Lateral accretion packages (LAPs): an important reservoir element in deep water sinuous channels

The Lower Miocene Green Channel Complex from the Dalia M9 Upper Field, Block 17, offshore Angola is an excellent example of a deepwater sinuous channel. This sinuous Channel Complex is located in the upper portion of a Confined Channel System, which is approximately 150 in deep, 2 km wide, and tens of kilometers long. The Green Channel Complex itself is approximately 40 m deep and 2 kin wide and was formed by the lateral migration and local avulsion of a single channel that was approximately 300 in wide and 40 in deep. An important characteristic of the Green Channel Complex is the presence of shingled seismic reflections at channel margins. These shingled reflections tend to be parallel to the channel, dipping toward the channel in most cases and sometimes dipping down flow. The shingled reflections form well-defined packages always in the inner side of the channel bends. They are interpreted to be associated to continuous lateral migration during channel evolution, resulting in the deposition of accretion packages in the inner side of the channel and erosion at the outer side of the channel. These accretion packages are named in this paper Lateral Accretion Packages (LAPs). Typically, lateral migration of individual sinuous channels produces laterally amalgamated Channel Complexes that have varying degrees of internal amalgamation depending on the nature of the channel-fill. Integration of high-resolution 3D seismic and well data from Block 17, offshore Angola with outcrop analogs of interpreted sinuous channels has even further improved the understanding of these types of deepwater channels. Dominating the fill of many sinuous channels observed in outcrops are inclined sandbodies that dip toward the channel axis, perpendicular to the paleoflow direction. These inclined sandbodies are interpreted to be analogous to the LAPs described on seismic data. Lithologic composition of LAPs described from outcrop and core data is variable. They tend, however, to be dominated by a mixture of coarse- and fine-grained sandstones at the base and finer grained, less amalgamated beds towards the top. Importantly, LAPs can form sizable reservoir elements in the subsurface, with an individual LAP reaching a thickness of 45 in over as much as 0.75 km(2) in the Green Channel Complex. (C) 2003 Elsevier Ltd. All fights reserved.