A New Experimental Technique for Studying Gas Mass Transfer in the Crude Oil byAnalysis of the Measured Dynamic and Equilibrium Interfacial Tensions

摘要

This paper presents a new experimental technique and itscomputational scheme for studying gas mass transfer in thecrude oil at high pressures and elevated temperatures byanalysis of the measured dynamic and equilibrium interfacialtensions. In the experiment, a see-through windowed highpressurecell is prefilled with a test gas at a prespecifiedpressure and a constant temperature. Then, a crude oil sampleis introduced by using a specially designed syringe deliverysystem to form a pendant oil drop inside the pressure cell. Dueto the dissolution of the gas into the pendant oil drop, thedynamic interfacial tension between the test gas and the crudeoil keeps reducing and eventually reaches its equilibriumvalue when the saturation state is achieved. The sequentialdigital images of the dynamic pendant oil drop are acquiredand analyzed by applying computer-aided image acquisitionand processing techniques to measure the dynamic interfacialtensions at different times. Theoretically, a mathematical masstransfer model is formulated to describe the diffusion processof the gas in the pendant oil drop. This model is numericallysolved by applying the semi-discrete Galerkin finite elementmethod to obtain the transient gas concentration distributioninside the pendant oil drop. With a pre-determined calibrationcurve of the equilibrium interfacial tension versus theequilibrium gas concentration in the crude oil, the dynamicinterfacial tension at any time is calculated. The mass transferBiot number and the gas diffusion coefficient are thusdetermined by finding the best fit of the theoreticallycalculated dynamic interfacial tensions to the experimentallymeasured data. This newly developed experimental techniqueis applied to measure the mass transfer Biot number, thediffusion coefficient, and the interface mass transfercoefficient of CO2 in a reservoir oil sample at P=0.1~5.0 Mpaand T =27°C.