Petroleum Charge to the Mill Creek Syncline and Adjacent Areas, Southern Oklahoma
A. A. Brown
Consultant, Richardson, TX
Woodford-generated oil is produced from fields in the Mill Creek Syncline, north of the Arbuckle Uplift, yet none of the preserved Woodford source rock in the syncline is thermally mature. The burial and tectonic history of the Ardmore Basin and Arbuckle Uplift were analyzed to understand where this oil came from.
Geohistory models of the deep Ardmore Basin demonstrate that Woodford oil generation initiated during Early Desmoinesian, reached peak oil window by middle Desmoinesian, and entered the gas generation zone during Late Pennsylvanian. An estimated 40 billion barrels of oil were generated from the Woodford Formation in the central and eastern Ardmore Basin.
Uplift of the Arbuckle Anticline and related structures initiated during Late Desmoinesian, after initiation of Woodford oil generation in the Ardmore Basin. Ardmore Basin oil generated before uplift could migrate to the Mill Creek Syncline by updip, stratal migration. After Late Desmoinesian deformation, the migration pathway was destroyed, and north-migrating oil seeped to the surface south of the uplifts. Woodford oil charge to the Mill Creek Syncline could only have occurred during the Desmoinesian. Stratigraphic evidence supports this timing. The Buckhorn asphalt is actually a sea-floor oil seep of Early Middle Desmoinesian age, demonstrating petroleum migration at this time. Major asphalt deposits are truncated by Late Virgilian strata, indicating charge prior to late Virgilian. Asphalt deposits form a migration chain documenting south to north migration.
Almost all Woodford-sourced oil accumulations in Southern Oklahoma date from the Pennsylvanian or Early Permian. Although Woodford shale over much of the western Ardmore Basin is now in the oil window, generation and migration since the Pennsylvanian has been negligible due to absence of renewed burial. Characteristics of older accumulations include large seepage anomalies, incomplete fill due to longer duration of leakage, and thick residual saturation zones which make identification of productive zones more difficult.
AAPG Search and Discovery Article #90905©2001 AAPG Southwest Section Meeting, Dallas, Texas