This paper describes the gas pools in the belt of mountain folding comprising the Arbuckle and Wichita Mountains of Oklahoma and the area between and south of these ranges.
In that area there are now 22 separate pools which have yielded natural gas and from which gas has been sold in commercial quantity, and 19 oil pools which have produced gas for field use only. All of the gas pools have produced oil also, and in most of them the oil produced has been of much greater value than the gas. In all of the oil fields, casinghead gas from oil wells has been utilized for local power, heat, and light in the fields.
Although their gas yield has been overshadowed by the much greater importance of their oil production, these 22 gas pools have sold to outside consumers to January 1, 1932, more than 200 billion cubic feet of gas, for which the producers have received approximately $20,000,000. This is about 5 per cent of the total amount of natural gas produced and sold to that date in Oklahoma, and not quite 1 per cent of the total for the United States. It is believed that at least 100 billion cubic feet of additional gas has been used in the oil and gas fields of southern Oklahoma for local purposes.
The known reserves of gas in this area, in sandstones now developed, probably do not exceed 50 billion cubic feet. But this region is believed to contain larger untapped reserves of both gas and oil than any other part of Oklahoma, both in additional pools not yet discovered, and (still more certainly) in deeper sandstones not yet reached, in fields already producing. Although in most of the pools in other parts of the state, the entire sedimentary section, or all of it that is believed to be worth testing, has already been tested by the drill, in many of the pools of southern Oklahoma the surface has hardly been scratched. There is here the thickest sedimentary section (a maximum of 25,000 feet) in the Mid-Continent oil region; and in some of these pools the drill has not yet penetrated one-fourth of the thickness. No test has been drilled deeper than 5,300 feet in any producing area discussed in this paper, and in several pools the deepest test is still far above the base of the Pennsylvanian system, beneath which lie, where the section is complete, 10,000–14,000 feet of older sedimentary rocks.
Stratigraphically, the area covered by this paper comprises the western extremity of the Ouachita geosyncline, and was exceptionally active in accumulation of sediments during Ordovician and Pennsylvanian time. Structurally, it differs from the other parts of the Mid-Continent region in having been subjected to close folding. This folding was accomplished in Pennsylvanian time as a part of the orogenic system then extending from Colorado and northern New Mexico southeastward to the Ouachita Mountains or beyond.
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Geology of Natural Gas
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.