Core Description

Sedimentary Structures

Sedimentary structures are those structures formed during the deposition of the sediments. Sedimentary structures, such as cross-bedding and graded-bedding, are used in sedimentological and stratigraphic studies to indicate the original position of strata in geologically complex areas and, very importantly, to better understand the sediment’s depositional environment.

Sedimentary Structures

Cross-Bedding

Cross-bedding includes ripples, dunes and any cross-stratification caused by currents. There is an angle between flat bedding and the inclined bedding of the cross-bed, hence the term “cross-bedding” (Figure 1).

Graded Bedding

Graded bedding occurs when the current velocity reduces and grains are progressively dropped out (Figure 2).

Ripple Marks

Ripple marks form in conditions with flowing water; they can be symmetrical when formed by a two-directional current, or asymmetrical when formed by a one-way current (Figure 3).

Once the depositional environment is well understood, the highest and lowest quality areas of the reservoir can be inferred and, consequently, development well placement and spacing optimized appropriately. This applies to both conventional and unconventional reservoirs.

The sedimentary structures are normally noted to the right of the grain size curve.