87
that are and have been used in a variety of methods to estimate the volumes released.
In addition, the usual remoteness of a subsea release—both in terms of depth of
releases and remote geographical areas where many deep exploration prospects are
developed—presents many logistical and technical challenges to data collection.
These data collection challenges need to be addressed both during spill response
and mitigation and during environmental injury assessment. To understand the overall impact of released oil and gas, it is important to overcome these challenges to
understand how the oil moves and the physical and chemical changes it undergoes
once it is released (Table 6.1).
The initial priority during and immediately after an oil spill is the response,
which aims to minimize damage and protect resources. Concurrent with the emergency response is the urgent need to collect “ephemeral” data that will be needed to
assess environmental injuries (Boehm et al. 2013). In the following days and weeks,
the effort shifts to understanding the environmental impact and potential injury
from the oil, and key to that is understanding the fate and transport of the oil. Besides
providing information about the geographical extent and temporal trends of the
chemical concentrations of oil and oil compounds for use in environmental damage
assessments, the sampling efforts are aimed at characterizing the changes in the
surface and subsurface distribution and composition of the oil over time. Sampling
is usually combined with fate and transport modeling to provide a three- dimensional
understanding (Spaulding et al. 2017).
The Deepwater Horizon (DWH) spill resulted in an unprecedented scope of
investigations of the fate and transport of the released oil. However, studies of the
fate, transport, and degradation (also known as “natural attenuation”) of oil and gas
have been important topics in oil spill research and environmental assessment for
many years, and there are many examples of environmental investigations of oil
spills from the past 50 years where such extensive environmental studies were also
undertaken. Although there is variability in the focus and intensity of the studies,
due to both trends over time and the relative magnitudes of the releases, more
recently, comprehensive data sets in combination with modeling have provided a
picture of the impact of each spill to the environment.
For example, in 1978, the tanker Amoco Cadiz ran aground near the shore of
France and released approximately 230,000 tonnes of light crude oil (API gravity
32.8). Studies from this release showed that the weather resulted in the formation of
a stable emulsion and tarballs on the ocean surface, and evaporation resulted in the
loss of a large fraction of the oil (Gundlach et al. 1983; Mille et al. 1998). The
remaining oil that reached shorelines was highly weathered, and periodic follow-up
studies in 7 years after the release showed further degradation of the remaining
petroleum and led to the description of stages of weathering (Page et al. 1989). In
March 1989, the Exxon Valdez tanker ran aground in Prince William Sound, Alaska,
spilling 35,470 tonnes of Alaska North Slope Crude (API gravity 32.3) over a 6-hour
period. A storm 2 days after the release resulted in the mixing of the slick and the
formation of mousse and tarballs, which were distributed over a geographical area
more than 500 miles in length. The resulting environmental investigation was one of
the largest in US history and led to the development of standardized procedures for
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…
that are and have been used in a variety of methods to estimate the volumes released.
In addition, the usual remoteness of a subsea release—both in terms of depth of
releases and remote geographical areas where many deep exploration prospects are
developed—presents many logistical and technical challenges to data collection.
These data collection challenges need to be addressed both during spill response
and mitigation and during environmental injury assessment. To understand the overall impact of released oil and gas, it is important to overcome these challenges to
understand how the oil moves and the physical and chemical changes it undergoes
once it is released (Table 6.1).
The initial priority during and immediately after an oil spill is the response,
which aims to minimize damage and protect resources. Concurrent with the emergency response is the urgent need to collect “ephemeral” data that will be needed to
assess environmental injuries (Boehm et al. 2013). In the following days and weeks,
the effort shifts to understanding the environmental impact and potential injury
from the oil, and key to that is understanding the fate and transport of the oil. Besides
providing information about the geographical extent and temporal trends of the
chemical concentrations of oil and oil compounds for use in environmental damage
assessments, the sampling efforts are aimed at characterizing the changes in the
surface and subsurface distribution and composition of the oil over time. Sampling
is usually combined with fate and transport modeling to provide a three- dimensional
understanding (Spaulding et al. 2017).
The Deepwater Horizon (DWH) spill resulted in an unprecedented scope of
investigations of the fate and transport of the released oil. However, studies of the
fate, transport, and degradation (also known as “natural attenuation”) of oil and gas
have been important topics in oil spill research and environmental assessment for
many years, and there are many examples of environmental investigations of oil
spills from the past 50 years where such extensive environmental studies were also
undertaken. Although there is variability in the focus and intensity of the studies,
due to both trends over time and the relative magnitudes of the releases, more
recently, comprehensive data sets in combination with modeling have provided a
picture of the impact of each spill to the environment.
For example, in 1978, the tanker Amoco Cadiz ran aground near the shore of
France and released approximately 230,000 tonnes of light crude oil (API gravity
32.8). Studies from this release showed that the weather resulted in the formation of
a stable emulsion and tarballs on the ocean surface, and evaporation resulted in the
loss of a large fraction of the oil (Gundlach et al. 1983; Mille et al. 1998). The
remaining oil that reached shorelines was highly weathered, and periodic follow-up
studies in 7 years after the release showed further degradation of the remaining
petroleum and led to the description of stages of weathering (Page et al. 1989). In
March 1989, the Exxon Valdez tanker ran aground in Prince William Sound, Alaska,
spilling 35,470 tonnes of Alaska North Slope Crude (API gravity 32.3) over a 6-hour
period. A storm 2 days after the release resulted in the mixing of the slick and the
formation of mousse and tarballs, which were distributed over a geographical area
more than 500 miles in length. The resulting environmental investigation was one of
the largest in US history and led to the development of standardized procedures for
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…