Natural Gas in Quebec and the Maritime Provinces
Much of the greater part of the Province of Quebec lies within the Canadian or pre-Cambrian shield. The rocks underlying this area are, excepting for a veneer of early Paleozoic strata (generally Ordovician) over relatively small areas, of pre-Cambrian age, and consist of igneous rocks and strongly metamorphosed sedimentaries, which give no prospect for either natural gas or petroleum. Certain shales and limestones were evidently bituminous in their original condition, but are now graphitic or carbonaceous.
The part of the province lying southeast of a line between the city of Quebec and the head of Lake Champlain belongs to the Appalachian Mountain region. The rocks are steeply and intricately folded, are greatly faulted, and are intruded by large masses of igneous rock. The sedimentary rocks are of Cambrian and Ordovician age and, although not so intensely metamorphosed as those of the pre-Cambrian shield, are too much altered and broken over most of the region to be considered favorable for gas or oil accumulation. The St. Lawrence lowlands lie between the pre-Cambrian shield and the Appalachian Mountains. A part of this area, a part of the Gaspé Peninsula, and the island of Anticosti are the only areas in Quebec which may be considered as having any prospects for oil and gas.
The St. Lawrence lowlands comprise an approximately triangular area between the Laurentide Mountains, the southern part of the pre-Cambrian shield on the north, and the Appalachian Mountains on the southeast. This area is limited on the west by an “isthmus”
Figures & Tables
Alberta is the only western Canadian province in which a production of natural gas and oil has been developed. Natural gas was discovered in 1885, and at present there are seven producing fields and 330 miles of main pipe lines.
Alberta is divided into eight structural provinces; four of these are gas-producing regions, one is prospective, and the others are of no interest as gas areas. The stratigraphic column has three persistent features, namely, the Palaeozoic limestone section, the profound unconformity superimposed on it, and the succeeding Mesozoic section of transgressive-regressive deposits.
The Turner Valley field is the only developed field producing from formations of Palaeozoic age, though there have been significant discoveries suggesting that other fields are present. A theory is advanced in this paper to explain a Palaeozoic origin for the heavy oil and bitumen in the basal sandstones of the Mesozoic. The gas accumulations in the basal sands were later derived from the bitumen and heavy oil. The reserves of gas in Palaeozoic rocks and the basal sands of Mesozoic age are large.
During Mesozoic time there were at least five marine transgressions of the seas, and there is a marked relation between the marine shales and the gas-bearing horizons in rocks of Mesozoic age. Gas is generally found in the sandstones immediately overlying, within, or immediately underlying the marine shales.
Gas is found in rocks of Jurassic age in the Southern Plains and the Southern Foothills. The reserves are estimated to be about 80 billion cubic feet. Only small amounts of gas are now produced from Jurassic horizons. Gas is found in marine formations of Comanche age in northern Alberta, but there are no developed fields, and the reserves are unknown. There are three gas-bearing horizons in the Colorado (Gulf series), with several fields, including the Foremost, Viking, and Medicine Hat fields. The possible reserves are large and are probably in excess of 600 billion cubic feet. The Lower Montana and Upper Montana rocks (Gulf series) produce gas over large areas, but the yields are small and the horizons are of minor importance. There are no marine rocks of post-Mesozoic age, and the only gas occurrences are small flows from lacustrine deposits.
The analyses of natural gases in Alberta when arranged according to geologic horizons and localities appear to show an increase in the proportion of higher hydrocarbons to methane in a westerly direction for a given gas-bearing horizon. This may be due to the effect on the source material of increasing metamorphism westward.