Asphaltene Flocculation During Oil Production and Processing: A Thermodynamic Collodial Model

Abstract

Abstract The need for understanding the nature of asphaltenes and asphalts and their role in the production and processing of crude oil is well recognized around the world as manifested by the current activities in the Petroleum Industry towards the exploration, drilling, production and processing of heavier oils (higher in asphaltene content). Asphaltene deposition during production and processing of oil ranks as one of the costliest technical problems the Petroleum Industry faces today. In the present report a thermodynamic-colloidal model has been developed capable of predicting the onset of flocculation of colloidal asphaltenes in oil mixtures due to either changes in composition (i.e.: solvent addition) or electrical phenomena (i.e.: streaming potential generation due to flow of asphaltenes containing oil in conduits or porous media). For oil mixtures from which flocculation is caused simply by flow, the model can make predictions as to the velocity ranges where colloidal asphaltene flocculation can be avoided. This could have a significant impact on allowed reservoir drawdown rates, well spacing, and tubing design. Introduction Field Experience and Related Research Asphaltene deposition is a very serious problem the oil industry has faced for many years. The significance of this problem was discussed in lengths in an earlier paper by the authors. Asphaltene or asphalt deposition around the well bore, well tubings, flowlines, separators, pumps, tanks and other equipment has, in many occasions, threatened the economic recovery of the oil or increased considerably the cost of producing it. Such cases were reported in the Prinos Field, Greece, the Mata-Acema Field, Venezuela, Hassi-messaoud Field, Algeria, Ventura Avenue Field, California, and other places throughout the world. The asphaltene problem is so insidious that, in all cases known to us, it was not foreseen either during the exploration or even development phase of the oil discovery. As a result, the oil producer became aware of the problem after a very large portion of the capital expenditure was spent making it difficult, if not impossible, from an economic standpoint to quit the project. So it is important to the producer that any potential asphaltene problems be predicted and the impact of remedial measures, if any, in the economics of the project evaluated before development of the field takes place. This evaluation could be very crucial in the decision whether or not to develop the field. Past Laboratory Studies Substantial research both in the industrial and academic communities has been taking place steadily on the topic of asphaltene flocculation since the late 1930's, (2,3,4,5,6,7,15,16,17,20,23). At this stage it seems that the solution of this problem calls for detailed analyses of asphaltene containing systems from the statistical mechanics and colloidal science standpoint and development of microscopic models which could describe the macroscopic behavior of asphaltenes in hydrocarbon mixtures. The available laboratory and field data it is proven that asphaltenes which exist in oil consist of very many particles having molecular weights ranging 1000 to several hundred thousands. As a result distribution curves are used to report their molecular weight. The extensively wide range of asphaltene size distribution suggest that asphalters may be partly dissolved and partly in colloidal state (in suspension) peptized (or stabilized) primarily by resin molecules that are adsorbed on asphaltene surface. P. 149^