Intermittent Flowing Wells. Where the oil and gas-pressure has diminished on steadily-flowing wells, they often flow for some time at intervals, maintaining a steady production. Many wells in the older fields start their initial production in this way. Enough oil accumulates in the column of casing to hold down the gas temporarily, causing the pressure to rise, and the tents to discharge through the lead line. The gas continues blowing after the oil has been expelled, until such time as the oil rises high enough in the casing. Then, after a period of quiet, the flow is repeated. Eventually the gas pressure becomes so low that other means must be resorted to for inducing the flow.
Artificial Flowing of Oil Wells. In some localities, particularly where the gravity of the oil is low, the oil-string is pulled back to the top of the sand and the next smaller size inserted to the bottom. The latter, called the 'agitating-string,' is moved up and down by the calf wheels through a space of 50 or 75 ft. in order to enliven the gas, thus making a flow by capillary attraction in the small annular space between the strings. A tee is placed on the oil-string with a stand-pipe sufficiently high to prevent the oil running over, thus forcing it through the lead-line to storage. Where the gravity is light, the oil-string can be pulled back to the top of the sand and set on packing clamps, upon the next larger string, the latter having a collar (Fig. 137) with two 2-in. holes tapped and threaded, into which the lead-lines are screwed.
It is not unusual to see a well flowing between the strings at the same time that pumping is being carried on inside the oil string. A packing-clamp is also made similar to a stuffing box; it is screwed into the collar of the next larger size of pipe and the oil-string raised or lowered through it for 'agitation' purposes.
The swab is often used to start the flow by being run into the well and rapidly withdrawn. With two ropes, a column of from 1600 to 1800 ft. of fluid can be lifted, but only in screw casing, as the inside lap of stove-pipe casing would cause ex cessive leakage. The swab (Figs. 138 and 139), which is run on the stem, has a rubber ring placed over 3-in. pipe, the latter threaded at the lower end to permit tightening to expand the rubber to the bore of the casing. Holes are drilled through the body to communicate with the 3-in. pipe in order to permit pas sage of the oil when the swab is being run in. A vertical check-valve is attached to the bottom to prevent leakage when lifting the column. Swabs are also used to clear the perforations by drawing the sand or shale into the casing where it can be bailed or drilled out.
Bailing is often successful in inducing a well to flow, the bailer being run to bottom and rapidly withdrawn. This agitates the gas and causes the oil to flow. Again, a 2 or 3-in tubing with a packer (Figs. 140 and 141) is placed at a safe distance from the bottom to prevent its becoming sanded. The oil will then rise in the smaller column and often flow steadily. Care should be taken in placing the packer that no leakage occurs around it or that no passages are cut through the rubber later on, for once sand gets above it, considerable risk is at tached to its withdrawal from the well. In
fact, many operators prefer running on the tubing a swage-nipple of nearly the same diameter as the oil-string instead of the packer, for this reason.
Pumping. When a well has ceased flowing, or cannot be made to flow by reason of a low gas-pressure when the sand is first struck, it is usually put to pumping. This is the common method of extracting oil from the wells through out nearly all fields. Pumping is ac complished by means of a deep-well pump, which is lowered on tubing to a sufficient depth to insure ample submer sion, but in wells where the production is light the walking beam need only be run at intervals as the oil accumulates. The size of the tubing is generally 3-in. with 11%-thread couplings, although 2 to 4 in. is used, the latter having 8-thread couplings. All tubing is heavier than the same sizes of line-pipe, and wells 4000-ft. deep may be pumped with profit. The actual lift of fluid, however, should not exceed 3000 ft., for at deeper levels the strain on the equipment is excess ive, and parting of rods or tubing might result.
The pump or working-bar rel is from 3 to 20 ft. long, 6 ft. being the common length (Fig. 143). For a 3-in. work ing-barrel, the inside bore is 2/ in., some manufacturers using a liner of this size rather than to bore the bar rel itself. A hollow steel plunger, which closely fits the barrel, is equipped with a valve at the top, while a nut is screwed into the lower end, which supports the gar butt-rod when pulling the sucker rods. The garbutt rod, 3A in. by 3 ft., has a (three-winged nut at its up per end which rests upon the (nut of the barrel. The lower end of the garbutt-rod is connected to the lower or standing valve and lifts the latter from its seat when the sucker-rods pull the plunger from the barrel. The stand ing valve is securely seated upon a beveled shoe or shoul der at the bottom of the working-barrel, having a long tapered sleeve for this purpose. Each valve consists of a round steel ball resting upon a seat and has three or four-wing cages to allow the balls the necessary play, at the same time acting as guides for their proper seating. The valves act as an ordinary check-valve when pumping is in progress, the 3-in. seat having an opening of inches. Some operators use two and often three balls when pumping wells making quantities of gas, the latter often holding the balls up and preventing the valve from lifting. In the eastern as well as some of the southern fields of the United States, where the percentage of sand is small, an upper valve as shown in Fig. 144, is substituted for the steel plunger. These valves have leather or linen rings as in the Lewis or Kinney pattern, or are wound with cotton or hemp rope as in the Landas pattern. 'Valves are also made which have a spring to keep the cups tight, expanding them fully to the working barrel. The Parker valve (Fig. 145) differs from the ordinary valve in that a plunger draws the valve up against the seat, which is placed above, making a positive action which is often successful in heavy gas-pressures as well as in handling sand.