Thermodynamic Modelling for Prediction of Asphaltene Deposition in Live Oils

Abstract

Abstract Original phase equilibria data on asphaltenic mixtures show that the principal modellistic approaches described in the literature do not accurately reproduce asphaltene phase behaviour. A new, more reliable modellistic approach is proposed in this paper, and a procedure for predicting the stability of asphaltene solutions is outlined. Application of the new model to two oils gives satisfactory results when compared with field observations. Introduction Asphaltene deposition in wells and in production facilities is more and more frequently encountered. The in situ formation of asphaltene deposits can very seriously damage the reservoir formation, leading to a decline in the oil productivity. The occurrence of such a phenomenon in the early stage of production in a major Italian field has been described elsewhere and led to the organization of an ambitious, multidisciplinary study of the problem. One of the goals of the study was the development of a reliable, predictive model for asphaltene destabilization, in order to assist the petroleum engineer in optimizing the production strategy. In this paper a modelling approach based on polymer solution thermodynamics has been followed. The model has been developed using experimental phase behaviour data from laboratory tests. Accurate data for asphaltene phase stability have therefore been produced: on the basis of such data a new thermodynamic interpretation for asphaltene stability is proposed. The model allows the prediction of asphaltene stability from a limited amount of experimental data. The asphaltene stability predictions relative to two oils from Italian fields suffering from asphaltenic deposition are presented and compared with the observed field behaviour. Background Asphaltene stability in crude oils has been studied since the 30's; many fundamental aspects of the problem, however, have yet to be solved. Though recent studies address asphaltene aggregation in oils, the details of asphaltene stabilization mechanism have not yet clarified. Attempts to model asphaltene solution behaviour, therefore, suffer from this lack of fundamental insight. Consequently, of the modellistic approaches proposed in the last ten years, some have relied on a colloidal mechanism to describe the asphaltene phase stability, some have adopted a fully thermodynamic approach. P. 499