Abstract

The South Baggs-West Side Canal gas field is located in northwestern Colorado and south-central Wyoming on the eastern end of the Cherokee Ridge arch which separates the Washakie Basin from the Sand Wash Basin.

The field was discovered in 1947 and now has approximately 60 commercial wells producing from the Cretaceous Williams Fork (Mesaverde), Lewis, Fox Hills, Lance, and Tertiary Fort Union formations. Cumulative production (through May 1969) is in excess of 24,250,000 MCF with ultimate reserves estimated to be in excess of 200,000,000 MCF.

Marine Lewis Shale was deposited during the final transgressive phase of the Cretaceous sea. Non-marine Lance and transitional Fox Hills formations were deposited during regressive phases of the Late Cretaceous sea. The non-marine Fort Union Formation rests unconformably on Lance throughout the area.

Events in the structural history of the area are as follows: (1) minor folding during and after Lance deposition forming ancestral structural highs (indicated by isopach thins), (2) pre-Fort Union erosion, (3) deposition of Fort Union and Wasatch formations, and (4) uplift accompanied by folding and high-angle to vertical faulting.

Reservoirs appear to be combination structural-stratigraphic traps. For future exploration the north-south trend of the Lewis middle sandy member should be tested in T. 12 N., R. 92 W. in both Wyoming and Colorado. The source of the gas is probably the rocks adjacent to the reservoir rocks, i.e., the highly organic non-marine rocks of the Williams Fork, Lance, and Fort Union, and the marine shales of the Lewis and Fox Hills.