The only known natural gas fields in the world that yield gas sufficiently rich in helium to warrant the extraction of the element on a commercial scale occur in the United States. Rich helium and nitrogen gas occurs in several fields in southeastern Kansas, in Vinton and Meigs counties, Ohio, in southeastern Colorado, in the Texas Panhandle, and eastern Utah. The percentage of helium in the richest gases ranges between 1.0 and 8.0 per cent. The age of the helium gas-producing formations ranges from Cambrian to Tertiary. In Canada, gas containing as much as 1.0 per cent of helium has been found in Ontario, but the supply of gas is too small and the rock pressures are too low for commercial helium processing. Elsewhere in the world, so far as known, natural gases are poor in helium. The occurrence of many of the rich helium gases in reservoirs lying close to the crystalline rocks strengthens the theory that the helium in some natural gases, at least, has been derived from the disintegration of the radioactive elements in the basement rocks.
Deep wells yielding natural gas rich in carbon dioxide are confined chiefly to the western part of the United States and to the Pánuco district, Mexico. The gas occurs in rocks ranging in age from Cambrian to Tertiary and probably originated from the metamorphism of basement rocks lying at relatively shallow depth, the oxidation of hydrocarbons through contact with mineralized waters, and the reaction of hot magmas on limestone.
Natural gas rich in hydrogen sulphide is produced chiefly from limestone in many areas, especially in the Permian fields of western Texas.
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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.