Fundamental Research On The Asphaltene Deposition And Wettability Alteration In A Pore Caused By CO₂ Injection

In the process of crude oil recovery,due to changes in fluid composition,temperature and pressure,the stability of the crude oil can be destroyed.This causes that the solid asphaltene particles precipitate and deposite from the crude oil.Asphaltene deposition behavior at the micropore was directly investigated in this work.In-situ visualization experiments were carried out.Wettability alterations in a pore caused by asphaltene deposition were quantified.The CO₂-induced asphaltene deposition behavior in model oil was studied in two states,which are liquid CO₂ and supercritical CO₂ respectively.It is found that the particle size of asphaltene deposits becomes larger as the deposition time increases.Effects of different gas injections on asphaltene deposition in model oil were compared.Compared with N₂ and CH₄,the injection of CO₂ resulted in larger particle size of asphaltene deposits.Meanwhile,the factors affecting asphaltene deposition were explored,including asphaltene concentration,temperature,pressure and CO₂molar concentration.The results show that the higher asphaltene concentration,temperature,pressure and the CO₂molar concentration could accelerate asphaltene deposition.The influence of asphaltene deposition on the change of pore wettability was studied.As more asphaltene is deposited in the pore,the alteration of the surface wettability in the pore is more significant.At high pressure,in-situ visualization experiments of asphaltene deposits in the pores caused by CO₂ injection were carried out.Micros-cale in-situ visualization studies were conducted under static and dynamic conditions.The experimental results can quantitatively describe the deposition behavior of asphaltene particles in static and dynamic systems.Finally,based on the sedimentation model of solid particle,the sedimentation times of asphaltene particles of different sizes in different systems were predicted,and the the factors influencing the sedimentation behavior of asphaltene particles were discussed.