Abstract

The sedimentary strata of southern Saskatchewan and southwestern Manitoba, 220,-000 square miles in area and 165,000 cubic miles in volume, form a broad shelf dipping into the Williston basin. These beds are 95 per cent marine, and divisible into 3 major categories:

(a) a basal clastic group, early Paleozoic in age, and 12.4 per cent of the sedimentary volume;

(b) a middle carbonate group, Ordovician through Mississippian in age, and 47 per cent of the volume; and

(c) an upper clastic group, Mesozoic and Cenozoic in age and 40.6 per cent of the sedimentary volume.

There are two major petroleum producing districts. That across southeastern Saskatchewan and southwestern Manitoba contains 65 per cent of the recoverable reserves (2 billion barrels) in Mississippian reservoirs. The other, with the remaining 35 per cent, occupies a north-trending belt in southwestern Saskatchewan, it includes reservoirs Jurassic and Cretaceous in age, as well as the two major non-associated natural gas fields.

The initial recoverable reserves of the Williston basin region (including North Dakota and eastern Montana) are 3 billion barrels. These are 1.7 billions less than the initial recoverable reserves of the 4 billion barrel Illinois-Michigan basin region — a region exploited since the early part of the century. It is deduced that the deficit in the Williston basin region represents undiscovered exploitable reserves, and that 1.15 billion barrels are yet to be found in the study area. Current gas reserves of 1 trillion cubic feet are expected to quadruple.