A Study On Prediction Method Of Asphaltene Deposition In Crude Oil

In the process of production and transmission of crude oil,asphaltene deposition can cause damage of formation,crude oil production decline,wellbore scaling and other production problems.First of all,the monomolecular structure parameters of asphaltene were investigated,and the average model of asphaltene single molecule was constructed in this paper.The radial distribution characteristics of asphaltene were studied by molecular dynamics method.Based on the study of the asphaltene mathematical model at home and abroad and some reasonable assumptions,the asphaltene liquid-solid two-phase deposition model was improved.The optimal method of the crude oil component and the expression of the deposition judgment were studied,and by PVTsim predicted injecting CO2,N2 and dry gas to affect the temperature and pressure of asphaltene.Finally,the calculation method of the amount of asphaltene in the wellbore was improved based on the existing model.The feasibility of the model proved by calculating the pressure and temperature along the process.The research of single molecular model of asphaltene showed that the CVFF,Compass and Dreiding force fields can meet the requirements of intermolecular forces in different situations.The research of radial distribution function analysis showed that the main force between asphaltene molecules was Van der Waals' force.Amorphous Cell can assemble asphaltene molecular group.In the quality-silica-water molecular simulation system,annealing optimization can make the molecular chain fully relaxed,which can be used to simulate the energy of the molecular structure more accurately.The research of molecular migration showed that asphaltene would enhance aggregation of asphaltene by the ?-? stacking.The asphaltene molecules in the system were adsorbed by the molecular surface of the rock surface.In the asphaltene deposition model,the asphaltene saturated deposition curves of two different properties of crude oil were obtained by PVTsim.The higher the content of heavy components was more prone to asphaltene deposition.In addition,by changing the way of composition ratio of many different injections and the formation of asphaltene deposition curve,the results showed that injection of CO2,N2 and dry gas would aggravate asphaltene deposition.Finally,based on the advection-turbulence theory,it was pointed out that the asphaltene particles should follow three mechanisms of diffusion such as Brownian motion,eddy current diffusion and collision in the wellbore.The results of the calculation of asphaltene deposition model by increasing wellbore flow and increasing wellbore radius indicated that the deposition of asphaltene would increase.