Recuperación Térmica De Petróleo

ROD PUMPING OVERVIEW
(Figure 1) shows the different parts of a sucker rod pumping system, including (from the top down) its five major components: the prime mover, which provides power to the system; the gear reducer, which reduces the speed of the prime mover to a suitable pumping speed; the pumping unit, which translates the rotating motion of the gear reducer and prime mover into areciprocating motion; the sucker rod string, which is located inside the production tubing, and which transmits the reciprocating motion of the pumping unit to the subsurface pump; and the subsurface pump.

Figure 1

(Figure 2) is a cross-sectional representation of a subsurface pump at two different stages of the pump cycle. Note the location of the standing valve at the bottom of the tubing, and thetraveling valve at the bottom of the sucker rods. Note also the changing position of the plunger.

Figure 2

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On the left-hand side of the figure , the plunger is approaching the bottom of its downstroke. The traveling valve is open, and so the standing valve is closed because it is carrying the weight of the fluid above it. At this point in the cycle, the fluid above the standing valve ismoving upward through the open traveling valve. On the right-hand side of the figure , the plunger has reached the bottom of the stroke and is just beginning to move upward. The plunger starts to lift the weight of the fluid above it, and the traveling valve closes. As the plunger continues to move upward, the volume in the working barrel—between the standing valve and traveling valve—increases,while the pressure in the working barrel decreases. As soon as this pressure becomes less than the flowing bottomhole pressure, the standing valve opens and formation fluids flow upward. During each upward movement of the plunger, wellbore fluids are lifted a distance equal to one full stroke length.

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When the plunger reaches the top of its stroke, its movement is reversed—the travelingvalve opens, the standing valve closes and the cycle repeats its reciprocating movement of the rods and the opening and closing of the two valves. With each stroke, fluid is moved up the tubing toward the surface. If the produced fluid contains free gas, there are two points to note regarding the pump cycle: 1. The valves will not necessarily open and close at the exact top and bottom of the stroke.The point in the upstroke at which the standing valve opens will depend on the spacing (the volume that exists at the bottom of the stroke, between the traveling and standing valves), and on the amount of free gas present in this volume. On the downstroke, the traveling valve remains closed until the pressure below the plunger is greater than the pressure above it. The traveling valve then opensand allows fluid to pass through it into the tubing. The exact point in the downstroke at which the traveling valve opens depends on the free gas volume in the fluid below the valve. The greater the volume of free gas, the greater the proportion of the stroke that is taken up in gas expansion and compression, without any true pumping action taking place.

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For wells producing a reasonablevolume of gas, a gas anchor is normally installed on the tubing below the pump. This device allows the separated gas to be produced up the annulus before it would otherwise enter the pump.

ADVANTAGES AND DISADVANTAGES OF ROD PUMPING SYSTEMS
Rod pumping systems can be used to reduce bottomhole pressures to very low levels, and offer great flexibility for low-to-medium production rates. They arerelatively simple with respect to design, operation and maintenance, and can be adapted to a wide range of operating conditions. They account for the large majority of artificial lift wells, and are one of the most well-known and generally understood systems in the field. Surface and downhole equipment can easily be refurbished, and tends to have high salvage values. While they have a very wide...