Characterization of Mississippian Osage Chat in South-Central Kansas

Kansas Geological Survey Open-file Report 2002-50

Conclusions

Understanding petroleum production from, and future potential of, the chat requires understanding the nature of deposition and diagenesis, the role of tectonics, lithofacies controls on petrophysical properties, and log response to these properties. Important conclusions are:

Depositional, Diagenetic, and Tectonic

• During the Mississippian sponge-microbe communities forming low relief biostromes and bioherms Favorable ramp/slope development appears to be related to basement reactivation.
• Transgressive-regressive cycles on a shelf to shelf margin setting resulted in a series of shallowing cycles. Sponge spicule content may increase upwards with increasing cycle thickness.
• During inter- and post- Mississippian subaerial exposure these facies underwent further diagenesis including sponge spicule dissolution, vuggy porosity development in moldic rich rocks, and autobrecciation. Structural movement led to overall elevation of the area accentuating weathering. Locally sponge-spicule facies were preserved with block faults or flexures and became porous and permeable chat.
• Meteoric water influx and mixing-zone diagenesis is limited in depth below the exposure surface and in lateral distance downdip into unaltered cherty Cowley Formation facies.

Lithofacies

• Combination of original accumulation, block fault movement, sponge spicule concentration (correlate to porous reservoir), and possibly thickness of overlying bioclastic wacke-grainstones (tight, non reservoir) resulted in variable reservoir properties and the creation of pods of production separated by non-productive cherty dolomite mudstones. Variations in depositional cycles produce a variable series of lithofacies with unique petrophysical properties.

Petrophysics

• Examining the properties of each lithofacies, autoclastic cherts exhibit the maximum porosity and permeability with porosities ranging from 25-50% and permeabilities >5 md. Permeability variance within this lithofacies at any given porosity can be attributed primarily to sponge-spicule mold and vug content and non-tectonic fracturing.
• Both the chert conglomerate and autoclastic chert with clay infill facies exhibit routine air permeabilities at any given porosity as much as a factor of 2 to 5 times greater than the regression trend for the autoclastic chert but can exhibit poor larger-scale permeability due to blockage by infilling clay in fractures.
• Cherty dolomite mudstones, and argillaceous dolomite mudstones can exhibit porosities below 22% with permeabilities less than 1md. The bioclastic crinoidal wacke/grainstones are highly cemented and cluster below 5% porosity and permeabilities less than 0.01 md.
• Whole core exhibits permeabilities 5-10 times greater than plugs due to non-tectonic microcracks and enhanced porosity and permeabilities in intraclast pore space. Reservoir production and simulation indicate chat reservoirs can exhibit permeabilities similar to either plug or whole core values indicating fracturing can be present in the reservoirs.
• Capillary pressure data indicate the presence of microporosity and can explain high water saturations and low resistivity observed in wireline logs. Relative permeabilities decrease rapidly for saturations > 60% and may be influenced by dual pore systems.
• Detailed modified Pickett plot analysis of logs reveals major variations in the chat reservoir and can provide reliable indications of reservoir properties useful in defining pay.

These models provide some additional insight from the extensive work that has preceded this study into the chat of south-central Kansas. They also provide additional data in understanding the nature of controls on reservoir properties that could apply to other shallow shelf chert reservoir systems.

Selected References

Brunton, F.R., And O.A. Dixon, 1994, Siliceous sponge-microbe biotic associations and their recurrence through the Phanerozoic as reef mound constructors: Palaios, v. 9, p. 370-387.
Cole, V.B., 1976, Configuration of the top of Precambrian rocks in Kansas: Kansas Geological Survey, Map Series, no. M-7, 1 sheet, scale 1:500,000.
Curtis, G.R., 1968, Nichols field, Kiowa County, Kansas, , in Beebe, B.W.; and Curtis, B.F., (eds.); Natural gases of North America; part 3 (natural gases in rocks of Paleozoic age), v. 2, American Association of Petroleum Geologists, Memoir, no. 9, p. 1582-1587.
Duren, J.D., 1960, Some petrophysical aspects of the Mississippian "Chat", Glick Field, Kiowa County, Kansas: Shale Shaker, p. 316-321.
Duren, J.D., 1967, Some petrophysical aspects of the Mississippian "Chat", Glick Field, Kiowa County, Kansas: The Log Analyst, p. 34-39.
Elster, T., 1965, Donald field: Kansas Geological Society, Kansas Oil and Gas Fields, vol. 4, p. 68-77.
Euwer, R.M., 1968, Glick field, Kiowa and Comanche counties, Kansas, in B. W. Beebe and B.F. Curtis, eds., Natural gases of North America; part 3 (natural gases in rocks of Paleozoic age), vol. 2, American Association of Petroleum Geologists, Memoir, no. 9, p. 1576-1582.
Frensley, R.W. and J.C. Darmstetter, 1965, Spivey-Grabs field: Kansas Geological Society, Kansas Oil and Gas Fields, vol. 4, p. 221-228.
Gerlach, P., 1998a, Pre-Pennsylvanian subcrop map: Kansas Geological Survey, Digital Petroleum Atlas, http://crude2.kgs.ku.edu/DPA/Plays/ProdMaps/miss_sub_gas.html, posted Nov., 1998.
Gerlach, P., 1998b, Structure on Mississippian System: Kansas Geological Survey, Digital Petroleum Atlas, (http://crude2.kgs.ku.edu/DPA/Plays/ProdMaps/miss_oil.html), posted Nov. 3, 1998
Goebel, E.D., 1968a, Mississippian rocks of western Kansas: AAPG Bulletin, v. 52, p. 1732-1778.
Goebel, E.D., 1968b, Mississippian System, in D.E. Zeller, ed., Kansas Geological Survey Bulletin 189, p. 17-21.
Gutschick, R.C. and C.A. Sandberg, 1983, Mississippian continental margins of the conterminous United States, in D.J. Stanley and G.T. Moore, eds., The shelfbreak: critical interface on continental margins, SEPM Special Publication No. 33, p. 79-96.
Kruger, J.M., 1997, On-line Gravity and Magnetic Maps of Kansas: KGS Open-file Repts. 96-51 and 97-72, http://crude2.kgs.ku.edu/PRS/PotenFld/potential.html (posted August 25, 1997).
Kruger, J.M., W.L. Watney, and R.A. Olea, 1999, Use of gravity and magnetics for low cost exploration and development in mature areas such as Kansas: Transactions, American Association of Petroleum Geologists, MidContinent Section, p. 51.
Lambert, M.W., 1988, Sub-Pennsylvanian subcrop map of Mississippian units in the Salina basin: Kansas Geological Survey, Open-file Report, no. 88-37, 1 sheet, scale: 1:500,000.
Lane, H.R., and T.L. De Keyser, 1980, Paleogeography of the late Early Mississippian (Tournaisian 3) in the central and southwestern United States: in T.D. Fouch and E.R. Magathan, eds., Paleozoic Paleogeography of west-central United States, Rocky Mountain Section, SEPM, p. 149-159.
Maples, C.G., 1994, Revision of Mississippian stratigraphic nomenclature in Kansas, in D. L. Baars, comp., Revision of Stratigraphic Nomenclature in Kansas: Kansas Geological Survey Bulletin 230, p. 67-74.
Merriam, D.F., 1963, The geologic history of Kansas: Kansas Geological Survey Bulletin, 162, 317 p
McCoy, J.R., 1978, Character of the Mississippian formation in south-central Kansas: Kansas Geological Survey, Open-File Report 78-9, 10 p.
McGinness, D.H., 1985, Hardtner Field, in P.M. Gerlach and T. Hansen, eds., Kansas Oil and Gas Fields, v. 5, p. 83-92.
Montgomery, S.L., J.C. Mullarkey, M.W. Longman, W.M. Colleary, and J.P. Rogers, 1998, Mississippian "Chat" reservoirs, south Kansas: Low-resistivity pay in a complex chert reservoir: American Association of Petroleum Geologist Bulletin, v. 82, p. 187-205.
Parham, K.D. and R.A. Northcutt, 1993, MS-3, Mississippian Chert and carbonate and basal Pennsylvanian sandstone Central Kansas uplift and northern Oklahoma, in D.G. Bebout, W.A. White, T.F. Hentz, and M.K. Grasmick, eds., Atlas of Major Mid-Continent Gas Reservoirs, Gas Research Institute, p. 57-60.
Peeler, J.A., 1985, Reservoir characterization of the Mississippian "Chat", Hardtner Field, Southern Barber County, Kansas, M.S. Thesis, Wichita State University, 120 p.
Rogers, J.P., M.W. Longman, and R.M. Lloyd, 1995, Spiculitic chert reservoir in Glick Field, South-central Kansas: The Mountain Geologist, v. 32, p. 1-22.
Rogers, S.M., 1996, Depositional and diagenetic history of the Mississippian Chat, North Central Oklahoma, M.S. Thesis, University of Oklahoma, 120 p.
Watney, W.L., Guy, W.J., And Byrnes, A.P., 2000, Characterization of the Mississippian chat in south-central Kansas, American Association of Petroleum Geologists Bulletin, v. 85, p. 85-113.
Zajic, W.E., 1956, Nichols pool, Kansas Geological Society, Kansas Oil and Gas Pools, vol. 1 (South Central Kansas), pp. 69-73.

Appreciation is extended to General Atlantic and Ocean Energy, Inc. for supporting the Petrofacies Project and providing considerable information on Spivey-Grabs Field. Jim Rogers is also thanked for providing encouragement on this project. Patricia Acker is thanked for graphic arts support.