MODELING STRATIGRAPHIC CONTROL OF FLOW AND TRANSPORT CHARACTERISTICS WITH FLUVSIM

FLUVSIM is a 3D stratigraphic forward model of fluvial sedimentation designed to test joint inversion of stratigraphic and ground-water models using shared information and observations. FLUVSIM incorporates: (1) a nonlinear dynamic, self-organized critical representation of the stratigraphic process-response system; (2) fuzzy logic to determine the location, amount, and type of sediment deposited in splay complexes; and (3) the concept of stratigraphic base level.

FLUVSIM was used to evaluate parameter sensitivity and uniqueness via 175 experiments. All parameters were identical except subsidence (Y) and the long-term rate of sea-level change (C). The sum is the rate of long-term accommodation space change (Z=Y + C). These experiments were designed to examine: (1) changes in attributes as a function of the magnitude of Z; and, (2) uniqueness with respect to the dominant processes generating Z (sea-level dominates when Y < C and subsidence dominates when Y > C). Stratigraphic results were combined with a constant hydrologic regime using MODFLOW and particles were tracked using MODPATH.

The magnitude of Z was found to affect sediment volumetric partitioning into channel and splay facies tracts. At low Z, channel and splay facies tracts had equal proportions. Fluid flow was faster and more direct due to the increased connectivity of the sand-rich, permeable channel aquifers. As Z increased, the proportion of splay facies increased producing poorly connected aquifers with tortuous flow paths and longer fluid travel times.

The stratigraphic system was uniquely affected by processes which create accommodation. When subsidence dominated, a higher proportion of channel facies were created compared to a sea-level dominated system at the same Z. Consequently, subsidence-dominated systems had shorter fluid travel times.

These experiments demonstrate: (1) fluvial architecture is sensitive to the rate of change in accommodation space; (2) fluvial architecture is uniquely sensitive to the processes responsible for creating accommodation, and; (3) these processes uniquely influence fluid flow and transport. Subsidence and sea-level change can be differentiated by sedimentologic and fluid-flow and transport characteristics because stratigraphic responses to the process stimuli are nonlinear.