A New Semi utomatic PVT Apparatus for Characterizing Vapex Systems

摘要

Knowledge of fluid properties is critical to the design of Vapex projects and other enhanced oil recovery processes that use solvent vapor extraction, yet very few pertinent data exist in the published literature. This paper describes a new apparatus for the efficient and accurate measurement of the physical and phase behaviour properties of mixtures of heavy oils and solvents such as propane and butane. The apparatus combines advanced capabilities that make it superior to conventional designs: The automated functions improve the speed at which the data are acquired and reduce operator error. Inline density and viscosity measurements add the capability of multi-phase detection. High-pressure filtration permits measurement of asphaltene and wax precipitation at reservoir conditions. Dual gasometers allow accurate measurements of gas solubility over a wide range of solvents and reservoir pressures. Sub-ambient temperature control makes it suitable for Canadian operations. The apparatus was tested against published measurements for the n-hexadecane–carbon dioxide system, and then used to gather a comprehensive suite of data at two isotherms for a Lloydminster heavy oil–propane system. Random scatter in the resulting data was very small. The equipment is well suited to the acquisition of fluid property measurements for both field design and correlation purposes. With the improvements in both the precision of measurements and the speed of operation offered by the new equipment, it was possible to test some assumptions used in measuring vapor–liquid equilibrium in heavy oil–solvent systems. The results suggested that a noticeable uncertainty may be associated with conventional methods used to determine saturation pressures in these systems.