--> --> Entrenched Slope Channel Complex Systems: Reservoir Opportunities Through Understanding Architectural Element Distribution and Application to West Africa E&P

2018 AAPG International Conference and Exhibition

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Entrenched Slope Channel Complex Systems: Reservoir Opportunities Through Understanding Architectural Element Distribution and Application to West Africa E&P

Abstract

Slope channel complexes, are described from a range of settings. In West Africa, they form a family of reservoirs with a wide range of quality, connectivity, trapping style and recovery factor. Models focus on the main channel belt, showing that phases of channel occupancy go from bypass, through stacked channels, an aggradational phase with smaller, meandering channels, to an end phase of progressive switch off. Channel complex systems range widely in lithology. They also vary in channel element style, from (i) amalgamated sand bodies that are made entirely of channel elements, to (ii) stacked channel elements that underfit the channel complex, to laterally equivalent inside levees and terraces, to (iii) skinny, later stage meanderform channels with attached internal levees, crevasse splays, frontal splays, or passive drape. The channel complex wall has a range of morphologies from lateral rotational failure of the wall, to erosional entrenchment and other types of terrace, to passive onlap of internal levee. Lateral failure and associated scalloped slump scar wall morphology, is difficult to distinguish from internal levee and associated meander cut banks. External to many slope channel complexes are master levees that record multiphase occupancy of the channel complex, with each phase recording (i) external crevasse splay build, followed by (ii) spill cap aggradation of the master levee, terminating in (iii) shutdown and hemipelagic drape of the external master levee. Some systems are highly entrenched and have excavated headwards, where they form canyons, cutting into highstand systems. Down system, slope they are often preceded by MTDs, that may have initiated system entrenchment by providing access to sand on the shelf. Channel complexes may touch down onto, or erode through these, leaving residual erosional remnants lateral to the channel complex margin. Channel complexes further downslope may also touch down into or erode through precursive frontal splay complexes that are difficult to distinguish from unrelated highstand deposits, and crevasse splays. A unified model for slope channel complexes is proposed that captures all architectural elements, based. With the large amount of reservoirs of this style offshore West Africa and elsewhere have come an array of models that are mostly field specific without generic use. This paper draws on many years of work on a large number of global examples.