Engineering Wonders of the World
Volume I

328 ENGINEERING WONDERS OF THE WORLD. INTERIOR OF A DERRICK, SHOWING ENGINE AND DRILLING TACKLE. A, the huge auger used for the uppermost sections of the wall. provision has to be made for removing the latter. This is done by means of a long baler Removing- Sludge. or piece of pipe with a drop- valve at the bottom. A wire rope is attached to the upper end of the baler, and the drum hold- ing the rope is worked by friction off the belt wheel on the crank shaft already men- tioned. Every time a few feet have been drilled the tools are pulled out and the baler is lowered. When the hole has been cleaned a barrel or two of water are poured down and drilling recommenced. The depth, to which drilling can be con- tinued without the walls falling Lining1. . . m necessarily depends on the nature of the strata perforated. When caving becomes troublesome, it is necessary to line the well with iron or steel casing. Drilling is then carried on with a smaller size of bit until the ground again begins to give way, when another column of pipes has to be lowered. Thus, to finish a well of, say, 1,500 feet depth may require as many as five different strings of casing ranging from 12| to 4j inches in diameter. Except when these are required for shutting off water, they may all be pulled out except the last one, which is left in the oil sand. The appearance of a well before the casing is removed may be likened to a telescope with the eyepiece buried in the ground. On the Russian fields enormous quantities of casing are required, owing to the loose nature of the ground. In certain sections, where the strata are particularly troublesome,