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Three different periods of CO 2 dissolution into a light crude oil
Author(s) -
Du Fengshuang,
Ma Hongze,
Gu Yongan
Publication year - 2019
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.23204
Subject(s) - light crude oil , crude oil , dissolution , chemistry , thermal diffusivity , diffusion , analytical chemistry (journal) , mass transfer , thermodynamics , mineralogy , chromatography , petroleum engineering , geology , organic chemistry , physics
In this paper, phase behaviours and mass‐transfer mechanisms of a Bakken light crude oil‐CO 2 system are studied. A series of PVT tests of the light crude oil‐CO 2 system are conducted to measure CO 2 solubilities, oil‐swelling factors, and CO 2 ‐saturated oil densities at different equilibrium pressures and the actual reservoir temperature of T res = 56.0 °C. Five CO 2 diffusion tests in the light crude oil are performed at five different initial test pressures ( P i = 4.1, 5.2, 6.3, 7.7, and 9.0 MPa) and T res = 56.0 °C by applying the pressure decay method (PDM). The graphical method (GM) is used to analyze the measured test pressure versus time data of each diffusion test and determine CO 2 average diffusivity in the light crude oil. It is found that the so‐called density‐driven natural convection can occur in the CO 2 ‐saturated light crude oil as its measured density is much higher than that of the dead light crude oil. Three distinct periods of CO 2 dissolution into the light crude oil are identified: the natural convection‐dominated period (I), the transition period, and the molecular diffusion‐dominated period (II). The determined CO 2 effective diffusivities ( D eff ) in Period I and CO 2 molecular diffusivities ( D ) in Period II from the GM are in the ranges of 0.28–1.75 × 10 −6 m 2 /s and 0.87–1.94 × 10 −9 m 2 /s at the initial test pressures of P i = 4.1–9.0 MPa, respectively. Finally, it is also found that the constant Z ‐factor approximation used in the GM may cause a relatively large error in the determination of D eff or D .