234 / 2022-03-22 17:11:45

泥质含量对细粒河控浅水三角洲平面形态的控制作用——沉积正演数值模拟的启示

Shallow-water meandering river delta; Distributary channel; Sand body; High-frequency lake level change; Reservoir architecture

Different growth processes result in different morphologies and stratigraphies. Shale content, as an important sediment property, is one of the controlling factors for the deltaic planform. However, few studies have been conducted concerning the planform variation between silt-dominated and mud-dominated fluvio-deltas. Based on hydrodynamics of modern fluvio-deltaic systems, Delft3D, an open-source physics-based numerical model, was used to simulate the early deltaic process where silt and mud sediments within steady low-to-middle water discharge infill a linear scaling water body. An experimental (model 1) and a comparative (model 2) setting were designed to simulate the silt-dominated and mud-dominated deltaic growth, respectively. The results also indicate that both silt-dominated and mud-dominated fluvio-deltas underwent channel avulsion, bifurcation and abandonment from initial mouth bars to distributary systems. Silt-dominated deltaic systems have slower growth speeds, smaller dimensions, larger length-to-width ratios and better symmetries. Deltaic lobes of the silt-dominated deltaic systems are flower-shaped, whereas those in mud-dominated deltaic systems are branch-shaped. As for stratigraphies, main channels in mud-dominated systems have stronger undercutting rates than silt-dominated systems. Abandoned channels in mud-dominated systems outnumber those in silt-dominated systems. It can also be inferred that nodes connecting abandoned channels and main channels are controlled by shale content and subsequently influences deltaic morphologies. Compared with silt-dominated deltas, mud-dominated deltas are likely to develop more joints. As for hydrocarbon implications, influenced by deltaic geometries, mud-dominated deltas have more isolated and poorly-connected sand bodies in spite of its larger extension, and are closely associated with source rocks.