--> Stratigraphic Evolution of a Submarine Slope Channel Complex Set: Implications for Reservoir Connectivity and Reservoir Quality Distribution

AAPG ACE 2018

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Stratigraphic Evolution of a Submarine Slope Channel Complex Set: Implications for Reservoir Connectivity and Reservoir Quality Distribution

Abstract

Ancient submarine slope channel systems are key hydrocarbon exploration targets and reservoirs worldwide, typically identified and appraised using seismic reflection and well-log/core data. However, these methods lack the spatial resolution to capture the complicated 3D heterogeneity and associated reservoir quality distribution. Outcrop analogues can help bridge this gap, although most outcrops only afford 2D constraints of the depositional architecture, and are derived from relatively coarse-grained, tectonically active systems, making them poor analogs for passive margin systems. A rare example of an accessible slope channel complex set that offers seismic-scale, 3D down-dip and across-strike exposure is the Klein Hangklip area, Tanqua-Karoo Basin. An architectural hierarchy is documented, in which channel elements stack to form 2 channel complexes that form the channel complex set. Twenty-three detailed sedimentary logs, 3D models, physical correlation of key surfaces in a 3km2 area, and thin-section analysis reveal that: 1) successive channel-complexes are offset laterally, whereas their constituent channel elements typically stack aggradationally; 2) basal channel elements in the channel complexes fill relatively deep channel axes, are sigmoidal in shape and show the greatest lateral facies variability. Younger channel elements are bound by relatively flat erosion surfaces and are more tabular in geometry; 3) channel axis facies are dominated by amalgamated, structureless and mud-clast rich sandstones, whereas channel margins are characterized by bedded, laminated and climbing-ripple dominated sandstones; 4) stratigraphic architecture is predictable at seismic-scale both down-dip and across-strike in 3D; and 5) grain-scale data reveals systematic textural and compositional variation in channel complex axis and margin deposits, which is linked to reservoir quality distribution. Channel axis deposits are coarser-grained, more poorly-sorted and cleaner compared to channel margin deposits. Results demonstrate that facies variability within the channel-fill can be consistent across-strike and down-dip on a km-scale in both channel axis and channel margin deposits. The data presented provides insights into the stratigraphic evolution and architecture of slope channel-fills in passive margin settings and can be utilized to improve prediction of reservoir quality distribution and interpretations form lower resolution and 1D well data.