Page:International Library of Technology, Volume 93.djvu/94

 of the Caspian Sea, those in Western Pennsylvania and California, and the recently opened Texas deposits.

31. In Pennsylvania, New York, and West Virginia, petroleum is found in sandstone of various geological formations in the shape of several distinct layers, known as the first, second, third, fourth, and fifth oil sands. Wells of various depths are thus found; while a well, say 60 or 70 feet deep, may be drilled to the first sand and produce oil; another must perhaps be drilled to the third or fourth sand before oil is found, and may be 600 feet or more deep.

32. Petroleum was at first gathered from shallow wells and from excavations in the neighborhood of deposits close to the surface. The latter were usually filled indirectly from natural-flowing wells close by. It was later found that, by boring, there could be produced artesian oil wells whose daily output of oil was enormous. An artesian oil well is one in which the oil rises to the surface without having to be pumped; quite frequently it jets out in the form of a fountain many feet in height. The Droobja fountain in the Russian Caucasus spouted up to a height of between 200 and 300 feet, while the Markoff fountain sent up a column of oil mixed with sand 400 feet high. In the Pennsylvania oil fields, the driller has often had his set of heavy iron tools thrown out of the well by the rush of gas and oil.

The great waste that was formerly caused by the oil flowing away on the surface of the ground is now avoided. The driller has a cap prepared beforehand, placing it on top of the well very soon after the first flow of oil. In course of time, the pressure that causes the oil to rise to the surface subsides, and the oil has to be pumped from below the surface.

33. Petroleum, as usually found, comes from beds of sand, or porous rocks of various kinds, where, in the little crevices and spaces, it has found room for storage. In many cases, it has not been formed there, but has been forced in by pressure from the original deposit. These reservoirs are called secondary deposits^ the sand or loose rock being often found in crevices of the harder rocks, so that very often,