Regional Stratigraphic Differentiation of Deepwater Fan and Channel Geometries, Offshore Tanzania and Mozambique: Size Matters

Abstract

The emerging deepwater gas province offshore East Africa presents great opportunities and also dilemmas in high-grading a vast region for petroleum potential. Known hydrocarbon play elements are Cretaceous and Early Tertiary deepwater fan systems, structurally-enhanced stratigraphic traps, and a functioning gas petroleum system with unknown liquids potential. The fan/channel reservoirs contain remarkable reservoir properties and a high degree of connectivity; however, their distribution is more problematic. The ability to map reservoir spatial and temporal distribution is a critical undeveloped play element. We outline a workflow that enables this mapping by generating high-resolution horizon interpretations of a coarse regional 2D seismic grid over a 400,000 square kilometer area. Regional mapping of time-correlative stratal packages outlines the broader depositional and tectonic-stratigraphic framework. Detailed mapping of various architectural elements within these stratal packages reveals systematic variation both within and between stratal intervals. Channel morphology and related geo-body types and dimensions vary both up- and down- depositional gradient, but also according to stratigraphic position. Geo-body dimensions and distribution are dictated by the geomorphic gradient and profile controlling sediment deposition. Steeper profiles have greater potential energy and thus higher incision in up-dip positions, with little levee development and more aggradational frontal splays and lobes occurring down-dip. Sediment partitioning favors down-profile deposition and channel concentration in fewer channels. The resulting stratigraphic record favors single-story channel systems and smaller, multi-storied lobes. Lower-gradient profiles generate more low-energy density flows, resulting in less up-dip incision and significant, symmetric levee development and shingled or progradational frontal splays in down dip positions. The resulting stratigraphic record favors multiple, along-strike channel development creating laterally persistent, single-storied sands and aerially larger, shingled fan lobes. Understanding the distribution and stacking of these different architectural elements through time has significant implications for trapping, reservoir distribution and connectivity. Application of this work provides enhanced predictability to exploration efforts, including distribution of reservoir properties in a regional basin context.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015