Engineering Wonders of the World
Volume I

ENGINEERING IN THE WORLD’S OIL FIELDS. 329 DRIVING DOWN A LENGTH OF WALL LINING, L, BY MEANS OF A HEAVY WEIGHT, M. wells have to be started with casing 36 inches in diameter, and as much as 150 tons of different-sized casing may be required to drill a well 2,000 feet deep. At £12 a ton this is equivalent to £1,800. It is therefore important to recover as much of the metal as possible when a well has been completed, and to this end special ap- paratus is provided for cutting off the portion of each column extending above the base of that encircling it and drawing it out. Never- theless in the Baku fields some £7,200,000 worth of casing—all irrecoverable—has been sunk into an area of four square miles, and this total increases by 40,000 tons annually. The cost of, and the time occupied by, the sinking of a well necessarily depend upon the depth of the oil-bearing bed, the nature of the ground, and a number of other things. In some oil fields a well i ixi* p Cost of may be completed in a few Drilling- days at a cost of several hundred pounds. At Baku a boring of 2,000 feet may represent the expenditure of £10,000 and two years of time. One trouble that always threatens the driller is the possibility of losing his instru- ments through the cable or rods breaking, or the joints of the tools becoming unscrewed. No drilling plant can be considered complete which does not include a set of instruments designed for recovering, or, as it is usually called, fishing for, lost tools. Even with these it is sometimes found necessary to construct