Flow Processes and Bed Type Distributions Documented from a Cored Submarine Slope Channel System – Implications for Reservoir Quality and Prediction

Abstract

Submarine slope channels can have very heterogeneous fills, often including a spectrum of deposits ranging from chaotic debrites to stacked sandy turbidites. Interaction between input flow parameters and slope gradients control overall channel grade and changes in either or both can initiate cycles of incision or aggradation at a range of scales. Slope erosion can locally modify the way flows behave through bulking, overloading or providing additional confinement and forcing parts of the flow to bypass. Where flows are erosional and become charged with mudclasts and clay, they may show features intermediate between classical turbidites and debris flows (transitional flow deposits), or contain components of both turbidity currents and debris flows as part of the same event (hybrid-event beds). Whereas deposits of transitional and hybrid flows are increasingly recognised in distributive lobe systems downslope from channels, the latter in particular are also starting to be recognised in channels, especially where these back-fill. This study utilises data recovered from a cored North Sea slope channel system to provide insights into the distribution of bed types axially along, and transverse to, the channel. Of notable interest is the character, distribution and context of units (up to 10m thick) containing hybrid event beds (HEBs) and their relationship to other channel fill facies. The HEBs typically comprise clean turbidite sandstone with few to no mudstone clasts overlain by argillaceous sandstone or sandy mudstone with more frequent clasts – this transition can be abrupt or gradual. Bed-tops are commonly bioturbated occasionally confusing the definition of linked debrites. The data shows the occurrence of HEBs either at the base of the channel or above embedded re-incision surfaces within it. Distribution analysis of these bed-types reveals a trend of increasing HEB frequency, together with increasing linked-debrite dominance, both marginally and distally in the system with some individual events apparently capable of dispersing non-reservoir sediments across large areas of the system. It was also noted that the style of HEB becomes increasingly debritic when stacked vertically and we ascribe this to the effects of knickpoint migration as erosion back-steps upslope and progressively further from the point of deposition.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014