127 / 2022-02-24 11:22:46

Geometric characteristics and their controlling factors of bar fingers in the shoal-water delta

Bar finger,Shoal-water delta,Ganjaing Delta,Geometric characteristics,Sedimentary simulation

Bar finger in the shoal-water delta is a kind of finger-like sand body, consisting of mouth bar, distributary channel and levee deposits. It is common seen in ancient hydrocarbon reservoirs, but it is unclear for their geometric characteristics and their controlling factors. Three metrics were adopted to quantify their geometric characteristics, including the average sinuosity, average nondimensional width (average width ratio between the bar fingers and distributary channels), nondimensional delta length (ratio between the delta length and average width of the distributary channels). These metrics measured from 10 modern bar fingers in the Ganjaing Delta and 27 sedimentary simulations exhibited wide-ranging values that were strongly affected by the fluvial and basinal conditions. The quantitative effects were revealed by performing Delft3D simulations: (1) the average sinuosity is positively related to sediment cohesion, concentration, and water discharge, but negatively related to sand-mud ratio, and basinal water depth; (2) the nondimensional length is positively associated with water discharge and sediment supply, yet negatively associated with basinal water depth; (3) the nondimensional width is positively correlated with sediment concentration and supply, yet negatively correlated with sediment cohesion, sand-mud ratio, water discharge, and basinal water depth. Three empirical equations from Delft3D simulations are established, which are proven effective in examinations of nine modern deposits and applied to help predict the distribution of a bar finger reservoir.