## 4645

where Rt is the total length of rod string in 1000 feet (kilometers).

sucker rod stretch, tubing shrink The sucker rod stretch starts when the plunger starts its upstroke and the fluid load is transferred from the tubing string to the sucker rod string. This occurs when the standing valve opens and the traveling valve closes. As the sucker rod string lengthens, the tubing string shortens. Both result in a stroke loss. The stroke loss due to rod stretch is shown in Table 2 as factor C, and the stroke loss due to tubing shrink is shown in Table 5 as factor K. Both are in inches per 1000 feet per 1000 pounds load (millimeters per kilometer per kilonewton).

net plunger stroke The formula below illustrates a method of computing the net plunger stroke for a tapered string of 1-, and f-in (25.4-, 22.2- and 19.0-mm) rods with the tubing suspended freely. If the tubing is anchored to the well casing near the pump, the KRt factor will be zero.

In USCS units Lp = L + OT - (CR1 + CR2 + CR3 + KRt)Wf X 10-3 In SI units Lp = L + OT - (CR1 + CR2 + CR3 + KRt)Wf X 10-6 where Lp = net plunger stroke, in (m)

R1 = length of f-in (19.0-mm) rods, 1000 ft (km) R2 = length of 7-in (22.2-mm) rods, 1000 ft (km) R3 = length of 1-in (25.4-mm) rods, 1000 ft (km) Rt = length of tubing string, 1000 ft (km)

For a single-size rod string, zero values are assigned to the sizes not used. The pump displacement can now be calculated with the formula in USCS units, Barrels/day = Lp X bore factor X spm X 0.8

in SI units Cubic meters/day = Lp X bore factor X spm X 0.8

The 0.8 factor assumes an 80% pump volumetric efficiency after correcting for sucker rod stretch and plunger overtravel. A lower efficiency should be assumed if the well is known to be gassy. If the pump displacement is more than required and the torque and structure capacity ratings of the unit are not exceeded, the calculations should be repeated using the next smaller size unit.

counterbalance The pumping unit is supplied with a counterbalance in order to load the prime mover equally on the upstroke and the downstroke. The counterweights balance out the wet weight of the rods and half the weight of the fluid. All of the work in lifting is done on the upstroke. The energy stored in the counterweights during the downstroke supplies about half of the energy required for lifting the fluid. Because it lifted no fluid on the downstroke, the prime mover expends its energy lifting the unbalanced portion of the counterbalance load. Counterbalance effect CB is

The pumping unit pictured in Figure 1 is known as a beam pumping unit. These are most common, but there are other types. One is a hydraulic surface unit, where a cylinder is set directly over the wellhead and a piston provides the reciprocating motion of the rods. These use commercial hydraulic pumps and control valves to supply the hydraulic power to the piston.

As shown in Table 3, standard sizes of beam pumping units have stroke lengths ranging from a little more than 1 ft (0.3 m) to a maximum of 16 ft (4.9 m). Recently a number of units have been marketed that permit stroke lengths up to 40 ft (12 m). The long stroke improves pump efficiency, prolongs sucker rod life, and reduces energy requirement. The unit pictured in Figure 5 uses wire line wound and unwound on a reversible drum to supply the reciprocating motion.

## Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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