Application of a Depositional and Sequence-Stratigraphic Model for Geocellular Modeling of the Woodford Formation, Oklahoma

Hlava, Kimberly; Alfred, Dicman; Ramirez, Benjamin; Rodriguez, Jesus

The late Devonian (Frasnian-Fammenian) Woodford Formation located in the Anadarko Basin of Oklahoma is a significant mudrock source rock and oil and gas reservoir. The Woodford Formation is a 200-500 ft (61-152 m) thick argillaceous to siliceous mudrock deposited in an organic-rich, basinal setting. This study provides a method for establishing sequence stratigraphy in a mudrock reservoir. This study also applys these methods to build a depositional model used to explain and build a seismically consistent, geocellular model in the southern Anadarko Basin. The 15 mi (24 km) x 9 mi (15 km) x 453 ft (138 m) reservoir model is used to identify sweet-spot lithofacies by predicting distribution trends in total organic carbon (TOC), clay, and permeability.

Three cores are described in detail over a regional (~90 mi2 [~145 km2]) study area. Correlations across the basin are made using conodont biostratigraphy and used to identify missing sections. Sequence boundaries are also identified based on the, changes in the depositional patterns and facies, mineralogical composition, oxygen/hydrogen index, and organic-matter type.

The Woodford Formation is divided into five sequence-stratigraphic groups. Groups 1-4 are transgressive and Group 5 is regressive. Three sequence boundaries are identified at the base of Groups 1, 3, and 4. Eight sedimentary facies are identified in the core and up scaled (3 ft [1 m] resolution) into environments of deposition (EODs) based on facies associations, organic-matter type, and log response (gamma ray, density, and neutron). Four EODs are identified in the model: (1) offshore (7.8%); (2) distal (27.4%); (3) hemipelagic (57.1%); and (4) pelagic (7.7%).

A correlation between TOC and relative clay is used to divide and model EODs by an algorithm defined from well logs (density and neutron). The acoustic impedance (AI) overprint on the TOC and relative clay relationship is utilized to populate the geocellular model. The resulting model shows that the hemipelagic EOD contains low clay and high TOC and has the most potential as a sweet spot lithofacies. Permeability shows a similar trend: the hemipelagic EOD has the highest permeability while the offshore EOD has the lowest permeability.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013