Effects of upstream conditions on digitate shallow-water delta morphology. (December 2021)

• Record Type: Journal Article
• Authors: Xu, Zhenhua; Wu, Shenghe; Yue, Dali; Zhao, Junshou; Deng, Meng; Liu, Zhao; Zhang, Jiajia; Liu, Mingcheng; Feng, Wenjie
• Is Part Of: Marine and petroleum geology. Volume 134(2021)
• Publication Date: 2021-12
• Subjects: Digitate shallow-water delta -- Bar finger -- Morphology -- Upstream conditions -- Delft3D simulation; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2021.105333
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Digitate deltas consist of one or multiple separate bar fingers, which can form hydrocarbon reservoirs after burial. This paper focuses on digitate shallow-water deltas, which are commonly seen in modern and ancient deposits with similar downstream conditions. Four metrics were adopted to quantify their morphologies, 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), and number of bar fingers. These metrics measured from 9 modern deposits and 21 Delft3D simulations exhibited wide-ranging values that were strongly affected by the upstream conditions. However, the effects of the upstream conditions remain unclear. The quantitative effects were revealed by performing Delft3D simulations: (1) the average sinuosity is proportional to the sediment cohesion and concentration and inversely proportional to the sand proportion and water discharge, and reaches equilibrium as sediment supply increases; (2) the average nondimensional width is proportional to the sediment concentration, is inversely proportional to the sediment cohesion and water discharge, has an inverse exponential relationship with the sand proportion, and is independent of the sediment supply; (3) the nondimensional delta length has a power-law relationship with the water discharge and is logarithmically related to the sediment supply; (4) the number of bar fingers is proportional to the sand proportion and sediment supply and inversely proportional to the sediment cohesion. Upstream conditions influence channel, mouth bar and levee growth, resulting in various bar finger morphologies. Empirical equations from Delft3D simulations were proven effective in examinations of nine modern deposits and applied to help predict the distribution of a digitate shallow-water delta reservoir. This work improves the fundamental understanding of the upstream controls in digitate shallow-water deltas and may help enhance the inter-well prediction of paralic reservoirs. Highlights: Various upstream conditions induce diverse morphologies in digitate deltas. Upstream conditions influence growth of channel, mouth bar, and levee in bar fingers. Sinuosity and width of bar fingers reach equilibrium with growth of digitate delta. We propose four effective empirical equations to predict digitate delta morphologies.