Study On The Wax Deposition Law Of Wellbore In Deep Water Oil Well

The low temperature environment in deep water is easy to cause wax deposition during oil and gas well production and testing,which affects the normal operation and increases operating costs and risks,and even lead to potential wellbore blockage accident,greatly increasing the difficulty and risk of waxy crude oil development.Therefore,it is of great significance to carry out research on the law of wax deposition in deep water oil wells to ensure the safe and efficient operation of waxy oil well testing and production.In this paper,a calculation model of wellbore temperature and pressure field considering the effect of wax deposition is constructed for deep water oil well production and testing conditions.The vertical pipeline gas-liquid two-phase flow wax deposition experiment is carried out,and the prediction model of gas-liquid two-phase flow wax deposition rate in vertical pipeline is established.The prediction methods of wax deposition region,deposition rate and thickness in deep water wellbore are proposed,and the influence of different factors on wax deposition on wellbore is analyzed.The calculation model of wellbore temperature and pressure field considering the influence of wax deposition is established,including mass conservation equation,momentum conservation equation and energy conservation equation.The numerical method is used to solve the model,and then analyzing the influence of wax deposition time and rate on wellbore temperature and pressure field.The results show that: deposition thickness and wellbore temperature increase with the increase of deposition rate and time,and wellbore pressure does not change much.The effects of different factors on wax deposition characteristics are analyzed,and the wax deposition experiment of gas-liquid two-phase flow in vertical pipeline are carried out.Based on the wax deposition experimental data under different gas-liquid superficial velocities and the classical Fick molecular diffusion law,and considering the shear peeling effect of pipe flow and the effect of oil entrapment in deposition layer,a wax deposition kinetics model for gasliquid two-phase flow in vertical pipeline is established.The maximum relative error between the model predicted value and the experimental value is 14.06%,and the average error is less than 7.5%.The prediction accuracy of the model is good.A method for predicting the wax deposition region in wellbore is proposed based on the temperature and pressure fields of deep water oil well and the wax precipitation calculation model.And the factors affecting the wax deposition region are analyzed.Combined with the temperature and pressure field calculation model and wax deposition kinetics model,the wax deposition rate and thickness in the wax deposition region of wellbore are predicted and calculated.The effects of deposition time,production rate,geothermal gradient,water depth,formation pressure and pipe diameter on the wax deposition rate and thickness are obtained.This study can provide a reference for the prediction of wax deposition in deep water oil wells and optimal design of prevention and management measures.