Monitoring marine oil seeps from space: the African case. DEFFONTAINES Benoît.1 RIAZANOF Serge 2, NAJOUI Zhour 1,2 , FACON Michael 2

1 Université Paris-Est, GTMC, Marne-la-Vallée, France 2 VisioTerra

Study framework

Data and

PS-InSAR method

References

A

Methodology

Oil slicks in radar images

Oil slicks floating on the sea surface becomes visible

on radar images because it damps the short gravity-

capillary waves that are responsible for the radar

backscattering (Fig.1).

A huge amount of radar data to detect oil slicks

VisioTerra has gathered more than 45 TB of ERS

SAR (Synthetic Aperture Radar) and Envisat ASAR

data across the world, whose 10383 segments for

Africa (Fig.2).

“World Oil Seepages “ database

Our goal is to locate, characterize, quantify and

modelize oil seepages using data acquired since

lunched of Radar satellites the scope to provide new

targets for oil exploration and production.

oil slick clean sea surface

Fig. 2: Studies performed around Africa in which at least 50 dates (red areas) have been collected.

Fig. 3: Numerous oil seeps observed on a ENVISAT ASAR image acquired on 25 February 2012 over Congo and Angola

Fig. 1: Backscatter radar waves on the sea surface.

Pre-processing

Original methods have been developed to numerically

process the images (Fig.4).

Co- occurences

The size, accessibility and gratuity of remote sensing

image archives allow to measure the repeatability of

events in one place. Thus, the seeps escaping from the

same fault appear on radar images on different dates

creating a astroseeps structures (Fig.5).

At least 50 acquisitions have been used in any point

within the 400 km away to the shore to guarantee the

statistical robustness of the discoveries (Fig 6).

Exogenous data

Geological data

Wind fields (Fig.8)

Bathymetric data

Petroleum platforms (Fig. 7)

AIS (Fig.9)

Fig. 4: Example of application of a model-based equalization and inter-swath correction

Fig. 8: Wind fields on 2012-03-15 at 21h42’38’’.

Oil seeps case examples

Application to structural geology

and oil exploration

current

sea surface outbreak

sea floor leak

source

sea surface outbreak e1(t1)

sea floor leak f1

source

current c(t2)

sea surface outbreak e1(t2)

current c(t1)

oil droplet

sea surface outbreak e2(t1)

sea floor leak 1

courant c(t1)

sea surface outbreak e1(t1)

sea floor leak 2

fault

outbreak segment

source

Fig. 5: Example of astroseeps structure observed in the Lower Congo basin (A). Min value of the images show an astroseeps (B).

2005-06-29

2005-05-09

2002-12-26

2002-11-21

2004-06-03

2003-11-25

2003-10-05

2012-02-25

A

B A. Gay, M. Lopez, C. Berndt, M. Sérane, 2007. Geological controls on

focused fluid flow associated with seafloor seeps in the Lower Congo

Basin. Marine Geology 244, p 68-92.

M. Brownfield, R. Charpentier 2006. Geology and total petroleum

systems of the West-Central coastal province (7203), West Africa. USGS

bulletin 2207-B, 52 p.

Z. Anka, R. Ondrak, A. Kowitz, Niels Schodt, 2013. Identification and

numerical modeling of hydrocarbon leakage in the Lower

Congo basin: Implication on the genesis of km-wide seafloor mounded

structures. Tectonophysics 604, p 153-171.

2012-03-26

2012-03-15 2005-02-19

2005-10-12 2005-10-12

2012-03-15

Fig. 10: Different astroseeps (multidates seeps).

Fig. 7: Mean images radar of West Africa.

Fig. 6: Occurrence map of west Africa.

Fig. 9: Automatic Identification System (AIS).

G. Marcano, Z. Anka, R. di Primo, 2013. Major controlling factors on

hydrocarbon generation and leakage in South Atlantic conjugate

margins: A comparative study of Colorado, Orange, Campos and

Lower Congo Basins. Tectonophysics 604, p 172-190

C. R. Jackson, J. R. Apel, 2004. Synthetic aperture radar marine

user’s manual. U.S. department of commerce, National Oceanic and

Atmospheric Administration.

S. Robla, E.G. Sarabia, J.R. Llata, C. Torre-Ferrero, J.P. Oria, 2010.

An Approach for detecting and tracking oil slicks on satellite

images. OCEANS 2010 , vol., no., pp.1,7, 20-23.

Fig. 11: Geological domains in the Lower Congo Basin.

Fig. 12: Weighted density map. Fig. 15: Line drawing of the seismic profile AB (modified after Rouby et al., 2002). The post-rift stratigraphy is characterized by two levels of seismic architectures: (1) an Albian to Eocene sequence containing the source rocks and (2) an Oligocene to Present sequence containing the reservoirs (turbiditic channels) and the sedimentary cover (affected by polygonal faults). Deep thermogenic fluids migrating from the source rocks are preferentially trapped into the silty–sandy channels (Gay and al. 2007).

Fig. 13: Events chart for the Congo Delta Composite Total Petroleum System and the Central Congo Delta and Carbonate Platform and the Central Congo Turbidites Assessment Units. Light blue indicates secondary occurrences of source rocks depending on quality and maturity of the unit. Age ranges of primary source, seal, reservoir, and overburden rocks and the timing of trap formation and generation, migration, and preservation of hydrocarbons are shown in green and yellow. Aptian Loeme Salt (regional evaporite unit) is shown in pink. Age, formation, and lithology modified from McHargue (1990), Schoellkopf and Patterson (2000), and Da Costa and others (2001) (Brownfield and al. 2006).

Fig. 14: Bathymetric map of Congo, extending from the Zaire estuary to the deep-sea fan, acquired during GUINESS (1992–1993) and ZAIANGO (1998–2000) projects (Gay and al. 2007).

www.visioterra.fr serge.riazanoff@visioterra.fr

tel.: +33 9 6130 6628