Measurement of Phase Changes in Live Crude Oil Using an Acoustic Wave Sensor: Asphaltene Instability Envelope

An experimental method is proposed for determining the asphaltene instability envelope of a crude oil or crude oil + antisolvent system under reservoir conditions by using a thickness shear mode acoustic wave sensor fully immersed in oil under pressure. The technique allows determining the upper asphaltene instability pressure by carrying out constant mass expansion experiments, whereas the lower asphaltene instability pressure can be determined during constant mass compression tests. The basis of the technique is presented, and measurements have been carried out in a bottomhole oil + CO2 system with various CO2 contents at reservoir temperature. Finally, the effect of temperature on the asphaltene instability envelope was studied on two systems with 45 and 55 mol % CO2.