The Elements of economic geology

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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

288 ECONOMIC GEOLOGY after nine years unsuccessful drilling, the Lucas * gusher ” in January, 1901, discharged 700,000 barrels of oil before it could be controlled ; it yielded 17 million barrels in 1902 ; it is also historically important as it provided the clue to the Mexican oilfields. The Rocky Mountain oilfields extend from Montana through Wyoming into Colorado. The rocks range from the Cambrian to the Cretaceous or occasionally Eocene, and have been bent into broad folds. Oil is sometimes found in an anti. cline, as in the Labarge field in Wyoming, although it contains no water and the oil is therefore not forced upward by water-pressure (cf. Schultz, U.S.G.S., Bull. 340, 1908, P. 369). In some of the fields, as in the Cretaceous of Mon- tana, the oil is found on the margins of synclinals, The Colorado fields are also in the main synclinal. The Florence oilfield (cf. Fig. 64, b), which by 1892 had yielded 95 per cent. of the Colorado oil, was discovered in the search for water. It is in a great elliptical syncline of Jurassic and Cretaceous rocks, the centre of which must be 8000 feet deep. A little oil comes from the Jurassic, but the bulk is from the Cre- taceous Pierre clays. The deepest well is 3650 feet, and the oil does not appear to occur lower as the slope below is too gentle to maintain the flow of the oil ; it collects at the foot of the steeper part of the syncline, in sandstone lenticles, which are separate as wells even 25 feet apart are fed in- dependently. The oil is obtained by pumping and wells paid with the yield of about 7 to8barrelsa day. The Range- ley field, also in Colorado, occurs in Jurassic or Cretaceous beds in an anticline and the wells occur in pockets in the Mancos Shale, Cretaceous (H. S. Gale, U.S.G.S., Bull. 350, 1908, pp. 44-6). California has made a sensational but anticipated addition to the American oil supply, the output being raised to 263 million barrels in 1923. Wells have been sunk to the depths of over 8300 feet. The Kainozoic rocks range from Eocene to Pleistocene, and are 34,000 feet in thickness, of which 20,000 feet are Miocene ; their oil is derived from the distilla- tion of the soft tissues of foraminifera, diatoms, etc. Some of the oil comes from the underlying Cretaceous beds. The structures of the Californian fields differ greatly. The central field near Coalinga yields oil from lenticles of sandstones

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