Abstract

Sour gas containing a large percentage (65%) of CO₂ was discovered on the western edge of the Green River Basin in 1961 when Paleozoic rocks were first penetrated by the drill. Continued periodic tests of the Paleozoic formations on the Moxa Arch generally recovered CO₂, and in 1979 the oil industry began to develop this untapped resource. The Mississippian Madison Limestone is presently the only formation which produces CO₂ gas on the Arch, although other Paleozoic formations have been tested.

The study of gas compositions has indicated that the CO₂ content increases with the age of the containing formation. For the Madison Limestone itself, where numerous analyses are available, there are indications that density stratification has occurred to some extent.

The Madison reservoir is productive from a very thick and extensive section at the crest of the Moxa Arch, locally called the LaBarge Anticline or LaBarge Platform. The Madison in that area appears to be productive over an area of about 21 miles by 65 miles (34 km by 105 km), and the structural trap appears to have some stratigraphic implications. There has been no indication of reservoir separation between wells drilled to date. Porosity zones in the Madison are correlatable across the structure, and the correlation of equivalent stratigraphic intervals suggests a continuous reservoir across the structure.