Phase Behavior Investigation of a Live Presalt Crude Oil from Short-Wave Infrared Observation, Acoustic Wave Sensing, and Equation of State Modeling

In this work, the phase behavior of a live presalt crude oil characterized by a high CO2 content was investigated by combining measurement and modeling techniques. Because of the complexity of the fluid–fluid phase transitions observed within this system, a combination of indirect and direct detection methods was necessary to determine the phase diagram of this reservoir fluid. A shortwave infrared camera was used for direct observation of the phase transitions occurring in an oil sample placed in either a full visibility cell or a high-pressure microscopy device. In addition, an acoustic sensor working in the thickness-shear mode was used to probe phase changes during constant mass expansion experiments. The phase transitions of the live crude oil were measured from temperatures of 310 to 383 K and reported in the form of a (p, T) diagram. The obtained diagram was modeled using the Peng–Robinson equation of state with a lumping procedure that allowed representing the oil in 8 cuts including carbon dioxide. Additional measurements were carried out in a pseudobinary oil + gas model system composed of the dead oil with a synthetic gas from an equimolar content of methane and carbon dioxide to validate the experimental observations and the model predictions.