Pumps – Expansible chamber type – Fluid serially moved to opposite side of pumping member
Reexamination Certificate
2000-06-21
2001-08-14
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Fluid serially moved to opposite side of pumping member
C417S553000, C417S554000, C091S041000, C091S402000, C092S143000
Reexamination Certificate
active
06273690
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to subsurface, or downhole, pumps, such as are used to pump oil and other fluids and bases from oil wells.
BACKGROUND OF THE INVENTION
When an oil well is first drilled and completed, the fluids (such as crude oil) may be under natural pressure that is sufficient to produce on its own. In other words, the oil rises to the surface without any assistance.
In many oil wells, and particularly those in fields that are established and aging, natural pressure has declined to the point where the oil must be artificially lifted to the surface. Subsurface pumps are located down in the well below the level of the oil. A string of sucker rods extends from the pump up to the surface to a pump jack device, or beam pump unit. A prime mover, such as a gasoline or diesel engine, or an electric motor, or a gas engine on the surface causes the pump jack to rock back and forth, thereby moving the string of sucker rods up and down inside of the well tubing.
The string of sucker rods operates the subsurface pump. A typical pump has a plunger that is reciprocated inside of a barrel by the sucker rods. The barrel has a standing one-way valve, while the plunger has a traveling one-way valve, or in some pumps the plunger has a standing one-way valve, while the barrel has a traveling one-way valve. Reciprocation charges a chamber between the valves with fluid and then lifts the fluid up the tubing toward the surface.
One problem encountered in downhole pumps is that the chamber between the valves fails to fill completely with liquid. Instead, the chamber contains undissolved gas, air, or vacuum, which are collectively referred to herein as “gas”.
Such failure to completely fill the chamber is attributed to various causes. In a gas lock situation or a gas interference situation, the formation produces gas in addition to liquid. The gas is at the top of the chamber, while the liquid is at the bottom, creating a liquid-to-gas interface. If this interface is relatively high in the chamber, gas interference results. In gas interference, the plunger (on the downstroke) descends in the chamber and hits the liquid-to-gas interface. The change in resistances causes a mechanical shock or jarring. Such a shock damages the pump, the sucker rods and the tubing.
If the liquid-to-gas interface is relatively low in the chamber, gas lock results, wherein insufficient pressure is built up inside of the chamber on the downstroke to open the plunger valve. The plunger is thus not charged with fluid and the pump is unable to lift anything. A gas locked pump, and its associated sucker rods and tubing, may experience damage from the plunger hitting the interface.
In a pump off situation, the annulus surrounding the tubing down at the pump has a low fluid level, and consequently a low fluid head is exerted on the barrel valve. In an ideal pumping situation, when the plunger is on the upstroke, the annulus head pressure forces annulus fluid into the chamber. However, with a pump off condition, the low head pressure is unable to force enough fluid to completely fill the chamber. Consequently, the chamber has gas or air (a vacuum) therein. A pump (and its associated equipment) that is in a pump off condition suffers mechanical shock and jarring as the plunger passes through the liquid-to gas interface. A restricted intake can also cause pump off.
Still another problem is sand. The plunger and the barrel are both made of metal. In order to provide for lubrication inbetween these two parts, a small clearance between the two is provided to allow oil to enter. When the well is producing sand, some sand may enter this clearance or spacing between the plunger and the barrel. The sand abrades the components, thereby shortening the life of the pump.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a downhole pump that does not suffer from the problems of gas and sand.
It is another object of the present invention to provide a downhole pump that does not become gas locked.
It is another object of the present invention to provide a downhole pump that minimizes pump damage caused by gas interference or pump off conditions.
The present invention provides a downhole pump having an unperforated barrel and a plunger. The barrel has first and second ends with a first one-way valve being located in the second end of the barrel. The plunger also has first and second ends. The plunger has a second one-way valve therein. The plunger second end is located inside of the barrel such that reciprocal movement between the plunger and the barrel can occur. There is a barrel chamber inside of the barrel and extending between the first one-way valve and the plunger. The barrel chamber expands when the reciprocal movement between the plunger and the barrel is an upstroke movement and the barrel chamber contracts when the reciprocal movement between the plunger and the barrel is a downstroke movement. A bypass channel is located between the plunger and the barrel. The bypass channel is closed when the reciprocal movement is beginning the upstroke movement and is open when the reciprocal movement is near an end of the upstroke movement. The open bypass channel allows communication from the barrel chamber around the plunger.
With the pump of the present invention, pressure across the plunger can be equalized as the plunger finishes its upstroke. Such pressure equalization may be necessary to correct for a pressure differential caused by gas in the chamber. The gas is vented through the bypass channel. Consequently, the pump does not suffer gas lock and stress on the sucker rods is reduced. Also, circulation through the bypass minimizes the buildup of sand.
In accordance with one aspect of the present invention, the plunger comprises an outside diameter. The bypass chamber is formed by a reduction of the outside diameter near the plunger second end.
In accordance with still another aspect of the present invention, the plunger comprises an outside diameter. The bypass channel is formed by at least one groove in the outside diameter extending in a generally longitudinal direction along the plunger. The groove is located near the plunger second end.
In accordance with still another aspect of the present invention, the bypass channel has a cross-sectional area that increases as the reciprocal movement between the plunger and the barrel nears the end of the upstroke movement.
In accordance with still another aspect of the present invention, the barrel comprises an inside diameter. The bypass channel comprises an increase of the inside diameter near the barrel first end.
In accordance with still another aspect of the present invention, the barrel comprises an inside diameter. The bypass channel comprises at least one groove in the inside diameter extending in a generally longitudinal direction along the barrel. The groove is located near the barrel first end.
The present invention also provides a downhole pump comprising a barrel and a plunger. The plunger has one end located inside of the barrel. The plunger end forms part of a chamber located inside of the barrel. The barrel and the plunger are structured and arranged so that reciprocal movement therebetween can occur, wherein the volume of the barrel chamber changes with the reciprocal movement. The barrel and the plunger are separated by a first clearance and by a second clearance, with the second clearance being larger than the first clearance. The plunger and the barrel are separated only by the second clearance when the volume of the barrel chamber is near a maximum, wherein pressure across the plunger can equalize by way of the second clearance. The plunger and the barrel are separated by the first clearance when the volume of the barrel chamber is at a minimum, wherein the pump can lift fluid.
In accordance with one aspect of the present invention, the first clearance is between 0.002-0.005 inches and the second clearance is greater than 0.005 inches.
In accordance with still another aspect of the present invention, the second cl
Fischer, Jr. Charles K.
Williams Benny J.
Freay Charles G.
Harbison-Fischer Manufacturing Company
Hayes Eric
Mantooth Geoffrey A.
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