BEDFORMS TO STRATAL ARCHITECTURE AND PLAY FAIRWAYS OF MARINE MUDDY DEPOSITIONAL SYSTEMS

Large volumes of hydrocarbons are hosted in muddy fine grained strata, often referred to as shale gas or shale oil. This necessitates a better understanding of such relatively poorly understood depositional systems. We will present the link between bedforms, depositional processes, and stratal architecture, and their relation to the laterally continuous hydrocarbon accumulations.

While mudstones are often perceived as mainly deposited from suspension, detailed examination show they are dominantly deposited by traction currents as mudstone aggregates. The mudstone aggregates was often co-transported with detrital silt and sand sized grains reflecting their hydrodynamically equivalency. The composition of the mudstones aggregates often varies between the parasequence sets, indicating relative sea level induced changes in the geostrophic currents and influx of mudstone aggregates from different parts of the basin.

Mudstone successions commonly show relative uniform thicknesses to gentle tapering geometries, however the often have internal clinoform geometries. This clinoform geometry, being inconsistent with deposition from suspension can easily be explained by the recognition of deposition of mudstone ripples by bedload processes. Cross sections of closely spaced well logs with amble core coverage will showcase examples of shoreline detached mudstone clinoforms, which often have complex 3D clinothem geometries.