When the plunger becomes worn, production gradually lowers to a point where a renewal of the pump is necessary. Nearly all oil carries with it more or less sand, which cuts and wears the plungers rapidly. Many wells, particularly in the fields of the Eastern and Southern United States, may be pumped for long intervals before renewals are required, while in some of the Western fields, it is not uncommon for the pump to last only a few days. A pulling-gang of three or four men is kept by every oil company to perform this work. When 'pulling' a well, the beam is 'taken down' by disengaging the pitman from the crank and lowering the end of the beam which points towards the engine house, so that the end inside the derrick swings up and is out of the way. The rods are pulled, including both valves, three joints at a time. The tubing is pulled in stands of three joints and stood back in the derrick. This work requires the better part of a day where the well is being pumped at a depth of 2000 ft. Should the pump 'sand up,' the plunger is held fast so the rods and tubing are pulled together. This is a disagreeable task, as the tubing is always full of fluid and when a stand is unscrewed, the oil spurts over the floor. The bull-wheels are used for this character of work, except in deep holes, where the calf-wheels are sometimes employed.
Many pumping-wells do not throw oil out of the lead-line at every stroke of the beam, for the gas usually expels the contents of the tubing at intervals when the weight of the column of oil has been reduced sufficiently by the gas to cause a flow. The sucker-rods by their movement, keep the gas agitated and cause the flow to be re peated, the valves often working intermittently to raise the oil. Again some wells will make a small production through the tubing without aid from the pump, while others require a constant agitation of the gas to cause the well to flow. Only by experimenting with each individual well can the right method be determined for obtaining the maximum production. One well may produce satisfactorily with a packer or swaged nipple, another by compressed air, while a neigh boring well may use pumps to the best advantage. There is no set rule as to the depth to tube a well for pumping, but in most instances the tubing should be lowered as near to bottom as possible without danger of 'sanding up' the pump. Many wells, however, make more oil when pumped a hundred feet or so from the sand, while a few may require tubing several hundred feet up to obtain any production whatever. Sand-plugs or 'bridges' make their appearance in produc ing-wells and are removed from the casing by bailing or drilling. The forms of bailers shown in Figs. 156 and 157 are successful for getting out the sand. The presence of water in the well is always a source of expense and annoyance, for it aids in bridging the sand and plugging the pump. Gas pockets often form in the pump-chamber, interfering with the action of the valves by being alternately ex panded and compressed. This condition is hard to overcome, the gas-anchor not always preventing admission of gas to the working barrel. Constant improvements, however, are being made and it is to be hoped that this trouble will finally be eliminated.
Multiple Pumping. For pumping deep wells and wells which give considerable trouble from sanding, the walking-beam is used with steam, gas engines or electric motors, for power. Where the wells are grouped, particularly in shallow territory, it is customary to install multiple pumping-powers. The ordinary power (Fig. 158) consists of a horizontal shaft which, through bevel gearing, drives a vertical shaft upon which is placed one or more eccentrics. Holes are bored
in the outer flanges of the latter, to which the jerker, or transmis sion-line leading to the well is attached. The jerker-line is pulled a distance corresponding to the throw of the eccentric at each revolution, producing a horizontal stroke of from 18 to 30 inches. The power is furnished by steam, gas engine, or motors and can be arranged to pump as many as 25 1600-ft. wells or 18 2500-ft. wells. The jack, made of iron or wood (Fig. 159), is placed over the'well at the der rick-floor and securely fastened to the casing head or floor. The horizontal motion imparted by the jerker-line is changed to a recipro cating vertical motion (Fig. 160). Multiple pumping, wherever prac ticable, reduces the cost of producing oil very materially.
Compressed Air. The use of compressed air as a medium of lifting the oil has found favor in many oil fields, especially where the encroachment by water has rendered it impossible to obtain production by plunger-pumping or other means. The air-lift, however, is not sat isfactory for raising oil of heavy gravity. The oil is so viscous that the air collects in large globules and finally 'blows through' the fluid without carrying the oil with it. On light-gravity wells, or on wells where the percentage of water is high, it works successfully, main taining a large production at low cost. A slight drop in gravity gen erally results when a compressor is ii.sed. The ordinary compressor for blowing wells is of the compound type, capable of a maximum pressure of at least 500 lbs. and with a working of 350 lbs., while the output of air is about 300 cubic ft. of free air per minute under nor mal conditions. 'Mr. Edward A. Rix* says: "In a test of air-lift systems in the Kern River field made by the Peerless company, pumping 'a mixture of water with 20% oil at an average lift of 470 ft., with an average submergence of 40% and an average length of discharge pipe of 800 ft., they found as the average of many tests, air-pressure, 152 lb.; free air per minute, 140 cu. ft. ; gallons of fluid per minute, 93 ; cubic feet of free air per gallon of fluid, 1.5; ratio of free air to fluid pumped, 11. Ninety-three gallons of fluid per minute is equivalent to 3400 bbl. per day. The above pumping was done through 3-in, tubing with PA-in. air pipes, and both the straight air systems and also two other so-called patented systems, with the result that no gain was shown by the patented sys tems; and while on this subject it might be well to say that one well was piped as many as thirteen times, using the straight air system and after each piping better results were shown; in fact, the variation in pipe sizes and ratio of submergence, all within reasonable limits, show a marked variation in economy. The results show conclusively that the ratio of submergence, but also the relative amounts of air and water being pumped influence the economy ; the gravity of oil also offers its troubles, and there is, over and above all these, the question of the size of the discharge pipe for the fluid, and it is a vital question. Too large a pipe is fatal, because the air slips by ; too small a pipe is equally bad, because the air escapes and the expansion is checked. The proper size is a matter of experience based on an average velocity of from 6 to 8 ft. per second in the pipe or about 12 to 18 gal. per square inch of area of discharge pipe." Various forms of air-lifts have been tried out, A. Beeby Thompson having successfully used an apparatus (Fig. 161) in which 4-in.