Channel Scaling and Dynamics in the Fluvial Marine Transition

Abstract

Channels are pervasive features in the modern landscape and stratigraphic record. They occur at various scales in nearly all depositional environments, and represent one of the fundamental reservoir architectures in petroleum systems. This work documents the morphological, kinematic, and architectural changes that channelized systems undergo in the fluvial marine transition (FMT), in terms of physical controls and boundary conditions. In this study, the FMT channels are not considered in isolation. They are compared with other environments (e.g. continental fluvial and deepwater systems) to highlight unique aspects versus commonality in terms of process and product. As the basis of this study, an extensive database of modern systems and shallow analogs has been constructed, sourced from remote sensing, high resolution seismic, and vertical data (core/well). Multiple scales of channelized features are extracted and analyzed including: the geomorphic channel form, oxbow-cutoffs, and channel belts. Geometric statistics measured on these features are used to derive scaling relationships specifically relevant to reservoir characterization. The scaling observations are coupled with known process controls (boundary conditions) to identify and highlight the first order physical controls on channel morphology, kinematics, and resultant architecture. These controls form a process classification that (1) predicts the relative lengthscale of the FMT, ranging from O(< 1 km) to O(1000 km), and (2) polarizes/classifies channelized systems according to process dominance. Process dominance in the FMT is viewed as the significance of episodic fluvial floods in relation to regular tidal flows. The contrasts in morphology that arise from differences in FMT hydrodynamics are mirrored by contrasts in stratigraphy. In particular, the streamwise location of maximum sediment divergence and deposition. As a concrete illustration, we contrast the Mississippi and Amazon systems. Lastly, we examine the interaction of FMT hydrodynamics (the stage-discharge relationship) with relative base level change and avulsion theory, which results in stratigraphic deposits with fundamentally different scaling than their purely fluvial counterparts. Theory coupling hydrodynamic processes, subsidence, and avulsion illustrates the relevance of short-term hydrodynamic processes on the long-term stratigraphic record.

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