Extension of the Lower Cretaceous Glauconite Sand Play into Northwest Montana

William B. Hansen
Consulting Geologist, Jireh Consulting Services, Great Falls, MT

Northwest Montana is plagued by a confusing array of reservoir sand names in the Lower Cretaceous (Albian) Kootenai Formation (Mannville equivalent). This situation is further complicated by the Lower Cretaceous/Jurassic unconformity, and the lack of a centralized Montana core repository. In some cases, the unconformity cuts downward into the Jurassic Swift Formation, and the Cretaceous Glauconite sand has been incorrectly labeled as Jurassic Swift Sandstone. Unlike Alberta, detailed studies of the non-marine valley-fill sand sequences in the lower Cretaceous of Montana have been limited, and published studies of this complicated stratigraphy are even rarer.

A correlation across the international border between Canada and the U.S. indicates that the Glauconite Sand of Southern Alberta extends into northwest Montana. A series of detailed well log correlations has been conducted from prolific producing Glauconite fields in Southern Alberta into Glacier County, Montana. It appears that what has historically been called the Sunburst and/or Moulton sands in Montana often (but not always) correlate into the Glauconite sands of Alberta. These sands have produced both oil and natural gas from Northwest Montana fields for many decades, but there have been no systematic stratigraphic studies published of the area. Additional detailed subsurface studies should be successful in identifying the channel trends, and in the process should identify numerous gas and oil drilling opportunities at relatively shallow depths.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005