HELIUM IN SOUTHERN SASKATCHEWAN, CANADA (Invited Presentation)

Helium-bearing sediments of southern Saskatchewan lie within the northern part of the intracratonic Williston Basin and range in age from Middle Cambrian to Upper Cretaceous. The entire Phanerozoic succession in the province can be roughly broken down into three lithological entities: a Paleozoic basal clastic unit; a middle carbonate sequence with local and regional evaporitic intervals; and an overlying Mesozoic and Cenozoic sequence of mainly fine marine and terrigenous clastic rocks. Numerous unconformities intersect the Phanerozoic strata, and several span significant intervals of time.

Elevated concentrations of helium (>0.3% - 7.26% molarity), identified from gas analyses from over 88,000 oil and gas wells, exist throughout the southern quarter of the province. Most of these analyses are from hydrocarbon pools and are skewed toward the major producing strata in the Cretaceous and Jurassic successions in the west half of the area in question, and in the Mississippian and Mississippian-Devonian successions in the eastern half. However, a significant number of elevated helium shows are related to the less explored Lower Paleozoic rocks, in clastic sediments that lie immediately above the Precambrian where helium can be trapped by local siliceous lenses, and in overlying carbonate strata that underlie evaporitic intervals. The sources of helium, based on location of the shows and recent analytical data, are most likely from the basement through a series of long-lived faults and fractures that were reactivated during Sevier-Laramide compression and extension. These sources may have been supplemented by helium from shales older than 100 Ma. (e.g. Cambrian-Ordovician shales). The migration and trapping of helium is further complicated by complex hydrogeologic patterns of less-saline fluids in the southwest on the Swift Current Platform advancing and encroaching the pore space of more stagnant saline brines found eastward in the province, in the deeper portion of the Williston Basin.