Congo Canyon Depositional Systems: Lower Miocene to Present, Block 14, Deep-Water Angola

Arthur Saller¹, Robert Brandt¹, Steve Haas², Kevin Doyle¹, Paula Joao¹, and Maria Lima^1
1Chevron, Houston, TX
²Chevron, Luanda, Angola

Sands in slope valleys are the dominant reservoir type in many parts of deep-water west Africa. Slope valleys and canyons have been dominant in the Congo Canyon area of Block 14 Angola since the late Oligocene. Slope valleys in the Lower to Middle Miocene of Block 14 were 150-300 m deep, 1-3 km wide at the base and 2-5 km wide at the top. The lower parts of those slope valleys show erosion and incision, but the upper parts have aggradational levees. Sand-rich channels at the base of valleys are frequently sinuous with sinuosity increasing upward. Sinuous channels in many slope valleys migrate by downslope erosion and lateral accretion. In other slope valleys, sinuous channels change by avulsion. Isolated channels are generally 70 to 200 m wide, however, channels commonly amalgamate into complexes ~1 km wide. Seismic attribute maps indicate substantial downslope variation in amount of sand. Amalgamated sands are locally thick on the flanks of salt domes where syndepositional uplift decreased slope gradient causing sand to drop out of turbidites. Sands have arcuate channel-like morphologies (in map view) in areas of more isolated channels. Other sands have pod-like morphologies due to lateral channel migration and accretion. Sands in channel axes are 20-30 m thick and dominated by amalgamated massive sands. Upper Miocene slope valleys were commonly deeper (~400 m) than older slope valleys. The modern Congo Canyon is 1200 m deep and 10-15 km wide at the top; however, the channel at the base of the modern canyon is only 70-200 m wide. The modern Congo Canyon channel also shows downslope migration and lateral accretion packages.

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