--> Abstract: A Lobe Story, through Spectral Decomposition, by Fabre, Gregori; Delhaye-Prat, Vincent; and Imbert, Patrice; #90166 (2013)

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A Lobe Story, through Spectral Decomposition

Fabre, Gregori1; Delhaye-Prat, Vincent; and Imbert, Patrice
1[email protected]

Many hydrocarbon discoveries have been made within turbidite plays during the last decades, and intensive studies have greatly improved concepts on turbidite sedimentology. Deep offshore channelized fairways are now well known and documented. Terminal lobes are gaining more attention and are far more complex than originally thought. Therefore, more studies of detailed internal architecture are needed to tackle the heterogeneity issues specific to such objects. The semi-regional study of a complex turbidite system presented in this paper highlights the possibility to predict the distribution of lithological heterogeneities in terminal lobes, as well as possible disconnection by interlobe deposits. Those two points are critical when evaluating lobe reservoirs in an exploration process.

The Congo margin is affected by long term gravity sliding of the entire Tertiary sedimentary sequence. At the toe of the system, in the deep offshore domain, mini-basins are created between compressive structures (salt-cored anticlines or thrusts associated with salt diapirs). Some of the salt diapirs have created low relief highs on the paleo-seafloor which evolves through time, clearly influencing the turbidite fairways and therefore deposition of the Oligo-Miocene sands. Moreover, in the studied mini-basin, the complex tectono-sedimentary architecture results in the presence of several entry points, associated to compensation between the fairways.

This example takes advantage of the latest imaging techniques and spectral decomposition method to analyze a 300 sqkm mini-basin, 30 km long between the main entry point and the end of lobe deposits, with a 250m thick sequence of Miocene turbidites, just before a starvation event. The study demonstrates that the architecture of those deposits is organized in three main steps from base to top: (1) multiple braided channels spread over a wide area; (2) low-relief levees were built stabilizing the location of the channel axis; (3) finally, the system started to retrograde, and four large terminal stacked lobes (4 to 17 sqkm, 100m thick) were deposited. Seismic imaging reveals the internal structure of these sedimentary bodies. A comparison is also proposed between the morphology of the latest lobe and published present-day lobes from the Bering Sea, imaged by sidescan sonar. Although the sizes are very different, the comparison is used as a basis for discussion on their respective heterogeneities and architecture.

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013