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EXPLORE MINNESOTA
Minnesota
Midcontinent Rift
United States of America
CONTACTS
Minnesota Department of Natural
Resources, Division of Lands and
Minerals, 500 Lafayette Road, St. Paul,
MN 55155-4045 USA;
[email protected]
Natural Resources Research Institute,
5013 Miller Trunk Highway, Duluth, MN
55811 USA;
[email protected]
Minnesota Geological Survey, 2642
University Ave. W., St. Paul, MN
55114-1057 USA;
[email protected]
Telephone 612-627-4780 ext. 224;
Fax 612-627-4778
Highlights: Precambrian Midcontinent Rift Play (Palacas, 1995)
2006
Geology: Volcanic horsts flanked by sedimentary basins up to 30,000 feet thick,
sedimentary basins up to 6,500 feet thick atop the horsts
Reservoirs: Sandstones, conglomerates, fractured shales; porosities up to 18%;
probable shale and fault gouge seals
Source rocks: Nonesuch Formation shale, up to 700 feet thick, up to 3% total
organic carbon (TOC), type II & I kerogens, mature to overmature, known oil
seeps in Michigan
Traps: Fault related structures, large anticlinal features, drag folds, stratigraphic
traps likely
V E Y
G E O L
R
1872
O
G
U
Resource potential: A high-risk play with few wells drilled and mature to
overmature source rocks; source rocks may have favorable thermal maturity along
basin flanks
NESO
A
M
IN
T
Exploration status: Five wells drilled from Kansas to Michigan; seismic
refraction data available for parts of the rift; increasing awareness of source rock
potential and oil seeps, improved knowledge of large reserves in other rifts and
Precambrian terranes
I C A L S
Sponsored by:
Produced by:
Minnesota Minerals Coordinating Committee
Minnesota Geological Survey
Richard Lively, Lori Robinson, and Harvey Thorleifson
Photos used with permission
MIDCONTINENT RIFT GAS
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Exploration status: Very few wells have penetrated the lower
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(after Ojakangas et al., 2001)
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EXPLORE FOR MINNESOTA GAS
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Overview : The U.S. Geological Survey National Oil and Gas
Assessment (Palacas, 1995) indicated that the hypothetical
Precambrian Midcontinent Rift System Play consists of possible oil
and gas accumulations in structural and stratigraphic traps within the
800-mile long Midcontinent Rift System. This 1.1 billion year-old rift
extends from Kansas to Michigan. Broad, transverse-faulted medial
volcanic horsts are bounded by high-angle faults and flanked by
asymmetric sedimentary basins up to 30,000 feet thick, with basins up
to 6,500 feet thick atop the horsts.
Potential reservoirs: Primary targets would be fluvial, deltaic, and
shoreline sandstones of the Nonesuch Formation and the underlying
upper Copper Harbor Conglomerate, both with porosities up to
13%. Fractured shales also occur in the Nonesuch Formation, and
sandstones with porosities up to 18% occur in the overlying Freda
Sandstone.
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Resource potential: The rift is regarded as a high-risk play by
the U.S. Geological Survey because few wells have been drilled,
potential source rocks may be overmature, and reservoir porosities
in some regions may be unfavorable. However, it is reasonable
to speculate that source rocks may have more favorable levels of
thermal maturity if present at shallower depths of burial along the
basin flanks. Drilling depths would vary from 3,000 feet to as much
as 25,000 feet.
References
Chandler, V.W., McSwiggen, P.L., Morey, G.B., Hinze, W.J., and Anderson,
R.R., 1989, Interpretation of seismic reflection, gravity, and
magnetic data across Middle Proterozoic Mid-Continent Rift System,
nor thwestern Wisconsin, eastern Minnesota, and central Iowa:
American Association of Petroleum Geologists Bulletin, v. 73, no. 3,
p. 261-275.
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The State of Minnesota is encouraging the growth of economically
significant and environmentally responsible resource industries in the
State. The Minnesota Minerals Coordinating Committee therefore is
promoting awareness of the potential for natural gas production from
the Midcontinent Rift in Minnesota. Recent world-class natural gas
discoveries in Siberia have demonstrated the potential in a similar
setting.
Keweenawan Supergroup rocks that have the highest potential for
hydrocarbon reserves. Drilling at sites from Kansas to Michigan
was stimulated by increasing awareness of source rock potential and
oil seeps, and also improved knowledge of large reserves in other
rift basins such as the Nor th Sea, Gulf of Suez, and Pripyat Basin,
as well as other Precambrian terranes such as the Lena-Tunguska
Petroleum Province of eastern Siberia, the Sichuan Basin of southern
China, and the Huqf Group of Oman.
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Seals: Probable seals include shales of the Nonesuch Formation, as
well as tight horizons in the overlying Freda Sandstone and Bayfield
Group. Fault gouge may also account for some seals.
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conditions, with varying styles of fault-related structures. Tectonic
inversion may also have created structural features of varying scale
that could contain large accumulations of hydrocarbons. Drag folds
against reverse faulting offer multiple reservoir possibilities. It is
likely that stratigraphic traps also occur.
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Traps: Dual stages of tectonism would have produced many trapping
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STRATIGRAPHY
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R.W., Morey, G.B., and Green, J.C., 2001, The
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AEROMAGNETIC
AND
GRAVITY DATA
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Mesoproterozoic Midcontinent Rift System, Lake Superior region,
USA: Sedimentary Geology, v. 141-142, p. 319-341.
Palacas, J.G., 1995, Superior Province: U.S. Geological Survey National
Oil and Gas Assessment, http://energy.cr.usgs.gov/oilgas/noga/
index.htm.
SEISMIC REFRACTION AND MODELING
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Source rocks : Nonesuch Formation shales up to 700 feet thick
contain up to 3% total organic carbon by weight, and live oil seeps in
Michigan confirm that liquid hydrocarbons have been generated in this
formation. Kerogens are type II and type I, and moderately mature
Tmax values of 435 to 440°C have been determined. Although the
organic matter is oil prone, gas is the more likely target due to the
typical degree of thermal maturity.
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Timing and migration of hydrocarbons: During extensional
tectonism, the Nonesuch Formation and equivalents may have
generated oil and gas, especially in the deeper por tions of the
basins, prior to compressional tectonism. In the shallower por tions
of flanking basins, a second phase of oil and gas generation probably
occurred following deposition of Paleozoic sediments. In addition,
hydrocarbons that might have accumulated during initial rifting may
have re-migrated into structures formed during compression.
(after Chandler et al., 1989)