Exploration and development in Montana during 1962 was particularly significant both in terms of successful wildcats which opened large new areas for future exploration, and field extensions which revealed unexpected economic potential in dormant field areas.

Two areas are discussed, the Williston basin in northeastern Montana and the Sweetgrass Hills province in northwestern Montana. A sequence of prolific pre-Mississippian Paleozoic discoveries in northwestern Montana since 1960 had earlier revived interest in this area. During 1962, exploration of this area was further stimulated by three widely separated new-field discoveries: Spring Lake, Lone Tree, and East Benrud, as well as successful development wells in Dwyer and Southwest Richey. McAlester Fuel's Spring Lake discovery, dually completed in the Devonian Nisku and the Ordovician Red River for a combined flow of 742 BOPD on choke was the most significant.

A regional structure map, field maps, and cross sections illustrate how these 1962 discoveries have broadened the areas of active exploration interest and extended the reservoir objectives throughout the entire lower Paleozoic section, with multiple pay zones occurring in carbonate reservoirs at depths ranging from 7,500 feet to 12,000 feet. The significance of the existing production for future exploration includes: (1) location of the new discoveries off of known major structures, (2) distance from established production, (3) characteristic, subdued low-relief structural expression with regional dips averaging 30 feet to 60 feet per mile, and productive closures typically 50 feet to 75 feet, and (4) influence of facies, pore-size distribution and hydrodynamic factors in controlling il accumulation.

In the Sweetgrass Hills province of northwestern Montana, 1962 extensions to existing production in the Flat Coulee and Whitlash field areas have revealed better quality reservoirs than were previously known and opened new pools. Cross sections illustrate the Jurassic Swift and Lower Cretaceous Sunburst sandstone reservoirs in which this production occurs at depths of 2,800-3,000 feet. Field maps show the accumulations to be combination stratigraphic-structural traps located down-flank on known structures.

Numerous structural domes uplifted by deeply buried igneous intrusions, combined with rapid lateral variations in facies and porosity development in both Cretaceous and Jurassic reservoirs, holds forth the promise that many additional pools and fields will be found by future exploration in the Sweetgrass Hills province.

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