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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 � ��������� ������� ����������� ���������������� ��������� ������������������� ������������������ � ������������� ������� Exploration status: Very few wells have penetrated the lower ��������� ������������������������� ������������������� ��������� �� �� �������������� ��������� ������������������ ����������������������� ����������� ������������� ������������������ ���������� ��������������� ���������������������������������� (after Ojakangas et al., 2001) ����� EXPLORE FOR MINNESOTA GAS ������ �������������� �� ������� ��������� 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. �������� 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. ���� 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. � �� �� � ����������� �������������� ��������� ��������� � � ����������������� ��������������� ������������ ��������� ������������ ������������� 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. ��� ���� � �� ������������������ �������������������������� ������ �� ��������������� �������������� ��������������� ������������ ������ ������������ ��������� ��� �� ��� ��� 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. �� �� �� �� ��� �� � ����������� ��������� ����������� ��������� � Traps: Dual stages of tectonism would have produced many trapping ������ � �� ��� �������� �������������� ������� ��������� �������� ����� ������ ����������� �������������� � ������� ����������� ��������� ������������� ��������� �������� � � � � � � � � � � ������ � � � � � � � � � ����������� ��������� ����������� ����� �������� �������� ��� �������� ��������� ��������������� ��������� ��������� � �������������� ������������� �� ���� STRATIGRAPHY ����������� ������������� ���� ��� � � R.W., Morey, G.B., and Green, J.C., 2001, The ��Ojakangas, ��������� �������� � ������� ������� AEROMAGNETIC AND GRAVITY DATA ���� �� � � 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 �������� 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. ������ 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)