3

100 y

0 500 1000 1500 2000 2500 3000

PRODUCTION RATE, BPD

FIGURE 13 Typical characteristic curves for a jet pump. Numbers adjacent to curves are power fluid in barrels (cubic meters) per day. Jet pump operation must be above and to the left of cavitation line.

Manufacturers offer a broad range of nozzle and throat sizes to cover the varied requirements of depths and volumes. Published data show the smallest nozzle requires 13.5 hydraulic hp (10 kW) and the largest requires 506 hydraulic hp (377 kW) at 4000 lb/in2 (276 bar) power pump pressure. It requires a complex calculation to determine the optimum nozzle and throat sizes for any given set of well conditions. Manufacturers offer computer solutions, usually in graphical form. Variable factors such as tubing friction, changing specific gravity due to gas, and changing well conditions all contribute to the need of a graphical presentation. The chart in Figure 13 shows a jet pump calculation for an 8000-ft (2440-m) well to predict the anticipated production volume versus pump intake pressure for power fluid pressures of 2000, 3000, and 4000 lb/in2 (138, 207, and 276 bar). Note that at 4000 lb/in2 (276 bar) power oil pressure, the pump would be cavitating, and this condition must be avoided. Cavitation occurs when the pressure at the entrance of the throat is less than the vapor pressure of the fluid pumped. The collapse of cavitation bubbles in the throat is so damaging that no known metal can resist destruction. Throat life in severe cavitation can be as short as two or three days. It may also be noted from the chart that the jet is very sensitive to pump intake pressure. Both the production rate and the overall hydraulic efficiency increase as pump intake (suction) pressure increases. A down-well pressure-recording instrument may be installed with the jet pump. It records pump intake pressure versus time for a six-day period, at the end of which the jet pump with the instrument is pumped out and the pressure recording read and analyzed. This information is then used to determine if the nozzle and throat sizes are optimum and to select the power fluid pressure that will maximize production but still avoid cavitation.

Subsurface Progressing Cavity Pumps A positive displacement screw-type pump (Section 3.7) can be used for handling the range of oil field fluids. Rotative speed can be varied to match well production with a smooth and steady delivery. No valves are required for pump operation. This type of pump is well suited to handling gaseous formations.

As shown in Figure 14, the rotor is a single rounded-cross-section external screw. The stator is a double internal helix molded of synthetic rubber. As the rotor turns, cavities

FIGURE 14 Subsurface progressing cavity pump (Fluids Handling Division, Robbins & Myers)

form, and these cavities remain the same size as they progress from the bottom suction to the top discharge. The pump stator is suspended from a standard API tubing string and driven by standard API sucker rod. The pump is electric-motor-driven through belts and sheaves to obtain desired speeds.

Pumps of this type are available for oil well services (or for pumping fluids out of gas wells) to 3000 ft (914) or more. For pumping light or heavy crudes, pump sizes are available up to 100 barrels/day (16 m3/day) with speeds varying up to 550 rpm and power ratings to 5 hp (3.7 kW), depending on the well depth and flow required. A sucker rod size of 8 in (15.9 mm) is common.

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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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