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Oil seepage mapping by SAR detection
Offshore oil exploration service
VisioTerra provides you with offshore oil seepage studies by using a large amount of SAR images from Envisat ASAR, at least 50 radar image are used to cover each point of the area of interest. The studies have been realised by a team of petroleum geologists and GIS specialists with skills in Earth observation images interpretation. The oil seeps studies are the first data available for New Ventures exploration, chiefly for deep and ultra-deep offshore.
 
  • Input data - The oil seepage study is based on different types of data in order to provide the most accurate photo interpretation. We use SAR and MERIS images from the Envisat satellite (ESA), wind field data (database since 1983), ship and petroleum platform location. (Fig 1a)
 
  • Output maps - VisioTerra provides you with -a map of oil seepage occurrences, -the oil seeps table and -shapefiles. We may also provide you with the data that have been used for the interpretation. (Fig 1b)

 

  • Integrated study - A geological study based on scientific research papers has been done for each area of interest for a better mastering of the area, and to evaluate a possible correlation between geology and the oil seeps location.
 
 

Fig 1a- SAR image showing oil slicks, Angola offshore.
 

Fig 1b- Occurrences map produced over Angola offshore.
 


Our methodology:

 

1- Radar images pre-processing


The raw SAR images are not interpretable in the offshore domain. VisioTerra has a specific pre-processing to allow a better visualization in the offshore field. The better contrast allows us to draw a distinction between bright and black "bodies".
 

Fig 2 - example of application of a model-based equalization and inter-swath correction
 
 

 

2- Photo-interpretation

 
For each radar image we sequentially interpret and model oil seeps and oil spills. Ancillary data, like wind field, platform and ship location, are used to discern oil seeps (from ) oil spills , to find the outbreak point on the sea surface.
 

 
 
 

3- Multi-date synthesis

 
For an accurate interpretation, a multi-date synthesis is done. This provides useful elements for oil seeps studies and supplies a ground to distinguish between oil seeps and oil slicks as a consequence we can locate the surface outbreak point of the repetitive oil seeps.
 
 
 

 

 

4- Ambiguity removal

 
Oil seeps are usually repetitive phenomenon. The presence of oil slicks at the same location and at different dates is a strong evidence to rank an oil slick as an oil seep rather than oil spills.
 
 
 

 

 

 

 

 

5- Outbreak point location

 
Sometimes wind data do not allow us to determine with certitude the location of the outbreak point. Multi-date synthesis display specific structures of repetitive oil seeps, the center of this structure show the location of the outbreak point.

 

 

 

6- Ascension model

 
 In order to locate the outbreak point on the seafloor, we develop an ascension model. Thus, we combine an oceanic current model (HYCOM) together with a model of rise velocity for oil droplets in seawater.
 
 
 
  • Presentation at HGS-PESGB 13th conference on Africa E&P
    PDF, 4.5 Mb
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