A subsurface study of the Lower Red Fork Sandstone in the deeper part of the Anadarko Basin in Caddo and Washita Counties, Oklahoma

Abstract

The Lower Red Fork Sandstone in the Anadarko Basin is of Pennsylvanian age (Desmoinesian Series), within the Cherokee Group. This subsurface analysis of the Lower Red Fork Sandstone in Caddo and Washita Counties, Oklahoma incorporated three hundred and forty eight wells, two cores, including core plug porosity and permeability measurements, and thin section petrography.

The Lower Red Fork Sandstone was split into four sequence stratigraphic packages, three of which contain complete lowstand to highstand cycles. Each sequence stratigraphic package was based on gamma ray, resistivity, and conductivity log characters. Three distinct log characters define systems tracts and their bounding surfaces. A blocky log character represents a Lowstand Systems Tract, a bell shape log represents a Transgressive Systems Tract, and a funnel shaped log character represents a Highstand Systems Tract. Changes in log characteristics over the entire study area are directly related to the distribution of marine and non-marine depositional facies and environments.

Structure maps were constructed for the base and the top of the Lower Red Fork Sandstone. The base structure map revealed the paleo-shoreline and paleo-shelf break at the onset of Lower Red Fork Sandstone deposition. Gross sandstone, net sandstone, porosity sandstone maps were constructed for each sequence stratigraphic package. The maps display three distinct trends. First, Highstand Systems Tract deposits of submarine fans were identified and mapped in the northwestern portion of the study. Second, northwest-southeast trending linear shallow marine shoreface bars were indentified and mapped to the northeast, landward of the paleo-shoreline. Third, northeast-southwest trending incised channel sandstones comprising parts of fluvial-deltaic complexes were identified and mapped farther southwest, towards the deeper part of the basin.

Successive episodes of progradational shoreface bars/distributary channels were deposited progressively southwestward, towards the deeper parts of the basin as the paleo-shelf edges and paleo-shore lines migrated. Detailed subdivision of shallow marine sands revealed two distinct sandstone trends with lowstand distributary channels crosscutting shallow marine shoreface bars. Deep water deposits may occur farther basinward and warrant further exploration.