A Comparative Study of the Cubic-Plus-Association Equation of State and a Peng-Robinson Equation of State–Based Solid Model for Asphaltene Simulation in the Wellbore

Abstract

Summary Asphaltene is one of the main flow-assurance concerns in oil production. Its precipitation and further deposition along the flow path (wellbore or reservoir) can cause reduced hydrocarbon flow rates and even a total blockage. These potential damages have caused a growing interest in computationally efficient methods to predict asphaltene precipitation, depending on flow conditions. This paper presents two different approaches: (i) a model from Li and Firoozabadi (2010), using a simplified version of the cubic-plus-association equation of state (CPA EOS), and (ii) a version of a solid model based on the Peng-Robinson (PR) EOS, with no association term. The two approaches are compared in isolated flash calculations and wellbore flow simulations with asphaltene deposition. The comparisons are made using the same fluid parameters for both approaches as much as possible. Results show that, if provided with adequate input data, the solid model can consistently match results from the more complex CPA model quite successfully for several fluid compositions. An attempt is made to explain the “success” of the solid model in reproducing CPA model results. The solid model cannot adjust to fluid-composition changes in a manner similar to that of CPA. Therefore, the solid model seems more suitable for wellbore than reservoir simulation, which tends to involve a higher level of fluid mixing. However, the efficiency of the solid model can reduce the computational time by a factor of 2 in comparison with CPA.