Region: Northern Midcontinent Las Animas Arch Province This description of the Las Animas Arch Province is from the U. S. Geological Survey 1995 National Assessment of United States Oil and Gas Resources (available on CD-ROM from the U.S.G.S. as Digital Data Series DDS-30, Release 2).

Las Animas Arch Province

Introduction

The Las Animas Arch of southeastern Colorado is a north-northeast striking structural high, bounded on the south by the Apishipa Uplift. It separates the Denver Basin of northwestern Colorado from the Hugoton Embayment of southeastern Colorado and southwestern Kansas. The arch extends northeastward out of the Las Animas Arch Province, where it meets the Cambridge Arch of Nebraska and the Central Kansas Uplift; it occupies an area of approximately 6,300 sq mi in Cheyenne, Kiowa, Otero, and Bent Counties. The Las Animas Arch has a complex history but has been a positive feature since at least the Mississippian. Within the Las Animas Arch, sedimentary rocks range in thickness from approximately 2,000 ft at the southern end of the arch, to approximately 8,000 ft along its western margin.

Sedimentary strata in the subsurface range in age from Upper Cambrian (Reagan Sandstone) through Upper Cretaceous. Upper Cretaceous strata are unconformably overlain by Pleistocene and Holocene alluvium and eolian deposits. Hydrocarbon-bearing strata are limited to strata of mid-Mississippian (Osagean) to Upper Pennsylvanian (Virgilian). Three conventional plays were assessed within this province. The plays are, from youngest to oldest, Middle and Upper Pennsylvanian Carbonates Oil Play, Lower Pennsylvanian (Morrowan) Sandstone Oil, Gas, and Natural Gas Liquids Play, and Mississippian Carbonate Play.

Middle and Upper Pennsylvanian Carbonates Oil Play, producing oil from Middle and Upper Pennsylvanian (Desmoinesian, Missourian, and Virgilian) carbonates, is the least productive play; Brandon and Bledsoe Ranch fields have cumulative oil production (to 1991) of 1.1 MMBO and cumulative gas production of 3.7 BCFG. The Lower Pennsylvanian Play produces from Lower Pennsylvanian Morrow sandstones in Cheyenne and Kiowa Counties. The nine most productive fields in Cheyenne County have cumulative production (through 1991) of 33.4 MMBO and 36.6 BCFG; three fields in Kiowa County have cumulative production of 0.3 MMBO and 6.8 BCFG. Discoveries were made as early as 1952, but most significant discoveries were later (late 1970's and 1980's); drilling activity is still high. A series of recent reports on the Morrow Formation is available in Sonnenberg and others (1990). The Mississippian Carbonate Play yields oil from five fields in Cheyenne and Kiowa Counties and approximately 60 percent of the cumulative production of 21.7 MMBO is from the Brandon and Cavalry fields in Kiowa County.

Acknowledgments

Scientists affiliated with the American Association of Petroleum Geologists and from various State geological surveys contributed significantly to play concepts and definitions. Their contributions are gratefully acknowledged.

References

Burruss, R.C., Blakeney, B.A., Castle, R.A., and Kirkby, K.C., 1990, Petroleum source rock potential and thermal maturation of the Mississippian "Harrison" and Spergen Formations and Pennsylvanian Morrow Formation and Marmaton Group, southeastern Colorado, in Sonnenberg, S.A., and others, eds., Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Association of Geologists, p. 59-66.

Clayton, J.L., King, J.D., Threlkeld, C.N., and Vuletich, A., 1987, Geochemical correlations of Paleozoic oils, northern Denver basin - Implications for exploration: American Association of Petroleum Geologists Bulletin, v. 71, no. 1, p. 103-109.

Higley, D.K., 1987, Central Kansas uplift-Cambridge Arch province oil and gas play summary: U.S. Geological Survey Open-File Report 87-450E, 16 p.

Merewether, E.A., 1987, Oil and gas plays of the Las Animas Arch, southeastern Colorado: U.S. Geological Survey Open-File Report 87-450D, 22 p.

Sonnenberg, S.A., Shannon, L.T., Rader, K., von Drehle, W.F., and Martin, G.W., eds., 1990, Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Association of Geologists, 236 p.

Thomas, D., 1993, Basement paleogeography key in Colorado Morrow channel oil play: Oil and Gas Journal, v. 21, no. 29, p. 56-60.