Improving predictions of the internal heterogeneity of large‐scale point‐bar deposits through geophysical logging and morphometric analysis: False River, Louisiana

ABSTRACT Point‐bar deposits are sand‐prone units of meandering fluvial stratigraphy and can form important hydrocarbon reservoirs or carbon capture sites. Large‐scale (>10 km wide) point‐bar deposits are typically deposited over >1000 years and show greater complexity than those in smaller‐scale systems (10 2 to 10 3 m wide). False River is an oxbow lake adjacent to the Lower Mississippi River, which encloses a large Upper Holocene point‐bar deposit (12.5 × 8.5 km and 20 to 20‐30 m thick). In this study, we assess the planform evolution of the point‐bar deposit and identify nine phases of meander growth, with the ninth being meander abandonment. The point‐bar deposit grew by phases of extension, downstream accretion, expansion, and then lastly rotation. The predicted planform lithological heterogeneity was mapped, and tested using a combination of coring, natural gamma ray (NGR), electrical conductivity (EC) and hydraulic pressure tool (HPT) logging. EC logging shows the best alignment with lithology showing mud‐prone sediments commonly near the top of the point‐bar deposit, sand‐prone sediments in the lower part and a greater prevalence of mud‐prone sediment towards the terminal apex. Complexities include docked mid‐channel bar deposits in the upstream limb of the point‐bar deposit and the lithological detail caused by micro‐adjustments of scroll bar growth. Also, the meander plug that formed during the meander abandonment phase shows both laterally and vertically accreted sediment deposits. The laterally accreted sediment tends to fine upwards as they were deposited in a waning flow, and the vertically accreted sediment tends to coarsen upwards having formed by deltaic processes. The geophysical findings are added to the lower‐resolution predictive models and though we find broad correlations, there is missing detail and complexity. As such, this study presents insights that improve the global understanding of how the planform of the point‐bar deposit connects to the underlying sedimentology and refines predictive techniques for better interpreting the subsurface.