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 Midwest
Region
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Shallow Gas in the
Michigan Basin
By Dr. William B. Harrison, III, Professor
Emeritus, Michigan Geological Repository for Research and
Education, Department of Geosciences, Western Michigan
University, Kalamazoo, MI.
Shallow gas production is significant from
the Michigan Basin. Approximately 40% of Michigan's gas
production is shallow (<1500 feet). Total cumulative
Michigan gas production exceeds 6.5 TCF, with Antrim Shale
production at approximately 2.5 TCF. All other shallow
formations have produced about 250 BCF.
Over 1200 wells have shown commercial
production from less than 1000 feet deep and nearly 5200
wells produce gas from less than 1500 feet depth. About 91
percent of the shallow gas in Michigan is produced from the
Upper Devonian Antrim Black Shale. Most of the 2.5 TCF of
gas produced from the Antrim around the Basin's northern
margin is biogenic in origin. The Antrim Shale in this area
has seen low thermal maturation (Ro approximately 0.6). The
presence of an extensive natural fracture network is the key
to commercial production. Although there had been occasional
Antrim producing wells since 1940, the recent development
began in the late 1980s as a result of new |
Figure 2. Distribution of Michigan natural
gas wells by geologic formation. Data compiled from records
of Michigan Geological Survey. |
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technology, access to
underutilized Silurian Niagaran Reef well infrastructure,
and a federal non-conventional fuels tax credit
(section 29). To date, the Antrim Shale in Northern
Michigan, has produced over 2.5 TCF of gas from over 9000
wells. Production in 2006 was nearly 140 BCF. The Antrim
Shale is a classic black shale that produces natural gas by
desorption processes into a complex network of fractures.
The distribution of high total organic carbon and natural
fractures are keys to good productivity. This play, mainly
in north-central Lower Michigan, has been developed through
the use of vertical wells. The abundance of fractures in the
primary development area makes vertical wells effective.
Initial well spacing was on |
40-acre units; unit size
was increased to 80-acre units in 1995. Today some operators
even use 160-acre units. Horizontal drilling has not become
widely used in the Antrim Shale play. Few horizontal wells
have performed significantly better than vertical wells.
Shallow gas is produced from Devonian, Mississippian,
Pennsylvanian and even sporadically from the Pleistocene
Glacial Drift. Most other formations in the Michigan Basin
have produced only small amounts of gas from shallow depths.
Mississippian sandstones of the Michigan Formation and the
Berea Sandstone have small amounts of commercial production.
The Michigan Formation "Stray" Sandstone has been the most
productive, with wells in seven different fields. The
largest of these fields, Shaver Field in Gratiot County,
produced over 11 BCF of gas before being converted to gas
storage.
Middle Devonian carbonates of the Traverse Limestone have
limited gas production from a few shallow conventional
reservoirs, often associated with oil production. Gas-oil
ratios are generally low (typically less than 5000).
Historically much of the associated gas from these
reservoirs was flared and accurate records of total gas
production are poor.
Very
limited gas production is also known from the Mississippian
Marshall and Parma Sandstones, the Pennsylvanian Saginaw
Formation and the Pleistocene Glacial Drift. Although the
production of shallow gas from the Michigan Basin is
dominated by the unconventional Upper Devonian Antrim Shale
gas play, there are several other shallow conventional-type
plays that should not be overlooked. If these other horizons
were exploited with the intensity of the Antrim Shale
development, other significant gas reserves may be found in
the Michigan Basin.
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Figure 1. Modified from Michigan Geological
Survey Map online
www.deq.state.
mi.us/documents/deq-ogs-gimdl-GGMOG05.pdf |
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