Microfluidic PVT--Saturation Pressure and Phase-Volume Measurement of Black Oils

Summary In this work, we present a small-scale pressure/volume/temperature (PVT) cell that allows for the measurement of saturation pressure and phase-volume ratio by use of only a few microliters of black-oil samples. This novel PVT measurement technique has been successfully tested on live samples at elevated pressure (86 MPa) and temperature (150°C). In the microfluidic PVT platform, the small microfluidic device performs the same function as the laboratory-scale pressurized visual PVT cell. At the heart of the microfluidic device, is a long and narrow capillary, densely packed in a serpentine shape, embedded on the device. The capillary is nearly 1 m long and has a total volume of 5 µL. The microfluidic device is fabricated with glass and silicon, which allow visual monitoring of a fluid sample at various pressures and temperatures. To acquire PVT data, the pressure in the capillary is systematically reduced to accurately detect the appearance of micron-sized gas bubbles in a sample at saturation pressure. Because of the small thermal mass of the device, the temperature of the sample can be changed rapidly, which enables the measurement of multiple saturation pressures in quick succession. Below the saturation pressure, the growing gas bubbles form a segmented gas/liquid distribution in the capillary. The lengths of the liquid and gas segments are measured in real-time with an automated image-capturing and analysis tool to determine the gas/liquid phase-volume ratio at a given pressure. Validation tests have proved this technique to be repeatable and feasible for rapid PVT measurements of black oils [gas/oil ratio (GOR) ranging from 102 to 143 m3/m3]. The results presented in this study demonstrate that the microfluidic PVT system can measure saturation pressure and phase-volume with data quality comparable to that of the conventional PVT method, however, with significantly smaller sample volume and faster turnaround. The microfluidic PVT system is demonstrated to have the potential to become a reliable and portable measurement platform.