West of Mississippi River natural gas, in commercial quantities, was first discovered in Miami County, Kansas, in 1877. This and subsequent supply discoveries were from rocks, mostly sandstones, of Pennsylvanian age. As most of these sandstones are lenticular, few gas occurrences are controlled by folding. It is estimated that about 350 square miles of gas-bearing rocks have been discovered since 1900.
Occurrences of natural gas in rocks of Pennsylvanian age in eastern Kansas are here, for analytical purposes, divided into post- and pre-Fort Scott. The supply contributed by post-Fort Scott rocks has been small, but pre-Fort Scott rocks have been the major source of natural gas supply. The pre-Fort Scott section of Pennsylvanian rocks is divided into an upper and a lower division. The upper division, consisting of the upper 350 feet of Cherokee formation, covers all of eastern Kansas. In its upper 50 feet are found most of the gas- and/or oil-bearing shoestring sandstone bodies; in the lower part the oil-bearing sandstones of Greenwood and Butler counties. The supply of gas from these formations has not been of major importance. The lower division, with a maximum thickness of about 300 feet, contains many large sandstone bodies (also lenticular) from which natural gas was the dominant product. The important fields, producing gas from the lower division, were located in Allen, Neosho, Wilson, Montgomery, and Labette counties. They are now either abandoned or nearly exhausted.
At the contact between the Pennsylvanian and Mississippian systems occurs the Burgess (Hogshooter) sandstone. This sandstone, also lenticular, is extremely erratic in distribution. Where productive, notably at Elk City in Montgomery County, it is very prolific but short-lived.
Limestones in the upper 50 feet of the Mississippian system have produced gas in eastern Kansas, notably in Elk and Chautauqua counties on the Longton anticline.
Rocks of Ordovician age have yielded very little gas in eastern Kansas.
Occurrences of gas in post-Fort Scott rocks are up-dip accumulations, commonly found on plunging anticlines or domes. In pre-Fort Scott sandstones, the entire body may be gas-filled with bottom water, if it parallels isopach lines of the Cherokee formation, but it may be distinctly up-dip with edge and bottom waters where the body pitches with the regional dip. The upper surfaces of pre-Fort Scott sandstone bodies show structural closure (lenticularity) ; the overlying Fort Scott limestones usually show a similar structure, but the underlying Mississippian rocks are usually undisturbed excepting for regional tilting and warping. Gas-bearing areas in rocks of Mississippian age are restricted to anticlines and domes, most of which were folded and partly eroded before deposition of Cherokee sediments. The thickness of Mississippian rocks is everywhere reduced over these folds.
Most of the important gas fields in Kansas were discovered and developed prior to the use of surface or subsurface geology. A few important gas fields have been found on surface structure forms, notably at Elk City in Montgomery County; a few were recognized as major subsurface folds before their importance as gas fields was known, notably the Longton anticline.
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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.