Note: Descriptions are shown in the official language in which they were submitted.
1 A_K ROUND OF T~IE INVENTION
2 Oil is commonly produced from a subterrarlean Formation
3 through a string of tubing extendlng to -the sur-Face. The oil is commonly
4 lifted through the tubing by the action oF a downhole pump actuated by a
sucker rod string which is reciprocated at surface by a pump jack.
6 A sucker rod string is made up of a multiplicity of
7 individual sucker rods threaded together end to end to form the string.
8 Each sucker rod comprises a main stem, typically having a length of about
9 30 feet and a diameter of 3/4 inches. ~t one end, the sucker rod has an
enlarged coupling member having an externally threaded pin; at its outer
1l end, it has a second enlarged coupling member having an internally
12 threaded box. These coupling members -typically have a diameter of 1-7/8
3 inches. The tubing in which the rod string moves typically has an
4 inside diameter of 2-1/2 inches.
The use of sucker rod strings in directional or slanted
16 wellbores has been attended with problems. The steel rod string tends
7 to lie along the low side of the tubing string and, with time~ recipro-
18 cation of the rod string tends to wear away the wall of the tubing
19 string.
This problem has been comprehendecl and grappled with in
21 the prior art. One concept which has been explored involved incorpora-
22 ting centralizing anti-friction means into the rod string7 to space the
23 rods from the tubing and reduce wear of the tubing wall. Patents which
24 exemplify the prior art solutions based on this concept are: U.S.
2,198,720 (Edgecomb et al); U.S. 1,5087845 (Giles); U.S. 2,783,028
26 (Jamison), UOS. 2,601,478 (Weir); U.S. 1,541~791 (Christofferson); and
27 U.S. 1,507,972 (Loop).
28 The present invention gre~ out of a series of different
29 embodiments which ~ere built and tried.
- 2 -
~f~6~
l The First embodiment involved cut-ting a circumferential
2 slot in the surface of each rod string coupling. This slot was filled
3 with a wrapping of rawhide. The rawhtde had two desirable qualities:
4 it was slippery and, if it separated from the coupling and dropped down
the tubing, it did not cause damage (as would be the case with steel
6 'junk'). However the rawhide would s~ell and restric-t clearance needed
7 for the movement of oil between the rod and tubing strings.
8 The next version tried involved using a split ring
9 plastic sleeve in place of the rawhide. eut these sleeves came off easily
and dropped down the annulus between the strings and interfered with the
ll proper operation of the rod string and downhole pump.
12 Consideration was then given to mounting small~ protruding
13 wheels in the coupling body. The concept considered was to cut slots
14 partway into the body, in the manner shown by Edgecomb, and mount the
wheels on pin axles. However this approach was discarded for the
16 following reasons:
17 - the wheels and axles would be small in dimension, due
18 to space limitations, and thus would be liable to fail
19 and drop out of the slot;
- and, because these components would be made of steel,
21 such failure would result in steel junk dropping to the
22 base of the tubing string onto the pump, which is
23 undesirable.
24 Another problem~ which was making itself apparent during
this design and testing stage, had to do with the nature of the produced
26 oil stream being dealt with. The couplings were being used in slanted,
27 shallow wells producing heavy oil conta1ning much sand. Parrafin wax
28 is commonly associated with such heavy oil. The combination of wax and
29 sand would readily clog up moving parts.
-- 3 --
1 SUMMARY OF_rllE I_V ~lrI0~l
2 At this point in the evolution of the invention, it ~as
3 decided to form substantially diametrical slots which extended right -through
4 the coupling body. This meant tha-t larger wheels and pins could be used
within the constraints of the space limitations involved. These larger
6 wheels and pins would be less likely to fail. In addition, the wheels
7 would project out each side of the coupling and contact the tubing wall.
8 If a pin failed, the wheel and pin would tend to remain in place within
9 the slot, because the wheel would be held there by the bracketing surfaces
of the tubing wall. In addition, it was hoped that the slot, which was
11 open on both sides, would permit of ejection of collecting wax and sand,
12 thereby reducing likelihood of the wheel seizing up due to the slot
13 becoming clogged with the wax and sand.
14 When this version of the device was -tes-ted~ it was found
that mechanical failure of the wheel and pin was not a significant
16 problem. However, seizing up of the wheel with wax and sand was not
17 eliminated - it typically occurred within a rnonth in the wells in which
18 the device was tested.
19 This initial "diametrical"-version had wheels which had
close clearances (about .01") from the adjacent slot walls.
21 A coupling was then made and tried having diametrical
22 slots, but the wheels had a "sloppy fitl' ~ that is, there was provided
23 a clearance of about .1" between each side of the wheel and the
24 adjacent surface of the slot side wall, when the wheel was centrally
positioned on the pin.
26 When tested, it was found that this "sloppy fit" version
27 gave much improved performance, with respect to seizure of the wheels.
28 Tests showed that the wheels were still rotating freely several months
29 after insertion in wells in which the initial diametrical couplings
had been seized up in about a month.
1 It is believed that the use of an open-ended slot and
2 provision of the transverse movement capability of the wheel along the
3 pin axis combine to provide an assembly which in use is characterized
4 by the slot being cleared of the wax and sand that would otherwise clog
it and seize up the wheel.
6 In accordance with the invention~ therefore, there is
7 provided an improved anti-friction sucker rod coupling for connecting a
8 pair of sucker rods and centralizing -them in a tubing string. The
9 coupling comprises: an elongate, rigid, substantially cylindrical body
member, having means at each end of said body member for connection with
11 a sucker rod, said body further forming a plurality of transversely
12 extending, substantially diametric, generally vertical slots extending
13 there-through, said body further defining a plurality of pin bores, each
4 such pin bore extending transversely through the body member so as to
intersect one of said slots substantially perpendicularly; a plurality
16 of wheel members, each such wheel member being positioned within one
17 of said slots to rotate in a generally vertical plane, each wheel member
18 having a portion thereof extending beyond the periphery of said body
19 member to engage the inner surface of the tubing string and centrali~e
the coupling; and a plurality of pins, one mounted in each of said pin
21 bores and supporting a wheel member thereon, whereby the wheel member is
22 rotatable within said slots; each such wheel member having a clearance
23 between its side surface and the wall surface of the slot, when the wheel
24 member is centered on the pin, where~y the wheel member may shift slightly
along the pin, to assist in ejecting sand and oil from the slot.
~Q~
1 DESCRIPTION OF THE DRAWINGS
2 Figure 1 is a side viéw of the coupling; and
3 Figure 2 is a side view showing a wheel pos;tioned
4 in a slot of the coupling.
DESCRIPTION OF'THE PREFE~ED EMBODIMENT
____ ___ _ __
6 The anti-frictional, central'izing sucker rod coupling A
7 comprises a body member 1. This body menlber 1 is solid, rigid, elongate
8 and cylindrical. An internally threaded bore 2 extends longitudinally
9 into each of its endsg for connection with the threaded pin ends of the
sucker rods 3 which it joins together.
11 A plurality of diametric and Yertically directed slots 4
12 extend transversely through the body member 1. As shown, the slots 4 are
13 spaced one above another around the circumference of the body member.
14 A plurality of horizontally directed pin bores 5 extend
through the body member 1. Each such pin bore 5 intersects one of the
16 slots 4 perpendicularly.
17 A plurality of wheel members 6 are mounted on pins 7 in
18 the slots 4 and pin bores 5. More particularly, a wheel member 6, ha~ing
19 a diameter selected to just fit into the tubing which is to receive the
rod string, is positioned longitudinally in each slot 4. A pin 7
21 extends through the bore 5 and the wheel member 6. The pin 7 is press
22 fit in the body member'l. The wheel member 6 is thus adapted to rotate
23 within a vertical plane and projects beyond the periphery of the body
24 member, whereby it is functional to engage the inner surface of the
tubing string (not shown) and centralize the coupling.
26 Since the wheel member 6 substantially corresponds in
27 diameter with the inside diameter of the tubing string, the tubing wall
28 will retain said wheel member in the s'lot, should the pin break. Thus~
29 the danger of junk falling to the base of the well bore is reduced.
-- 6 --
l As shown in Figure 2~ the thickness of the wheel member 6
2 is less than the width of the slot 4.; Thus there is a clearance between
3 each side surface 8 of the wheel member 6 and the adjacent wall surface 9
4 of the slot 4, when the whee1 member is centered on the pin, as shown.
Typically, for a wheel member having a d1ameter and maximum thickness of
6 2.36" and .45" respectively, I provide a slot having a length and width
7 of 2.75" and .550" r~spectively. The slot remains constant in dimension,
8 although the diameter of the wheel will vary with differing tubing sizes.
9 As previously stated, the provision of clearance as
aforesaid permits the wheel member 6 to shuttle back and forth a short
ll distance within the confines of the slot walls - this movement assists
12 in clearing wax and sand out of the slot~
3 In a preferred design, I provide wheel members 6 having a
4 lenticular configuration, as illustrated in Figure 2. It is my belief
that this design is particularly conducive to the ejection of wax and
16 sand from the slot.
17 The wheel members 6 are formed of a hard, non-abrasive
18 material, to minimize the possibility of scoring the tubing wall. I
19 have found hard nylon to be suitable for most applications.
In summary, the wheel members function as an anti-
21 frictional centralizing means, to minimize wear of the tubing by the
22 rod string reciprocating therein. The provision of wheel members having
23 approximately the same diameter as the tubing safeguards against the
24 possibility of broken parts dropping down the hole. In combination,
the slot, the lenticular configuration of the wheel member, and the
26 lateral movement of the wheel member in the slot function to prevent
27 wax and sand build up in the slot.
