Control of Key Boundary Conditions on the Depositional Processes of Lacustrine Braided River Deltas: Insights from Sedimentary Numerical Simulation

Key words: 
• braided river delta /
• sedimentary numerical simulation /
• boundary conditions /
• evolutionary traits /
• related sand bodies

Abstract: [Objective] Braided river deltas are one of the most important types of hydrocarbon reservoirs. Extensive studies have been conducted on their depositional processes, evolutionary characteristics, and controlling factors. However, how key boundary conditions quantitatively control the growth, evolution, and genetic sandbody characteristics of lacustrine braided river deltas still requires further investigation.[Methods] UThe Delft3D sedimentary numerical simulation software was employed to design a series of single-factor comparative experiments involving five key boundary conditions, including lake-inflow discharge, basin slope, total sediment concentration, sand–mud ratio, and lake-level variation. By quantitatively extracting relevant indicators, the differences in depositional characteristics under different parameter settings were systematically analyzed. [Results](1) Lake-inflow discharge shows a significant positive correlation with delta area and sandbody scale. As discharge increases, distributary bifurcation becomes more active, the number of distributary mouth bars increases, and chute channels on bar tops become more developed.(2) Basin slope mainly controls the lateral and vertical distribution of sediments. With increasing slope, the delta changes from a broad and gentle morphology to a narrow and thick one, lateral bifurcation is suppressed, and distributary mouth bars become fewer but thicker.(3) An increase in total sediment concentration accelerates the rapid progradation of the delta front during the middle to late stages of simulated evolution. However, under higher concentration conditions, accelerated frontal deposition tends to promote channel siltation and abandonment, thereby reducing both the frequency and number of channel bifurcations.(4) A lower sand–mud ratio promotes the distal transport of fine-grained sediments, resulting in greater elongation in the source-to-sink direction and a more divergent channel pattern.(5) Lake-level fall triggers rapid progradation, forming depositional bodies with larger areal extent, deeper channel incision, and better-developed chute channels, whereas lake-level rise leads to enhanced vertical aggradation and planar shrinkage. [Conclusions] Strong hydrodynamic conditions and lake-level fall are favorable for the development of dominant sandbodies interconnected by chute channels. Steeper slopes and higher sediment-concentration settings tend to form thicker sandbodies with better extension in the sourceward direction. These experimental results provide a theoretical basis for reservoir prediction of braided river deltas in continental basins.