Upgrading SAR Slick Interpretations in West Africa with Piston Cores, Oil Samples and Potential Fields Data

William Dickson¹, Craig Schiefelbein², Alan Williams³, Mark E. Odegard⁴, and James M. Brooks^5
1Dickson International Geosciences (DIGs), Houston, TX
²Geochemical Solutions International, Shenandoah, TX
³NPA Group, Edenbridge, United Kingdom
⁴Grizzly Geosciences, Inc. (GrizGeo), Sugar Land, TX
⁵TDI-Brooks International, Inc., College Station, TX

In a 2006 AAPG poster, the authors found correlations among several data sets that helped identify the origin and geologic setting of numerous slicks along the West African margin, particularly in the Niger Delta and basins offshore Angola. This encouraged a closer look at both SAR and potential field data to improve resolution and discrimination of features. A new generation of gravity & magnetic grids was coupled with layers of new compliant SAR imagery. Harmonization of the latter included screening images at post-seismic event times when seepage levels might be elevated. Additional attributes permit the classification of seeps with respect to tidal variation and geologic controls (toe thrust belts, transfer zones, transforms, basin edges, gas hydrates) determined from multiple data types described in our earlier work.

From a working set of observations, we provided re-classification candidates to the seep screening experts. Previously “Unassigned” slicks were moved to higher confidence categories. The strongest rank increase came from a combination of structural correlation to features mapped on potential fields with identification of active migration from piston cores. A further, definitive ranking step would be to take swab samples of selected seeps (at the ocean surface) for analysis. We include one beautiful example associated, opportunistically, with a piston coring program.

Seep distribution is, unsurprisingly, related to geology. The strongest correlations are to locations of intersecting major structural trends and to seal limits. Examples are shown from the Niger Delta, Ogooue Delta (Gabon Coastal Basin), Congo Fan and Kwanza Basin (Angola).

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas