On a structural anomaly at Jackson, Mississippi, known since 1860, and surface structural closure proved in 1926, the first commercial gas well was completed in 1930. The proved and potential gas-bearing area should cover about 8,560 acres, and produce more than 128 billion cubic feet of gas. The gas reservoirs occur in the uppermost part of the Selma chalk (Cretaceous) and just below an unconformable contact with the Clayton limestone (Tertiary).
The initial well-head pressures were about 1,010 pounds per square inch; initial open-flow volumes ranged from 1 to 54 million cubic feet. The original water table, probably not horizontal, is believed to have been at about 2,200 feet subsea. Deliveries from 117 gas wells that are or were connected to pipe lines amount to 31,077 million cubic feet (from the date of discovery to September 26, 1934).
The Jackson gas field occurs on the top of a large uplift. Surface rocks, of Jackson age, show at least 325 feet of structural closure. More than 1,500 feet of structural closure are now known on the upper surface of the Selma chalk. On the highest parts of the uplift the Selma probably rests directly on igneous rocks of syenitic composition. No wells have been drilled through the Selma (normally about 450 feet thick) on top of the uplift. Flank wells encounter 320–450 feet of Selma and as much as 800 feet of Eutaw-Tuscaloosa. But wells drilled 160–300 feet below the crest of the uplift pass from Selma chalk into igneous rocks.
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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.