Swelling/Extraction Test of a Small Sample Size for Phase Behavior Study

Abstract

Abstract Swelling/extraction tests are single-contact phase-behavior experiments to measure the solubility of CO2 dissolved in crude oil and the amount of hydrocarbon that CO2 can extract or vaporize from crude oil. The tests are commonly conducted in a visual PVT cell with a large sample size (40–100cc). In this paper, an easy operated apparatus capable of determining phase behavior with a significantly smaller sample size (3 to 14 cc) is described. The apparatus consists of a high-pressure view cell, high-pressure and precision syringe pump filled with CO2, a water bath, and accessories to measure the temperature and pressure. The device is capable of determining vapor-liquid, liquid-liquid and vapor-liquid-liquid equilibrium commonly observed in a high pressure CO2 enhanced oil recovery process. The solubility of CO2 in oil, the expansion volume of oil due to the dissolution of CO2 as well as the phase transition during the test were quantified with excellent reproducibility. The molar volume of oil saturated with CO2 correlated linearly with the mole fraction of dissolved CO2 suggesting ideal mixing in the liquid phase. The phase behavior between CO2 and crude oil samples with different composition, temperature and pressure is discussed.