ABSTRACT

Thin beds form an important part of submarine fan deposits. They can be found in five different subenvironments: top of a channel fill, channel margin, levee-overbank area, sandwiched between thick layers in the updip non-channelized depositional lobes, and fan fringe. At the present we are not able to distinguish clearly one depositional subenvironment from the other, using thin beds as a criterion.

In the "passive margin" or "Atlantic margin" setting of the Gulf of Mexico and in a number of areas in the Atlantic Ocean, massive sands belonging to a submarine fan can be wet while thin-bedded sandstones may be oil prone. Such a condition makes it important to be able to determine the depositional setting needed to provide information about reservoir geometry, connectivity between successive sandstone layers, porosity/permeability trends, and orientation of the reservoir sands.

Depending on the layer thickness of the thin-bedded turbidites and the sand/shale ratios, it might be difficult to recognize the sandstones on conventional well logs. A good seismic survey, however, may permit indication or detection of a channel cross section from which inferences can be drawn as to where thin-bedded sections can be expected. Initial studies on outcrops have shed some light on characteristics of the levee-over-bank and channel top fill thin bedded series. Using existing depositional models, circular reasoning is often involved as to the identification of each depositional environment.