Asphaltene flocculation caused by CO2 injection during enhanced oil recovery: an experimental investigation of a model system at high pressure

F. Marcano1,2, H. Carrier1, M. Ranaudo2, J. Chirinos2, S. Acevedo2 and J. Daridon1

1Laboratoire des Fluides Complexes, UMR 5150, Université de Pau et des Pays de l´Adour, France
2Laboratorio de Fisicoquímica de Hidrocarburos, Caracas, Venezuela

Keywords: asphaltene, CO2, high pressure, onset
property: phase equilibria
material: crude oil

It is well known in the petroleum industry that injections techniques involving CO2 are useful for increasing oil mobility and simultaneously combat greenhouse effect. In the same time, CO2 injection may produce dramatic effects in oil fields which contain asphaltenic crudes. Indeed, CO2 may destabilize asphaltenes from crude oils and therefore lead to operational problems such as rock reservoir plugging, deposits formation in production wells (generally around the depths corresponding to the bubble point) or during the transportation and treatment (i.e. mixing of fluids with different compositions) to name few of them. Those problems are reported all over the world and promote many research teams that try to understand and to model the physical laws which govern asphaltenes behavior. However, despite the very good research done in that area during the last decades, the effects of pressure, temperature or composition remain poorly defined.

An experimental setup has been developed to detect the asphaltenes flocculation onset in the pressure range 1-100 MPa for temperatures between 25 and 200°C. The device is assembled around two automatic moving piston high pressure cells, equipped with a sapphire window, allowing the homogenization of the fluids by a magnetic stirrer. The cells are used to recombine, in predefined proportions, dead oil or synthetic mixtures with gases. The setup allows the determination of the state of aggregation of asphaltenes by an optical detection when samples are clear enough or by a high-pressure filtration process, with filters of porosity of 0.5 mm, for dark fluids.

Focusing on deposits related to enhanced oil recovery or gas storage, we have reproduced a pressure drop, at constant temperature, similar to the one occurring in pipelines production. This work presented focus on the behavior of a model system containing asphaltenes extracted (IP 143) from a South America crude oil, in heptane/toluene solutions under CO2 addition.

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