Infrared Devices for dark fluids phase behavior detection and monitoring: Desktop PVT

Several approaches for investigating phase behavior have been proposed and are commonly classified into direct and indirect methods. Among the direct methods, visual techniques stand out, including fully visual PVT analyses and the use of high-pressure microscopy (HPM), which are applied in studies of asphaltene precipitation, liquid–vapor equilibrium, and wax formation. In contrast, indirect methods rely on detecting changes in fluid properties, encompassing light-scattering techniques for solid identification, viscosity measurements, and calorimetric methods. Conventional PVT experiments, such as constant-composition expansion with pressure–volume monitoring, enable the identification of liquid–vapor transitions based on variations in system compressibility. Spectrometric analyses of crude oils have demonstrated increased transmittance at wavelengths around 1550 and 2100 nm, indicating the potential use of infrared-based sensors, such as SWIR cameras and spectrometers, for real-time monitoring of the phase behavior of complex crude oil–CO₂ mixtures. Accordingly, to assess the applicability of infrared sensors to optically opaque fluids, a supervisory system was developed in LabVIEW for the remote control of a high-pressure PVT system. This system is responsible for adjusting experimental conditions (temperature and pressure), acquiring thermodynamic variable data, and performing the acquisition and processing of both video data (SWIR camera) and spectrometric measurements. For lighter crude oils, with lower asphaltene contents (<0.1 wt%), visual and light-scattering techniques enabled the detection of precipitation of the heavy and paraffinic fractions of the crude oil, as well as the identification of the bubble point. However, for heavier oils with higher asphaltene contents (>1 wt%), the increased optical opacity of the fluid limited sensor performance, allowing the detection of the mixture bubble point and the occurrence of liquid–liquid equilibrium.