Regional Petroleum Systems Evaluation and New Play Identification in an Uplifted Paleozoic Basin: Arkoma Basin, Oklahoma, USA

Cander, Harris¹, Thomas L. Patton² (1) BP America, Houston, TX (2) BP Exploration, Sunbury on Thames, United Kingdom

A detailed basin modeling, petroleum migration, and pore pressure study of the Arkoma Basin, Oklahoma, was used to identify new exploration opportunities and maximize resources in a heavily exploited province. We determined the specific pathways, timing, and mechanisms of petroleum migration, as well as the timing and location of formerly overpressured compartments. The resulting maps explain known accumulations and delineate new opportunities. This study also provides insights into the effects of uplift on gas migration, pore pressure history, and reservoir quality that are applicable to uplifted basins around the world.

Woodford oil and gas initially migrated laterally in the pre-Atokan autochthon in late Pennsylvanian time through both sandstone and carbonate carrier beds. Vertical migration above the Spiro sand was inhibited by a pressure seal near the base of the Atoka-age synorogenic, foreland sediments. With continued burial, most oil was flushed from the system but remaining oil was cracked to gas in reservoirs. During subsequent uplift, the supra-Spiro pressure seal was breached and large volumes of gas were able to migrate vertically upward into the foreland sediments. Uplift also caused expansion of gas that flushed water from down dip, cemented reservoir sections and created a tight gas play. Today, most of the Arkoma foreland is normally pressured, but we believe that sonic and resistivity logs preserve the record of paleo-overpressure proposed by this study. Gas isotopes and petrography also support the results of the petroleum migration analysis. Deep autochthon and shallow foreland reservoirs have similar isotopic compositions with consistent vertical trends that include very heavy methane compositions, indicating a similar origin. Pyrobitumen is ubiquitous in autochthon petroleum carrier beds but far less common in the synorogenic sequence, indicating that most oil migration was restricted to the autochthon by the paleo-pressure seal.