Wells – Valves – closures or changeable restrictors – Fluid operated
Reexamination Certificate
1999-02-16
2001-03-13
Pezzuto, Robert E. (Department: 3671)
Wells
Valves, closures or changeable restrictors
Fluid operated
C166S325000
Reexamination Certificate
active
06199636
ABSTRACT:
TECHNICAL FIELD
My invention relates to subsurface, positive displacement, ball check valve actuated, cylindrical, reciprocating plunger pumps which are typically used in oil wells to produce crude oil. In particular, my invention relates to the cage which locates and contains the lower, stationary or standing ball check valve.
BACKGROUND OF THE INVENTION
The standard “closed barrel cage” as specified in American Petroleum Institute publication,
Specification
11AX For Subsurface Sucker Rod Pumps and Fittings 9th edition, 1989 (A.P.I. Spec. 11AX), and designated as C14-15, C14-20-125, C14-20, C14-25, and C14-30, has been the only cage offered by the major pump manufacturers for use in standard, stationary barrel, top or bottom anchored, rod insert pumps (i.e.—A.P.I. Spec. 11AX pump designations: RSA, RSB, RHA, RHB, RWA, and RWB). These cages have proven to be economical, relatively free flowing, and durable under most average pumping conditions. And they have been modified, with some degree of success, to enhance durability and performance in more demanding conditions. However, closed barrel cages have some inherent design deficiencies that cause problems with pumping systems which have plagued their users for years.
The first and foremost design limitation is in how they position the lower stationary or standing ball and seat valve. All current designs of these cages are quite long, which is necessary to give the closed design adequate fluid passage, and to allow for the long, external thread on top (A.P.I. Spec. 11AX “C11” pin thread) which screws into the bottom of the pump barrel. This results in a great deal of space or unswept volume between the lower standing valve (i.e.—the suction) and the upper travelling valve (i.e.—the discharge) when they are closest together at the bottom of the plunger down-stroke. This unswept volume presents no major problem if the fluid being pumped is all or mostly all liquid because liquids are nearly incompressible. Crude oil, however, usually contains dissolved natural gas, some of which separates from the liquid when subjected to the drop in pressure caused by the up-stroke of the pump plunger. In addition, free natural gas is usually found in the formation and will inevitably gravitate to the pump suction. If enough of the swept volume of the pump is filled with gas instead of liquid, then a condition known as “gas locking” can occur. Gas lock occurs when the gas in the pumping chamber is not compressed to a sufficiently high pressure, during plunger down-stroke, to overcome the hydrostatic pressure being exerted on the top of the closed travelling valve check ball. This hydrostatic pressure is due to the weight of the fluid column above the pump inside the production tubing. This failure of the travelling valve to open prevents the pump from discharging the fluid inside the pumping chamber.
A further limitation of the closed barrel cage design is that its internal passages are more intricate and therefore more restrictive than their open cage counterparts. This is a considerable disadvantage when used in the standing (suction) valve position because the potential pressure differential is not as great as is possible in the travelling (discharge) valve position. This restrictive design also tends to aggravate any potential problem with gas locking because they are more likely to cause the dissolved natural gas to separate, much like the effect of agitating carbonated water. Closed barrel cages also have more of a tendency to become clogged by foreign matter from the formation which can further restrict flow and cause even more undesirable gas separation.
There have been attempts to remedy some of the problems associated with closed barrel cages such as reducing the cage volume, using various types of inserts to guide and contain the ball with much less restriction to flow, and some have even modified other parts of the pump, or used mechanical devices to force the operation of the valves. However, seemingly none of the previous efforts have been in wide acceptance by the marketplace as a universal and foolproof solution to any of the before mentioned problems, especially gas lock. In fact, the closest thing to a cure for the problems associated with the use of closed barrel cages probably pre-dates their invention—the long defunct McGregor Working Barrel Pump Co. of Bradford, Pa. produced a 1⅝″ bore, stationary, rod pump which had a seating mandrel which screwed into the bottom of the pump barrel tube, and just above the barrel threads on the mandrel was another threaded section, smaller in diameter, which screwed onto an open type cage (similar to A.P.I. Spec. 11AX designation C17-150) which contained a “rib type” ball and seat check valve. This design placed the standing valve up inside the barrel about two or three inches (instead of two inches below the barrel like a closed barrel cage does) and yielded a very small unswept volume with a very high compression ratio. The drawbacks were that the travelling valve was placed on top of the plunger instead of below it, and that the pump required many special “McGregor only” parts rather than A.P.I. types which caused its eventual demise.
SUMMARY OF THE INVENTION
The “open barrel cage” is of one basic design with two somewhat different variations. This is necessary due to the constraints of inventing a cage that is a direct replacement (i.e.—using A.P.I. standard parts and threaded connections) for the closed barrel cage in five different sizes, but without its inherent limitations. The “small bore” version of the open barrel cage is a direct replacement for A.P.I. Spec 11AX closed barrel cage designations C14-15 and C14-20. There is also an open barrel cage to replace C14-20-125, but requires a change from the standard 1⅛″ check ball to a smaller 1″ diameter ball. The “large bore” version of the open barrel cage is a direct replacement for the C14-25 and C14-30 cages, and there is also a “McGregor” version of this cage.
The open barrel cage designed for small bore pumps consist of a cylindrical section that is about one-third of the overall length of the cage and has the same outer diameter as that of the barrel which it screws into, except for the one that replaces C14-20-125, which is slightly larger than the barrel. This is followed by a smaller, exteriorally threaded section, equal to about another one-third of the overall length, which screws into the barrel tube. The remaining cylindrical section is of a smaller diameter than the threaded section and is closed on the top. Three equally spaced (radially) slots are cut longitudinally from the top section and extend down about two-thirds of the way into the threaded section. Inside, these cages have a large, cylindrical, inner diameter that is open on the bottom of the large, cylindrical, outer diameter section, and is about {fraction (3/16)}″ shorter than the same large, outer diameters length. The large, inner diameter is threaded for about two-thirds of its length and accepts a standard sized, A.P.I., flat type ball and seat, and the seating mandrel threads on bottom anchored pumps, or the ball and seat and the barrel cage seat bushing threads on top anchored pumps. A smaller, cylindrical, inner diameter section extends from the large inner diameter and passes into the exteriorally threaded section and the smaller top section, but does not go through. This small, inner diameter forms the ball chamber, and the slots are machined through this section which allows for fluid passage.
Likewise, the open barrel cage for large bore pumps has a very short, cylindrical section that has the same outer diameter as that of the pump barrel tube to which it assembles. Next comes an exteriorally threaded section of smaller diameter, which in conjunction with the previous section, is equal to approximately one-half of the cages overall length. This threaded section screws into the bottom of the pump barrel tube. Finally, there is a smaller diameter section, slightly longer than the total of the other two, whic
Petravick Meredith C.
Pezzuto Robert E.
LandOfFree
Open barrel cage does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Open barrel cage, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Open barrel cage will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461288