Prediction of sedimentary architecture and lithological heterogeneity in fluvial point-bar deposits

Point-bar deposits in meandering rivers preserve lithological heterogeneities that influence hydrocarbon production. Here, a series of methodologies are used to determine the lateral extent, accretion history, and internal facies heterogeneity of fluvial point-bar deposits to improve subsurface prediction and reconstructions of exhumed meander belts. A novel quantitative Intersection Shape methodology has been developed to describe the morphology of meandering fluvial reaches using data from 260 active and 10 abandoned meander bends from 13 river reaches in different physiographic environments. The resulting classification scheme describes 25 meander morphologies in 4 parent groups (open asymmetric, angular, bulbous, open symmetric). Results are expressed graphically enabling visual assessment and comparison. The overall scroll-bar pattern type (22 shapes in 8 parent groups) can be divided into growth phases and shapes derived from the Intersection Shape methodology overlain on the scroll-bar pattern to find best-fits and determine a meander-bend accretion history. A map of predicted relative heterogeneity can be constructed that accounts for the bend growth history and downstream fining trends. Abandonment mechanisms that individual meanders undergo (neck cut-off, chute cutoff, neck cut-off on converging limbs) affect the lateral extent of the resultant point-bar deposits. Active point-bar deposits are dominantly equidimensional (1:1) whereas abandoned point-bar deposits exhibit both rounded (1:1) and elongated (1:<1) shapes in near-equal proportion. Focussing on abandoned point-bar deposits in an active reach may lead to underestimation of the lateral dimensions of amalgamated fluvial point-bar deposits. By rigorously describing the shape, dimensions, and relative proportions of point-bar deposits in meandering fluvial systems the methodologies developed here avoid such underestimation and can be applied to: (i) generate testable hypotheses of heterogeneity for modern systems; (ii) develop models of lithological heterogeneity in ancient systems based on identification of analogous processes between modern and ancient fluvial systems; and (iii) infer the accretion history of exhumed systems.