Abstract
The reduction of sulphates in natural waters through the agency of sulphate-reducing bacteria with the generation of hydrogen sulphide has been thoroughly established by the work of many observers dating back to 1886. The situations in which such bacteria have been found include river muds, brackish canal muds, sewerage, soils, lake sands, dune sands at depths to 37 meters, black muds of the ocean bottom to depths of 16 fathoms, and bottom muds of the Black Sea to depths of 2,118 meters. Three species of sulphate-reducing bacteria have been isolated and described. Many of the waters associated with petroleum in oil pools are so low in sulphates as to indicate that a natural reduction of sulphates has been in progress. This fact has been recognized by several observers but the reduction was attributed by them to the petroleum, that is, to dead organic matter. Available experimental data fail to afford any evidence that dead organic matter is capable of reducing sulphates at ordinary temperatures although such reduction can proceed at high temperatures. With the usual precautions observed in bacteriological work, water samples were collected from thirty producing oil wells of Illinois ranging in depth from 400 to 1,866 feet and producing from Ordovician, Mississippian, and Pennsylvanian horizons. These waters were low in sulphate, and all but two carried sulphate-reducing bacteria. The active bacterium was isolated from pure cultures and photographed. The study was extended to the Sunset-Midway and Coalinga oil fields of California, and a sulphate-reducing bacterium was found to be abundant there in many of the low sulphate waters of oil wells producing from depths ranging from 760 to 3,090 feet. The productive horizons are Miocene and Pliocene. Waters of the eastern and deeper part of the Sunset-Midway field though low in sulphates do not at present carry sulphate-reducing bacteria although they may previously have done so. The temperatures of many of the California waters are higher than for the Illinois waters, 40°-47° C. being not uncommon. The sulphate-reducing bacterium of the California wells functions similarly in general to that in the Illinois waters but appears to be tolerant of higher temperatures. It has not et been isolated from pure cultures.
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