DRILL PIPE TORQUE-REDUCTION AND PROTECTION APPARATUS

Abstract: A torque-reduction and/or protection device for use in a drill string comprises a generally cylindrical body (10) including a mandrel portion (18) and a rotatable collar (20) mounted on the mandrel portion between first and second shoulders (22, 24), one of which is defined by a ring member (24) secured to said body after the collar has been located. A low friction bearing is provided between the collar and the mandrel including at least one of the following on the bearing surfaces of each of the collar and mandrel: low friction alloy coating; low friction ceramic coating; low friction alloy insert; low friction ceramic insert; magnetic elements. The collar has a low friction coating (30) on its outer surface comprising a composite coating having an inner layer of hard low friction material and an outer coating of relatively softer low friction material. The device may be incorporated into a sub but is preferably incorporated in a tool joint of a length of drill pipe.

Description: "Drill Pipe Torque-Reduction and Protection Apparatus" The present invention relates to improved pipe torque-reduction and protection devices for use m drill strings. More particularly, the invention relates to improved drill pipes and sub-assemblies ("subs") incorporating means for protecting drill pipe, boreholes or borehole casings and/or reducing the torque generated when rotating a drill string within a borehole or borehole casing. When a drill string is rotated within a borehole, which may or may not be lined by a borehole casing, it is common for portions of the drill string to contact the interior walls of the borehole or borehole casing during drilling. This causes wear and tear on the walls of borehole or casing and on the drill pipe forming the drill string, and increases the torque generated in the drill string by friction between the drill pipe and the borehole or casing. This is a particular problem in directional drilling where the borehole is curved m the longitudinal direction so that the drill string is more likely to contact the interior walls thereof. A variety of devices are known for protecting drill pipe/casing and for reducing torque. These include collars or sleeves which are secured around the main tubular body of the drill pipe. Such collars may be securely fixed to the drill pipe so as to rotate with the drill pipe under all conditions ("rotating" collars) or may be rotatable relative to the drill pipe, so that the collar ceases rotating (or reduces its rate of rotation) m the event of contact with the interior of the borehole or casing ("non- rotating" collars); i.e. the drill pipe rotates relative to the non-rotating collar. Known devices also include sub-assemblies ("subs") incorporating rotating or non-rotating collars which are connected between adjacent lengths of drill pipe. Protective collars of these types are formed from a variety of materials including plastics, elastomers and alloys, generally including low-friction materials on the outer surfaces of the collars and, m the case of non-rotating types, including a variety of bearing arrangements to allow rotation relative to the pipe body or the body of the sub-assembly. It s also known to incorporate protective and/or torque- reducing upsets into the mam body of the drill pipe. Devices of this type perform an additional function in stabilising the drill string and thereby reducing vibration of the string m use. The present invention relates to improved torque- reducing and/or protection devices which can be configured as subs and which can also be incorporated into the tool joints of lengths of drill pipe. It has not hitherto been known to incorporate devices of this type into the tool joints of drill pipe. The invention, m its various aspects, relates to a torque-reduction and/or protection device for use in a drill string, of the type comprising a generally cylindrical body adapted to form part of a drill string, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion. In accordance with a first aspect of the invention, the body and the collar member are formed from suitable rigid alloys (normally steel) , and low friction bearing means is provided between the collar and the mandrel including at least one of the following on the bearing surfaces of each of the collar and mandrel : low friction alloy coating; low friction ceramic coating; low friction alloy insert; low friction ceramic insert; magnetic elements. In preferred embodiments, the collar member and mandrel each include low friction ceramic inserts on their bearing surfaces. Preferably, the collar member includes cylindrical inserts extending around its inner circumference and the mandrel includes disk-shaped ceramic inserts located recesses on its outer surface. Preferably also, said bearing means defines two annular bands of bearing elements between the mandrel and collar, adjacent opposite longitudinal ends thereof. In accordance with a second aspect of the invention, the collar member has a low friction coating on its outer surface, said coating comprising a composite coating having an inner layer of hard low friction material and an outer coating of relatively softer low friction material. Preferably, said inner coating comprises ceramic material and said outer coating comprises plastic material (most preferably nylon) . Preferably also, the collar member has a generally convex outer surface in longitudinal cross section. In accordance with a third aspect of the invention, the collar member is mounted on the mandrel portion between first and second shoulders, one of said shoulders being defined by a ring member secured to said body after said collar member has been located thereon. Preferably, said ring member is secured to said body by thermal shrink fitting. Preferably also, mating surfaces of said ring member and said body are shot- blasted prior to the ring member being fitted to the body. Preferably also, mating surfaces of said ring member and said body are provided with complementary, interlocking projections and recesses providing a mechanical interlock therebetween. Preferably, said interlock is formed by cold forming the lock ring to engage a recess or recesses formed in the outer surface of the body. Alternatively, the lock ring is threadably secured to the body by a reverse hand thread (as defined herein) . In certain embodiments of the invention, said cylindrical body comprises a sub adapted for connection in a drill string. In other embodiments of the invention, said cylindrical body comprises a pipe tool joint adapted to form a tool joint of a length of drill pipe. In accordance with a fourth aspect of the invention, there is provided a drill pipe comprising a mothertube and first and second tool joints at either end thereof, wherein one of said tool joints incorporates a torque-reduction and/or protection device of the type comprising a generally cylindrical body adapted to form part of a drill string, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion. The device may incorporate any of the first to third aspects of the invention. In accordance with a fifth aspect of the invention, a method of manufacturing a drill pipe accordance with the fourth aspect comprises the steps of removing a tool joint, or portion thereof, from a conventional drill pipe and replacing said tool joint or part thereof with a modified tool joint or part thereof incorporating said device. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, which: Fig. 1 is a side view, partly section, of one embodiment of a sub incorporating a torque- reduction/protection device in accordance with the invention; Fig. 2A is a side view of a mam body portion of one embodiment of the sub of Fig. 1 ; Fig. 2B is a side view of a mam body portion of a preferred embodiment of the sub of Fig. 1; Fig. 2C is a detail view of part of the main body portion of Fig. 2B; Figs. 3A and 3B are, respectively, side and transverse sectional views of a portion of the sub of Fig . 1 ; Figs. 4A is a sectional side view of a main collar member of the sub of Fig. 1 and Figs. 4B and 4C are sectional side and end views of bearing inserts for use with the collar member of Fig. 4A; Figs. 5A, 5B and 5C are, respectively, a sectional side view and first and second end views of a locking ring forming part of the sub of Fig. 1 ; Fig. 6 is a cut-away side view of a preferred embodiment of the sub of Fig. 1, employing the main body portion of Fig. 2B; Fig. 7 is a cut-away side view of a portion of one embodiment of a length of drill pipe incorporating a torque-reduction/protection device, similar to that used in the sub of Fig. 6, in accordance with the invention; Fig. 8 is a sectional side view of a portion of a second embodiment of a length of drill pipe incorporating a torque-reduction/protection device in accordance with the invention; and Figs. 9A, 9B and 9C illustrate a preferred embodiment of a bearing which may be employed in embodiments of the present invention. Referring firstly to Figs. 1 to 6 of the drawings, a sub in accordance with the invention comprises a generally cylindrical main body portion 10 having a through bore 12, a threaded male connector ("pin") 14 at one end and a threaded female connector ("box") 16 at the opposite end. It will be understood that the pin 14 and box 16 could be replaced by any other suitable connector means for connecting the sub in a drill string. The body 10 includes a mandrel portion 18, upon which is mounted a generally cylindrical collar member 20 which is rotatable relative to the body 10. The mandrel portion 18 and collar 20 are located between first and second raised shoulder portions 22 and 24, which have an outside diameter greater than the outside diameter of the remainder of the body 10 which includes the mandrel portion 18. The first shoulder 22 is preferably formed integrally with the main body 10, whilst the second shoulder 24 preferably comprises a lock ring member which is fitted to the body 10 after the collar has been slid along the body 10 into location on the mandrel portion 18. Drill pipe and subs forming a drill string are normally inserted into a borehole pin-end down. It is preferred that the integrally-formed shoulder 22 is on the side of the mandrel 18 closest to the pin 14 (i.e. the "downward" end, in use) whilst the lock ring 24 is on the side of the mandrel 18 closest to the box 16 (i.e. the "upward" end, in use) . Some drill pipes and subs are designed to be inserted box-end down, in which case this arrangement would preferably be reversed. A stress-relief groove (not shown) , typically having a part circular cross section, is preferably formed around the angle between the integral shoulder 22 and . the body 10. The lock ring 24 would normally be non-removable, and may be secured to the body by any suitable means. Preferably, the lock ring 24 is shrink-fitted onto the body 10; i.e. the lock ring 24 is formed with an inner diameter slightly less than the outer diameter of the body 10, heated to increase its inner diameter so as to enable it to fit over the end of the body 10 and subsequently cooled so as to shrink onto the body 10. The inner surface of the lock ring 24 and the corresponding outer surface of the body 10 are preferably shot-blasted or otherwise treated to increase the friction between the two when the lock ring 24 is in place. In addition, the mating surfaces of the lock ring 24 and body 10 may be formed with complementary projections and recesses in order to provide a mechanical interlock between the two; e.g. one or more annular ridges could be formed on the inner surface of the lock ring 24 and complementary annular grooves formed around the external surface of the body 10. In preferred embodiments, the body 10 may be formed with an annular groove 60 (see Figs. 2B and 2C) and the lock ring provided with an annular groove 62 extending around its external surface (see Fig. 5A) . The lock ring is deformed by cold forming after shrink fitting so that its interior surface interlocks with the groove 60 of the body 10. Alternatively, in some embodiments the lock ring 24 might be threadably connected to the body, employing a left hand thread (i.e. a thread of opposite hand to the mam drill string connections) , as shall be discussed further below. The shoulder portions 22 and 24 have outer surfaces which taper from a maximum outside diameter to the outside diameter of the body, the directions towards the adjacent ends of the body 10. The body 10, collar member 20 and lock ring 24 are all formed of steel or other suitable alloy (s) . The annular bearing surfaces of the shoulders 22 and 24 and/or the annular end surfaces of the collar 20 are preferably formed from low friction alloy (s) . A low friction bearing is provided between the collar 20 and the mandrel 18. In the illustrated embodiment, the mandrel 18 is formed with recesses its outer surface, in which ceramic discs 26 are mounted and machined to form a smooth, continuous surface. The inner surface of the collar member 20 is formed to receive cylindrical ceramic inserts 28 inserted from either end thereof . Other arrangements of ceramic inserts on the mandrel 18 and collar 20 may be employed. For example, the inserts 28 could be of low friction alloy or could be formed from steel with ceramic elements inserted therein. Alternatively, the bearing surfaces can be provided with low friction coatings; e.g. ceramic or low friction alloy material applied by spray fusion methods. Where ceramic materials are used, these are preferably of a relatively pliable type. Alternatively or additionally, the mandrel 18 and/or collar 20 may include magnetised elements so as to provide a magnetic repulsion bearing. The configuration of the bearing and the types of materials employed may be varied provided that the resulting bearing is capable of sustaining high loads over a reasonable lifetime. Figs. 9A, 9B and 9C illustrate a preferred form of bearing which may be employed in any of the embodiments of the invention. First sets of inner ceramic disks 70 are provided on the mandrel, located in holes formed around the circumference of the outer surface of the mandrel. The inner disks 70 have convex outer surfaces 72 which match the curvature of the mandrel surface. Second sets of outer ceramic disks 74 are provided on the collar, located in holes formed around the circumference of the inner surface of the collar. The outer disks 74 have concave outer surfaces 76 which match the curvature of the inner surface of the collar. As shown in Figs. 9B and 9C, the positions of the disks 70 and 74 on the mandrel and the collar are offset relative to one another and spaced apart by distances less than the diameter of the disks so as to provided continuous ceramic- ceramic contact around the circumference of the bearing. As seen m Fig. 9C, the bearing may comprise two annular bands of ceramic disks, each band comprising a pair of rings of ceramic disks, located adjacent either end of the mandrel/collar. The outer surface of the collar 20 preferably has a slightly convex configuration m longitudinal cross section, most preferably arcuate but alternatively a non-arcuate curved profile or a combination of straight line segments and/or curved segments, so as to minimise the contact area between the collar and a casmg/borehole wall. In use, the outer surface of the collar 20 will contact the interior surface of the borehole casing and/or the open borehole wall . When such contact occurs, the body 10 will rotate within the collar 20. In order to minimise longitudinal friction, the outer surface of the collar 20 is preferably provided with a low friction coating 30 (the thickness of the coating is exaggerated the drawings) . Typically, when the drill string is being run, the collar will firstly contact the casing wall and will subsequently contact open borehole wall. Preferably, the coating 30 comprises a composite coating having an inner layer of hard-wearing, low friction material 13 such as ceramic or alloy materials (suitably similar to those which may be employed m the mam collar bearing) applied oy spray fusion methods, and an outer layer of relatively softer low friction material, suitably a polymer material such as nylon, which may also be applied by spray techniques. When the collar 20 is passing through casing, the outer coating will provide low friction contact without damaging the casing wall. Once the collar 20 passes into open borehole, the outer coating will erode relatively quickly, exposing the hard-wearing inner layer. The inner layer might typically be about 0.5 mm (0.02 inches) thickness and the outer layer about 2 mm to 2.5 mm (0.08 to 0.1 inches) in thickness . The design of the sub is relatively simple and very robust, being relatively inexpensive to manufacture and refurbish. The collar 20 may be removed by machining off the lock ring 24, which may be regarded as a consumable item, to allow refurbishment of the outer and inner bearing surfaces of the collar 20 and/or the outer bearing surface of the mandrel 18. Figs. 2B and 6 show a slightly modified embodiment of a sub, in which the profiles of the shoulder portions 22A and 24A differ from those of the preceding embodiment. It is still preferred that the pm-end (downward end) shoulder 22A is integrally formed with the mam body 10 and the box-end (upper end) shoulder 24A comprises a lock ring, as previously described. Whilst the embodiments of the invention described thus far improve upon existing sub- type designs of torque-reduction/protection devices, there are disadvantages m employing subs a drill string. Expense is incurred in making up connections between drill string components and it is desirable to minimise the number of connections for this reason and also to avoid reducing the mechanical integrity of the drill string. Also, subs generally produce local increases in the stiffness of the drill string which is disadvantageous, particularly m directional drilling. This is exacerbated by the fact that subs must have a certain minimum length to allow them to be gripped by power tongs for making up threaded connections. Accordingly, m accordance with a further aspect of the invention, the present torque- reduction/protection device may be incorporated into the tool joint of a length of drill pipe, as illustrated m Figs. 7 and 8. Fig. 7 shows a box-end portion of a length of drill pipe comprising a mothertube portion 40 and a tool joint portion 42, as is well known the art. In accordance with one aspect of the present invention, the tool joint portion 42 incorporates a torque- reduction/protection device which may be similar to those previously described with reference to Figs. 1 to 6. In this embodiment, the device is 15 substantially identical to that of Fig. 6, like features being designated by like reference numerals, and will not be described m detail. The drill pipe could be manufactured initially the manner illustrated, or a conventional drill pipe could be converted by removing the conventional tool joint, or a part thereof, and replacing it with a modified tool joint portion 42 incorporating a torque-reduction/protection device m accordance with the present invention. For example, the conventional tool joint could be cut at line 44 and a replacement tool joint portion 42 friction welded to the end of the remaining drill pipe, or the conventional tool joint could be cut at line 46 and a replacement tool joint portion stub welded to the remaining drill pipe. It will be understood that the device incorporated into the tool joint 42 may include any of the features or variations previously described in relation to Figs. 1 to 6. Fig. 8 illustrates a second embodiment of a pipe tool joint incorporating a device m accordance with the invention. In this case, like reference numerals designate features corresponding to features of Fig. 7. The basic mandrel, collar and bearing arrangements may be the same as or similar to those described relation to the preceding embodiments. With the configuration shown, this embodiment may be implemented by removing the conventional tool joint of a drill pipe welding the tool joint to end of the remaining pipe at line 44A by friction welding. The principal differences between this embodiment and that of Fig. 7 are that the integral shoulder 48 is adjacent the free end of the tool joint 42 and the lock ring 50 threadably engages a corresponding threaded portion 52 formed on the other side of the mandrel 18 from the integral shoulder 48. In this embodiment, intended for a conventional "pin-down" drill pipe which is to be rotated clockwise a borehole, the lock ring 50 has a left handed thread, so that any torque applied to the lock ring as a result of rotation of the drill string in normal use will tend to tighten the lock nut 50. The "hand" of the thread to achieve this effect will thus depend on which end of the drill pipe incorporates the device, the intended direction of rotation of the drill pipe etc. Generally, the lock ring thread will be of opposite hand to the threads of the box/pm connections of the drill pipe. The term "reverse- hand thread" is used herein to specify a thread of hand which will tend to tighten in response to rotation of the drill string in its usual working conditions. The lock ring 50 is preferably formed with a uniform outer diameter and secured to the tool joint 42 after the collar 20 has been installed. Thereafter, the shaded area 50S of the lock ring 50 is machined off to provide an inclined surface facing the direction of insertion of the drill pipe, suitably co-linear with the adjacent profile of the tool joint. The inner diameters of the collar 20 and lock ring 50 are sufficiently large to pass over the pin-end tool joint (not shown) of the drill pipe. For this reason, it is preferred that this embodiment be applied to the box-end tool joint of the pipe. It will be understood that embodiments of the present invention may incorporate features which are known from existing torque-reduction/protection devices, if considered necessary or desirable in particular circumstances, such as flutes or other fluid passages in the main bearing between the collar and the mandrel and/or in the outer surface of the collar. Improvements and modifications may be incorporated without departing from the scope of the invention.

Claims: Cl aims 1. A drill pipe comprising a mothertube and first and second tool joints at either end thereof, wherein one of said tool joints incorporates a torque- reduction and/or protection device of the type comprising a generally cylindrical body, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion. 2. A torque-reduction and/or protection device for use m a drill string, of the type comprising a generally cylindrical body adapted to form part of a drill string, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion; wherein: the collar member is mounted on the mandrel portion between first and second shoulders, one of said shoulders being defined by a ring member secured to said body after said collar member has been located thereon. 3. A device as claimed m claim 2, wherein the other of said shoulders is formed integrally with 4. A device as claimed m claim 2 or claim 3, wherein said ring member is secured to said body by thermal shrink fitting. 5. A device as claimed any one of claims 2 to 4 , wherein mating surfaces of said ring member and said body are shot-blasted prior to the ring member being fitted to the body. 6. A device as claimed in any one of claims 2 to 5 , wherein mating surfaces of said ring member and said body are provided with complementary, interlocking projections and recesses providing a mechanical interlock therebetween. 7. A device as claimed m any one of claims 2 to 6 , wherein a mechanical interlock is formed between mating surfaces of said ring member and said body by cold forming the lock ring to engage at least one recess formed in the outer surface of the body. 8. A device as claimed m claim 2 or claim 3, wherein the lock ring is threadably secured to the body by a reverse hand thread. 9. A device as claimed m any one of claims 2 to 8, wherein the body and the collar member are formed from rigid alloys. 10. A torque-reduction and/or protection device for use in a drill string, of the type comprising a generally cylindrical body adapted to form part of a drill string, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion; wherein: the body and the collar member are formed from rigid alloys and low friction bearing means is provided between the collar and the mandrel including at least one of the following on the bearing surfaces of each of the collar and mandrel: low friction alloy coating; low friction ceramic coating; low friction alloy insert; low friction ceramic insert; magnetic elements. 11. A device as claimed claim 10, wherein the collar member and mandrel each include low friction ceramic inserts on their bearing surfaces. 12. A device as claimed in claim 11, wherein the collar member includes cylindrical inserts extending around its inner circumference and the mandrel includes disk-shaped ceramic inserts located in recesses on its outer surface. 13. A device as claimed claim 11, wherein the collar member includes disk-shaped ceramic inserts located in recesses on its inner surface the mandrel includes disk-shaped ceramic inserts located in recesses on its outer surface. 14. A devices as claimed any one of claims 10 to 13, wherein said bearing means defines two annular bands of bearing elements between the mandrel and collar, adjacent opposite longitudinal ends thereof. 15. A torque-reduction and/or protection device for use in a drill spring, of the type comprising a generally cylindrical body adapted to form part of a drill string, said body including a mandrel portion, and a collar member rotatably mounted on said mandrel portion; wherein: the collar member has a low friction coating on its outer surface, said coating comprising a composite coating having an inner layer of hard low friction material and an outer coating of relatively softer low friction material. 16. A device as claimed in claim 15, wherein said inner coating comprises ceramic material and said outer coating comprises plastic material. 17. A device as claimed in any one of claims 2 to 16, wherein the collar member has a generally convex outer surface m longitudinal cross section. 18. A device as claimed in any one of claims 2 to 17, wherein said cylindrical body comprises a sub adapted for connection in a drill string. 19. A device as claimed any one of claims 2 to 17, wherein said cylindrical body comprises a pipe tool joint adapted to form a tool joint of a length of drill pipe. 20. A drill pipe as claimed in claim 1, wherein said torque-reduction and/or protection device comprises a device as claimed in any one of claims 2 to 17. 21. A method of manufacturing a drill pipe as claimed in claim 1 or claim 20, comprising the steps of removing a tool joint, or portion thereof, from a conventional drill pipe and replacing said tool joint or part thereof with a modified tool joint or part thereof incorporating said device.

Inventors: CRAIG MARK WILLIAM, SCHMIDT KARL, STEWART ARTHUR DEACEY, CRAIG, MARK, WILLIAM, SCHMIDT, KARL, STEWART, ARTHUR, DEACEY
Applicants: CRAIG MARK WILLIAM, SCHMIDT KARL, STABLE SERVICES LTD, STEWART ARTHUR DEACEY, CRAIG, MARK, WILLIAM, SCHMIDT, KARL, STABLE SERVICES LIMITED, STEWART, ARTHUR, DEACEY
Application year: 2001
Main classification: E21B17
IPC codes: E21B17