It is a well-known fact that oil, as well as natural gas, is usually under more or less pressure within the earth. The pressure is so great in some cases that where, in the course of drilling, oil or gas accumulated under proper conditions, as for example those shown by [Figure 79], are encountered the pressure may be hundreds of pounds per square inch, or enough to blow to pieces much of the drilling outfit. It is under such conditions that great “gushers” are struck. A wonderful case in point was the famous Lakeview gusher, struck in California in 1910. “Within a few days the well was far beyond control. It continued to flow (for a time shooting high into the air) for eighteen months, finally stopping after it had produced over 8,000,000 barrels of oil, about 6,000,000 of which had been saved. The daily production of the well varied greatly, reaching a maximum of 65,000 barrels.” (Pack.) One very common cause of oil pressure is the expansive force of the associated imprisoned gas which steadily increases as the gas is generated. Another cause which is seemingly applicable in many cases is hydrostatic pressure, where under certain structural conditions the pressure of water in a long-tilted layer is exerted against oil accumulated toward the top of an anticline (or upbend) in the strata.
The world’s output of petroleum for 1917 was nearly 559,000,000 barrels, of which the United States produced nearly 338,000,000 barrels, Mexico 87,000,000 barrels, and Russia 34,000,000 barrels of 42 gallons.
Natural Gas. The most perfect fuel with which nature has provided us is natural gas. Not only is it easily transported even long distances through pipes, but also as a fuel it is easily regulated, leaves no refuse, and is less damaging to boilers than coal. It is a colorless, odorless, free-burning gas, consisting very largely of the simple hydrocarbon called marsh gas or fire damp. Petroleum nearly always has more or less natural gas associated with it, but in some cases considerable quantities of gas may exist alone. Natural gas, like petroleum, is of organic origin—a product of slow natural distillation of vegetable or animal matter, or both, within the earth’s crust.
One of the most common modes of occurrence of gas is at the top of an anticline (upfold) in porous rock (like sandstone) between impervious layers (like shale). [Figure 79] well illustrates the principle, the gas lying above the oil, and the oil above the water; that is, the three substances are arranged according to specific gravity. Gas may also exist in considerable quantities in irregular bodies of porous or fractured rocks. Natural gas is nearly always under pressure within the earth, hundreds of pounds per square inch being common, while more exceptionally, as in certain West Virginia wells, pressures of over 1,000 pounds have been registered.
The United States is by far the greatest world producer of natural gas, the output for 1918 having been 720,000,000,000 cubic feet. West Virginia easily headed the list, with Oklahoma and Pennsylvania next in order. Areas underlain with natural gas are, in the main, the same as for petroleum, and they total more than 10,000 square miles. During the last forty years the waste of natural gas in the United States has been appalling. In many cases wells in quest of oil have encountered gas and often such abandoned wells have been allowed to play millions of cubic feet of gas daily into the air for years. A striking example was the Murraysville well of western Pennsylvania, which shot 20,000,000 cubic feet of gas per day into the air for six years!
METAL-BEARING (ORE) DEPOSITS
Iron. Without question the most useful of all metals is iron. As such it is rare in nature, but in chemical combination with other substances it is extremely widespread and very common. Iron makes up about 5 per cent of the weight of the earth’s crust, but in the form of ore (i.e., a metal-bearing mineral or rock of sufficient value to be mined) it is notably restricted in occurrence. The three great ores of iron are the minerals hematite, magnetite, and limonite, whose composition and characteristic properties the reader will find stated in the preceding chapter on “Mineralogy.”
One of the worst impurities in iron ore is phosphorus, which makes iron “cold short,” i.e., brittle when cold. Ore for the manufacture of Bessemer steel must contain very little phosphorus (less than 1/1000 of the metallic iron content of the ore). Sulphur as an impurity in the ore tends to make the iron “hot short.” Silica (quartz) is bad because it necessitates the use of more lime for flux in the furnace.
Iron ores occur in rocks of most of the great geologic ages, but in the United States principally in the pre-Paleozoic and Paleozoic. The United States is by far the greatest producer of iron ore in the world, the output for 1917 having been about 75,288,000 tons, the greatest in the history of this or any other country. This one year’s output loaded into cars of 40 tons capacity would have made a train about 15,000 miles long! All but about 5,000,000 tons of this tremendous production was hematite ore. In 1919 the output of iron ore dropped to about 60,000,000 tons.