Oklahoma geology notes, 2011, v.71 no.2

              Volume 71, No. 2 • 2011
A NEWSLETTER OF THE OKLAHOMA GEOLOGICAL SURVEY
The University of Oklahoma MEWBOURNE COLLEGE OF EARTH & ENERGY
71
Mississippian Play Workshop a Sellout!
One of the Oklahoma Geological Survey’s primary
missions is the dissemination of information necessary
to assist operators in the development of the State’s oil
and natural gas resources. Towards that end the Survey
hosted a workshop dedicated to one of the most actively
sought reservoirs in Oklahoma. The Mississippian Play
Workshop that was held on May 18th was bittersweet for
Survey staff. Although we obviously selected a topic of
tremendous interest to our audience, we unfortunately
could not begin to accommodate the number of people
that wanted to attend this workshop. On the plus side,
an audience of approximately 300 was able to attend
the workshop, which received excellent reviews for its
fresh and varied look at the Mississippian Play.
Due to the overwhelming popularity of this workshop,
the Survey is offering it again on August 2nd. This has
been made possible through the kindness and assistance
of Kurt Rottmann, the workshop’s technical coordinator,
and several other speakers from the May workshop who
graciously committed to present their material for a
second time.
The Mississippian of northern Oklahoma, often called the
Mississippi Lime, has long been an important producing
horizon. In some areas, such as the Sooner Trend, which
is located on the shelf of the Anadarko Basin in north-central
Oklahoma, it has been the primary producing
formation since the 1960’s. However, in most other areas
it has been regarded as little more than a convenient
‘bail out’ zone for wells that were unproductive in their
primary objective. The fact that it was almost always oil-saturated
gave it the ability to produce almost anywhere.
Unfortunately, its low matrix permeability meant that
while it could usually produce enough to pay for the
completion, this was rarely suffi cient to pay for an entire
well.
Usually appearing on well logs as a massive limestone, in
places the Mississippian contains zones that are siliceous.
The most prolifi c of these cherty intervals, which often
have excellent reservoir properties, occurs at the very top
of the interval and is usually referred to as the Mississippi
Chat. It was this facies that was developed fi rst. The
limestone beneath consists of alternating porous and
impermeable strata that are often barren. Diffi culties in
correlating various facies within the limestone made them
appear in an erratic and seemingly random pattern. This
lead to a fundamental misunderstanding of the reservoir’s
potential, which in turn has lead to bypassed reserves.
Operators today, armed with modern horizontal drilling
and completion techniques and the benefi t of high
crude oil prices, have been able to breathe new life
into this reservoir’s development. Horizontal wells are
ideally suited to Mississippian reservoirs that are usually
Continued on pg. 2
G. Randy Keller, Oklahoma State Geologist and Dan Boyd, OGS Geologist