Note: Descriptions are shown in the official language in which they were submitted.
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DRILL PIPE PROTECTOR
10
FIELD OF THE INVENTION
This invention relates generally to non-rotating drill pipe
protectors attached to a drill string, and more particularly, to
improved low-friction drill pipe protectors by incorporating a
soft elastomer liner and low-friction end pads.
2p 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 string. 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 surface into a well or "wellbore" which
is formed by the rotating drill bit. As the drill bit penetrates
deeper or further into an underground formation, additional
sections of drill pipe are added to the drill string.
Casing is generally installed in the wellbore from the
drilling surface 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
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entering the wellbore. The casing also provides a means for
recovering the petroleum if the well is found to be productive.
A drill string is relatively flexible, being subject to
lateral deflection, especially at the regions between joints or
couplings. In particular, the application of weight onto the
drill string or resistance from the drill bit can cause 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 "directional
drilling." Directional drilling also causes potential contact
between portions of the drill string and the casing or well bore .
Contact between the drill string and the casing and well
bore creates frictional torque and drag. In fact, a considerable
amount of torque can be produced by the effects of frictional
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 string 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 of the well bore or,
where lined, the casing. Drilling tools and associated drill
string devices encounter similar problems.
To alleviate these problems, drill pipe protectors are
typically spaced apart along the length of the drill pipe. These
drill pipe protectors were originally made from sleeves of rubber
or other elastomeric material which were placed over the drill
pipe to keep the drill pipe and its connections away from the
walls of the casing and/or formation. Rubber or other
elastomeric materials were used because of their ability to
absorb shock and impart minimal wear.
Previously available drill pipe protectors have an outside
diameter (O.D.) greater than that of the drill pipe joints, and
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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,
discloses a drill 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 :luring 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
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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,
discloses a drill pipe/casing
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 modern 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 and forgoes 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 drill string against the casing is highly
desirable.
Another problem to which the present invention is directed
is the reduction of friction between the protector sleeve and the
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thrust bearings or collars positioned on either end of the
sleeve. Improvements in economic value through increased product
life without loss of structural integrity is also desirable.
SUMMARY OF THE i:~VENTION
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 string. The 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
pipe/protector combination relative to the casing or well wall.
By providing a drill pipe protector assembly having a fluid
pathway which directs a portion of the drilling mud moving
through the annular space between the drill pipe protector and
the drill pipe to the annular space between 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 of the protector,
increased hydraulic lift is developed.
In one embodiment, the present invention is generally
directed to a drill pipe protector 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 between 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
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and a second end. The tubular body is adapted to be deployable
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. The 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. The ridges are spaced
apart sufficient so as to form the described channels
therebetween. At least one, and preferably, all of the channels
include an opening which allows the drilling fluid to pass from
the inner surface to within the channel.
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
well wall. The 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 another 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
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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 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. 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
a hydraulic lift relative to the casing wall and also enhance the
flow of the drilling mud therebetween.
In another aspect of the present invention, the protector
assembly includes a tubular sleeve for use with drill tool
assemblies. 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. The protector
can have a plurality of curved surfaces.
In another embodiment of the present invention, the
protector incorporates a multi-stave multi-material sleeve that
includes use of a soft elastomeric liner having a preferred
hardness of 60 Shore A, although can be in the range of 40-85
Shore A, in a urethane sleeve having a preferred hardness of 95
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Shore A, although can be in the range of 75-95 Shore A for
urethane, and 75 to 123 Rockwell R for harder plastics. The
flexible inner liner material produces a more efficient fluid
bearing and thus a lower coefficient of rotational friction
between the drill pipe and the sleeve.
Studies have been undertaken to improve the performance of
the fluid bearing of a drill pipe protector while providing the
same or better strength of previous polyurethane formulations and
improving protector assembly economic life. Testing determined
that friction losses were manifest between the drill pipe and the
protector sleeve on the inside diameter of the sleeve and at the
interface between the sleeve and the collar on the ends of the
sleeves and collars. The combination of these two sources of
friction is the net resultant coefficient of frictional loss per
drill pipe protector assembly. Quantification of the rotational
frictional loss on the sleeve I.D. and the rotational loss at the
interface of the sleeve to the collar varies for different types
of materials used for the protector sleeves.
For urethane sleeves with 95 A Shore hardness, approximately
50 to 600 of the total frictional loss comes from the friction
between the ends of the sleeve and the collar. The frictional
loss between the sleeve I.D. and the drill pipe provides the
other significant friction dissipation. The friction between the
ends of the sleeve and the collar is the source for the wearing
of the ends of the sleeves and, hence, most frequently becomes
the factor that limits the useful economic life of the protector
sleeves and collars. Therefore, in another embodiment of the
present invention, the protector consists of a unique composite
sleeve design to reduce frictional forces and wear on the ends
of the sleeves and collars, without loss of structural integrity.
This is accomplished by incorporating low-friction abrasion-
resistant end pads integrally molded into the sleeve during the
manufacturing process. The end pads are pre-stamped into a
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preferred configuration wherein the pre-formed low-friction end
pad is placed at the bottom of the mold during the manufacturing
process. Depending upon the configuration, a metal cage would
then be inserted before the urethane is poured into the mold.
Low-friction end pads can be positioned at one or both ends of
the protector sleeve during the manufacturing process.
Alternatively, multiple segments of low-friction abrasion-
resistant end pads can be positioned at the end of the sleeve,
which are placed at the bottom of the mold before the urethane
is poured.
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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevational view, partly in
cross-section, showi-ng a string of drill pipe having drill
pipe/casing protector assemblies according to this invention
installed between tool joints of the drill pipe in a deviated
well being drilled in an underground formation;
FIG. 2 is a detail view of FIG. 1 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 ports;
FIG. 4 is a cross-sectional view of an alternative
embodiment hydrolift drill pipe protector;
FIG. 5A is a side view of the protector of FIG. 4;
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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 wedgelift type drill pipe
protector constructed according to the principles of the present
invention;
FIG. 8 is a partial perspective view of a first alternative
wedgelift type drill pipe protector shown mounted over a section
of drill pipe;
FIG. 9 is a partial perspective view of a 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. 11 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-
friction non-rotating drill pipe protector of the present
invention;
FIG. 14 is a cross-sectional 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;
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FIG. 16 is a partial cross section of a wedgelift type drill
pipe protector incorporating low-friction studs;
FIG. 17 is a perspective view of a drill pipe protector
having single piece low-friction pads integrally molded into the
protector with flexible multi-stave I.D. pads; and
FIG. 18 is a perspective view of a drill pipe protector
having multiple segments of low-friction end pads molded into the
protector with flexible multi-stave I.D. pads.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a well drilling system for drilling a
well in an underground formation 10. ~ rotary drill string
comprises a plurality of elongated tubular drill pipe sections
12 which drill a well bore 14 with a drilling tool 15 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 initially 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 wells 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 a casing.
Therefore, in the description and claims to follow, where
references are made to contact with the wall or inside diameter
(I. D.) of a casing, the description also applies to contact with
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the wall of the well bore, and where references are made tc
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 of the drill string 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,
plastic (such as nylon) is greater than that of the drill pipe
and its tool joints. Such an installation 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 hold is deviated from vertical as shown in
FIG. 1. This adversely affects drilling operations, primarily
by producing friction which reduces the rotation and torque value
generated at the surface and which is then translated to the
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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 or sleeve 18 is sandwiched loosely between upper and
lower thrust bearings or collars 22 and 24 which are rigidly
affixed to the O.D. ~f 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 the drill pipe using
techniques which hold the protector on the drill pipe and which
allow the sleeve to normally rotate with the 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 effect,
reduces the distance at which the friction associated with drill
pipe rotation is applied to the drill pipe.
HYDROLIFT TYPE DRILL PIPE PROTECTOR
Referring now to FIGS.3A and 3B, a hydrolift type non-
rotating drill pipe protector 30 is shown.
The hydrolift non-rotating 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
configuration. The I.D. further includes a plurality of
elongated longitudinally extending, straight, parallel axial
grooves 34 spaced apart circumferentially around the I.D. of the
sleeve. The grooves are open ended in the sense that they open
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through an annular first end 34 and annular opposite second end
36 of the sleeve.
The 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 O.D. 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 I.D. 32 to the O.D. 40. The
diffuser 44 can be rigidly connected to cage 38 by fasteners 48
or alternatively can be integrally molded into the sleeve.
The wall thickness of the protector 30 is such that the
drill pipe protector has an O.D. greater than the O.D. of the
adjacent drill pipe tool joints 20. The annular first 34 and
second 36 edges of the protector sleeve have a configuration that
functions to draw fluid between the sleeve and the collar,
thereby assisting in the formation of a fluid bearing between the
I.D. of the protector and the O.D. 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. The 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 fords. The 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.
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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. 3A 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 extends
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 38 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 form the reinforcing member from a
steel sheet stock with holes uniformly distributed throughout the
sheet.
The confronting top and bottom thrust bearings or collars
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 thrust bearings (also referred to as
collars) are metal collars made of a material such as aluminum,
bronze alloys or a hard plastic material, such as, composites of
glass or graphite fibers in a matrix such as nylon to encircle
the drill pipe and project outwardly from the drill pipe. The
collars project a sufficient axial distance along the drill pipe
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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.
The 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 of
the 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 collar.
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 casing
or wellbore. The sleeve, which is normally fixed in place on the
drill pipe, rotates with the drill pipe during normal drilling
operations. However, under contact with the inside wall of the
casing, the sleeve stops rotating, or its rotational speed is
greatly reduced, while allowing the drill pipe to 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 bearing surface of the 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
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interface of the sleeve and the drill pipe and this fluid becomes
forced into the bearing surfaces between the grooves. This
deforms or spreads apart the bearing surface regions to produce
a pressurized thin film of lubricating fluid between the sleeve
I.D. and the drill pipe O.D. which reduces frictional drag
between these two surfaces . This action of the 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 I.D. of
the sleeve due to the fact that a thin film of fluid is
separating the two surfaces. Since the fluid separates these two
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 further 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 0. 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. The fluid movement through the exit
ports also tends to clean cuttings 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 example rotating the pipe more rapidly increases
the pressure thus improving sliding and lifting of the drill
pipe. The number of exit ports also can be varied to adjust the
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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 are
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
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 diffuser 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 such as Rulon (Tellon
and bronze composite).
The protector 60 has two types 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 returning the mud to the
annulus between the protector and the casing. Alternatively, a
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portion of the drilling mud in the reinforcement tubes can be
redirected through feeder tubes 72 to the bearing surface between
the I.D. of the protector and the O.D. of the drill pipe, thus
replenishing regions of the 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.
20-800 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 I.D. 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.
The 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 benefits of reduced drilling torque and
reduced sliding resistance. The hydrolift bearings can also be
placed on the ends of the 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
diffuser and exit port configurations are possible as shown in
FIG. 6., but is not limited to these configurations, as someone
skilled in the art would know. Configurations 74 and 76 are
based upon a thrust bearing principle whereas configurations
78-84 are designed to primarily offer improved lubrication.
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TABLE 1
HydroLift Design Computations
Input
Safety factor 1.1
Fluid Thickness layer for lift 0.01 in
Fluid Viscosity ~ 20 cp
Fluid Density 9.5 lb/gal
Radius of Port 0.1 in
Radius of Lift 1 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
Coefficient 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%
2 0 Calculated Inputs
Number of Hydrolift required 5
Fluid Density 0.041 Ib/in~3
Eccentricity Ratio (e) 10.417 Ratio of eccentricity to radial clearance
Diametrical Clearance Ratio(m) 0.002 Ratio of diametrical clearance/diameter
Using the hydrolift design computation table recited above,
the benefits of the hydrolift design are seen. For 9.5 lb/gal
drilling mud operating the hydrolift protector on a 5 in. drill
pipe and rotating at 120 rpm, the hydrolift protector provides
approximately 350 lbs of lift, thus reducing the normal weight
of the pipe at the sleeve and improving sliding. The benefits
of improved lubrication improve sliding characteristics
substantially.
The use of the reinforcement 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
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material than existing sleeve designs. FIG. 5 illustrates that
the sleeve is approximately twice as long as prior existing
sleeves, however, because of the reduced material used in the
hydrolift protector, the sleeve is only 25o heavier but is 1000
longer than conventional designs. The hydrolift protector can
be made from various materials for different applications. For
cased holes, the hydrolift protector could be a polymer material,
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 diffuser design balance the features
of hydraulic lift of the pipe from the casing and the lubrication
of the pipe to the casing. Because lift is provided by pressure,
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. -.n.
and the pressure is 40 psi, the lifting force is 4 pounds. If
the area of the diffuser is increased to 1 in and the pressure
remain constant, 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 diffusers could
25. 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
diffuser is lubrication. The result of improve. lubrication and
lift is to allow the hydrolift protector to act as a hydraulic
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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 0.25-0.35. The hydrolift
protec'or 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 lifting 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. The result is cuttings dams and many
associated problems. The hydrolift protector design allows the
pressurized fluid to wash away the dams 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.
WEDGELIFT TYPE DRILL PIPE PROTECTOR
Referring now to FIGS. 7-12 a wedgelift type non-rotating
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 circumferentially around
the I.D. of the sleeve. The grooves are preferably spaced
uniformly around the I.D. of the sleeve, extend vertically, and
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are open-ended in the sense that they open to an annular first
end 94 and an opposite annular second end 96 of the sleeve.
The inside wall of the sleeve is divided into intervening
wall sections of substantially uniform width extending parallel
to one another between adjacent pairs of grooves 92. Each wall
section has an inside bearing surface which can be a curved or
a flat surface.
The wall thickness of the 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 of
the sleeve. The 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 outer ribs with curved
outer surfaces along the outside of the 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 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 string when at rest. The
width, height and depth pf the channel and outer ribs can be
varied based upon the amount of deformation of the tool under
resting loads. The design of the wedge shaped channel and outer
ribs can be adjusted to the required size of pressurized region
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and expected loads by varying the width, depth, length and taper
of the channel. The 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
configurations 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 allowing drill cuttings ~.o exit from the back side
of the sleeve. In addition placing the wedge 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
drilling 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.
Referring again to FIG. 7 the wedgelift protector 90 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. The sleeve is split longitudinally along one
edge 104 which is fastened by a latch pin 106 as is typical in
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the art. In 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 releasably fastened on
an opposite side by a latch pin or they may be secured along both
opposite sides by bolts. A metal cage (not shown) forms an
annular reinforcing ring embedded in the molded body of the
sleeve as discussed above.
Top and bottom thrust bearings 22 and 24 as described in
FIG. 2 maintain the protector 90 along the length of the drill
pipe.
An alternative wedgelift protector 110 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 110. 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.
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FIG. 10 illustrates the wedgelift concept as incorporated
into the drill pipe tool joint 130. In this embodiment the wedge
shaped channels 132 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 protectors, or integral to drill collars,
stabilizers, drill pipe, or other down hole tools.
FIGS. 11 and 12 show yet another embodiment of the 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 I.D. 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 string 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 drive systems, then
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 fresh and pressurized lubrication would assist
the overcoming of the static friction and assist the function of
the wedgelift in the remainder of the movement of the drill pipe.
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MULTI-SIDED LOW-FRICTION SLIP-SURFACE
NON-ROTATING DRILL PIPE PROTECTOR
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 protectors, 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. Other materials can
be a cage-reinforced rubber of various types including NBR
(Nitrile Butadiene Rubber, hydrogenerated or nonhydrogenated),
Aflas (fluorethylene rubber), with and without additives to
improve performance, in addition to various other types of
thermally 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 around
the I.D. of the sleeve and extend vertically from end to end of
the sleeve. The metal reinforcing cage 156 is embedded between
the I.D. wall 152 and the O.D. wall 158.
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 O.D. wall 158 of the protector. Unlike
conventional drill pipe, protectors that typically have an
external radius that is approximately circular with respect to
the drill pipe, protector 150 includes an outer surface having
four distinct curves that are designed to contour the common
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casing size, thus increasing sliding contact surface area. Each
section 160 and 162 includes two sides 174 and 176, and 178 and
180, respectively. By having multiple high radius external
curved surfaces allows more even distribution of the weight of
the drill string through the protector's sliding surfaces. 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
areas of the sides. The low coefficient of friction inserts
preferably include the use of a base material of polyurethane
with Teflon bonded to its exterior. Other Teflon composites,
coated aluminum or other low-friction material also could be used
as the insert material. The inserts may be attached by an
adhesive after the sleeve body is molded or inserted during the
molding process. The inserts may contain beveled edges 184 or
holes 186 to create a mechanical 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 1828 to assist in
wiping of the 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
casing 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 smooth
transition between the inserts and the O.D. wall of the
protector. A suitable adhesive is Tristar TCE211 which has
suitable mechanical bonding strength at elevated temperatures.
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The Rulon inserts may be reinforced with an aluminum backing
plate that facilitate manufacture and operations.
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 subsequent protectors
that slide over the region. The 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 encroac'_~_ment of the
drilling mud and reduces the coefficient of friction between the
protector and the casing.
FIG. 14 illustrates 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. The 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 the use of low coefficient of
friction inserts in combination with the wedgelift protector
previously discussed. FIB. 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
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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 useful 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 arrays 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 area, thus fewer tendencies to damage
the casing.
MULTI-COMPONENT
NON-ROTATING DRILL PIPE PROTECTOR
Also shown in Figure 16 is an alternative materials
configuration for the protector 220. The alternative materials
configuration can be utilized for any configuration protector
disclosed herein. Material 226 is a liner which 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 lower hardness ( 60 and less Shore A) than the exterior
material 228 (90 Shore A). For example, material 226 is a soft
elastomer or rubber having a Shore A hardness of 60 or less and
material 228 is a urethane and has hardness of 95 Shore A.
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Material 226 and 228 may be the same material with different
hardness or different materials, such as polyurethane with
different hardnesses resulting from different amounts of
plasticizer. Alternatively, the materials 226 and 228 may be
substantially different such as Aluminum for material 228 and
rubber for material 226 or a soft elastomer for material 226 and
a polyurethane for material 228. Further material 228 can be a
high-strength low-friction high-temperature plastic having a
hardness of 75 to 123 Rockwell R. In this embodiment no metal
reinforcing cage would be necessary wherein the material 228
would be injection molded and hinges (See Fig. 4) would be
integrally formed. The material 228 can be molded as a hinged
cylinder and have multiple distinct curved surfaces. 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 material 228 with its
greater hardness is more resistant to abrasion between the
exterior of the protector 220 and the casing or borehole wall.
Another advantage of having a softer elastomer for material 226
is a greater fluid bearing performance. The load carrying
capacity of a 60 Shore A elastomer fluid bearing is at least
twice that of a 95 Shore A elastomer fluid bearing of the same
geometry. Friction is also significantly lower in softer 60
Shore A fluid bearings than in harder 95 Shore A fluid bearings .
A problem with a sleeve that utilizes a soft elastomer is
that they have significantly lower strength, tear resistance,
chemical resistance, and temperature resistance than harder
elastomers. Therefore, a composite sleeve with materials 226 and
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228 can obtain the optimum fluid bearing performance while
maintaining high strength. Material 226 which would be
approximately 0.125 to 0.250 inches thick inside material 228,
the resulting combination provides a significant improvement in
load carrying capacity and reduction in friction compared to
single component designs in all operating conditions while
maintaining or improving the strength and toughness of the
overall design.
The soft elastomer material 226 would be formed with the
polygonal geometry (i.e., axial grooves), as shown herein, which
provides optimum pressure distribution across the fluid bearing
surface because the surface deforms under the contact load to
distribute the load of the rotating element and maintain fluid
bearing hydrodynamic lift over a greater area. The fluid bearing
performance is directly related to the area and pressure of the
fluid bearing between the rotating drill pipe and the stationary
sleeve. The softer elastomeric materials in the area of the
fluid bearing greatly increases the fluid bearing capability of
the sleeve and seen in more detail in FIGS. 17 and 18. Material
226 can be a one-piece liner or inserted as several pieces or
strips on the I.D. of the sleeve and seen in more detail in FIGS.
17 and 18. Material 226 can extend from one end to the other of
the sleeve or only extend through part of the length of the
sleeve as shown in FIG. 16. When the elastomeric liner extends
only partially through the length of the sleeve, it may be
necessary to provide a tapered recess in the harder urethane body
to prevent wear of the drill pipe over that region of the sleeve.
NON-ROTATING DRILL PIPE PROTECTOR
WITH LOW FRICTION END PADS
Quantification of the rotational frictional loss at the
interface of the sleeve and the collar varies for different types
of materials used for the sleeves. For urethane sleeves with 95
A Shore hardness, approximately 50 to 600 of the total frictional
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loss comes from the friction between the ends of the sleeve and
the collar. The friction between the ends of the sleeve and the
collar is the source for the wearing of the ends of the sleeves
and, hence, most frequently becomes the factor that limits the
useful economic life of sleeves and collars. Consequently, tr._
present invention defines a sleeve configuration that reduces the
friction at the sleeve/collar interface while also improving
economic value through increased product life without loss of
structural integrity. The present invention achieves this
objective by providing a drill pipe protector 300, as shown in
FIG. 17, which incorporates low-friction abrasion-resistant end
pads 302 positioned on each end of the sleeve 304. Although the
end pads 302 are shown in connection with sleeve 304, it is to
be understood that low-friction abrasion-resistant end pads can
be utilized in connection with any of the sleeve designs
disclosed herein.
End pads 302 are a single piece that is integrally molded
into the sleeve 304 during the manufacturing process. The ?nd
pads 302 are pre-stamped into the preferred configuration that
includes castellations 306, which allow fluid to pass from the
I.D. of the sleeve/drill pipe interface and over the end of the
sleeve and collar interface, thus assisting with lubrication and
cooling and reducing wear, as previously discussed herein. For
use in connection with a polyurethane sleeve, during
manufacturing the pre-formed low-friction end pad is placed at
the bottom of the mold, and the inner cage ( FIGS . 13 and 14 ) are
placed in the mold on top of the end pad. The cage can prevent
the flotation of the end pad during molding or can be
mechanically attached to the cage by rivets, or other mechanical
interlocking components cqmmonly known in the art . Protector 300
can have only one low-friction end pad 302 positioned on the
sleeve 304 or can have a second end pad added during the
manufacturing process, resulting in an end pad positioned at
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either end of the sleeve 304. Factors, such as manufacturing
cost, economic life, and application, can dictate whether one or
two end pads are incorporated into the protector 300.
FIG. 18 illustrates another embodiment protector 400 wherein
multiple segments of low-friction abrasion-resistant end pads 402
are placed at the ends of the sleeve 404. In this configuration,
instead of having a single integrally formed end pad, as shown
in FIG. 17, multiple individual segments which together form the
end pads would be placed at the bottom of the mold, and the
polyurethane or other plastic would be poured around the pads to
position it in the sleeve. For both embodiments shown in FIGS.
17 and 18, the preferred low-friction abrasion-resistant end pad
material is an ultra high molecular weight polyethylene averaging
3.1 to 6 million molecular weight compliance with ASTM 4020-81
standards. This material is non-abrasive, has a low coefficient
of friction less than 0.2, is 6000 more abrasion-resistant than
steel, has no notch sensitivity or cold embrittlement t155F to
+200F). The ultra high molecular weight polyethylene is
available under various trade names, including Ultra Fend by
UltraPoly Corporation.
Ultra-high molecular weight polyethylene is available in
various shapes and sizes that can be utilized for the end pads
of the sleeves. The material can be available as rings with the
appropriate diameter of the sleeve, which then would be stamped
to include the surface features of castellations 306, and the
bottom surface that interfaces with the cage. The bottom surface
can include flanges 308 to provide the mechanical locking feature
with the cage and the poured polyurethane sleeve 304.
Alternatively, the end pads for either embodiment may be stamped
from flat sheets of material. By way of example, the sleeve
shown in FIGS . 17 and 18 is made of polyurethane also having
low-friction side pads 310 and 410, respectively, which could be
made of Rulon or the ultra high molecular weight polyethylene
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material used for the end pads. The inside surface 312 and 412
can include a soft elastomer liner, as discussed with respect to
FIG. 16. Similarly, any of the other features disclosed herein
can be incorporated into the protector, such as hydrolift ports,
wedgelift channels, or a plurality of curved surfaces around the
outside diameter of the sleeve. Similarly, the sleeve can be
made of rubber or metal, which incorporates the low-friction end
pads.
Although the present invention has been discussed with
various embodiments 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.
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