US2572309A - Cementing plug - Google Patents

Description

CL CL EHQCDVVPJ CEMENTING PLUG Oct. 23, 1951 Filed Aug. 9, 1948 C. C. Brown Patentecl ct. 23, 1951 UNITED sTATEs PATENT oFFIcE 2,572,309 lClllVlENTlNGr PUG Cicero C. Brown, Houston, Tex. Application August 9, 1948, Serial No. 43,297

8 Claims.

This invention relates to cementing plugs.

Cementing plugs are conventionally employed in connection with operations for cementing pipes in wells and generally comprise a cylindrical body slidable through the bore of the pipe, being ordinarily inserted at the inter-face between the column of cement and the column of displacing fluid which normally follows the cement into the pipe. In some cases, cementing plugs may also 'be inserted between the cement and the column of fluidpreceding or below the cement, and m others both above and below the body of cement. Such plugs serve various useful purposes, 'such as preventing contamination of the cement by the preceding or following fluid, Wiping the pipe wall clean of cement, and in the case of a following plug, to engage a landing collar or other suitably placed abutment in the pipe when the cement has been fully displaced therefrom, to thereby form a closure for the pipe which will develop back pressure against the displacing fluid and thereby indicate completion of the discharge of the cement from the pipe.

Conventional cementing plugs, however, do not prevent return flow of cement or other fluid from the annular space into the interior of the pipe. Conventional back pressure check valv-es are normally placed in the lower end of the pipe to prevent this return movement, but frequently fail to hold properly with the result that the cement will often flow back into the pipe and produce failures in the cementing operation.

The present invention has for its principal object the provision of an improved form of cementing plug.

An important object is the provision of novel form of cementing plug which, in addition to performing all the functions of the more conventional plugs, includes means for automatically locking the plug to the pipe in response to movement of fiuids in the reverse direction through the pipe.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate a useful embodiment in accordance with this invention.

In the drawings:

Fig. 1 is a longitudinal quarter-sectional view of a cementing plug in accordance with one embodiment of this invention showing the device inserted in a pipe and the positions of 'the parts thereof when engaging the pipe walls;

Fig. 2 is a view 'similar to Fig. 1 showing the plug latched to a landing collar;

Fig. 3 is an enlarged fragmentary view in longitudinal section of some of the parts of the device; and

Fig. 4 is perspective view, partly in section, of the pipe-gripping elements of the device.

Referring to the drawings, the plug comprises a hollow body IO having an inwardly and upwardly tapering, generally conical exterior surface which merges into an axially straight portion l la at the upper end ofbody Ill and into an outwardly extending annular shoulder Ill) adjacent the lower end of the body. Body IO is provided at its upper end above portion lla with an internally threaded extension |2 of somewhat smaller external diameter than portion Ila to provide thereon an upwardly facing annular shoulder IS. A ring M, slidable over the exterior of extension l2, is seated on shoulder [3 with its upper edge substantially flush with lthat of extension |2. Ring [4 is of somewhat greater wall thickness than the width of shoulder |3 forming a downwardly facing annular abutment |5 extending outwardly from the upper end of portion Ha of the body. Screwed into extension 12 is a tubular sleeve IB having an annular fiange Il on the exteror thereof extending laterally over the upper end of ring |4 and the upper end of extension |2. Seated on the 'upper face of flange ll and molded firmly to the body of sleeve 16 is a collar 18, constructed of fl-exible, resilient material, such as natural or synthetic rubber or the like, and provided with an integral peripheral lip |9 which flares upwardly and outwardly from the body of collar 18. The upper end of sleeve |6 is threaded internally at 20 for the recep'tion of a threaded cap 2| which is adapted to form a closure for the bore of body IO. A packing ring 22 is suitably installed between adjacent faces of cap 2| and sleeve |6 to form a fluidtight seal therebetween.

The lower end of body IO is internally threaded at 23 to receive a tubular sleeve 24 similar in form to sleeve 16 and likewise provided with a laterally extending fiange 25, one face of which is adapted to seat against vthe lower end of body lll and the opposite face of which supports a collar 26 which is firmly molded to the body of sleeve 24. Collar 26 is also constructed of flexible resilient material, such as natural or synthetic rubber or the like, and has an integral peripheral lip 21 which flares downwardly and outwardly from the body of collar 25. The lower end of sleeve 24 is internally threaded at 28 to receive the threaded end of a tubular bushing 29 which extends from the lower end of sleeve 24. The exterior of the extended portion of bushing 29 has an outwardly and downwardly sloping shoulder 30 on which is seated a split ring 3| provided with a plurality of radially extending teeth or lugs 32.

Slidably disposed on tapered surface H of the body is a slip assembly, indicated generally by the numeral 33, and comprising a collar 34 constructed of fiexible resilient material, such as natural or synthetic rubber or the like, which surrounds portion Ha and the adjacent portion of surface ll. A metallic insert ring 35 is molded into the upper end of the bore of collar 34 to assure free sliding movement of the collar along surface portion Ha. The upper edge of ring 35 is adapted to strike abutment 15 formed by the lower edge of ring M to limit the relative longitudinal movement between the collar and body III at the upper end of the body. The upper edge of collar 34 is provided with an integral peripheral lip 36 which fiares upwardly and outwardly therefrom,-and a'plurality of circumferentially paced orifices 3'I' extend through the base of lip 36' to provide communication betweenv the inner and outer faces thereof. The lower edge of collar 34 is provided with a depending annular tongue 38 integral with collar 34v and formed of the same material. A plurality of wedge shaped slips 39 having upwardly facin-g teeth 49 on the exterior thereof, are connected to tongue 38 in angularly spaced arrangement about body IG and slidable on surface II. The taper of surface II co-acts with slips 39 to cause radial expansion an'dcontraction of the slips in response to appropi'iate relative longitudinal movement between the slips and body IB, collar 34, due to its fiexible Character, forming a hinge connection permitting this movement. Shoulder IIb serves to limit relative longitudinal movement between the slips and body IEl at the lower end of the body.

The aboVe-'described plug is adapted to coop'erate with a landing collar, indicated generally by the numeral 4|, which will ordinarily be installed at a suitable point in a pipe 42 in which the plug is designed to operate and will 'be designed to engage the plug to firmly lock the latter against further movement in either direction in pipe 42. Landing collar 4I comprises an upwardly tapering hollow conical body 43, provided at its upper end with an inwardly extending annular fiange 44 having an axial bore 45. A plurality of angularly spaced passageways 46 eX- tend' between the lower face of fiange 45 and the exterior of body 43'. The base portion of body 43 is externally threaded at 4'! for engagement in a suitably threaded' seat 48 which, as illustrated, may be the7 box connection for one of the 'Sections of pipe 4'2.

The above=described plug operates in the following manner': Landing collar 4I will normally be installedat a suitable' point in pipe 42 at LV which it is desired to finally stop the desce'nt of the plug. In cementing Operations, this will ordinarily be the point which, when attained by the plug, Will mark completion of the displacement of the column of cement slurry from the interior of thepipe to the annular space outside the pipe. The plug will no'rnially be inserted into pipe 42 at the surface immediately following the introduction therein of the pre-determined volume of cement slurry and will be followed by a suitable displacing fluid, such a's a mud-laden' fiuid, which will be pumped into the pipe onV top of the plug andthe column' of cement slurry. Under pressure applied by the usual purnps (not shown) the plug will act as a piston driven by the displacing fluid to forceV the cement slurry down the pipe and out suitable opening's, normally provided at a suitable point below the landing collar. When the plug is thus inserted in the pipe, the pressure of the displacing fluid will act on the upwardly flaring inner face of the fiexible lip 36 to compress the latter against the wall of the pipe, thereby maintaining a fluidtight sliding seal with the pipe wall as the plug is forced downwardly. The reaction pressure of the cement will, of course, act against the inner downwardly and outwardly fiaring face of flexible lip 2'I to also hold the latter in compressive sealing engagement with the pipe wall during downward movement of the plug. As the plug moves downwardly in the pipe, flexible lip 36 of slip assembly 33 will bleV in frictional contact with the pipe wall which will be sufiicient to maintain ring 35 in contact with abutment 15. O-rifices 3`I will allow equalization of the pressure of any fluid tr'apped between the sliding seals formed by lips I 9' and 21, so that lip 36 will slide freely down the pipe under the thrust of abutment I5 against ring 35. Slips 34 will thus remain in the retracted position (Figs. 2 and 3) and the plug as a whole will move downwardly through the pipe. The contact of the several flexible lips with the pipe wall will serve to wipe the pipe wall clean of cement as the plug moves downwardly in the pipe and the seals formedv by lips 19 and 21 will efectively prevent any inter-mixing ofl the cement an'd the displacing fiuid.4

If, for any reason, during the downward' move'-` ment of the plug, a condition shouldoccur which would cause the fluid beneath the plug to attenipt to fiow in the upward direction', the upward pressure of the fluid against the lower end o'f the plug will tend to drive it upwardly. When this occurs, the friction of lip 33' against the pipe wall will act to hold collar 34 and its attachedslips 39 relatively stationary while the plug moves upwardly' relative thereto. The upward movement of tapering surface I I relative to slips 38 will expand the latter radially and drive teeth 4B into the pipe walli thus effectively stopping further upward movement of the plug body (see Fig. 1). The flexible character ofco'llar 34 to which the slips are attached provides a exible hinged connection which allows the slips to engage in the desired radial movement. Stopping of the plug in this manner will of course effectively stop any further revei'se movement of the fluid, until the condition responsible for the reversal of flow has been overcome. When downward movement of the fluid-is again started, the pressure on the upper end of the plug will' move body IG downwardly relative to the 'slip assernbly, due to the continuingV frictional engagement of lip 3% with the pipe wall. This relative downward movement will allow slips 39 to retract, the slips, collar 34- and ring sliding upwardly on surfaces II and IIa until ring 35 will again contact abutment I5` and the entire plug structure will again be free to Continue its normal down- Ward movement.

When the plugreaches landingV collar 4I, the lower end of bushing 29 will enter bore and the pressure on the plug will drive ring' 3I carrying teeth 32 through bore 45. The outside diameter of teeth 32 is made somewhat greater' than the diameter of bore 45. lIowever, a'sring 3I' is split, it will contract sufiifc'iently to allow the ends of the teeth to pass through bore 45.' v After ring 3I' has passed below flange' 44, the

ring will expand and engage the lower face of flange 44 and thereby lock the'plug to' the landing collar. The upward pressure of fluid against the plug will produce a cammiiigi action of sloping shoulder 38 against the lower face of ring 3| tending to eXpand the ring and thereby maintain the looking engagement of teeth 32 with the lower face of fiange 44. When the plug has thus been locked to the landing collar, passageways 46 will assure that the pressure of the fluid beneath the plug will Continue to be applied againstV lip 21 to maintain the latter in tight-sealing engagement with the pipe wall to thereby preclude leakage of the fiuid upwardly past the plug.

With a cementing plug of theA above-described character, it will be evident that cementing may be conducted with complete safety against return flow of cement at any stage of the operation due to pump failure, or due to failure or lcakage of back-pressure check valves such as awasoe are conventionally used in cementing Operations. As will be evident, the plug in accordance with this invention may itself be employedfas a backpressure check valve, thereby eliminating the use of the conventional valve, if desired. It will be understood that the metallic parts of the plug may be made of readily drillable metals, such as brass or aluminum, so that the plug may be easily drilled out when desired to clear the bore of the pipe. i

It will be understood that various changes and alterations may be made in the details of the illustrative embodiment herein described within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. A cementing plug, comprising, an upwardly tapering generally conical body insertible in` a well pipe and closed against passage of fluid therethrough, annular fiexible sealing elements carried by the opposite ends of said body slidably engageable with the pipe wall, a nonmetallic fiexible resilient collar member slidably mounted on said body between said sealing elements and frictionally engageable with said pipe wall, a plurality of circumferentially spaced pipe-gripping elements swingably depending directly from said collar member slidably disposed on the conical surface of said body for radial movement thereby relative to said pipe wall in response to longitudinal movement relative to .said body.

2. A cementing plug, comprising, an upwardly tapering generally conical body insertible in a 'well pipe and closed against passage of fluid therethrough, upwardly and downwardly directed outwardly fiaring flexible sealing lips carried by the upper and lower ends, respectively, of said body slidably engageable with the pipe wall, a non-metallic fiexible collar member slidably mounted on said body between said lips, an upwardly and outwardly flaring flexible annular lip carried by said collar member frictionally engageable with said pipe wall, and a plurality of circumferentially spaced pipe-gripping elements depending directly from said collar member and slidably disposed on the conical surface of said body for radial movement thereby relative to said pipe wall in response to longitudinal movement relative to said body.

3. A cementing plug, comprising, an upwardly tapering generally conical body insertible in a well pipe and closed against passage of fluid therethrough, annular fiexible sealing elements carried by the opposite ends of said body slidably engageable with the pipe wall, pipe-gripping elements slidably mounted on the conical surface of said body for radial movement thereby relative to said pipe wall in response to longitudinal movement relative to said body, a nonmetallic flexible collar member connected directly to said pipe-gripping elements and frictionally engageable with said pipe wall to restrain upward movement of said pipe-gripping elements therein relative to said body, and a latching mechanism carried by the lower end of said body adapted to clutch a landing collar disposed in said pipe.

4. A cementing plug, comprising, an upwardly tapering slip-expanding cone insertible in a well pipe and closed against the passage of fluid therethrough, annular fiexible sealing elements carried by the opposite ends of said cone slidably engageable with the wall of said pipe, 'a non-metallic fiexible collar slidable on said cone between said sealing elements, a fiexible annular lip fiaring outwardly from the upper end of said collar into frictional engagement with the pipe Wall, and a plurality of pipe-gripping slips swingably depending directly from said collar in sliding engagement wtih said cone.

5. A cementing plug, comprising, an upwardly tapering slip-expanding cone insertible in a well pipe and closed against passage of fluid therethrough, an upwardly and outwardly fiaring flexible skirt carried by the upper end of said cone in slidable sealing engagement with the pipe wall, a downwardly and outwardly flaring flexible skirt carried by the lower end of said body in slidable sealing engagement with the pipe wall, a collar slidable on said cone between said skirts, a fiexible annular lip flaring outwardly from the upper end of said collar into frictional engagement with said pipe wall, a, plurality of radial orifices through said lip, 'and a plurality of pipe-gripping slips depending from said collar in sliding engagement with said cone.

6. A cementing plug slidable in a well pipe, comprising an upwardly tapering slip-expanding cone closed against passage of fluid therethrough,

' annular flexible sealing elements carried by the opposite ends of said cone slidably engageable p with the pipe wall, a non-metallic fiexible collar p opposite ends of said cone slidably engageable with the pipe wall, a non-metallic fiexible collar slidable on said cone between said sealing elements and having frictional engagement With said pipe wall, pipe-gripping slips swingably depending from said collar in sliding engagement with said cone, and a shoulder disposed on said cone above said collar and engageable therewith.

8. A cementing plug slidable in 'a well pipe, comprising, an upwardly tapering slip-expanding cone closed against passage of fluid therethrough, annular fiexible sealing elements carried by the opposite ends of said cone slidably engageable with the pipe wall, a non-metallic fiexible collar slidable on said cone between said sealing elements and having frictional engagement with said pipe wall, pipe-gripping slips swingably depending from said collar in sliding engagement with said cone, and a latching meehanism carried by the lower end of said body adapted to clutch a landing collar disposed in said pipe.

CICERO C. BROWN.

REFERENCES CITED The following references are of record in the

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