33
3.2.3 Density and Swelling
The densities of petroleum liquids are usually a nearly linear function of pressure.
The most common method to measure liquid densities at elevated pressures is the
oscillating tube (Eggers 2012). A bended tube is filled with the liquid under investigation and excited. The response in terms of the periodic time is related to the
density. The system requires thorough calibration in order to deliver reliable
results. It is even more challenging to determine the density of liquids that contain
dissolved gases. The influence of pressure in this case depends on the type of gas.
In Sect. 3.3.3 we report the density of Louisiana sweet crude (LSC) oil comparing
the pure liquid to the methane-containing liquid, including modeled data using the
Peng- Robinson EOS.
3.2.4 Viscosity
There are a large number of methods available for determining the viscosity at elevated pressures (Eggers 2012). Mainly two points have to be taken into account:
Newtonian flow and gas saturation. The main methods used are:
1. Vibrating crystal.
2. Capillary tube.
3. Rotational rheometer.
4. Rolling ball/oscillating piston.
In Fig. 3.4 the viscosity as determined by a capillary tube viscometer is depicted
as a function of pressure. For determining the viscosity of gas-saturated oils, a
piston accumulator similar to the one used to determine the bubble point is used to
prepare the mixture.
3.2.5 Diffusivity
Applying the setup described above, the diffusion of gas into the liquid phase can be
followed as a function of time until the liquid is saturated with gas (Knauer et al.
2017). The microbalance described in Sect. 3.2.2 is used to determine this sorption
kinetics. The analytical solution to the nonstationary Fick’s diffusion (Crank 1975)
is adjusted to the experimental data in order to deduce the diffusion coefficient.
Because of the higher viscosity, the diffusion coefficient of methane in crude oil
takes lower values than in an aqueous phase. Diffusivities at a pressure of 5 MPa are
found in the order of 1*10
−9
m
2
s
−1
for LSC compared to around 5*10
−9
m
2
s
−1
in
water, which is slightly higher than values reported in literature for atmospheric
pressure (Hayduk and Laudie 1974).
3 Physical and Chemical Properties of Oil and Gas Under Reservoir and Deep-Sea…
3.2.3 Density and Swelling
The densities of petroleum liquids are usually a nearly linear function of pressure.
The most common method to measure liquid densities at elevated pressures is the
oscillating tube (Eggers 2012). A bended tube is filled with the liquid under investigation and excited. The response in terms of the periodic time is related to the
density. The system requires thorough calibration in order to deliver reliable
results. It is even more challenging to determine the density of liquids that contain
dissolved gases. The influence of pressure in this case depends on the type of gas.
In Sect. 3.3.3 we report the density of Louisiana sweet crude (LSC) oil comparing
the pure liquid to the methane-containing liquid, including modeled data using the
Peng- Robinson EOS.
3.2.4 Viscosity
There are a large number of methods available for determining the viscosity at elevated pressures (Eggers 2012). Mainly two points have to be taken into account:
Newtonian flow and gas saturation. The main methods used are:
1. Vibrating crystal.
2. Capillary tube.
3. Rotational rheometer.
4. Rolling ball/oscillating piston.
In Fig. 3.4 the viscosity as determined by a capillary tube viscometer is depicted
as a function of pressure. For determining the viscosity of gas-saturated oils, a
piston accumulator similar to the one used to determine the bubble point is used to
prepare the mixture.
3.2.5 Diffusivity
Applying the setup described above, the diffusion of gas into the liquid phase can be
followed as a function of time until the liquid is saturated with gas (Knauer et al.
2017). The microbalance described in Sect. 3.2.2 is used to determine this sorption
kinetics. The analytical solution to the nonstationary Fick’s diffusion (Crank 1975)
is adjusted to the experimental data in order to deduce the diffusion coefficient.
Because of the higher viscosity, the diffusion coefficient of methane in crude oil
takes lower values than in an aqueous phase. Diffusivities at a pressure of 5 MPa are
found in the order of 1*10
−9
m
2
s
−1
for LSC compared to around 5*10
−9
m
2
s
−1
in
water, which is slightly higher than values reported in literature for atmospheric
pressure (Hayduk and Laudie 1974).
3 Physical and Chemical Properties of Oil and Gas Under Reservoir and Deep-Sea…