Geochemical Studies of Natural Gas Part II. Acid Gases in Western Canadian Natural Gases

Hydrogen sulphide is of interest as an economic source of sulphur, fromconsideration of corrosion problems, as a health hazard, and as a geochemicalguide. It forms an essential link in the cycle of sulphur, it occurs widely innature, and, with carbon dioxide, is a byproduct of the bacterial reduction ofsulphates. The close association with low contents of dissolved sulphate information waters, and with the presence of sulphate-reducing bacteria in someoil-field waters, is consistent with a biogenic origin for these two componentsin the bulk of natural gases. The few exceptions (natural gases with commonlyless than five per cent hydrocarbons, no hydrogen sulphide and consistingpredominantly of carbon dioxide) probably owe their origin to metamorphism ofbituminous carbonates. The contents of both hydrogen sulphide and carbon dioxide in natural gasesfrom Western Canada vary regionally, although the trend patterns are not alwayssimilar. In some stratigraphic units hydrogen sulphide probably has beenremoved from the aqueous system through reaction with iron in solution and thesubsequent precipitation of pyrite. In other units, oxidation of crude oils mayhave relatively increased the content of carbon dioxide in the natural gases.In spite of the probable operation of these phenomena, the major factorcontrolling the content of hydrogen sulphide and carbon dioxide in naturalgases is the environment of deposition of the sediments, a view that is inaccord with a biogenic origin for both acid gases. Introduction This paper is the second of a series concerned with the geochemistry ofnatural gas in Western Canada. It discusses the acid gases hydrogen sulphideand carbon dioxide. The first paper dealt with the hydrocarbons and the thirdpart will treat the inert gases.