surrounding rock pressure and temperature are relatively small.?3?The multicomponent CO₂ equations,including seepage equation,continuity equation,and the state equation,is established to calculate the phase distribution and the corresponding boundary conditions and initial conditions are determined,which lays a theoretical foundation for the subsequent calculation.The model is validated with the experimental data,and the results show that the theoretical model and the experimental data are in good agreement.?4?Taking use of the Oil and gas seepage mechanics,rock mechanics,convection diffusion theory,a multi-field coupling CO₂ miscible displacement model is established.The model is solved by using the finite difference method and the influence factors such as injection pressure,injection temperature and basic geological conditions are analyzed.The results show that the model can comprehensively consider the effect of convection diffusion and fluid solid coupling on the seepage,which shows the practicability to improve the simulation precision of CO₂ miscible displacement.?5?We design and develop a multi-field coupling simulation software based on the above research.This software can realize numerical simulation and optimization of injection in multi field coupling process under the condition of CO₂ flooding.The results show that the software has a potential to provide theory and technique support for the field application.