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"Nothing great was ever
achieved without enthusiasm," noted Ralph Waldo Emerson. With
enthusiasm as the measure, numerous speakers involved in
unconventional energy and 345 energetic participants at the
recent Unconventional Energy Resources in the Southern
Midcontinent conference portend further significant growth for
unconventional energy from shale, coalbed methane and tight
gas sands. Insights from hundreds of millions of dollars of
project experience were revealed, which accelerated progress
in the remaining learning curve. The event was organized by
the Oklahoma Geological Survey, with special compliments to
Brian Cardott, and co-sponsored by the U.S. Department of
Energy's National Energy Technology Laboratory and PTTC's
South Midcontinent Region.
Unconventional
Energy for an Unconventional Future
A recent National Petroleum
Council study points out that increasing natural-gas-supply
diversity is a serious national issue. Our current energy
landscape forewarns a strong dependence on increasing
unconventional gas production in the lower 48 and Canada. As
David Fleischaker, Oklahoma Secretary of Energy and the
conference's lunch speaker, points out, "Non-conventional
fuels will play an important role in the short- to
mid-term—serving as an essential bridge until the time that we
increase imports by building a pipeline to the North Slope and
increasing our Liquified Natural Gas imports."
The Newark East Barnett Shale
field, the largest active gas field in Texas, now produces
more than 220 Bcf of natural gas per year. Unconventional
energy resources in Oklahoma include Hunton de-watering and
coalbed methane (CBM) activity in the Arkoma and Cherokee
basins. According to Cardott, CBM activity in Oklahoma's
Arkoma Basin produced about 70 Bcf of gas cumulatively through
mid-2003. About two-thirds of this production is from vertical |
wells, but horizontal
production is rapidly overtaking that from vertical.
Cherokee Basin CBM cumulative production is about 45 Bcf, all
from vertical wells. CBM wells in southeast Kansas are now
producing about 10 Bcf per year, and activity is strong.
Arkansas CBM production is just now taking off.
Barnett Shale
Ignites Imagination
As Jeff Hall, Manager of
Exploration and Exploitation with Devon Energy, pointed out
during his presentation, the Barnett Shale is still one of the
most exciting discoveries around. With its first completion in
1981, the Barnett isn't a secret. Estimated resources are as
high as 140 Bcf per square mile across its 54,000 square
miles. Though about 2,500 wells have been drilled in this
field, there is a lot of action forthcoming. Devon, who
operates about 60 percent of the wells in the field, estimates
that recovery from conventional vertical wells will be 10 to
12 percent, with an additional 5 to 10 percent from re-fracs
and additional production enhancements. That leaves 80 percent
of gas-in-place for innovative thinkers who can successfully
leverage new technology!
About 60 companies currently
work the play. Its strong activity stems from evolving Barnett
stimulation knowledge, including re-fracing and horizontal
drilling. Progressive Barnett Shale developers, armed with
frac mapping and tiltmeter technology, noticed that as their
wells produced for a few years, the rock stress environment
changed. When it was re-fractured, orientation |
of the new fractures was
different from the original fractures.
Because the Mississippian-age
Barnett is so tight, and its drainage area so limited, even a
minor re-orientation of fracs essentially opened up a new
reservoir to production. It is similar to getting a whole new
well at times. Currently, most well workovers involve re-fracing
the Lower Barnett with better frac technology and adding Upper
Barnett perforations. About two-thirds of the production
increase and reserves observed in re-frac treatment
completions come from the Lower Barnett. Although the first
series of re-fracs have proven profitable, none of the wells
are mature enough to test the potential of additional rounds
of re-fracing.
When one considers shale, one
typically thinks of natural fracturing delivering increased
recovery. Not in the Barnett, where fractures are not as
important as thermal maturity. Given the optimum thermal
maturity, the Barnett Shale becomes a stimulation technology
play. "Technology is going to extend the play beyond its core
area," noted Devon's Hall. The play also has surface access
challenges, with the subdivision and strip-mall laden
Dallas-Fort Worth suburbs sprawling just above the action.
Stimulation considerations led to the current trend of
horizontal wells. In the heart of the play, Ordovician tight
limestone provides barriers to keep the large frac treatments
in
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State-of-the-Art
Summary