Heterogeneity and Connectivity of Low Sinuosity Single Thread Channel Belts in Distributive Fluvial and Delta Plain Depositional Systems.

Abstract

Hydrocarbon production from distributive fluvial depositional systems and/or their down-dip upper delta plains can be significantly impacted by heterogeneity. Typically, these depositional systems are dominated by single thread, rectilinear channel belts formed through upstream river avulsion. This upstream bifurcation results in discrete radiating distributor channel belts remaining spatially separated for tens of kilometres. Anastomosing networks of channel belts commonly occur near the backwater limit. Immature avulsion belts with numerous narrow (10-100m wide) juvenile avulsion channels typically evolve to mature distributor channel belts (most commonly 0.5-2km wide). Bank-full channel depths range from 5-20m deep, unless entrenched or amalgamated (which can exceed 40m). Channel threads typically show low sinuosity (10-100m wide) with long half-wavelengths (2-10km). Downstream-migrating elongate point barforms are typically composed of trough- and planar-cross bedded, medium- to very coarse-grained sands with tightly constrained paleoflow indicators but can be shale or coal-prone when abandoned, especially the leading edge of the barforms. Floodplain interfluves are mud-prone, with crevasse splays, paleosols and coal-prone in some humid climates, acting as lateral seals between these channel belts. In low accommodation settings these may amalgamate into sheet-like geobodies via numerous avulsions, but in higher accommodation settings increasing isolation leads to reduced connectivity and a labyrinthine network of sand bodies. Examples from modern analogues, ancient outcrops and subsurface datasets (well logs, seismic) are used to illustrate the main characteristics, and are useful for guiding static modelling of analogous reservoir systems.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019