--> Lithofacies Association, Stratal Geometries and Stratigraphic Stacking in Deepwater Slope Channel Systems: Examples from Ainsa Basin (Spain), and Edop Field (Offshore Nigeria), by V. Abreu and R. Hill; #90037 (2005)

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Lithofacies Association, Stratal Geometries and Stratigraphic Stacking in Deepwater Slope Channel Systems: Examples from Ainsa Basin (Spain), and Edop Field (Offshore Nigeria)

V. Abreu1 and R. Hill 2
1 ExxonMobil Research Company, Houston, TX
2 ExxonMobil, TX

Slope-channel systems outcropping in the Ainsa Basin (Middle Eocene) provide excellent analogs to slope-channel reservoirs being produced and developed in offshore West Africa (e.g., Edop Field, offshore Nigeria). Specifically, the outcrops offer an opportunity to investigate the: range and distribution of reservoir and non-reservoir lithofacies within slope-channel complexes, range of non-amalgamated to laterally amalgamated channel architectural styles, hierarchical organization of slope channel systems, and basin-scale stratigraphic evolution.

The Ainsa Basin was formed due to the interaction of the African plate with the European plate and Iberian micro-plate during the Cenozoic. The Ainsa Basin is formed by a series of second-order depositional cycles that are bounded by sharp angular unconformities resulting from thrust-induced oversteeping during tectonically active periods. During the Middle Eocene, the second-order cycle is defined by four third-order sequences: Gerbe-Banaston, Ainsa, Morillo, and O Grau. As an example, the Morillo outcrops display striking channelized juxtaposition of reservoir and non-reservoir facies within a slope-channel complex, as well as an overall vertical organization with traction-conglomerate and muddy debrites dominating the basal part and high and low-concentration sandy turbidites dominating the upper part of the succession.

The Edop Field (offshore Nigeria) is represented mostly by Lower Pliocene Slope Channel Systems, and is under production since the late 80's. Similar to the Ainsa Basin, the Edop field is composed of higher frequency deepwater sequences, forming a lowstand sequence-set (Rubble Beds and IQI-1 to IQI-4), corresponding to the Qua Iboe Member of the Agbada Formation. The IQI-3 reservoir is a slope channel system similar in dimensions and lithofacies association to producing in offshore Angola (e.g., Girassol Field). The 101-3 system is about 2 kilometers wide and 200 meters deep, with strong similarities with the Morillo System in terms of dimensions, lithofacies association, stratal geometries and stratigraphic stacking.