Energy &
Geoscience Institute at the University of Utah
Abstract: Hydrocarbons in the Ames Feature: The Oil Creek—Arbuckle (!) Petroleum System, Major County, Oklahoma
A petroleum system includes a mature hydrocarbon
source rock,
genetically related oil and gas accumulations, and the geologic
elements and processes responsible for the formation of the
hydrocarbon
deposits. This study defines the Oil
Creek—Arbuckle (!) petroleum system located within the Ames
feature, a Paleozoic structural depression believed to be an
astrobleme. The effective source rock is the lower member of the
Ordovician Oil Creek Shale, although some researchers suggest a
biostratigraphic correlation of this facies with the McLish Shale
(Repetski, 1995). The source interval is entirely contained within
the depression, consisting of predominantly marine Type II, oil
prone organic matter. Average total organic carbon (TOC) is 0.88%,
but can locally exceed 2%. Optical and chemical methods indicate
that the section has achieved a maturity level equivalent to
1.2%-1.3% vitrinite reflectance. Based on this information, Curtiss
and Wavrek (1995) calculated pre-
hydrocarbon
generation TOC values
of 2%-5% and hydrogen index (HI) between 400 and 600 for this
interval.
Geochemical analyses indicate a correlation of this source rock
to the oils reservoired in the underlying, highly fractured,
Cambro-Ordovician Arbuckle Group. They are chemically distinct from
the oils produced from shallower horizons, and consist of two
genetically related types; one group of oils has an enhanced
abundance of low molecular weight (LMW or lower than
nC15) compounds, most likely attributable to a higher
thermal stress required for hydrocarbon
generation and
expulsion
. A
burial history reconstruction for the petroleum system indicates
that the “critical moment,” or time of peak
hydrocarbon
generation and
expulsion
, occurred at 225 Ma.
The generation accumulation
efficiency (GAE) compares the amount
of hydrocarbons generated by the source interval to the amount
trapped in reservoirs. This petroleum system generated 145MMBO
(million barrels of oil), which contrasted with ultimate reserve
estimates, establishes a GAE of 37%. The remaining 63% of the
hydrocarbons generated were either lost (i.e., not trapped) or
represent the potential for future discovery.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas