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5Asphaltene deposition in wellbores has been recognized as the cholesterol of petroleum for decades 6 causing billions of dollars in losses to the oil and gas industry every year. This necessitates great 7 efforts in precise and fast forecasting of the production problems induced by asphaltene deposition. 8From perspective of the large length-to-diameter ratios of wellbores and the unidirectional nature of 9 the crude oil flow, this work presents a numerical procedure to predict the coupled velocity, 10 pressure and concentration distribution in a transient one-dimensional one-way framework. This 11 procedure is general-purpose for flow passages of large aspect ratios with the precipitation rate, 12 aggregation rate and deposition rate embedded in known forms. In this numerical procedure, the 13 governing equations are solved using the finite volume method on a regular mesh arrangement with 14 fully implicit spatial and temporal schemes. For verification purpose, a few cases having exact 15 solutions are studied. Then, application of the presented procedure to capillary asphaltene 16 deposition is illustrated where good agreement is achieved between the simulation results and the 17 experimental measurements. This case demonstrates that the proposed procedure can be used to 18investigate oilfield asphaltene problems and assist reservoir engineers in assessing the potential 19 asphaltene deposition risk in wellbores. 20 Key Words: asphaltene deposition, large length-to-diameter ratios, one-dimensional one-way 21 22 NONMENCLATURE 23 Ac flow passage original cross-sectional area (m 2 ) Cdis concentration of the dissolved asphaltene (kg/m 3 ) Ceq equilibrium asphaltene concentration (kg/m 3 ) Cpre concentration of the precipitated asphaltene (kg/m 3 ) cp specific heat (J/kg·K) 2

Asphaltene deposition on the walls of wellbore or pipeline during oil production and processing will cause dire consequences if left untreated. A better understanding of this phenomenon is required. This study presents a general modelling framework based either on the level-set approach or the concentration approach for modelling asphaltene deposition processes. Both the level-set method and the total concentration approach belong to the family of front capturing methods. Therefore, the dynamics of the depositing front can be captured implicitly on fixed mesh. The presented frameworks are validated against each other for general deposition process. Preliminary parametric studies are then performed to study the influences of various factors on the deposition process.

Abstract-Asphaltene deposition in wellbores