Simulação e otimização do fator de recuperação de óleo via injeção de fluidos em reservatórios de petróleo: efeitos da precipitação e deposição de asfaltenos.

Abstract

Core flooding methods developed for enhanced oil recovery (EOR) aim to reduce the interfacial tension of these fluids and oil mixtures. The injected fluids can be the associated gas, CO2, water, etc. Gas injection for EOR methods can cause the precipitation and deposition of asphaltenes, causing changes in the reservoir properties, such as the reduction of permeability and porosity, and, consequently, losses in oil production. The present work investigates the mechanisms by which asphaltenes precipitate in the oil phase and subsequently deposit on the rock surface, including the impact of these phenomena on the oil and rock properties and on the oil recovery factor. Three EOR methods were evaluated using the computer modeling group (CMG's®) commercial simulator: injection of associated gas, CO2 injection, and water alternating CO2 injection. In the precipitation modeling, the solid-liquid approach was adopted; in the deposition modeling, models considering single-layer adsorption and mechanical entrapment of asphalt particles were used. In the case of associated gas injection, the results showed that the oil recovery factor increases with the flow rate or injection pressure, and changes in the injection pressure have a greater impact on the final recovery factor. In this case, the influence of asphaltene deposition on the oil recovery factor was not observed. There is a point from which a further flow increase does not significantly increase the recovery factor. In the case of CO2 injection, the injection conditions were optimized, to maximize the recovery factor. Decision variable were injection pressure, injection flow rate and the composition of the injection gas. With this optimization, the recovery factor increased 28% concerning a simulation base case. This recovery factor increase would correspond to an additional production increase of 6.7% if the same conditions were adopted in the reservoir. It was also observed that the optimal injection condition for this reservoir proved to be economically viable, with a gain of approximately US$6.83 million/year. In the CO2WAG injection process, the results showed that the asphaltene precipitation in the injection well was minimized for cycles of shorter duration, reducing their deposition. The best results were obtained for production with WAG 1:1 ratios. Asphaltenes deposition negatively impacted around 2.0% of the oil recovery factor. These results drive decisions to prevent damage caused by precipitation and deposition of asphaltenes, increasing the efficiency of field production.