Red Fork Sandstone of Oklahoma: Depositional History and Reservoir Distribution

John W. Shelton, Richard D. Fritz, Chris Johnson

The Middle Pennsylvanian Red Fork sandstone formed as a result of progradation across eastern Kansas and most of Oklahoma. The Red Fork is one of several transgressive-regressive sequences (cyclothems) developed within the Desmoinesian "Cherokee" Group. Sea level changes, together with varying subsidence, were dominant factors controlling the general stratigraphic (correlative) characteristics of the Red Fork interval. Progradation was episodic, with sand deposition in the more active part of the basin during lower sea level stands and valley-fill deposition in the more stable areas during sea level rises.

A map of Red Fork sand trends reveals an alluvial-deltaic complex covering most of Oklahoma. The Red Fork consists primarily of alluvial-valley and plain (fluvial) bodies in the northernmost part of northeastern Oklahoma, alluvial-deltaic bodies in most of the remaining parts of the shelf area, and off-shelf submarine-fan and slope basinal-floor complexes within the deeper part of the Anadarko basin.

Determination of reservoir trend and genesis requires integration of rock and log data. Logs need to be calibrated to cores in order to estimate depositional environments accurately and to make a reasonable assessment of diagenetic overprints.

Much of the oil and gas has been trapped in stratigraphic traps, and a significant amount of oil is in channel sandstones with trends at high angles to the structural grain. In some areas, secondary clay, in particular chloritic clay, has resulted in microporosity, high water saturation, and correspondingly low resistivities in oil reserves.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.