Measurement of the Rheology of Crude Oil in Equilibrium with CO₂ at Reservoir Conditions

Abstract

A rheometer system to measure the rheology of crude oil in equilibrium with carbon dioxide (CO2) at high temperatures and pressures is described. The system comprises a high-pressure rheometer which is connected to a circulation loop. The rheometer has a rotational flow-through measurement cell with two alternative geometries: coaxial cylinder and double gap. The circulation loop contains a mixer, to bring the crude oil sample into equilibrium with CO2, and a gear pump that transports the mixture from the mixer to the rheometer and recycles it back to the mixer. The CO2 and crude oil are brought to equilibrium by stirring and circulation and the rheology of the saturated mixture is measured by the rheometer. The system is used to measure the rheological properties of Zuata crude oil (and its toluene dilution) in equilibrium with CO2 at elevated pressures up to 220 bar and a temperature of 50 °C. The results show that CO2 addition changes the oil rheology significantly, initially reducing the viscosity as the CO2 pressure is increased and then increasing the viscosity above a threshold pressure. The non-Newtonian response of the crude is also seen to change with the addition of CO2.

Suppression of Phase Separation as a Hypothesis to Account for Nuclei or Nanoaggregate Formation by Asphaltenes in Toluene

“…For decades, the aforementioned phase separation was confused with “inverse micelle” formation because of its similarities with the behavior of surfactants in oily media. This confusion has made the term “asphaltene micelle” common in the past as well as in recent years. − The references cited here are only a small sample of the many published articles that mention asphaltene micelles, which, according to Science Direct, is approximately 1200 papers over the course of 40 years and approximately 200 papers in the last two years. In the case of surfactants in an oily medium, however, aggregation may occur via the stepwise formation of multimers .…”