International Journal of Applied Earth Observation and Geoinformation
Chronology and backtracking of oil slick trajectory to source in offshore environments using ultraspectral to multispectral remotely sensed data
Introduction
With the high demand for energy resources, still founded on fossil fuels, petroleum exploration has migrated to deeper waters, particularly along the South American Atlantic coast. In view of its certified deep-water reserves, Brazil is set to become a top world oil producer and net oil exporter by 2017, possibly reaching the world’s sixth-largest oil production by 2035 (IEA, 2013).
In deep-water conditions, and consequently far from the coastlines, optical remote sensing is an essential tool for the detection and analysis of oil traces in the ocean. Such traces, when related to the natural escape of hydrocarbons (HCs) from the sea bottom to the surface (i.e., seepage), are of interest to oil exploration for ensuring, at least, that there is generation and migration of HCs in the sub-surface. The traces could also result from leakages of oil tankers, pipelines or rigs and their early detection helps to control marine pollution, which is the aim of environmental monitoring agencies.
Recent remote sensing studies have provided advances in the analysis of the compositional features (i.e., API gravity degree) of oil seepages found in the ocean (e.g., Wettle et al., 2009, Clark et al., 2010, Lammoglia and Souza Filho, 2011, Lammoglia and Souza Filho, 2012, Leifer et al., 2012, Prelat et al., 2013). Inverse modelling has also been tested as an attempt to identify areas in the seafloor from which petroleum seeped (Mano et al., 2011). This type of information enriches the remotely detection of seepages or leaks and, furthermore, can assist the exploratory or oceanic monitoring workflow.
Considering modern positive results achieved through the use of optical remote sensing data to estimate the composition of trace oil in the ocean, this work now seeks further science advances in remotely estimating the duration of oil exposed at the ocean surface based on spectral signatures.
Section snippets
Oil samples and spectroscopy measurements
Three crude oil samples were selected from the oil collection of the University of Campinas (UNICAMP). Oil samples 1–3 have API degrees of 19.2°, 19.4° and 27.7°, respectively. The API classification is inversely proportional to the oil’s specific gravity (density). Viscosities of samples 1–3 at 50 °C are 84.9, 78.5 and 20.4 mm2/s, correspondingly.
Experiments to analyze the spectral characteristics of crude oil, oil film and oil emulsions were carried out separately for each type of oil.
Results and temporal spectral model for oil emulsions
Despite the influence of water reflectance and emulsion bubbles, the spectral reflectance yielded from different types of HCs allows for their separation and characterization (Kallevik et al., 2000, Clark et al., 2010, Lammoglia and Souza Filho, 2011).
The spectral measurements of oils along time (Fig. 2, Fig. 3) show that the longer the oil and water are shaken in the Dubnoff waterbath incubator, the more consistent is the emulsion and the more the diagnostic spectral features of the oil become
Application of the model in a real case scenario
As a case study to demonstrate how well the model would fit to real scenarios, we selected an ASTER scene acquired in 23rd November 2004, which registered an event of extensive oil seepage in the Campos Basin, on the coast of Rio de Janeiro. This seepage has been previously investigated by Lorenzzetti et al. (2006), Bentz et al. (2007) and Lammoglia and Souza Filho (2012), under different approaches.
The seepage registered by the ASTER sensor was situated over the Marlim Sul oil field (Fig. 5),
Discussion and conclusions
From the laboratory experiments, it was possible to characterize the spectral signatures of different oil–water emulsions and their variations with time of exposition and degree of emulsification. We demonstrate that an increase in the emulsification of the oil–water solution is followed by an enhancement of the diagnostic spectral features of the HCs at ∼1.2 μm, 1.73–1.75 and 2.31–2.35 μm. The contrast between extremes of reflectance in the oil films are in the order of 7%. In the spectra of
Acknowledgements
The authors are thankful to Jarbas J.R. Rohwedder (University of Campinas) and Wilson Oliveira (PETROBRAS) for supporting the research. CRSF thanks CNPq for the Research Grant.
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