GB2361498A

GB2361498A - Drill pipe protector assembly

Info

Publication number: GB2361498A
Application number: GB0116875A
Authority: GB
Inventors: Norman Bruce Moore; Andrew Dale Fuller
Original assignee: WWT International Inc
Current assignee: WWT International Inc
Priority date: 1999-01-06
Filing date: 2000-01-06
Publication date: 2001-10-24
Anticipated expiration: 2020-01-06
Also published as: GB2361499B; GB0116875D0; GB0116876D0; GB2361498B; GB2361499A

Abstract

A drill pipe protector comprises a cylindrical sleeve having wedge shaped channels 142 separated by ribs 144 on the outside thereof. The channels narrow in width and depth to facilitate a fluid bearing between the sleeve and an adjacent wall of a wellbore. The protector also includes a port 146 in each of the channels to allow pressurised fluid to enter the channel from the interior of the sleeve.

Description

DRILL PIPE PROTECTOR ASSEMBLY

FIELD OF THE INVENTION

This invention relates generally to non-rotating drill pipe protectors attached to a drill string, and more particularly, to drill pipe protectors that provide hydraulic lift and/or improved sliding lubrication when moving in a borehole.

BACKGROUND OF THE INVENTION

The drilling of holes or bores into underground formations and particularly, the drilling of oil and gas wells, is typically accomplished using a drill bit which is attached to the lower end of an elongated drill suing. The drill string is constructed from a number of sections of tubular drill pipe which are coupled at their ends to form the "drill string." The drill string extends from the drilling surfitce into a well or "wellbore" which is formed by the rotating drill bit As the drill bit penetrates deeper or fi=her into an underground formation. additional sections of drill pipe -15 are added to the drill string.

Casing is generally installed in the wellbore from the drilling surfi= to various depths.

The casing lines the wellbore to prevent the wall of the wellbore from caving in and to prevent seepage of fluids from the surrounding formations from entering the wellbore. The casing also provides a means for recovering the petroleum if the well is found to be productive.

A drill suing is relatively flexible, being subject to lateral deflection, especially at the regions betweenjoints; or couplings. In particular, the application of weight onto the drill string or resistance from the drill bit can cam axial forces which in turn can cause lateral deflections.

These deflections can result in portions of the drill string contacting the casing or wellbore. in addition, the drilling,operation may be along a curved or angled path, commonly known as "directio ' nal drilling." Directional drilling also causes potential contact between portions of the drill suing and the casing or well bore.

Contact between the drill string and the casing and well bore creates frictional torque and drag. In f6ct, a considerable amount oftorque can be produced by the effects offrictional. forces developed between the rotating drill pipe and the casing or the wall of the well bore. During drilling operations, additional torque is required while rotating. the drill suing to overcome this resistance. In addition, the drill string is subjected to increased shock and abrasion whenever the drill string comes into contact with the wall ofthe well bore or, where lined, the casing. Drilling tools and associated drill string devices encounter similar problems.

To alleviate these problems, drill pipe protectors am typically spaced apart along the length ofthe drill pipe. These drill pipe protectors were originally made from sleeves of rubber or other elastomeric material which were placed overthe drill pipe to keep the drill pipe and its connections away from the walls of the casing and/or formation. Rubber or other clastorneric materials were used because of their ability to absorb shock and impart minima wear.

4- I Previously available drill pipe protectors have an outside diameter (O.D.) greater than that of the drill pipe joints, and were installed or clamped rigidly onto the drill pipe at a point near the joint connections of each length of drill pipe. The O.D. is specifically sized to be larger than the tool joint, but not too large as to restrict returning fluids which could result in "pistoning" of the protector in the hole. Such an installation allows the protector only to rub. against the inside wall of the casing as the drill pipe rotates. Although wear protection for the casing is the paramount objective when using such drill pipe protectors, they can produce a significant increase in the rotary torque developed during drilling operations. In instances where there may be hundreds of these protectors in the wellbore at any one time. they can generate sufficient accumulative torque or drag to adversely affect drilling operations if the power required to rotate the drill pipe approaches or exceeds the supply power available.

In response to the problems of wear protection and torque build up, improvements have been directed toward producing drill pipe/casing protectors from various low friction materials in different configurations. However, such an approach again has only been marginally effective, and oil companies still are in need of an effective means to greatly reduce the wear and frictionally-developed torque normally experienced particularly when drilling deeper wells and deviated wells.

U.S. Patent No. 5,069,297 to Krueger, et al., assigned to the assignee of the present application, and incorporated herein by reference, disclosesadrill pipe/casing protector assembly which has successfully addressed the problems of providing wear protection for the casing and reduced torque build up caused by the drill pipe protectors during drilling operations. The protector sleeve in the '297 patent rotates with the drill pipe during normal operations in which there is an absence of contact between the protector sleeve and the casing, but the protector sleeve stops rotating', or rotates very slowly, while allowing the drill pipe to continue rotating within the sleeve unabated upon frictional contact between the sleeve and the casing. Thrust bearings are rigidly affixed to the drill pipe at opposite ends of the protector sleeve. and these. in combination with the internal configuration of the protector sleeve, produce a fluid bearing effect in the space between the inside of the sleeve and the outside of the drill pipe. The fluid bearing effect is produced by circulating drilling fluid through the space between the sleeve and the drill pipe so that it reduces frictional drag between the rotating drill pipe and the sleeve when the sleeve stops rotating from contact with the casing.

U.S. Patent No. 5,803,193, to Krueger., et al., assigned to the assignee of the present application, and incorporated herein in its entirety by reference. discloses a drill pipelcasing protector assembly which provides an enhanced fluid bearing effect that reduces frictional drag between the rotating drill string and the protector sleeve during use.

Although modem drill string protector designs have improved the lubrication and protection of both the drill string and the casing, there is still, a need for improved sliding lubrication. In addition, there is a need for hydraulic lift to overcome the heavy normal forces I and torques encountered bY the operating drill string. This problem is especially significant in extended reach drilling. In long holes and as depth increases. the friction of. the drill string against the hole wall increases resulting in difficulty in putting weight on the drill bit or a tendency for the weight to surge forward then reduce in a 'Stickion" type process. Thus. a drill pipe protector that both reduces the torque from the drill string and increases the sliding ability of the driff string against the casing is highly desirable.

SUMMARY OF THE INVENnON

The present invention overcomes the aforementioned problems by providing in one embodiment a drill pipe protector assembly that provides hydraulic lift and improved sliding lubrication to a drill strine. Ile creation of hydraulic lift and forced lubrication reduces wear on the protector and on the casing or well wall as well as reducing sliding friction of the drill pipelprotector combination relative to the casing or well wall.

By providing a drill pipe protector assembly having a fluid pathway which directs a portion ofthe drilling mud moving through the annular space between the drill pipe protector and the chill pipe to the annular spacebetween the protector and the casing or outer well wall, hydraulic lift is created and sliding lubrication is achieved. By providing shaped channels along the longitudinal length of the outer surface ofthe protector. increased hydraulic lift is.developed.

In one embodim=L the present invention is generally directed to a drill pipe protector 20- which defines a tubular sleeve that fits over the drill pipe. The sleeve is attached to a section of drill pipe and resides over the drill pipe. The sleeve is positioned betwem the outer diameter of the drill pipe and an associated well casing or Well hole. The sleeve is adapted to provide hydraulic lift and lubrication relative to the well casing and thus, increase the proclivity of the drill pipe to slide down the hole while also reducing the development of cutting dams.

More specifically, the drill pipe protector assembly comprises a tubular body having an inner surface and an outer surface and extends along a longitudinal axis between a first end and a second end. Ile tubular body is adapted to be disposable about the outside of a drill string and within the wellbore or casing. A channel is formed on the outer surface of the body and extends substantially along the longitudinal axis from the first end to the second end. The channel directs the -flow of drilling fluid between the outer surface and the inside surface of the casing. An opening extends radially from the inner surface to the outer surface of the tubular body. 17he opening allows the passage of the drilling fluid from the inner surface to the outer surface.

In this embodiment the protector is a generally cylindrical shaped tubular body having a plurality of spaced apart channels along its outer surface. The outer surface includes a plurality of radially outwardly protruding ridges which extend substantially along the longitudinal axis.

Ther idges are spaced.apart sufficiezit so as to form the described channels therebetween. At lean one, and preferably, all ofthe channels include an opening which allows the drilling fluid to pass ftorn the inner surface to within the channel.

3- The sleeve includes a plurality of spaced apart radial openings or diffusor ports which directs a portion of the drilling mud moving longitudinally through the annular space between the inside of the sleeve and drill pipe to the annular space between the outside of the sleeve and the casing or outer we] I wall. 'Me outside surface of the sleeve also includes a plurality of shaped channels which are in communication with these radial openings. The channels direct the flowing mud to lubricate the outer surface of the sleeve and create hydraulic lift relative to the casing wall.

In a second embodiment of the present invention, the drill pipe protector assembly is a tubular sleeve having a plurality of longitudinally extending and radially protruding ridges formed on its outer surface. The ridges or ribs are spaced apart to define channels therebetween and at least some of the channels are configured to define a longitudinally extending channel having a double wedge shape. The double wedge shaped channels form passageways for the longitudinal flow of the drilling mud along the outer surface of the sleeve. Each channel or passageway includes a radially oriented internal passageway that interconnects the drilling fluid I passing through the annular space between the sleeve a nd the drill pipe and the annular space between the outside of the sleeve and the casing. Each double wedge shaped channel defines an increasingly narrower and shallower passageway which transitions to a increasingly wider and deeper passageway along its longitudinal length. The double wedge shape accelerates and then decelerates the flow to create ahydraulic lift relative to the casing wall and also enhance the flow of the drilling mud therebetween.

In another aspect ofthe present invention, the protector assembly includes a tubular sleeve for use with drill tool assemblies, such as a logging line stand off protector. The sleeve includes channels formed on the outer surface for directing the flow of mud in the annular space between the channels and the casing. In addition. the sleeve includes a plurality of spaced apart radially oriented internal passageways that interconnects the drilling mud passing through the annular space between the sleeve and the drill pipe and the annular space between the outside of the sleeve and the casing.

In another embodiment of the present invention, the protector incorporates low-friction material pads on the external surfaces. The pads are made of Teflon composites.

These and other features and advantages of the invention will be apparent and more fully understood by those of skill in the art by referring to the following detailed description of the preferred embodiments which is made in reference to the accompanying'drawings, a brief description of which is provided below.

DESCREPTION OF THE DRAWINGS FIG. I is a schematic side elevadional view, partly in cross-section, showing a string of drill pipe having drill pipe/casing protector assemblies according to this invention installed between tooljoints of the drill pipe in adeviated well being drilled in an underground formation; PCTAISOO/00299 FIG. 2 is a detail view of FIG. I illustrating one drill pipe joint and one drill pipe protector; FIG. 3A is a front cross-sectional view of a first embodiment of a hydrolift drill pipe Protector assembly constructed according to the principles of the present invention; FIG. 3B is a side cross-sectional view of the drill pipe protector assembly of FIG. 3A.

showing diffuser exit pons; FIG. 4 is a cross-sectional view ofan alternative embodiment hydrolift drill pipe protector; FIG. 5A is a side view of the protector of FIG. 4; FIG. 5B is a cross-sectional view of the diffuser of FIG. 5A:

FIG. 6 is a detail view showing different cross-sectional configurations of the diffuser ports; FIG. 7 is a perspective view of a wedgeelift type drill pipe protector constructed a=rding to the principles of the present invention; FIG. 8 is a partial perspective view of a first alternative wed-gelift type drill pipe protector shown mounted over a section of drill pipe; FIG. 9 is a partial perspective view ofa second alternative embodiment of a wedgelift type drill pipe protector shown mounted over a section of drill pipe and positioned in a section of casing; FIG. 10 is a perspective view of a drill pipe tool joint constructed according to the principles of the present invention and showing the wedgelift configuration on the external surface; FIG. I I is a partial perspective view of a drill pipe protector constructed according to the principles of the present invention and showing a hydrolift type opening and a wedgelift configuration on the external surface:

FIG. 12 is a side cross sectional view of the drill pipe protector assembly of FIG. 10 showing the hydrolift ports and the wedgelift. channels on the external surface; FIG. 13 is a cross-sectional view of a four-sided low ftiction non-rotating drill pipe protector of the present invention; FIG. 14 is a cross-sedional view of a two-sided low -friction non-rotating drill pipe protector of the present invention; FIG. 15 is a partial cross section of a wedgelift type drill pipe protector incorporation low friction pads: and FIG. 1 6 is a partial cross section of a wedgelift type drill pipe protector incorporating low friction studs.

DETAELED DESCRIPTION OF THE INVENTION

FIG. I illustrates a well drilling system for drilling a well in an underground formation 10.

A rotary drill string comprises a plurality of elongated tubular drill pipe sections 12 which drill I a well bore 14 with a- drilling tool IS installed at the bottom of the drill string. An elongated cylindrical tubular casing 16 can be cemented in the well bore to isolate and/or support formations around the bore. The invention is depicted in a deviated well which is drilled initialiv along a somewhat straight path and then curves near the bottom and to the side in a dog leg fashion. It is the drilling of wells of this type that can substantially increase the torque applied to the drill string during use, and where the present invention, by reducing the amount of torque build up, makes it possible to drill such deviated wcs to greater depths and to drill them more efficiently while preventing damage to the casing and drill pipe.

The invention is further described herein with respect to its use inside a casing in a well bore, but the invention also can be used to protect the drill pipe from damage caused by contact with the wall of a bore that does not have casing. Therefore, in the description and claims to follow, where references are made to contactwith the wall or inside diameter (I.D.) of a casing.

the description also applies to contact with the wall of the well bore, and where references are made to contact with a bore. the bore can be the wall of a well bore or the I.D. of a casing.

As illustrated. separate longitudinally spaced apart drill pipe protector assemblies 18 are mounted along the length of a drill string to protect the casing from damage that can occur when rotating the drill pipe inside the casing. The sections of the drill pipe are connected together in the drill string by separate drill pipe tool joints 20 which are conventional in the art. The drill pipe can produce both torque and drill pipe casing wear and resistance to sliding ofthe drill strin g in the hole. The separate drill pipe protectors 18 are mounted to the drill string 12 adjacent to each of the tool joints to reduce drill string torque, reduce sliding friction forces. reduce shock and vibration to the drill string and abrasion to the inside wall of the casing.

When the drill pipe is rotated inside the casing, its tool joints would normally be the first to rub against the inside of the casing, and this rubbing action will tend to wear away either the casing, or the outside diameter of the drill pipe,. or its tool joints, which can greatly reduce the protection afforded the well or the strength of the drill pipe or its.tool joints. To prevent this damage from occurring. the outside diameter of the drill pipe protector sleeve, which is normally made from rubber or a low fiiction polymeric material. is greater than that of the drill pipe and its tool joints. Such an instaIlation allows the protector sleeve only to rub against the casing.

Although they are useful in wear protection, these protectors can generate substantial cumulative torque along the length of the drill pipe, particularly when the hole is deviated from vertical as shown in FIG. 1. This adversely affects drilling operations, primarily by producing ffiction which reduces the rotation and torque valve generated at the surface and which is then translated to the drill bit. The present invention provides a solution to this problem.

FIG. 2 further schematically illustrates a drill pipe protector assembly of the present invention. Drill pipe protector 18 is sandwiched loosely between upperand lowerthmst bearings 22 and 24 which are rigidly affixed to the O.D. of the drill pipe section 12. A small gap exists between the drill pipe protector and the thrust bearings. The drill pipe protector is mounted to I the drill pipe using techniques which hold the protector on the drill pipe and which allow the sleeve to normally rotate with the i drill pipe during drilling operations; but when the drill pipe protector sleeve comes into contact with the casing 16, the sleeve stops rotating. or at least slows down substantially, while allowing the drill pipe to continue rotating inside the drill pipe protector. This change in point of rotation from the outside diameter, i.e O.D. of the protector to the O.D. of the drill pipe. in effecL reduces the distance at which the friction associated with drill pipe rotation is applied to the drill pipe.

HYDROLIFT TYPE DRILL PrPE PROTECTOR Referring now to FlGs.3A and 3B, a hydrolift type non-rotating drill PiPe Protector 30 is shown.

The hydrolift non-rotatingg drill pipe protector 30 comprises an elongated tubular sleeve made from a suitable protective material, such as, a low coefficient of friction, polymeric materiaL metal or rubber material. A presently preferred material is a high density polyurethane or rubber material. The sleeve has an inside diameter (I.D.) 32 in a generally circular configuratiorL The I.D. further includes a plurality of elongated longittuhnally extending, straight parallel axial grooves 34 spaced apart circurnferentially around the ID. of the sleeve.

The grooves are open ended in the sense that they open through an annular first end 34 and annular opposite second end 36 of the sleeve.

'Me inside wall of the sleeve is divided into intervening wall sections between adjacent pairs of the grooves 34. Each wall section has an inside bearing surface. For polyurethane.or rubber sleeves, a metal reinforcement cage 38 is embedded within the sleeve between the I.D.

wall 32 and the outer diameter (O.D.) wall 40. The metal reinforcing cage 38 has a retainer hinge 42 for attaching the protector 30 to the drill pipe 12. In the embodiment shown in FIGs. 3A and 3B the wall thickness of the protector 30 varies between the I.D. and the OD. so that the protector is egg shaped in cross section. Located at the base of the egg shaped'protector is a diffuser 44. The diffuser 44 has a plurality of exit ports 46a-46f which. with the exception of port 46f, extend from the IM. 32 to the O.D. 40. The diffuser 44 can be rigidly connected.to cage 39 by fitsteners 48 or alternatively can be integrally molded into the sleeve.

The wall thicimess of the protector 30 is such that the drill pipe protector has an O.D.

greater than the OD. of the ad acent drill pipe tool joints 20. The annular first 34 and second 36 edges ofthe protector sleeve have a configumtion that functions to draw fluid between the sleeve and the collar, thereby assisting in the. formation'of a fluid bearing between the' IA of the protector and the OM. of the drill pipe 12. The first edge 34 includes a generally flat annular inside edge section 50 extending horizontally and generally at a right angle to the vertical inside wall of the sleeve. Ile edge section 50 has a beveled edge section 52 leading to the vertical inside wall to prevent or reduce the wear to the drill pipe brought about by the action' of axial I forces. 'Me angular section 52 works to reduce wear experienced on the ends of the protector sleeve and the drill pipe when acted upon by heavy axial loading.

The drill pipe protector sleeve 30 is split longitudinally to provide a means for spreading apart opposite sides of the sleeve when mounting the sleeve to the O.D. of the drill pipe. FIG. 33A -5 illustrates a pair of diametrically opposed vertically extending edges 54 that define the ends of a longitudinal split that splits the sleeve into halves. The sleeve is split longitudinally and is fastened by a latch pin 56 which "tends through retainer hinge 42. Alternatively, the sleeve halves may be hinged along one side and releasably fastened on an opposite side bY a latch pin, or they may be secured along both opposite sides by bolts. The metal cage 3 8 forms an annular reinforcing ring embedded in the molded body of the sleeve. (A protector sleeve made of metal includes no reinforcing cage). The purpose of the cage is to reinforce the strength of the sleeve.

The cage can absorb the compressive. tensile and shear forces experienced by the sleeve when operating in the casing or wellbore. The reinforcing cage can be made from expanded metal, metal sheet stock, or metal strips or composite (fiber). One presently preferred technique is to is form the reinforcing member from a steel sheet stock with holes uniformly distributed throughout the sheet.

The confronting top and bottom thrust bearings 22 and 24 as described in FIG. 2 have adjacent annular end surfaces confronting the top and bottom annular end surfaces of the sleeve at essentially the same angular orientations. The upper and lower thrust bearings 22 and 24 are rigidly affixed to the O.D. of the drill pipe above and below the drill pipe protector sleeve. The thrustbearings (also refenvd to as collars) are metal collars made of a material such as aluminum, or a hard plastic material, such as, composites of TeflonTm 1/3-3/a graphite fibers to encircle the drill pipe and project outwardly from the drill pipe. The collars project a sufficient axial distance along the drill pipe to provide a means for retaining the sleeve in an axially affixed position on the drill pipe., restrained between the two thrust bearings. The thrust bearings are rigidly affixed to the drill pipe and rotate with the drill pipe during use. The means for securing the thrust bearings to opposite ends of the sleeve can be similar to fastening means shown in U.S. Patent No. 5,069,297. T'he upper and lower thrust bearings are affixed to the drill pipe to provide a very narrow upper working clearance between the bottom of the upper thrust bearing and the annular top edge ofthe sleeve and a separate lower working clearance between the top of the lower thrust bearing and the bottom annular edge of the sleeve. The lower clearance can be narrow, such as one quarter of an inch or a clearance as much as one inch. The bearings are preferably split and bolted or hinged and bolted with spaced apart cap screws on outer flanges of the coilar.

During use, when the rotary drill pipe is rotated within the casing or well, the outer surface of the drill pipe protector sleeve comes into contact with the interior surface of the csing or wellbore. 'Me sleeve, which is normally fixed in place on the drill pipe, rotates with the drM pipe during normal drilling operations. However. under contact with the inside wall of the casing, the sleeve stops rotating, or its rotational speed is greatlyTeducedL while allowing the drill pipe to -81 continue rotating inside the sleeve. The configuration of the I.D. of the sleeve is such that the drill pipe can continue rotating while the sleeve is nearly stopped or rotating slightly and yet its stoppage exerts minimal frictional drag on the O.D. of the rotating drill pipe. The inside beating surface ofthe sleeve, in combination with the axial grooves, induces the circulating drilling mud within the annulus between the casing and the drill pipe to flow under pressure at one end of the sleeve through the parallel grooves to the opposite end of the sleeve. This produces a circulating flow of drilling mud under pressure at the interface of the sleeve and the drill pipe and this fluid becomes forced into the bearing surfaces between the grooves. TIds deforms or spreads apart the bearing surface regions to produce a pressurized thin film oflubricating fluid between the sleeve I.D. and the drill pipe O.D. which reduces frictional drag between these two suzfaces. This action ofthe lubrication being forced into the region between the sleeve and the drill pipe acts as a fluid bearing to force the two surfaces apart. and such action thereby reduces the friction that would normally be experienced both on the O.D. of the drill pipe and the ID. of the sleeve due to the fact that a thin film of fluid is separating the two surfaces. Since the fluid separates these two Is surfaces the torque developed as a result of the rotation is greatly reduced.

In addition the thrust bearings at opposite ends of the sleeves, which retain the sleeves position on the drill part, also assist in producing a ftuther fluid bearing effect at the ends of the sleeve.

As previously stated pressure is generated by the hydraulic bearing formed in the space 58 between the O.D. of the drill pipe and the I.D. of the protector. The pressure is directed to the diffuser exit ports 46a-46f that delivers fluid to the region between the protector 30 and the internal surface of the casing 16. The pressurized fluid tends to exit. the diffuser tending to lift the protector and simultaneously lubricate the interface of the sleeve to the casing. Ilm fluid movement through the exit ports also tends to clean cuWW from the bottom of the hole thus helping to prevent "stuck pipe' conditions. The pressure at which the hydraulic bearing fluid exits the diffuser exit ports can be varied by the speed at which the drill pipe is rotated. For =ample rotating the pipe more rapidly increases the pressure thus improving sliding and liffing ofthe drill pipe. The number of exit ports also can be varied to. adjust the desired lift. The geometrical configuration of the exit ports 46a-46f can include circular, rectangular or other specialized shapes. Although_the exit ports direct fluid in between the outer surface of the diffuser and the inner surface of the casing, the exit ports can be placed on the ends of the sleeve to direct fluid towards the collar to improve life of the collar through reduced loads and improve lubrication. For example, exit port 46f directs fluid towards the collar.

The protector 30 incorporates an egg shaped configuration so that during lateral-drilling the diffuser exit ports am always positioned at the bottom of the hole to lift the drill pipe off of the casing.

An alternative embodiment hydrolift non-rotating drill pipe"protector 60 is shown in FIGs. 4 and 5. In this embodiment, protector 60 is eccentric relative to the drill pipe 12 resulting I in less wall thickness- near wear pads 62 and a greater wall thickness at the region near the retainer hinge 63. This configuration results in a self-positioning of the diff-user 64 at the lowest portion of the casing 16. Having a thinner area opposite the hinge 63 also facilitates in opening of the sleeve for installation onto the pipe. The region near the hydrolift exit ports 66a-66j thus substantially becomes the portion of the protector that interfaces with the casing. In this embodiment the thinner diffuser portion can be made from low friction material to improve sliding or alternatively the entire protector can be made from a low friction material.

The protector 60 has two tyM of reinforcements. a metal reinforcement cage 68 and reinforcement tubes 70. The reinforcement tubes can run the entire length of the protector or only portions of its length. The reinforcement tubes may be open to the drilling mud to aid in retuming the mud to the annulus between-the protector and the casing. Alternatively, a portion of the drilling mud in the reinforcement tubes can be redirected through feeder tubes 72 to the bearing surfitce between the ID. of the protector and the O.D. of the drill pipe, thus replenishing regions ofthc sleeve that deplete fluid through the hydrolift: exit ports. The tubes can be a simple void, or lined with tubing of various types such as aluminum or composite tubing. When the reinforcement tubes are properly -spaced i.e. 2MO% of cross-sectional area. the resulting composite sleeve has enhanced bearing resistance. Protector 60 has an I.D. configuration similar to protector 30 which creates a hydraulic bearing is created by drilling mud moving between the sleeve and the fluid bearing surface as discussed -with respect to protector 30. A hydraulic bearing is created by drilling mud moving between the ID. of the sleeve and the O.D. of the drill pipe by drilling mud flowing through the axial grooves 74 on the I.D. of the protector or feeder lines 72 from reinforcement tubes 70.

ne placement of the diffuser 64 and exit ports 66a-66j is to allow the continuous operation of the hydraulic bearing as well as the operation of the diffuser. It is this combination which provides the bmefits of reduced drilling torque and reduced sliding resistance. 7be hydrolift bearings can also be placed on the ends ofthe sleeve, pressurized by the thrust bearings, thus providing additional lubrication as well as some lift-off from the collar thus increasing the wear life of the ends of the sleeve. Numerous configurations of hydrolift diffiiser and exit port configurations are possible as shown in FIG. 6.. but is not limited to these configurations, as someone skilled in the an would know. Configurations 74 and 76 are based upon a thrust bearing principle whereas configurations 78-84 are designed to primarily offer improved lubrication. 35 TABLE I

HydroLAft Design Computadons Input Safety factor 1.1 Fluid Thickness lkyer for lift 0.01 in Fluid Viscosity 20 cp Fluid Density 9.5 lb/gal Radius of Port 0.1 in Radius of Lift I in Lift Required 350 lbs Diameter of Pipe 5 in Length of Section 10 in Eccentricity 0.0625 in Diametrical Clearance 0.012 in RPM 120 rpm C4efficient of side leakage (n) 0.77 Bearing Operation Characteristic(A) 12 Angle between load and entering edge of mud 50 deg Differential Pressure from Pump 2000 psid Required Pump Capacity 450 gpm Acceptable Pump Capacity Loss 15% ChIcs"edInpWs Number of Hydrolift required 5 Fluid Density 0.041 lb/in A 3 Eccentricity Ratio (e) I OA 17 Ratio of eccentricity to radial clearance Diametrical Clearance Ratio(m) 0.002 Ratio of diametrical clearance/diameter' Usimg the hydrolift design computation table recited above, the benefits of the hydrolift design are seen. For 9.5 lb/gal-driHing mud operating the hydrolift protector on a 5 in. drill pipe and rotating at 120 rpm, the hydroUft protector provides approximately 350 lbs of la thus reducing the normal weight of the pipe at the sleeve and improving sliding. The benefi ts of improved lubrication unprove sliding characteristics substantially.

The use of the rei tubes effectively reduces the amount of material needed to construct the sleeve. Specifically, the protector shown in FIGs. 4 and 5 use approximately 35% less material than existing sleew designs. FIG. 5 illustrates that the sleeve is ly twice as long as prior existing sle'eves. however, because of the reduced material used in the hydrolift protector. the sleeve is only 25% heavier but is 100% longerthan conventionat designs.

IMe hydrolift protector can be made from various materials for different applications. For cased holes, the hydrofift protector could be a polymeT materK using special low friction polymers for oPen-hole designs, or the sleeve could be coated with a low friction metal such amorphous titanium.

Configurations for the &ffuser design balance the features of hydraulic lift of the pipe from the casing and the lubrication ofthe pipe to the casing. Because lift is provided by pressure, I increasing the lift requires increasing the pressurized area- Typical hydraulic bearings produce pressure of 10-50 psi per inch of length for the range of typical pipe diameters. Thus. if the hydrolift diffuser has a normal area to the pipe of 0. 1 sq. in. and the pressure is 40 psi, the lifting force is 4 pounds. If the area ofthe diffuser is increased to I in and the pressure remain constant. 5 the lifting force is 40 lbs. per diffuser. Since a joint of 5-in. drill pipe typically weights approximately 660 lbs.. then a hydrolift protector with 15 diff4sers could effectively reduce the drill string drag observed at the rig floor.

This is of substantial importance to drilling operations. Because the normal force resulting from the pipe weight that produces the wear on the pipe on the casing, the effective weight reduction facilitates sliding in and out of the hole. The hydrolift protector provides the lift at exactly the point where it is required thus maximizing the benefits received.

The second factor of consideration for the hydrolift diffiiser is lubrication. The result of improved lubrication and lift is to allow the hydrolift protector to act as a hydraulic bearing with resulting improved sliding friction. Typically protectors have a sliding friction that is dependent upon the coefficient of friction between the protector and the casing or formation. For steel casing and rubber traditional protectors. the coefficient of friction is between 0.25-035. The hydrolift protector of the present invention provides a lubrication film and hydraulic lift which results in a coefficient of friction of 0.05-0. 1. The result is that ease of sliding into the hole is achieved. As drill string rpm increases. the lubrication benefit and the liffing benefit become more pronounced.

An associated benefit in the hydrolift protector design is hole cleaning. Typically in ERD wells as the build angle exceeds 55-60 cuttings have a tendency to settle out and fall to the low side of the casing. 'Me result is cuttings dams and many associated problems. The hydrolift protector design allows the pressurized fluid to wash away the dam from the bottom of the casing and back into the fluid stream. Thus three benefits of the hydrolift protector are provided being lift. lubrication. and hole cleaning.

WF DGELIFT TYPE DRILL PIPE PRO77ECTOR Referring now to FIGS. 7-12 a wedgelift type non-wtating. drill pipe protector is shown in various views and embodiments.

FIG. 7 illustrates a wedgelift drill pipe protector 90 which preferably comprises an elongated tubular sleeve made from a suitable protective material. such as. a low coefficient of friction, polymeric materiaL metal or rubber material. A presently preferred material is a high density polyurethane or rubber material. The sleeve has an inside diameter having a plurality of elongated, longitudinally extending, straight, parallel axial grooves 92 spaced apart circurriferentially around the I.D. of the sleeve. The grooves are preferably spaced uniformly around the I.D. of the sleeve, extend vertically, and are open-ended in the sense that they open to an annularfim end 94 and an opposite annular second end 96 of the sleeve.

-12.

I The inside wall of the sleeve is divided into intervening wall sections of substantially uniform width extending parallel to one another between adjacent pairs ofgrooves 92. Each wall section has an inside bearing surface which can be a curved or a flat surface.

The wall thickness ofthe sleeve is such that the drill pipe protector 90 has an O.D. greater.

than the O.D. of the adjacent drill pipe tool joints. The O.D. of the sleeve includes a plurality of circumferentially spaced apart longitudinally extending, parallel outer flutes 98 extending from end to end ofthe sleeve. Ile flutes are substantially wider than the grooves 92 inside the sleeve.

Positioned between adjacent flutes 98 are wedge shaped channels 100. Intervening outer wall sections 102 formed by the O.D. wall of the sleeve between the flutes and the wedge shaped channels form wide parallel outerribs with curved outer surfaces along the outside ofthe sleeve.

The wedge shaped channels provide hydraulic lift and improved sliding lubrication reducing the effective coefficient of friction between the drill pipe and the casing and increase the proclivity to slide down the hole. The wedge shaped channel located on the outer periphery of the sleeve generates a hydraulic bearing between the sleeve and the casing. Drilling mud is is directed to the wedge shaped -channels by the ribs of the outer wall sections 102 into the increasingly narrower and shallower wedge shaped channel. The outer ridges provide the dual function of directing the fluid flow and providing appropriate support for the drill suing when at rest. The width, height and depth of the channel and outer ribs can be varied based upon the amount of deformation of the tool under resting loads. The design ofthe wedge shaped channel and outer ribs can be adjusted to the required size of pressurized region and expected loads by varying the width. depth, length and taper of the channel. 7he fluid tends to move into the narrowing channel resulting in a region with elevated pressure, thus lifting and lubricating the region between the protector sleeve and the casing wall. Multiple wedge shaped channel configumtions can be placed on the same tool in various configurations such as more than one along the same line. along multiple parallel lines or along single or multiple spiral lines.

The wedge shaped channels 100 can be placed in a back-to-back configuration as shown in FIG. 7 thus allow the fluid movement through the channels facing the direction of movement and all drill cuttings to exit ftom the back sideofthe sleeve. In addition placing the wedge OwIng shaped channels in a back-to-back configuration allows reversibility of the tool.

The momentum of sliding into the hole actually helps to continue the sliding. This is of substantial importance to drilfmg operations considering the normal force resulting from frictional drag resistance of the pipe becomes increasingly greater at greater depths thus making tripping into and out of the hole increasingly difficult. Improved lubrication and lift'allows the wedgelift protector to act as a hydraulic bearing with resulting improved sliding friction. For steel casing and traditional rubber protectors, the coefficient of friction is between 0.25-0-35.

The wedgelift protector provides a lubrication film and hydraulic lift thereby reducing the coefficient of friction to between 0.05-0.1. Another benefit of the wedgelift protector is hole cleaning as previously discussed with respect to the hydrolift protector.

I Referring again to FIG. 7 the wedgelift protector 90 is split longitudinally to provide a ineans for spreading apart opposite sides of the sleeve when mounting the sleeve to the O.D. of the drill pipe. The sleeve is split longitudinally along one edge 104 which is fastened by a latch pin. 106 as is typical in the art. 1n this version. the sleeve is simply spread apart along the edge 104 when installed. Alternatively, the sleeve halves may be hinged along one side and releasabiv fastened on an opposite side by a latch pin or they may be secured along both opposite sides kv bolts. A metal cage (not shown) forms an annular reinforcing ring embedded in the molded bodv of the sleeve as discussed above.

Top and bottom thrust bearings 77 and 24 as described in FIG. 2 maintain the protector 90 along the length of the drill pipe.

An alternative wedgelift protector I'l 0 is shown in FIG. 8. In this embodiment the O.D.

of the protector is "egg" shaped wherein the wedge shaped channels 112 are positioned on the bottom surface of the protector. The wedge shaped channels are separated by outer ribs 114.

Flutes 116 are positioned on the top surface of protector I 10. The egg shaped protector configuration allows the non-rotating protector to orient the wedgelift channels on the bottom of the hole thus properly orienting the protector within the casing. The protector 110 may also include flow channels 118 to assist in the return of drilling mud to the annulus between the protector and the casing. FIG. 9 illustrates a second alternative embodiment for the wedgelift protector 120 having an eccentric configuration. As with the embodiment shown in FIG. 9 the wedge shaped channels 122 are positioned on the bottom of the protector and are separated by ribs 124. Flutes 126 are positioned on the upper surface of the protector. In this eccentric configuration the wall thickness is thinner at the bottom where the wedge shaped channels are located than at the top where the flutes are located. In this configuration the design tends to force the wedge shaped channels onto the bottom of the hole thus properly orienting the protector.

FIG. 10 illustrates the wedgelift concept as incorporated into the drill pipe tool joint 130.

In this embodiment the wedge shaped channels 1 33 2 are milled into a drill pipe tool joint 134.

The wedgelift configuration could be applied to virtually any type of down hole tool that needs assistance in sliding such as rotating drill pipe protectom or integral to drill collars, stabilizers, drill pipe, or other down hole tools.

FIGs. I I and 12 show yet another embodiment ofthe present invention incorporating both the wedgelift and hydrolift concepts. The protector 140 is similar to the protector shown in FIG. 7 which includes a plurality of wedge shaped channels 142 separated by ribs 144 on the O.D. of the drill pipe protector. The protector also includes a hydrolift exit port 146 extending from the IM. 148 of the protector to the wedge shaped channels, Protector 140 is particularly useful in connection with starting of sliding of the drill pipe down the hole. As static is typically greater than the sliding friction, it can be difficult to start the sliding of the drill suing after stopping to make or break a drill pipe joint (or stand). If the rig has the capability to rotate as well as lower or raise the pipe, as is frequently the case with rigs with top chive systems, then I rotating the drill pipe will pump pressurized fluid from the I.D. of the sleeve to the O.D. of the protector. This pressurized fluid would enter the wedgelift configuration at its center, providing pressurized lubrication at the exact point of contact. The combination of fiwh and pressurized lubrication would assist the overcoming of the static ffiction and assist the function of the wedgelift in the remainder of the movement of the drill pipe.

MULTI-SIDED LO)V--FRICTION SLIP-SURFA NON-ROTAITNG DRILL PIPE PRO Referring now to FIGs. 13-19, multi-sided low friction slip-surface non-rotating drill pipe protectors are illustrated. FIG. 13 illustrates a four-sided low friction non-rotating drill pipe protector 150. As with all the multi-sided low-friction slip-surface non-rotating drill pipe protectoM protector 150 comprises an elongated tubular sleeve made from a suitable protective material, such as a low coefficient of friction. polymeric material, metal or rubber material. A presently preferred material is a high density polyurethane having a metal reinforcing cage as previously discussed. Othermaterials can be a cage-reinforced rubber ofvarious types including NBR (Nitrile Butadiene Rubberhydrogenerated or nonhydrogcnated), Aflas (fluorethylene rubber),with and without additives to improve performance, in addition to various other types of theirmally and chemically stable plastics may be used. Protector 150 has an inside diameter in a generally polygonal or a curved shaped configuration. The I.D. wall 152 includes a plurality of elongated, longitudinally extending, straight, parallel axial grooves 154. The grooves are preferably spaced uniformly wound the ID. of the sleeve and extend vertically from end to end of the sleeve. The metal reinforcing cage 15 6 is embedded between the I.D. wall 152 and the 0D. wan 159.

. Protector 150 includes a first section 160 and a second section 162 connected by a hinge 164 at one end and a latch pin 165 at an end opposite from the hinge 164. Four spaced apart flutes 166, 168, 170 and 172 are spaced around the perimeter and located on the OD. wall 158 of the protector. Unlike conventional drill pipe protectors that typicalLy have an extemal radius that is. pproxhuately circular with respect to the drill pipe, protector 150 includes an outer surface having four distinct curves that are designed to contour the common casing sim thus increasing sliding contact sutface area Each section 160 and 162 includes two sides 174 and 176, and 178 and 190, respectively. By having multiple high ra'dius extemal curved surfaces allows more even distribution of the weight of the drill string through the protec-toes sliding surfitces. A more uniform weight distribution results in more uniform friction along the sleeve.

Each of the four sides 174-180 includes low coefficient of friction inserts 182a-h positioned on the wear area of the sides. The low coefficient of friction inserts preferably include the use of a base nuiterial of polyurethane with Teflon bonded to its exterior. Other Teflon composites, coated aluminura or other low friction material also could be used as the insert material. 7be inserts may be attached by an adhesive after the sleevebody is molded or inserted during the molding process. Theinserts may contain beveled edges 194 or holes 186 to create a mechmical bond with the sleeve body. The inserts can be flush with the O.D. of the protector or can be raised.02-.03 inches as shown with insert 182g to assist in wiping ofthe casing during operation and extend wear life.

More preferably the low coefficient friction inserts are made from a bronze impregnated Teflon (trade name Rulon 142) having a coefficient of friction of 0. 10-0. 12 against steel cas g ing in drilling mud. As previously discussed the inserts may be held in place with high-strength high temperature adhesive, by molding into the urethane, mechanical bonds in the shape of rivets. or by mechanically connecting the inserts to the metal reinforcement cage. Preferably the inserts are bonded to the protector as strips with a typical thickness of 0.090 inches. The surfaces of the inserts are typically beveled to allow smooih transition between the inserts and the O.D. wall of the protector. A suitable adhesive is Tristar TCE211 which has suitable mechanical bonding stren at elevated i uperatures.

An advantage of using bronze impregnated Teflon as the inserts or other similar material such as glass or graphite filled Teflon is that the inserts will actually reduce the coefficient of friction in the casing. As the inserts wear against the casing, they leave small deposits of bronze impregnated Teflon in the casing. Therefore. as more and more protectors slide over a particular torturous portion of the casing, the surface becomes impregnated into the casing and tends to reduce the coefficient of friction of subse'quent protectors that slide over the region. lie use of Teflon as the inserts also demonstrates the lowest coefficient of friction on dry or nearly dry surfaces. In instances-when the slide loads on the protector are so significant that the protector wipes the side of the casing, the Teflon inserts reduces encroachment of the drilling mud and reduces the coefficient of friction between the protector and the casing.

FIG. 14 filustrates an alternative low friction non-rotating drill pipe protector 190 having a two-sided 192 and 194 low-friction' slip-surface configuration. Protector 190 includes 4 axial flutes 196. 198.200 and 202. Although the protector 190 is illustrated with four axial flutes. it is to be understood that other numbers of flutes such as 2. 6 or 8 are also possible combinations.

Me advantage of a two-sided low friction non-rotating drill pipe protector is that two sides provide for greater wear surface to be in contact with the casing.

FIGs. 15 and 16 illustrate;.he use oflow coefficient offriction inserts in combination with the wedgelift protector previously discussed. FIG. 15 illustrates protector. 210 having low coefficient of friction inserts 212 positioned adjacent the wedge shaped channels 214. Also shown in the reinforcement cage 216 embedded in the protector 210. The ends 218 of the cage 216 are curved over substantially (up to 200 degrees) by having multiple split sections around the circumference. The curved end sections allow better bonding between the sleeve material and the cage, which is especially usefid in sleeves that are sliding within casing as better gripping between the cage and the protector material is achieved. Protector 220 shown in FIG. 16 illustrates the use of low coefficient of friction studs 222 positioned adjacent the wedge shaped channels 224. A plurality of aluminum studs with amphorous titanium coatings or other friction reducing coatings can be molded into the material or physically attached to the cage. The tips of the studs extend beyond the O.D. of the protector providing a multiplicity of extensions for the protector to slide upon. Extended tips can be placed in a variety of arTays that tend to maximize life and minimize potential damage to the casing.

Alternatively, either bars or plates could be used with the coatings applied to produce long life low coefficient of friction surfaces. Other variations could include the use of continuous ribs or bars of aluminum or similar material instead of short studs. Use of bars has the advantage of longer surface areas, thus fewer tendencies to damage the casing.

Also shown in Figure 16 is an altemative materials configuration for the protector 220. Material 226 is placed on the interior surface of the protector 220. Material 228 is placed on the exterior surface of the protector 220. Material 226 has relatively low hardness (75 and less Shore A) than the exterior material 228 (75 Shore A). Preferably, material 226 has Shore A hardness of 75 and material 228 has hardness of 90. Material 226 and 228 may be the same material with different hardness or different materials, such as polyurethane with different hardness resulting from different amounts of platicizer.

Alternatively, the materials 226 and 228 may be substantially different such as Aluminum for material 228 and rubber for material 226. One skilled in the art can see the wide range of material combinations that satisfy this design. The material 226 and material 228 may be chemically bonded, mechanically bonded, thermally bonded, or various combinations.

The advantage of this design is that the interior material 226 is capable of flexing around debris caught between the protector 220 and the drill pipe without abrading the drill pipe substantially. The exterior triaterial 228 with its greater hardness is more resistant to abrasion between the exterior of the protector 220 and the casing or borehole wall.

Although the present invention has been discussed with various embodiment thereof, it is to be understood that it is not to be so limited since changes and modifications can be made which are within the full intended scope as hereinafter claimed.

An underground drilling system comprising: a wellbore in an underground formation; a fixed tubular casing installed in the wellbore; a rotary drill pipe extending through the casing and having O.D. spaced from an LD. of the casing or wellbore during normal drilling operations; a protective sleeve mounted around the drill pipe and spaced from the I.D. of the casing or bore for preferentially contacting the I.D. of the casing or bore when the drill pipe deflects off-center in the casing or bore to protect the casing or bore from contact with the drill pipe or its tool joints during rotation of the drill pipe; thrust bearing collars rigidly affixed to the drill pipe above and below the sleeve for maintaining the sleeve in a fixed axially position on the drill pipe; the protective sleeve mounted to the drill pipe via an internal sleeve I.D. configuration that substantially reduces the rotational rate of the sleeve upon frictional contact of the sleeve with the I.D. of the casing or bore, while allowing the rotary drill pipe to continue rotating within the sleeve at a rotation rate sufficient to conduct drilling operations in the formation; said internal configuration comprising longitudinally extending and circumferentially spaced apart axial grooves formed in an I.D. wall of the sleeve for allowing fluid to circulate through a spaced formed between the I.D. of the sleeve and the O.D. of the drill pipe; a diff-user region having at least one diffuser exit port for allowing fluid under pressure to exit through the space formed between the I.D. of the sleeve and the O.D. of the drill pipe to lift the sleeve off the casing and wear pads positioned on the O.D. of the sleeve adjacent the diffuser exit ports.

The sleeve may have a plurality of diffuser exit ports and have a circular outer diameter. Alternatively, the sleeve has a non-circular O.D. such that the sleeve will align the diffuser exit ports in the bottom of the hole adjacent the casing.

The sleeve may include a plurality of channels formed on the O.D. of the sleeve, and the channels may be formed between an adjacent pair of spaced apart ridges extending radially outward from the O.D. of the sleeve. Also, one of the channels is wedged shaped which narrows in width and depth from a first end to a second end of the channel; the wedge shaped channel is in fluid communication with the diffuser exit port, and, low coefficient of friction wear pads are inserted on the O.D. of the sleeve adjacent the wedge shaped channels.

A drill pipe protector for use in a wellbore comprising: a cylindrical sleeve sized to be placed around a drill pipe; said sleeve having an I.D. having a plurality of grooves for generating a fluid bearing between the I.D. of the sleeve and the drill pipe; the sleeve having a diffuser portion having least one exit port extending through the diffuser between the I.D. and the O.D. of the sleeve for the passage of pressurized fluid from the fluid bearing between the LD. of the sleeve and the drill pipe to lift the protector away from a well of the wellbore. The diffuser portionhas a plurality of exit ports and the O.D. may be 5 circular or non-circular.

The O.D. may include low coefficient of friction wear pads on the surface of the O.D. of the sleeve adjacent the diffuser exit port, and the O.D. may have a plurality of channels formed between radially extending ridges. At least one of the channels is wedged shaped, and narrows in width and depth from a first end to a second end, the wedge shaped 10 channel forming a fluid bearing between the sleeve and wellbore.

The diffuser exit port is located in the wedge shaped channel, and two wedge shaped channels can be positioned in a back-to-back configuration on the O.D. of the sleeve, and low coefficient of friction inserts are positioned adjacent the wedge shaped channel and/or a plurality of low coefficient of friction studs adjacent the wedge shaped 15 channels.

30.

Claims

1. A protective sleeve for installation around a drill pipe used to drill a wellbore in an underground formation, the protective sleeve preferentially contacting the I.D. of a well casing or bore when the drill pipe deflects off center in the casing or bore to protect the casing or bore from contact with the drill pipe or its tool joints during rotation of the drill pipe, and in which the sleeve has a generally cylindrically configuration with an international I.D. for contact with the O.D. of the drill pipe and a plurality of wedge shaped channels extending in a longitudinal direction around the O.D. of the sleeve which narrow in width and depth to facilitate a fluid bearing between the sleeve and well casing or bore.

2. A drill pipe protector for use on a drill string in a wellbore comprising: a cylindrical sleeve having an I.D. for placement around the drill string and an O.D.; a plurality of channels extending in a longitudinal direction around the O.D. of the sleeve between radially extending ridges, wherein at least one of the channels is wedge shaped and which narrows in width and depth from a first end to a second end of the charmel, to facilitate an hydraulic bearing between the sleeve and adjacent wall of the wellbore.

3. A drill pipe protector as claimed in Claim 2, wherein the O.D. of the sleeve is circular.

4. A drill pipe protector as claimed in Claim 2, wherein the O.D. is non-circular.

1

5. A drill pipe protector as claimed in Claim 2, 3 or 4, wherein the two wedge shaped charmels are positioned in a back-to-back configuration on the O.D. of the sleeve.

6. A drill pipe protector as claimed in any Claim 2 to 5, wherein low coefficient of friction inserts are positioned adjacent the wedge shaped channel. 30

7. A drill pipe protector as claimed in any Claim 2 to 6, wherein the sleeve includes a plurality of low coefficient of friction studs adjacent the wedge shaped channels.

8. A drill pipe protector as claimed in any Claim 2 to 7, wherein the sleeve includes a diffUser portion having at least one exit port extending through the diffuser between I.D. and the O.D. of the sleeve for the passage of pressurized fluid to lift the protector away from a wall of the wellbore.

9. A drill pipe protector as claimed in Claim 8, wherein the diffuser portion has a 10 plurality of exit ports.

10. A drill pipe protector as claimed in Claim 8, wherein the diffaser exit port is located in the wedge shaped channel.

11. A protector sleeve for installation around a drill pipe as hereinbefore described, with reference to, and as illustrated by, the accompanying schematic drawings.

12. A drill pipe protector as hereinbefore described, with reference to, and as illustrated by, the accompanying schematic drawings. 20