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Known and Potential Oil and Gas Reserves in The Mississippian Carbonates of The Western Cordillera of North America

Pinnell, Michael *1; Moulton, Floyd 1; Wood, Greg 1; Newman, Gary 1; Holden, Natalie 1
(1) Consultant, Sandy, UT.

Mississippian carbonate reservoirs have accumulated over 209 TCFG, and Mississippian-Permo-Penn reservoirs have produced 3.7 BBO from cordilleran and foreland structures in western Canada, Wyoming, western Colorado and in northern Utah. These reservoirs have been filled during multiple phases of hydrocarbon generation from down-dip Paleozoic source rocks with lesser local contributions from subthrust Cretaceous shales.

In western Wyoming early maturation of western, down-dip Paleozoic source rocks (Permian Phosphoria Formation) expelled hydrocarbons which, for the most part, migrated eastward into early-formed foreland structures prior to Cretaceous development of the Wyoming thrust belt. The ten largest of these foreland structures have yielded over 3.5 BB of Paleozoic sourced oil. The single largest foreland structure, the 60 mile long LaBarge Anticline of western Wyoming, contains 167 TCFG (21% methane). Our best estimate is that this gas is the thermally degraded remnant of an early oil accumulation (possibly up to 28 BBO). The most prolific well, producing from these Mississippian carbonates, has yielded 440 BCFG to date and currently produces 79 MMCFG/D.

The Mississippian carbonates are major producers in both Canada and Wyoming-northern Utah salients of the western cordillera, where they are associated with fields which also produce from Mesozoic reservoirs. However, in the currently productive central Utah portion of the cordilleran thrust belt, which has about 150 MMBO in the Jurassic Navajo Sandstone, the underlying Mississippian section is untested. Wells and outcrops in structurally disrupted areas to the west and southwest document the existence of the Mississippian section across this region. Wolverine Gas and Oil, who discovered Navajo production at Covenant Field, has determined hydrocarbons were trapped prior to thrusting, probably during early Cretaceous. Subsequent to Sevier thrusting, oil from one of these ancestral anticlines filled Covenant with over 100 MMBO.

One could logically conclude that, like in Canada, Mississippian carbonates in Utah may contain the majority of oil and gas trapped in these thrusted anticlines. Unfortunately, not a single Mississippian test has been drilled since interest in the area was rekindled by the discovery of Covenant Field in 2003.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California