Experimental And Predicted Modeling Study Of Phase Behavior For Heavy Oil-CO₂/CH₄/C₃H₈ Systems

For complex heavy oil reservoirs such as low permeability and bottom water with edge,steam injection has many problems such as high heat loss and reservoir damage.However,solvent-based processes can avoid these problems.Solvent-based processes can enhance oil swelling,supplement the formation energy,reduce the density and viscosity of heavy oil,and improve the mobility of heavy oil.Solvent-based processes have well prospects.When heavy oil mixed with gas,the properties such as density and viscosity will change,and the phase behavior is of great significance to study the production mechanism of heavy oil and optimize injection and production parameters.This paper studyed the heavy oil-CO₂/CH₄/C₃H₈ system,get change rules of phase behaviors for heavy oil-CO₂/CH₄/C₃H₈ system,established the predicted model of heavy oil-CO₂/CH₄/C₃H₈ system,and lay a foundation for the study of CO₂/CH₄/C₃H₈ mixture injection in heavy oil reservoirs.This paper proposes PVT experiments of heavy oil-CO₂/CH₄/C₃H₈ system,density experiments and gas diffusion experiments.Then,the phase behaviors such as bubble point pressures,swell factors and densities with various mole fractions were measured.Gas diffusion coefficients with various temperatures,pressures and time were measured,too.The mechanisms of heavy oil solvent-based processes were summarized.In addition,theoretical models were proposed to predict bubble point pressures,swell factors,densities and gas diffusion coefficients.The predicted results of MATLAB software programming and experimental data were compared,and the errors were very small,so accuracy of the models were verified.Analysis results indicate that the gas diffusion coefficients reduce with the increase of diffusion time,and increase with the increase of injection pressures and experimental temperatures.The gas diffusion process can be divided into two stages.The first stage is called the original stage or latent stage,and the diffusion coefficients decrease sharply.The diffusion coefficients decrease slowly in the second stage,and the curve is flat.In addition,with the increase of the gas mole fractions,the bubble point pressures and expansion coefficients of heavy oil-CO₂/CH₄/C₃H₈ system increase,but the density and viscosity decrease.The mechanisms of enhanced oil recovery at solvent-based processes include combined viscosity and density reduction,solution gas driving,oil swelling,and the in situ upgrading of heavy oil.