COMPOSITIONAL MODELING OF ASPHALTENES FLOCCULATION OUT OF RESERVOIR CRUDES. APPLICATION TO GEOCHEMISTRY AND OIL PRODUCTION

摘要

The flocculation and precipitation of asphaltenes is a severe problem in the oil industry. The formation damage and the production level decrease due to the blocking of reservoir pores, well perforations and pipes, with the precipitated heavy components out of the crudes cost millions of dollars annually. Up to date, there is not an efficient predictive model to determine the boundary of asphaltenes precipitation at field conditions: pressure, temperature and composition of different maturity oils which migrate into the same reservoir. Experimental work has been conducted, including traditional PVT studies and a specifically developed equipment and procedure, to separate by filtration the precipitated deposit (made of asphaltenes as well as of other heavy components) and measure its amount as a function of the pressure depletion at reservoir temperature. This equipment has also been used to determine the asphaltenes precipitation resulting from the mixing of progressive amounts of different maturity oils in a given reservoir. In this case, a relationship with the Colloidal Stability Index of the crudes mixture has been observed. All of the experimental data are obtained at real conditions of pressure, temperature and composition in which both the "solvent" and precipitating phases are initially mixed within the reservoir oil. Based on the experimental results, a thermodynamic phase equilibrium model, previously developed at IFP, has been improved in order to obtain the asphaltenes precipitation conditions from the compositional analysis and characterization of crude oil samples. Such a development of a more reliable model improves the accuracy of the asphaltenes precipitation boundary determination, thus leading to a better risk-profit analysis in the oil production.