The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part V. Mineral fuels

Collection:: Economics Books

286 ECONOMIC GEOLOGY empty, and only an uncertain percentage of the oil is re- coverable. It is generally considered that under present conditions only from 10 to 20 per cent. of the oil in a bed is obtained, and that most fields, except under heavy water- pressure, do not yield more than 10 per cent. The life of a field can therefore be prolonged by an improvement in the recovery factor, either by more vigorous pumping, by the explosion of a torpedo at the bottom of a well to open up the fissures and to secure the better drainage of the ad- jacent beds, or by the increase of gas-pressure either by raising the temperature or by forcing down compressed air. The second, and more reliable method of estimating the oil reserves of a field is by the decline in yield of the wells. (Cf. Tables by C. H. Beal, U.S. Bur. Mines, Bull. 177, 1019). The output of a well is usually greatest when it is first opened ; the fall in yield is rapid during the first few weeks ; and the quick fall during the first year passes into a gradual decline. In the Oklahoma field, e.g. if the yield of a well in the first year is taken as I, in the second year it would be from 23 to -75, and the total yield would be 2 or 3. In California if the yield of a well in the first year is I, in the second year it is +75, and the total is 5. For most fields a diagram can be prepared showing that as the well approaches exhaustion the decline is very slow, so that after the large yield a small supply can be obtained for years by pumping at appropriate intervals, say for an hour a day or at intervals of a week. The future supply from a field can be estimated from its ** decline curves.” The different oilfields of the world are under such different conditions that a geographical summary is more useful than a systematic classification. THE O1LFIELDS OF THE UnrTED Stares—The oilfields of the United States had yielded by June, 1926, over 9000 million barrels of oil, and they contribute about 70 per cent. of the world’s supply. The eastern or Appalachian fields were the first discovered. Petroleum had long been known there to the Indians and a little was found in Pennsylvania while boring for brine between 1790 and 1820. The modern development of the American oil industry dates from 23rd August, 1859, when

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