Hydrodynamics and deposition in lacustrine shallow-water delta front: A combination of numerical simulations and modern sedimentation measurements

Abstract

With the exploration of tight oil and gas, shallow-water deltaic reservoirs have been attracting more and more attention. The sedimentary architecture of a shallow-water delta shows distinctive differences with that of a deep-slope delta. These differences may be associated with the mechanism and characteristics of the deposition in the area where the sediments unloaded. Based on modern sedimentary research of the Poyang Lake in China, this paper focuses on the processes of river flow entering a lake with a low dip angle. We conducted six sets of numerical simulations with different initial sedimentary flow velocities using Fluent software for analyzing the hydrodynamics and the sediment transportation in the shallow-water delta. We combined the simulation results with an analysis of the geomorphology of the Gangjiang Delta to reveal the deposition along the shoreline of the lacustrine shallow-water delta. The numerical simulation shows that the shallow-water delta is dominated by bed friction with an extensive hydrodynamical boundary layer. The bed shear stress, which varies with the changes in river flux, dominated the sediment transport and deposition at the shallow-water delta front, where the effluent flow mixes with lake water. The distributary channels show characteristics of repeatedly occurred erosion, scouring, filling, and reoccupation. We argue that the depositional characteristics are associated with the changes in bed shear stress controlled by variation of flow velocity. Mouth bars are less likely to grow to a reasonable scale because of the seasonal scouring of extreme floods. Moreover, the lake flow potentially reworks the mouth bars. Consequently, mouth bar deposits were difficult to preserve as hydrocarbon reservoirs in ancient shallow-water delta.

Evolution from shallow‐water deltas to fluvial fans in lacustrine basins: A case study from the Middle Jurassic Shaximiao Formation in the central Sichuan Basin, China

“…Therefore, sediments in J2s1 and J2s21 are mainly composed of subaqueous channel deposits, mouth‐bar deposits, and channel and mouth‐bar complexes (Figs 4F to H, 5A to C, 5E and 13A). The common occurrence of channel and mouth‐bar complexes is evidence that allows the recognition of distributary channels in shallow‐water conditions (Edmonds et al ., 2011; Zhu et al ., 2017; Went & Fielding, 2019; Zhang et al ., 2020; Cole et al ., 2021; Liu et al ., 2021; Xu et al ., 2021). These distributary channels, with high amplitude and weak meandering, are shown in Fig.…”

Sinuous bar fingers of digitate shallow‐water deltas: Insights into their formative processes and deposits from integrating morphological and sedimentological studies with mathematical modelling

“…Numerous previous studies have focused on the lobate part of the Ganjiang Delta (e.g. Huang et al ., 2013; Jin et al ., 2011, 2017; Duan et al ., 2014; Gao et al ., 2016; Li et al ., 2016; Feng et al ., 2017; Zhang et al ., 2020), but the BSD s are unexplored.…”

Sedimentary Evolution Laws and Main Controlling Factors of the Nenjiang Formation in the Songnan Da’anbei Area, China

“…Due to the significant differences in morphology and structure between lacustrine shallow-water deltas and traditional deltas [4,5], numerous scholars both domestically and internationally have conducted systematic studies on shallow-water deltas from various aspects such as formation conditions [6][7][8][9], controlling factors [10][11][12][13], sedimentary characteristics [14][15][16][17], and distribution patterns [18][19][20][21][22][23], achieving noteworthy results. However, controversies still exist regarding the sedimentary characteristics and morphological distribution of sand bodies in shallow-water deltas.…”