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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Document type:: Monograph

Structure type:: Chapter

Title:: Part V. Mineral fuels

Collection:: Economics Books

284 ECONOMIC GEOLOGY Seventh, suitable geological structures for the beds to act as oil reservoirs. Large areas of the earth can be dismissed as unlikely to yield oil, such as great massifs of plutonic rocks and areas of regional metamorphism and volcanic fields, unless they con- tain unaltered sedimentary rocks. Oil is found with different geological structures (Fig. 63, a-j). The first favourable position discovered was along an anticline. The early oil wells in Pennsylvania were sunk at random; certain lines were productive and were called “directive lines.” In 1859 Sterry Hunt recognized that they lay along the crests of anticlinals. He concluded (Canad. Na. vi, 1861, PP. 242, 250-1) that the oil had been concentrated along these upfolds, and he remarked we may reasonably expect to find others (i.e. good wells) along the line of the anticlinal or of the folds which are subordinate to it.” This view had been previously suggested for Burma by Oldham (1855, Mission Ava, p. 309). The anticlinal position is favourable in water-logged beds as the oil floats on the water and collects beneath an impermeable arch. Any natural gas present will collect at the top of the arch above the oil. If a bore pierces the impermeable beds of such an anticline the gas escapes first, the oil next, and water last (Fig. 63 a). Anticlines are especially favourable reservoirs because the oil beds are there nearest the surface and the oil is auto- matically discharged by the underlying water, Hence wells in anticlines are so convenient and economical that they are naturally sought for, and prospecting for oil has been described as simply prospecting for anticlines. A dome is even more advantageous, for the oil is compressed into a pool at its top. Nevertheless, the widespread expectation of * no anti- clinal no oil” is not justified. Oil is often absent from anticlines and found in synclines. In dry rocks owing to the absence of water-pressure, unless local heat raises gas- pressure, the oil works downward and collects in the trough or syncline. Even where anticlines are productive oil is often found along the synclines. In other fields, as in the Argentine and Colorado, the oil is dominantly synclinal. Oil is also largely found in beds with a uniform or homo-

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