173
detailed in Malone et al. (2020) and Pesch et al. (2020). Both explicit TDR- and
empirical Weber-based approaches have been deployed to assess the likely range of
oil droplet sizes generated at the Macondo blowout, which naturally result in a wide
distribution of behavior. However, the fundamental balance between turbulence and
interfacial tension provides key insight as to droplet formation: smaller droplets can
be generated by (i) increasing turbulence and/or (ii) decreasing interfacial tension.
The latter effect provides a basis for considering subsea dispersant injection (SSDI)
during deepwater blowouts but only in the limit of fully understanding and characterizing the inherent turbulence of the deepwater plume.
Deepwater conditions provide a unique reality for droplet formation, as the natural momentum of the blowout will be insufficient for droplets to reach the surface.
That is, droplet buoyancy – as controlled by droplet diameter and fluid properties –
is the primary surfacing mechanism in deepwater blowouts. To this end, the simulation community has adopted a bifurcated approach to characterize surfacing
behavior: (i) fundamental or semi-empirical methods are adopted to relate turbulence to the oil DSD, whereafter (ii) far-field simulations assess the vertical and
lateral migration of droplets in the water column. Malone et al. (2020) provides
further insight as to the mechanics of droplet breakup and dependence on TDR.
11.2.2 Biodegradation of Hydrocarbons in the Water Column
Removal of oil compounds from the water column due to bacterial activity (biodegradation) occurs at different rates, depending on the strain of bacteria affecting certain groups of hydrocarbons, and may be subject to variations in fate and partitioning
under deep-sea conditions (Bubenheim et al. 2020; Jaggi et al. 2020).
High-pressure reactors for biological experiments were constructed at the
Hamburg University of Technology in cooperation with the companies Technik
Service A. Meyer and Eurotechnica. High hydrostatic pressure characteristic of the
deep sea can be simulated within these reactors allowing the examination of various
biological processes under deep-sea conditions. The reactors made from stainless
steel and bronze can withstand a maximum pressure of 40 MPa. Reactors are
equipped with sensor and near-infrared (NIR) spectrometer to continuously monitor oxygen as a proxy for aerobic biodegradation and gaseous hydrocarbons,
respectively (Valladares Juárez et al. 2015). To overcome the limitation of oxygen
availability for aerobic biodegradation, the reactor setup has a headspace, which
acts as a reservoir of oxygen that can replenish oxygen used in aerobic biodegradation in the water phase. Nitrogen gas is used as a pressurizing medium to avoid the
toxicity of increased oxygen partial pressure occurring when the gas phase in the
headspace of the reactor is compressed via mechanical pressurization with a spindle press. Experiments clearly indicate that pressure influences different taxa of
microorganisms unequally. For example, the growth rate of alkane-degrading bacteria Rhodococcus qingshengii TUHH-12 is slightly affected by pressure. The
growth rate at 15 MPa decreased to 0.16 h
−1
, in comparison to 0.36 h
−1
at atmo11 Far-Field Modeling of a Deep-Sea Blowout: Sensitivity Studies of Initial…
detailed in Malone et al. (2020) and Pesch et al. (2020). Both explicit TDR- and
empirical Weber-based approaches have been deployed to assess the likely range of
oil droplet sizes generated at the Macondo blowout, which naturally result in a wide
distribution of behavior. However, the fundamental balance between turbulence and
interfacial tension provides key insight as to droplet formation: smaller droplets can
be generated by (i) increasing turbulence and/or (ii) decreasing interfacial tension.
The latter effect provides a basis for considering subsea dispersant injection (SSDI)
during deepwater blowouts but only in the limit of fully understanding and characterizing the inherent turbulence of the deepwater plume.
Deepwater conditions provide a unique reality for droplet formation, as the natural momentum of the blowout will be insufficient for droplets to reach the surface.
That is, droplet buoyancy – as controlled by droplet diameter and fluid properties –
is the primary surfacing mechanism in deepwater blowouts. To this end, the simulation community has adopted a bifurcated approach to characterize surfacing
behavior: (i) fundamental or semi-empirical methods are adopted to relate turbulence to the oil DSD, whereafter (ii) far-field simulations assess the vertical and
lateral migration of droplets in the water column. Malone et al. (2020) provides
further insight as to the mechanics of droplet breakup and dependence on TDR.
11.2.2 Biodegradation of Hydrocarbons in the Water Column
Removal of oil compounds from the water column due to bacterial activity (biodegradation) occurs at different rates, depending on the strain of bacteria affecting certain groups of hydrocarbons, and may be subject to variations in fate and partitioning
under deep-sea conditions (Bubenheim et al. 2020; Jaggi et al. 2020).
High-pressure reactors for biological experiments were constructed at the
Hamburg University of Technology in cooperation with the companies Technik
Service A. Meyer and Eurotechnica. High hydrostatic pressure characteristic of the
deep sea can be simulated within these reactors allowing the examination of various
biological processes under deep-sea conditions. The reactors made from stainless
steel and bronze can withstand a maximum pressure of 40 MPa. Reactors are
equipped with sensor and near-infrared (NIR) spectrometer to continuously monitor oxygen as a proxy for aerobic biodegradation and gaseous hydrocarbons,
respectively (Valladares Juárez et al. 2015). To overcome the limitation of oxygen
availability for aerobic biodegradation, the reactor setup has a headspace, which
acts as a reservoir of oxygen that can replenish oxygen used in aerobic biodegradation in the water phase. Nitrogen gas is used as a pressurizing medium to avoid the
toxicity of increased oxygen partial pressure occurring when the gas phase in the
headspace of the reactor is compressed via mechanical pressurization with a spindle press. Experiments clearly indicate that pressure influences different taxa of
microorganisms unequally. For example, the growth rate of alkane-degrading bacteria Rhodococcus qingshengii TUHH-12 is slightly affected by pressure. The
growth rate at 15 MPa decreased to 0.16 h
−1
, in comparison to 0.36 h
−1
at atmo11 Far-Field Modeling of a Deep-Sea Blowout: Sensitivity Studies of Initial…