Point bar Fine Deposits: Controls, Process and Pattern

Abstract:

Within point bar deposits, mud deposition as discrete layers has a significant effect on
reservoir performance, especially in unconventional (heavy oil) settings. This scale of stratigraphic heterogeneity is not represented in even relatively sophisticated static models. A 3D numerical study is conducted to investigate the controls, process and pattern for the fine deposits (mud deposits) over the point bars. The study covers the effect of river cross section, river planform shape, suspended load grain size, and the seasonal variation in river flow discharge. The distribution of the fine-grained deposits is found to be controlled by flow divergence. The river cross section is a major control on the presence of flow divergence as it controls the velocity patterns in the cross section and this acts as the major control in the sediment partitioning. Bend geometry also has a first order effect on the length scale of the divergence. Seasonal variation in river flow affects the deposition amount over the point bars. Higher flow discharge results in thicker deposits over point bars. Also, increasing the size of the suspended load grain size results in thicker deposits on the upstream part of the point bars.