The Impact of Conventional Core from Slope Channel Reservoirs in Offshore West Africa: Turbidite and Debrite Examples from the Lower Miocene

Michael Porter¹ and Anthony Sprague^2
1ExxonMobil Development Co., Houston, TX
²ExxonMobil Upstream Research Co., Houston, TX

The prolific hydrocarbon production from West African slope channel systems is in part due to an integrated geoscience approach to the characterization of these deep-water reservoirs. Pre-drill prediction of reservoir continuity and net-to-gross based on high quality 3D seismic data is greatly enhanced when calibrated with conventional core.

The energetic nature of turbidity current flows is well illustrated by coarse-grained sandstone lithofacies cored in Burdigalian-age channel-fills. Core from these Lower Miocene confined channel complexes confirmed the great resource potential of these reservoirs, and this early information then shaped much of the development strategy for production from multicycle reservoir sections. Conventional core also helped calibrate the mixed-impedance seismic signature of gravel- and sand-prone turbidites, and quantified their excellent reservoir properties.

Conventional core has been critical in well-log calibration of debrite-dominated channel-fills. Seismic facies can be ambiguous in differentiating the volume of turbidite to debrite fills in some Aquitantian-age channel systems. Vertical lithofacies successions can be misrepresented as waning-flow turbidite channel-fills when the well logs are interpreted without benefit of the conventional core. Conventional core in thickly-bedded sandy debrite successions shows the well-log response is due to large heterolithic rip-up clasts, interbedded muddy debrites and interstitial clay. Well planning and completion designs can accommodate these factors if the reservoir system is known to have a significant debrite component.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery