Northwestern Montana is geologically complex, and this complexity is fully reflected in the diversity of type and location of oil and gas accumulations. As a result, the oil and gas history of this area has been one of continual development of new and changing geological ideas.
Until 1963, drilling was concentrated primarily in and around old productive areas associated directly with the Sweetgrass arch. Subsequently, new discoveries essentially were extensions to already productive Cretaceous Cutbank sandstone and Madison carbonate reservoirs in the Cutbank, Kevin-Sunburst, and Pondera fields.
The present-day drilling boom is a product of new stratigraphic ideas in the shallower Cretaceous Sunburst and Moulton sandstone units. These ideas and improved drilling economics were spawned by several recent wildcat wells. Well completions to date have increased the annual production in northwestern Montana from 4 to more than 6.5 million bbls. of oil in less than 3 yrs.