Regional
Petroleum Systems Evaluation and New Play Identification in an Uplifted
Cander, Harris1, Thomas L.
Patton2 (1) BP America,
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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California