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Rh admit of sand-pumping. The drill is thus allowed to fall freely, instead of being partly upheld by the buoyancy of the water, as in earlier wells.

Wells in Pennsylvania now range in depth from 300 ft. to 3700 ft. Four strings of iron casing are usually employed, having the following diameters: 10 in, 8 in., 6 in. and 5 in., the lengths of tube forming the casing being screwed together. Contractors will often undertake to drill wells of moderate depth at 90 cents to $1 per foot, but the cost of a deep well may amount to as much as $7000.

The rotary system of drilling which is in general use in the oilfields of the coastal plain of Texas is a modification of that invented by Fauvelle in 1845, and used in the early years of the industry in some of the oil-producing countries of Europe. It is one of the most rapid and economical which can be employed in soft formations, but where hard rock

is encountered it is almost useless. The principle of this system consists essentially in the use of rotating hollow drilling rods or casing, to which is attached the drilling-bit and through which a continuous stream of water, under a pressure of 40 to 100 ℔. per sq. in., is forced.

The yield of petroleum wells varies within very wide limits, and the relative importance of the different producing districts is also constantly changing. I. C. White, state geologist of West Virginia, estimates that in fairly good producing sand a cubic foot of rock contains from 6 to 12 pints of oil. He assumes that in what is considered a good producing

district the amount of petroleum which can be obtained from a cubic foot of rock would not be more than a gallon, and that the average thickness of the oil-bearing rock would not exceed 5 ft. Taking these figures as a basis, the total yield of oil from an acre of petroliferous territory would be a little over 5000 barrels of 42 U.S. gallons.

A flow of oil may often be induced in a well which would otherwise require to be pumped, by preventing the escape of gas which issues with the oil, and causing its pressure to raise the oil. The device employed for this purpose is known as the water-packer, and consists in its simplest form of an india-rubber ring, which is applied between the tubing and the well-casing, so that upon compression it makes a tight joint. The gas thus confined in the oil-chamber forces the oil up the tubing.

For pumping a well a valved working-barrel with valved sucker is attached to the lower end of the tubing, a perforated “anchor” being placed below. The sucker carries a series of three or four leather cups, which are pressed against the inner surface of the working barrel by the weight of the column of oil. The sucker is connected by a string of sucker-rods with the walking beam. There is usually fixed above the sucker a short iron valve-rod, with a device known as a rivet-catcher to prevent damage to the pump by the dropping of rivets from the pump-rods.

On the completion of grilling, or when the production is found to decrease, it is usual to torpedo the well to increase the flow. The explosive employed is generally nitroglycerin, and the amount used, has been increased from the original 4 to 6 quarts to 60, 80, 100 and even 200 quarts. It is placed in tin canisters of about 3 to 5 in. in diameter and

about 10 ft in length The canisters have conical bottoms and fit one in the other. They are consecutively filled with nitroglycerin, and are lowered to the bottom of the well, one after the other, by a cord wound upon a reel, until the required number have been inserted. Formerly the upper end of the highest canister was fitted with a “firing-head,” consisting of a circular plate of iron, slightly smaller than the bore of the well, and having attached to its underside a vertical rod or pin carrying a percussion cap. The cap rested on the bottom of a small iron cylinder containing nitroglycerin. To explode the charge an iron weight, known as a go-devil, was dropped into the well, and striking the disk exploded the cap and fired the torpedo. Now, however, a miniature torpedo known as a go-devil squib, holding about a quart of nitroglycerin, and having a firing-head similar to that already described, is almost invariably employ ed. The disk is dispensed, with, and the percussion cap is exploded by the impact of a leaden weight running on a cord. The squib is lowered after the torpedo, and, when exploded by the descent of the weight, fires the charge. It must be borne in mind that although the explosion may increase the production for a time, it is by no means certain that the actual output of a well is increased in all such cases, though from some wells there would be no production without the use of the torpedo.

The petroleum industry in Canada is mainly concentrated in the district of Petrolea, Ontario. On account of the small depth of the wells, and the tenacious nature of the principal strata bored through, the Canadian method of drilling differs from the Pennsylvanian or American system in the following particulars:—

1. The use of slender wooden boring-rods instead of a cable. 2. The employment of a simple auger instead of a spudding-bit. 3. The adoption of a different arrangement for transmitting motion. 4. The use of a lighter set of drilling tools.

Although petroleum wells in Russia have not the depth of many of those in the United States, the disturbed character of the strata. with consequent liability to caving, and the occurrence of hard concretions, render drilling a lengthy and expensive operation It is usual to begin by making an excavation 8 ft. in diameter and 24 ft. in depth, and lining the sides of this with wood or brick. The initial diameter of the well drilled from the bottom of this pit is in some instances as much as 36 in., bore-holes of the larger size being preferred, as they are less liable to become choked, and admit of the use of larger bailers for raising the oil.

The drilling of wells of large size requires the use of heavy tools and of very strong appliances generally The system usually adopted is a modification of the Canadian system already described, the boring rods being, however, of iron instead of wood, but the cable s stem has also to some extent been used. For the ordinary 2-in. plain-laid manila cable a wire rope has in some cases been successfully substituted.

Rivetted iron casing, made of -in. plate, is employed, and is constantly lowered so as to follow the drill closely, in order to prevent caving. Within recent years, owing to the initiative of Colonel English, a method of raising oil by the agency of compressed air has been introduced into the Baku oil-fields.

In Galicia the Canadian system is nearly exclusively adopted In some instances under-reaming is found necessary. This consists in the use of an expanding reamer by means of which the well may be drilled to a diameter admitting of the casing descending freely, which obviously could not be accomplished with an ordinary bit introduced through the casing. Of late years the under-reamer has been largely superseded by the eccentric bit.

The Davis calyx drill has also been employed for petroleum drilling. This apparatus may be described as a steel-pointed core drill The bit or cutter consists of a cylindrical metallic shell, the lower end of which is made, by a process of gulleting, into a series of sharp teeth, which are set in and out alternately. The outward set of teeth drill the hole

large enough to permit the drilling apparatus to descend freely, and the teeth set inwardly pare down the core to such a diameter as will admit of the body of the cutter passing over it without seizing. The calyx is a long tube, or a series of connected tubes, situated above the core barrel, to which it is equal in diameter.

In conclusion it may be stated that the two systems of drilling for petroleum with which by far the largest amount of work has been, and is being done, are the American or rope system, and the Canadian or rod system. The former is not only employed in the United States, but is in use in Upper Burma, Java, Rumania and elsewhere. The latter was

introduced by Canadians into Galicia and, with certain modifications, has hitherto been found to be the best for that country. A form of the rod system is used in the Russian oil-fields, but owing to the large diameter of the wells the appliances differ from those employed elsewhere.

The wells from which the supplies of natural gas are obtained in the United States are drilled and cased in the same manner as the oil wells.

Transport and Storage.—In the early days of the petroleum industry the oil was transported in the most primitive manner. Thus, in Upper Burma, it was conveyed in earthenware vessels from the wells to the river bank, where it was poured into the holds of boats. It is interesting to find that a rude pipe-line formerly existed in this field for conveying the crude oil from the wells to the river; this was made of bamboos, but it is said that the loss by leakage was so great as to lead to its immediate abandonment on completion. In Russia, until 1875, the crude oil was carried in barrels on Persian carts known as “arbas.” These have two wheels of 8 to 9 ft. in diameter, the body carrying one barrel, while another is slung beneath the axle. In America, crude petroleum was at first transported in iron-hooped barrels, holding from 40 to 42 American gallons, which were carried by teamsters to Oil Creek and the Allegheny River, where they were loaded on boats, these being floated down stream whenever sufficient water was present—a method leading to much loss by collision and grounding. Bulk barges were soon introduced on the larger rivers, but the use of these was partially rendered unnecessary by the introduction of railways, when the oil was at first transported in barrels on freight cars, but later in tank-cars. These at first consisted of an ordinary truck on which were placed two wooden tub-like tanks, each holding about 2000 gallons; they were replaced in 1871 by the modern type of tank-car, constructed with a horizontal cylindrical tank of boiler plate.

The means of transporting petroleum in bulk commonly used at the present day is the pipe-line system, the history of which dates from 1860. In that year S. D. Karns suggested laying a 6-in. pipe from Burning Springs to Parkersburg, West Virginia, a distance of 36 m.; but his proposal was never carried into effect. Two years later, however, L. Hutchinson of New York, laid a short line from the Tarr Farm wells to the refinery, which passed over a hill, the oil being moved on the syphon principle, and a year later constructed another three miles long to the railway. These attempts were, however, unsuccessful, on account of the excessive leakage