MEASUREMENT AND PREDICTION OF ASPHALTENE PRECIPITATION FROM LIVE OILS

Recently developed experimental techniques permit reliable quantitative measurement of asphaltene precipitation direct from live crudes. An exten-sive database of such data has now been assembled. Using these data, a new model has been developed which can reproduce not only the asphaltene precipitation envelopes but also the amount precipitated at given conditions of temperature and pressure. It also gives reasonable predictions for the effect of gas removal and gas injection. Details of the experimental methods are described, which can be applied to all types of fluid under almost any experimental conditions together with the charac-terisation methods. The model is based on a cubic equation of state with additional terms to describe the association of asphaltene molecules and their solvation by resins. The physically based model is able to represent a wide range of data with minimal adjustable parameters. The ideal input is a compositional analysis of the oil, SARA characterisation and a limited amount of asphaltene precipitation measurements. If extensive precipitation data are available the model can be tuned to match them accurately. However, if data are not available the model can be run in predictive mode. A standard characterisation method has been developed for the equation of state that automatically adds the necessary information for performing asphaltene calculations. The new model is a validated practical engineering model which can be used to devise production strategies that will minimise the risk of asphaltene deposition. Coupled with a multi-phase equilibrium solver it can simultaneously predict the fluid phase behaviour and the asphaltene precipitation. 2