The Distinction between Lobe-Dominated and Distributive Channel-and-Lobe Deepwater Reservoirs

Lobe-dominated and distributive channel-and-lobe deepwater reservoirs possess comparable sedimentary attributes. Despite similarities, outcrop studies document important differences with implications to subsurface reservoir prediction. Outcrops of lobe-dominated systems of the Marnoso-arenacea Formation in Italy, and Sites Member of the Cortina Formation and Matilija Formation in California are contrasted with distributive systems documented from the Brushy Canyon Formation in Texas and Point Loma Formation in California. These examples are compared to the Grès d'Annot in France and Mount Messenger Formation in New Zealand, which contain both system types.

Lobe-dominated systems form when turbidity currents expand to the width of the structural confinement and are more common in intraslope basins and during initiation of deepwater sedimentation. Sand bypass and mud deposition on lateral intraslope basin flanks is followed by resedimentation of locally derived mud affecting seabed gradient and topography thereby promoting subsequent sand deposition. By contrast, channels limit lateral flow expansion and maintain longitudinal transmission of sediment in turbidity currents smaller than the structural confinement. Distributive systems advance through the creation of local depositional topography related to frontal lobes plugging channel mouths, followed by channel back-filling, avulsion and channel extension away from older channel courses.

Turbidite event magnitude is considered the critical factor governing the timing of sedimentation and the number and diversity of sedimentary bodies. Turbidity currents smaller than the structural basin produce thinner sedimentation units containing diverse facies thereby increasing heterogeneity and variability in reservoir quality. The determination of sedimentation units demonstrates turbidite event magnitude providing important recognition criteria for assessing reservoir heterogeneity.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California