Research On Patterns Of Wax Deposition In Offshore Oil Wellbore

The exploitation of waxy crude oil is usually affected by wax deposition in wellbore.Predicting the location and the amount of wax deposition is important for wax removal and prevention in offshore oil wells.In this paper,the wellbore temperature calculation model,the thermodynamic model for predicting wax precipitation and the dynamic model for predicting wax deposition in offshore oil wells are established respectively.At the same time,the calculation method of wellbore wax deposition location and wax deposition during shut-in operation and production is proposed based on the theory of multiphase flow in wellbore.The results show that the wellbore temperature decreases rapidly in the early stage of shut-in,and tends to be stable with the increase of shut-in time.The wax precipitation area and wax deposition amount in the wellbore affected by temperature factors increase during shut-in operation,but the growth trend slows down gradually.Generally,the temperature of riser section of offshore oil wells is low.Inserting insulating oil pipe in wax precipitation area can effectively reduce wax precipitation area and wax deposition.In the oil production process,the changes of flow rate and water content have an influence on wax deposition.The temperature near the wellhead of low-yield oil wells is lower and the radial temperature difference is larger,so the wax precipitation area and wax deposition amount are higher;the temperature in the whole wellbore of high-yield oil wells is higher,and the flow process is affected by shear erosion,so wax deposition is hardly appearance.At high water cut stage,the wax deposition in oil wells decreases obviously due to the change of fluid composition distribution.The method provided in this paper can provide a theoretical basis for wax removal and control operations in high waxy oil wells and realize the recovery of high waxy crude oil.