Prediction of asphaltene precipitation risk in oil wells using coupled thermohydraulics model

Abstract

Asphaltene precipitation and deposition is a major flow assurance challenge, which manifests itself in reservoir, production tubing, and flowline and process facility. Asphaltene may precipitate due to two main factors, namely high asphaltene content, and high difference between reservoir pressure and oil bubble-point pressure, i.e. precipitation driving force, even if asphaltene content is low. The objective of this study is to develop a predictive simulation tool to assess the risk of asphaltene precipitation in oil wells and to estimate the asphaltene risk window. Further objective is to use the developed simulation tool to generate well design and production scenarios to efficiently prevent, mitigate and manage asphaltene precipitation. A comprehensive asphaltene deposition workflow is developed to identify the major steps to enable a solution strategy. To implement the workflow, Ansari et al. (1994) mechanistic two-phase flow hydrodynamic model in vertical wells is coupled with two Asphaltene precipitation thermodynamic models, namely de Boer et al. (1995), and Wang et al. (2006). In this study, de-Boer et al. model is extended from a single point reservoir model to a multi-point wellbore model; while Wang et al. is used to predict and compare the asphaltene instability with live-oil instability along wellbore. The developed simulator was validated to predict the risk and depth window of asphaltene precipitation in Middle East oil wells, resulting in a reasonable agreement with the field data. In addition, the simulation tool is used to carry out a parametric study to investigate the impact of oil gravity, and reservoir pressure on asphaltene precipitation risk.