Sweetgrass Arch, Geologic Frontier: ABSTRACT
The Kevin-Sunburst, Pondera, Cut Bank, and Bannatyne oil fields are located along or across some part of the Sweetgrass arch. Oil has been produced from these fields since the 1920's. Relatively little is known and clearly understood of the importance stratigraphy and subsurface geology play in the accumulations of oil and gas in this province. Numerous wells have been drilled and are still being drilled in the continued search for oil and gas in this area. However, few electric or radioactive logs are run and few if any samples of the cuttings are taken for geologic study. Consequently, much valuable geologic information is going to waste. East-west stratigraphic cross sections show a pre-Middle Jurassic positive area east of the present Sweetgrass arch in the Chinook-Bearpaw mountain area. Between Middle and Upper Jurassic time this positive area was depressed and the Belt Island positive area came into being. The present northwestward plunge of the Sweetgrass arch was probably established at this time. Periods of erosion and truncation of sediments followed by redeposition have caused numerous wedge belts of porosity in sediments from Lower Mississippian to Lower Cretaceous. Changes in facies from the predominantly clastic sediments of the Big Snowy group (Upper Mississippian) into the limestone and dolomites of the miogeosyncline west to the present Sweetgrass arch offer multiple stratigraphic trap possibilities for the accumulation of oil and gas. Relatively little has been done to explore these stratigraphic traps or wedge belts. The wedge edge of the Middle Jurassic Sawtooth sandstone and limestone remains unexplored. Changes in tilt and hydraulic gradient may have caused oil accumulation off the top of structurally high areas forcing a re-evaluation of formerly condemned struct res. The area is further complicated by thrust faulting along its western margins. The Sweetgrass arch area offers a challenge to the petroleum geologist to solve its stratigraphic and structural complexities. Rewards will be high--the oil is here, find it! End_of_Article - Last_Page 947------------