Three different periods of CO₂ dissolution into a light crude oil

Abstract

In this paper, phase behaviours and mass‐transfer mechanisms of a Bakken light crude oil‐CO2 system are studied. A series of PVT tests of the light crude oil‐CO2 system are conducted to measure CO2 solubilities, oil‐swelling factors, and CO2‐saturated oil densities at different equilibrium pressures and the actual reservoir temperature of Tres = 56.0 °C. Five CO2 diffusion tests in the light crude oil are performed at five different initial test pressures (Pi = 4.1, 5.2, 6.3, 7.7, and 9.0 MPa) and Tres = 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 CO2 average diffusivity in the light crude oil. It is found that the so‐called density‐driven natural convection can occur in the CO2‐saturated light crude oil as its measured density is much higher than that of the dead light crude oil. Three distinct periods of CO2 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 CO2 effective diffusivities (Deff) in Period I and CO2 molecular diffusivities (D) in Period II from the GM are in the ranges of 0.28–1.75 × 10−6 m2/s and 0.87–1.94 × 10−9 m2/s at the initial test pressures of Pi = 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 Deff or D.

Diffusive and convective dissolution of carbon dioxide in a vertical cylindrical cell

“…However, after the onset of convection, the curve deviates, resulting in m = 2C sat A √ D c (t − t c )/π (dashed line) to be the best fit, with an effective diffusion coefficient of D c = 30D and t c = 160 s as the virtual time origin. Compared to other authors, who report finding D c /D ∼ 10 2 or 10 3 for experiments conducted in varying PVT or Hele-Shaw cells, this seems reasonable as variations in experimental conditions and cell configuration differences appear to severely affect the obtained effective diffusion coefficients [20][21][22][23][24].…”

“…Moreover, in the regimes where convection is contributing to the mass transport, apparent diffusive behavior is observed, albeit with a much higher effective diffusion coefficient. Depending on the experimental conditions, this effective diffusion coefficient can be several orders of magnitude bigger in comparison to the expected diffusive counterpart under similar experimental conditions [20][21][22][23][24]. However, little explanation has been given as to what drives the different observed regimes, the transitions between the regimes and why the system still appears to behave in a diffusive manner.…”

Full Characterization of CO2–Oil Properties On-Chip: Solubility, Diffusivity, Extraction Pressure, Miscibility, and Contact Angle

“…Above the extraction pressure, the crude oil composition changes due to the extraction of intermediate components of the crude oil into the CO 2 phase. Figure c compares the diffusion coefficient data (at 23 and 50 °C) determined using the microfluidic method developed in this study with the data reported elsewhere obtained by pressure decay and pendant drop experiments. − The literature reported values are all from light oil. While there is no exact match between the fluid samples, test conditions, and experimental methods, the results obtained here were in good agreement with the literature data.…”

Molecular Dynamics Simulation of Transport and Structural Properties of CO2–Alkanes

“…n-Alkanes with longer carbon chains have a larger viscosity reduction with increasing amounts of dissolved CO 2 . Gu et al measured viscosity of the light crude oil and reported a value of 1.48 cP at the atmospheric pressure and the reservoir temperature of 329 K. 56…”