Non-rotating plug set

Abstract: A non-rotating plug set (10) for use in cementing well bores in combination with a co-operating floating collar or the like, comprises an upper plug (12) with a toothed insert (28) and a lower plug (14) with both an upper (50) and a lower (58) toothed insert, and a diaphragm closure (56). In use, the toothed insert (28) of the upper plug keys into the upper toothed insert (50) of the lower plug to prevent relative rotation of the two plugs. Also, the lower insert (58) of plug (14) can key into a toothed insert at the upper end of the floating collar, to prevent relative rotation therebetween. The plug set and collar can be drilled out using a polycrystalline diamond drill bit.

Description: This invention is directed to an improved non-rotating plug set for use in cementing the casing in well bores. In cementing the casing in a well bore, a plug set is used to close the bore and, after the cement has set, the plug set is drilled out to re-open the bore. In the past, the plug set and residual cement in the casing have been removed by drilling operations using tooth-type rock bits. The teeth on these rock bits have proved effective in drilling the plug set, even though the individual plugs of the set were free to rotate with respect to each other and the floating equipment. However, with the advent of polycrystalline diamond compact (PDC) drill bits, it has been found necessary to use a non-rotating plug set during the well casing cementing process to facilitate the subsequent drilling of the plug set and residual cement. For whatever reasons, the teeth on a PDC drill bit do not drill through a conventional plug set as effectively as the previously-used tooth-type rock bit. However, if a non-rotating plug set is used, the PDC drill bit can drill through the plug set, residual cement and floating equipment in time periods comparable to that needed with a conventional tooth-type rock bit. US-A-4711300 discloses a combination comprising an anti-rotation plug set consisting of an upper plug and a lower plug and a co-operating piece of floating equipment for use therewith in well bores and comprising an annular housing with a float valve assembly mounted therein, the said upper plug having a row of downwardly extending teeth for interengagement with a row of upwardly extending teeth provided at the upper end of the lower plug, and the lower plug having at its lower end a row of downwardly extending teeth for interengagement with a row of upwardly extending teeth at the upper end of the valve assembly, the upper and lower plugs each having elastomeric wiper means about their respective outer surfaces, the upper plug having a closed, cross section and the lower plug having an axial bore therethrough initially closed by a frangible diaphragm. In that case, the plug parts are formed as unitary mouldings of plastics material, which involves compromising of the properties of the material selected, such as adequate resilience, strength and destructibility by chilling. The present invention is mainly characterised in that, in a plug set of the general form described in US-A-4711300, the upper plug has a cavity in the bottom thereof in which is secured a first insert on which the first downwardly extending row of teeth is integrally formed; the lower plug has cavities in its upper and lower ends in which are secured respective second and third inserts on which the respective rows of first upwardly and second downwardly extending teeth are formed; said diaphragm closes the axial bore of said lower plug; said wiper means are each formed as one separate covering respectively, secured about the bodies of each of the respective plugs; and the said valve assembly is retained in the said annular housing by a body of cementitious material and has secured to it a fourth insert formed with the said row of second upwardly extending teeth. With this construction, the bodies of the plugs are readily formed of one material, such as a plastics material which is readily drilled, the wiper means are each formed as a covering of an elastomeric material to ensure good sealing, and the first, second, third and fourth inserts are formed either of plastics or other drillable material, such as aluminium. Because the inserts are each formed with a row of teeth, positive and strong interengagement between respective inserts is readily assured. US-A-4190112 discloses a non-rotating plug set which utilizes at least one insert in an upper plug of the plug set which has a portion thereof engaging the adjacent surface of a lower plug. In order that the invention may be more fully understood, reference is made to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of one embodiment of plug set of the present invention; and Fig. 2 is a cross-sectional view of a float collar, a typical piece of floating equipment, for use with the plug set of Fig. 1. Referring to Fig. 1, the plug set 10 comprises an upper plug 12 and lower plug 14. The upper plug 12 comprises a body member 16 having, in turn, a generally cylindrical exterior surface 18, first interior cavity 20 and second interior cavity 22, elastomeric wiper covering 24 having, in turn, a plurality of wipers 26 thereon, and annular anti-rotation first insert 28 having, in turn, a plurality of first downwardly extending teeth 30 formed on one end thereof and bore 32 therethrough. The body member 16 may be formed of any suitable, easily drillable material, such as plastic, aluminum, etc. Similarly, the anti-rotation first insert 28 may be formed of any suitable, easily drillable material, such as plastic, aluminum, etc. The anti-rotation first insert 28 may be retained within the second cavity 22 of the body member 16 by any suitable means, such as adhesive bonding, threaded engagement, etc. The first downwardly extending teeth 30 may be formed in the anti-rotation first insert 28 by any suitable means, such as machining, molding, etc., if the first insert 28 is molded plastic, etc. The lower plug 14 comprises a body member 36 having, in turn, a generally cylindrical exterior surface 37 and, on the interior, first bore 38, second bore 40, third bore 42 and fourth bore 44, elastomeric wiper covering 46 having, in turn, a plurality of wipers 48 thereon, annular upper annular anti-rotation second insert 50 having, in turn, a plurality of first upwardly extending teeth 52 on one end thereof and bore 54 therethrough, elastomeric diaphragm 56 and annular bottom annular antirotation third insert 58 having, in turn, second downwardly extending teeth 60 on one end thereof and bore 62 therethrough. As with the upper plug 12, the lower plug 14 may have the body member 36 and upper 50 and lower 58 anti-rotation second and third inserts formed of any suitable material, such as plastic, aluminum, etc. Similarly, the upper 50 and lower 58 anti-rotation second and third inserts may be retained within the first bore 38 and fourth bore 44 of the body member 36 by any suitable means, such as adhesive bonding, threaded engagement, etc. Also, the first upwardly extending and second downwardly extending teeth 52 and 60 on the upper 50 and lower 58 anti-rotation second and third inserts respectively, may be formed thereon by any suitable means, such as machining, molding, etc. The elastomeric diaphragm 56 is retained within the body member 36 of the lower plug 14 by clamping the diaphragm 56 between the shoulder 64 of body member 36 having, in turn, an annular rib thereon and upper end 66 of lower anti-rotation third insert 58 with an annular rib 68 on the upper end 66 biting into the diaphragm 56. Referring to Fig. 2, a typical float collar 100 for use with the plug set 10 is shown. The float collar 100 comprises an annular housing 102, cementitious material 104, and float valve assembly 106 having anti-rotation fourth insert member 108 thereon having, in turn, a plurality of second upwardly extending teeth 110 thereon. It should be noted that the configuration of the first downwardly extending teeth 30 of anti-rotation first insert 28 of upper plug 12 and the first upwardly extending teeth 52 of upper anti-rotation second insert 50 of lower plug 14 geometrically match as well as the second downwardly extending teeth 60 of lower anti-rotation third insert 58 of lower plug 14 and the second upwardly extending teeth 110 of fourth insert member 108 of float collar 100. It should also be appreciated that the geometry of the various teeth 30, 52, 60 and 110 is such that, when engaged, the torsional shear area is equal to one hundred percent (100%) of the cross-sectional area of the respective insert containing the teeth thereby providing greater torsional resistance to rotating. Additionally, it should be appreciated that although a float collar 100 has been shown, any suitable piece of floating equipment, such as a float shoe assembly, may be used with the plug set 10 so long as the floating equipment includes an anti-rotation fourth insert 108 to engage the lower anti-rotation third insert 58 of the lower plug 14. Referring to Figs. 1 and 2, the float collar 100 is assembled into a string of casing (not shown) to be connected into a well bore by the threaded bore 112 and threaded surface 114 threadedly engaging the casing. When it is desired to cement the string of casing having the float collar 100 therein in the well bore, the lower plug 14 of the plug set 10 is pumped through the casing by cement until it lands on the cementitious material 104 and float valve assembly 106 of the float collar 100 with the second downwardly extending teeth 60 of the lower anti-rotation third insert 58 engaging the second upwardly extending teeth 110 of the anti-rotation fourth insert 108 of float collar 100. As the lower plug 14 is pumped through the casing, the outer wiper covering 46 wipes drilling fluid from the interior of the casing string. After the lower plug 14 has landed on the float collar 100, the pressure of the cement being pumped behind the lower plug 14 is increased until the pressure ruptures the elastomeric diaphragm 56 of the lower plug 14 allowing cement to be pumped therethrough. After the desired amount of cement has been pumped through the casing, lower plug 14 and float collar 100, the upper plug 12 is pumped through the casing having the elastomeric wiper covering 24 thereon wiping cement from the casing until the upper plug 12 lands on the lower plug 14 having the first downwardly extending teeth 30 of the anti-rotation first insert 28 of the upper plug 12 engaging the first upwardly extending teeth 52 of upper anti-rotation second insert 50 of the lower plug 14. After a suitable waiting period for the cement to set, a drill bit is then lowered through the casing to drill out the upper plug 12, lower plug 14, cementitious material 104 and float valve assembly 106. It will be appreciated that since the first downwardly extending teeth 30 of anti-rotation first insert 28 of upper plug 12 engage the first upwardly extending teeth 52 of upper anti-rotation second insert 50 of lower plug 14 and the second downwardly extending teeth 60 of lower anti-rotation third insert 58 of plug 14 engage the second upwardly extending teeth 110 of fourth insert 108 of float collar 100, rotation of the plug set 10 is minimized during the drilling process, thereby reducing the amount of drilling time required. It will be appreciated also that during well cementing operations, only the upper plug 12 of the plug set 10 may be used or multiple lower plugs 14 of the plug set 10 may be used, if desired.

Claims: A combination comprising an anti-rotation plug set(10) consisting of an upper plug (12) and a lower plug (14) and a co-operating piece of floating equipment (100) for use therewith in well bores and comprising an annular housing (102) with a float valve assembly (106) mounted therein, the said upper plug (12) having a row of first downwardly extending teeth (30) for interengagement with a row of first upwardly extending teeth (52) provided at the upper end of the lower plug (14) and the lower plug (14) having at its lower end a row of second downwardly extending teeth (60) for interengagement with a row of second upwardly extending teeth (110) at the upper end of the valve assembly (106), the upper and lower plugs (12,14) each having elastomeric wiper means (24,40) about their respect outer surfaces, the upper plug (12) having a closed upper end and the lower plug having an axial bore (54,40,62) therethrough, and a frangible diaphragm (56) sealing said bore, characterised in that the upper plug (12) has a cavity in the bottom thereof in which is secured a first insert (28) on which the first downwardly extending row of teeth (30) is integrally formed; the lower plug (14) has cavities in its upper and lower ends in which are secured respective second and third inserts (50,58) on which the respective rows of first upwardly (52) and second downwardly (60) extending teeth are formed; said diaphragm (56) closes the axial bore (54,40,62) of said lower plug; said wiper means (24,40) are each formed as one separate covering respectively, secured about the bodies of each of the respective plugs (12,14); and the said valve assembly (106) is retained in the said annular housing (102) by a body of cementitious material (104) and has secured to it a fourth insert (108) formed with the said row of second upwardly extending teeth (110). A combination according to claim 1, wherein the body member (16) of the upper plug (12) and the anti-rotation first insert (28) therein are formed of plastic; and/or the body member (36) of the lower plug (14), and the upper (50) and lower (58) second and third anti-rotation inserts therein are formed of plastic. A combination according to claim 1, wherein the body member (16) of the upper plug (12) and the anti-rotation first insert (28) therein are formed of aluminum; and/or the body member (36) of the lower plug (14), and the upper (50) and lower (58) anti-rotation second and third inserts therein, are formed of aluminum. A combination according to claim 1,2 or 3, wherein the anti-rotation fourth insert (108) of the piece of floating equipment (100) is formed of plastic or of aluminum. A combination according to any of claims 1 to 4, wherein the first downwardly extending teeth (30) of the anti-rotation first insert (28) of the upper plug (12) are engageable with the first upwardly extending teeth (52) of the upper anti-rotation second insert (50) of the lower plug (14), and the second downwardly extending teeth (60) of the lower anti-rotation third insert (58) are engageable with the second upwardly extending teeth (110) of the anti-rotation fourth insert (108) of the piece of floating equipment (100), to provide a torsional shear area of material which is equal to one hundred percent of the cross-sectional area of the respective insert containing the teeth. A combination according to any of claims 1 to 5, wherein the anti-rotation first, second and third inserts (28,50,58) of the upper (12) and lower (14) plugs are adhesively bonded to the respective plug body member (16,36). A combination according to any of claims 1 to 5, wherein the anti-rotation first, second and third inserts (28,50,58) of the upper (12) and lower (14) plugs are threadedly engaged with the respective plug body member (16,36). A method of cementing the casing in a well bore wherein there is used a combination of plug set (10) and floating equipment (100) as claimed in any of claims 1 to 7, and wherein after the cement has set the combination is drilled out using a polycrystalline diamond compact bit.

Inventors: FREEMAN T AUSTIN, WATSON BROCK W, FREEMAN, T. AUSTIN, WATSON, BROCK W.
Applicants: HALLIBURTON CO, HALLIBURTON COMPANY
Application year: 1989
Main classification: E21B33
IPC codes: E21B29, E21B33