49
emulsion at a certain speed. This approach avoids upscaling over several orders of
magnitude but allows only the investigation of an equilibrated system.
Among others, Boxall et al. (2012) measured the DSD of a water-in-oil emulsion
with a combination of the focused beam reflectance method (FBRM) and an endoscopic imaging system for a wide range of oil blends and stirrer speeds. Aman et al.
(2015) used the same approach to investigate the DSD under high hydrostatic pressure up to 110 atm in a methane-saturated system using high-speed video image
analysis.
4.2.3 DeepSpill: Field Experiment in the Deep Sea
In June 2000, SINTEF performed a field experiment at the Helland-Hansen site off
the coast of Norway in a water depth of 844 m. Four discharges of dyed seawater,
crude oil and marine diesel fuel in combination with LNG (liquefied natural gas) or
nitrogen were conducted in order to test numerical spill propagation models and
equipment for spill monitoring and surveillance (Johansen et al. 2000). The liquids
were discharged at a rate of 60 m³/h for 60 min each from a 120 mm nozzle; gas
flow was between 0.6 and 0.7 Sm³/s. Droplet sizes were evaluated manually from
ROV video data for one discharge of diesel fuel in combination with LNG at four
different heights over the discharge point. Images of the drops were taken by a
colour video camera (resolution 460 TV lines) with a ruler mounted in the foreground to provide scale. The reported volume median diameter varies from four
distinct values between 3 and 7 mm for the four measurement points (d v50 increasing
with increasing distance from the discharge point) (Johansen et al. 2000; Socolofsky
et al. 2015) to a single value of 5.5 mm (Brandvik et al. 2017).
4.2.4 Equipment for Field Measurements
In situ measurement of the DSD of a deep-sea oil spill remains a challenge. Apart
from the high-pressure environment, the equipment needs to detect a particle size
range of three orders of magnitude, from <10 μm to several millimetres. In addition,
the oil fraction in the jet near the discharge point can be very high, resulting in poor
light transmittance.
Although originally designed for the quantification of solid particles suspended
in the water column, the commercially available LISST laser diffractometers by
Sequoia Scientific Inc. have been widely used in the past years to measure oil droplet sizes as well (see Sect. 4.2.1). While the system is easy to deploy on ROVs for in
situ measurements and also available in a deep-sea configuration (depth rating
3000 m), its measurement range is limited to a maximum drop diameter of 500 μm,
a maximum particle concentration of 750 mg/L (less for large particles) and an
optical transmission rate >30%. The technology is therefore well suited for
4 Jet Formation at the Spill Site and Resulting Droplet Size Distributions
emulsion at a certain speed. This approach avoids upscaling over several orders of
magnitude but allows only the investigation of an equilibrated system.
Among others, Boxall et al. (2012) measured the DSD of a water-in-oil emulsion
with a combination of the focused beam reflectance method (FBRM) and an endoscopic imaging system for a wide range of oil blends and stirrer speeds. Aman et al.
(2015) used the same approach to investigate the DSD under high hydrostatic pressure up to 110 atm in a methane-saturated system using high-speed video image
analysis.
4.2.3 DeepSpill: Field Experiment in the Deep Sea
In June 2000, SINTEF performed a field experiment at the Helland-Hansen site off
the coast of Norway in a water depth of 844 m. Four discharges of dyed seawater,
crude oil and marine diesel fuel in combination with LNG (liquefied natural gas) or
nitrogen were conducted in order to test numerical spill propagation models and
equipment for spill monitoring and surveillance (Johansen et al. 2000). The liquids
were discharged at a rate of 60 m³/h for 60 min each from a 120 mm nozzle; gas
flow was between 0.6 and 0.7 Sm³/s. Droplet sizes were evaluated manually from
ROV video data for one discharge of diesel fuel in combination with LNG at four
different heights over the discharge point. Images of the drops were taken by a
colour video camera (resolution 460 TV lines) with a ruler mounted in the foreground to provide scale. The reported volume median diameter varies from four
distinct values between 3 and 7 mm for the four measurement points (d v50 increasing
with increasing distance from the discharge point) (Johansen et al. 2000; Socolofsky
et al. 2015) to a single value of 5.5 mm (Brandvik et al. 2017).
4.2.4 Equipment for Field Measurements
In situ measurement of the DSD of a deep-sea oil spill remains a challenge. Apart
from the high-pressure environment, the equipment needs to detect a particle size
range of three orders of magnitude, from <10 μm to several millimetres. In addition,
the oil fraction in the jet near the discharge point can be very high, resulting in poor
light transmittance.
Although originally designed for the quantification of solid particles suspended
in the water column, the commercially available LISST laser diffractometers by
Sequoia Scientific Inc. have been widely used in the past years to measure oil droplet sizes as well (see Sect. 4.2.1). While the system is easy to deploy on ROVs for in
situ measurements and also available in a deep-sea configuration (depth rating
3000 m), its measurement range is limited to a maximum drop diameter of 500 μm,
a maximum particle concentration of 750 mg/L (less for large particles) and an
optical transmission rate >30%. The technology is therefore well suited for
4 Jet Formation at the Spill Site and Resulting Droplet Size Distributions