Oil Droplet Size Distributions in Deep-Sea Blowouts: Influence of Pressure and Dissolved Gases

Abstract

To date, experimental investigations to determine the droplet size distribution (DSD) of subsea oil spills were mostly conducted at surface conditions, i.e. at atmospheric pressure, and with dead, i.e. purely liquid, oils. To investigate the influence of high hydrostatic pressure and of gases dissolved in the oil on the DSD, experiments with a downscaled blowout are conducted in a high-pressure autoclave at 150 bar hydrostatic pressure. Jets of "live", i.e. methane-saturated, crude oil and n-decane are compared to jets of "dead" hydrocarbon liquids in artificial seawater. Experiments show that methane dissolved in the liquid oil increases the volume median droplet diameter significantly by up to 97%. These results are not in good accordance with state-of-the-art drop formation models, which are based on oil-only experiments at atmospheric pressure, and therefore show the need for a modification of such models which incorporates effects of hydrostatic pressure and dissolved gases for the modeling of deep-sea oil spills and blowouts.

BP Gulf Science Data Reveals Ineffectual Subsea Dispersant Injection for the Macondo Blowout

“…(1) a sudden pressure drop at the BOP upon exit of the multiphase jet into the ambient seawater (Aliseda et al, 2010;Griffiths, 2012) leading to rapid expansion of the dissolved gas (Oldenburg et al, 2012), which would atomize the live oil into micro-droplets (Malone et al, 2018); (2) cold water and gas combined under high pressure (i.e., 5 • C and 15.45 MPa at Macondo; Oldenburg et al, 2012) enhanced the formation of gas hydrates that may have encapsulated some crude oil, which may have decreased their buoyancy (Joye et al, 2011); or (3) as live oil rises in the water column and hydrostatic pressure decreases, degassing should increase the apparent droplet size. "Growing" droplets would then rise faster than expected from their initial size at the wellhead (Paris et al, 2012;Pesch et al, 2018).…”

“…The lack of effect of the SSDI volume variation on the vertical distribution of petroleum hydrocarbons does not mean that the oil droplet interfacial tension with water was not affected, but rather indicates that thermo-physical and chemical processes had a stronger effect on the uncontrolled release of gas-saturated oil and free gas. There was an extreme pressure drop at the Macondo wellhead (Aliseda et al, 2010;Wereley, 2011), leading to rapid outgassing and fractioning of the oil into fine droplets (Malone et al, 2018;Pesch et al, 2018). Extensive GSD revealed no significant SSDI effect on the oil vertical distribution throughout the DWH spill.…”

Resolving the dilemma of dispersant use for deep oil spill response

“…The rise velocity of an oil droplet is an increasing function of its diameter and degree of saturation with natural gas components [1,4,5]. For an intermediateviscosity black oil like Louisiana sweet crude (which has been used as a proxy for DWH studies), oil droplets smaller than approximately 70 μm can be rendered neutrally buoyant due to small-scale ocean turbulence [1].…”

“…A number of studies have conducted or summarized experimental approaches to estimate oil droplet sizes from scaled-down laboratory experiments, in test tanks, and, in one case, a field-scale experiment [1,12,13]. Laboratory experiments to assess oil droplet diameters have been undertaken in a small number of facilities: the SINTEF facilities in Norway, the OHMSETT tank in New Jersey, the Southwest Research Institute highpressure vessel in Texas, the high-pressure test facility at the Hamburg University of Technology in Germany [4,5,12] and in stirred sapphire cells at the University of Western Australia [11] and elsewhere. Extrapolating droplet behavior from these laboratory apparatus to ultra-deep field-scale conditions is complicated by a number of factors.…”

Investigations on the Capability of the Statistical Extinction Method for the Determination of Mean Particle Sizes in Concentrated Particle Systems

“…Maaß was able to perform substance‐specific measurements with an endoscope technique even at a particle concentration of 45% by volume . For example, based on the research of Maaß, SOPAT GmbH developed photo‐optical probes for an inline monitoring, among others, of emulsification, dispersion, and crystallization processes . Fischer et al developed an image‐based measurement system with a digital camera, which is suitable for dilute particle systems under harsh conditions like in spray‐drying processes.…”