Note: Descriptions are shown in the official language in which they were submitted.
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FLEXIBLE DRILL PIPE
sAcKGRouND OF THE INVENTION
Field of the Invention
The present invention relates to a segmented, flexible
drill pipe having an improved configuration for the inter-
locking segments.
Prior Art
-
In drilling deviated well bores it is necessary to use
drill pipe that can bend through the curve of deviation from
the vertical. There have been a number of proposals for
segmenting regular drill pipe to make the pipe bend without
permanently distorting the pipe. For example, U.S. Patent
No. 2,515,366, issued to John A. Zublin, teaches forming a
plurality of generally circumferential slots, each cut
through the wall of a tubular drill pipe, so that the pipe
is divided into a plurality of sections.
While the slots are generally circumferential, they
deviate from a true circumference to form a plurality of
interengaging and loosely interlocking teeth having a
dovetail configuration. The tops and sides of each dovetail
configuration, in the Zublin patent, are each relatively
straight. Further, Zublin's dovetail cuts are vertically
true, each being straight in line with the next.
It has been found that the straight sides of the Zublin
dovetail cut allow excessive distortion in bending the drill
pipe and often cause damage to the cut if excessive force is
applied at the bend. Sometimes, on heavy-duty rotation of
the drill pipe, the pipe will fail at a particular stress-
weakened cut. This has been attributed to the vertical
alignment, as well as the straight sides of the cuts.
In U.S. Patent No. 4,328,839, there is shown a modified
flexible drill pipe in which the sides of the interlocking
teeth are formed in reversed intersecting semicircles to
provide an improved force bearing action between adjacent
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teeth upon bending of the flexible drill pipe. However, it
has been found that this configuration, while providing
improved characteristics over the Zublin type drill pipe,
nevertheless is subject to excessive elongation, and poten-
tial failure, upon substantial axial loading because of the
absence of a positive stop between adjacent segments to
prevent excessive axial distortion. Further, this configur-
ation remains subject to potential breakage upon excessive
bending because of the relatively narrow neck portion at the
base of each of the interlocking teeth, the configuration
being such that the tooth is narrowest, and therefore
weakest, at the point where it is subject to the greatest
concentration of bending moment forces.
Various other configurations of segmented drill pipes
are shown in U.S. Patents Nos.:
2,382,933 to ~ublin;
2,515,366 to Zublin;
2,585,207 to Zublin;
2,687,282 to Sanders;
2,694,549 to James;
3,160,218 to Crake;
3,903,974 to Cullen; and
4,067,404 to Crase.
Therefore, it is an object of the present invention to
provide an improved flexible drill pipe by providing a
unique configuration for the interlocking teeth thereof.
It is a further object to provide increased rotational
strength and tension strength in a flexible drill pipe.
Another object is to provide improved bending of the
flexible drill pipe while retaining integrity of the inter-
locking teeth.
Another object is to provide a positive lock against
excessive axial displacement between adjacent pipe segments
of the flexible drill pipe.
Yet another object is to provide improved rotational
strength of the drill pipe by providing an offset to each
succeeding cut forming the interlocking teeth.
5845-276
1~3~ 5
Another object is to provide such a flexible drill
pipe with improved bearing characteristics between adjacent
segments to reduce wear and improve the life of the drill pipe.
SUMMARY OF THE INVENTION
-
According to the invention, there is provided a flex-
ible pipe comprising an elongated tubular member subdivided
into a plurality of segments of rigid pipe of substantial wall
thickness in end-to-end relationship with a plurality of inter-
locking teeth and complementary recesses on each end of the
intermediate segments, the teeth of one segment being positioned
in the recesses and interlocking the teeth of the adjacent
segment with sufficient clearance to form a joint permitting
limited relative movement in any direction between the segments,
each of said teeth comprising an arcuate crown portion with
its arc extending generally axially of the pipe, a tapered base
portion and a substantially flat shoulder area extending between
the crown and base portions in a direction generally circum-
ferentially of the pipe.
The above and other objects and features of the inven-
tion will be apparent to those skilled in the art after a
consideration of the following detailed description taken in
conjunction with the accompanying drawings in which a preferred
embodiment of the invention is shown.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a portion of a
flexible drill pipe segmented using the improved interlocking
teeth configuration of the present invention.
Figure 2 is a perspective view of a portion of the
drill pipe of the present invention illustrating the offset
of each succeeding cut forming the teeth and complementary
recesses.
Figure 3 is a laid-out section of a portion of the
flexible drill pipe of the present invention in template
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form, showing in enlarged detail the interlocking teeth
configuration of adjacent segments of the pipe.
DESC~IPTION OF THE PREFERRED EMBODIMENTS
The flexible drill pipe of the present invention is
particularly useful in aiding in the drilling of lateral
bores deviating from a vertical bore hole. The particular
interlocking tooth cut, described hereinafter, is well
adapted for resisting the compressive, bending and torque
stresses encountered in drilling bore holes.
In drilling lateral bores from a vertical bore hole,
the drill pipe must be capable of bending through the radius
of an arc to enter the lateral bore hole and then resume an
essentially straight configuration for subsequent straight
drilling. In operation, the drill pipe string consists of
both regular drill pipe and flexible drill pipe.
Reference is made to U.S. Patent No. 4,343,369 entitled
"Apparatus for Drilling Straight Portion of a Deviated
Hole," which discloses a drill guide of the type normally
used in conjunction with the flexible pipe of the present
invention. In that patent, the flexible drill pipe is
referred to as a "drive pipe." As taught in such patent, a
plurality of flexible drill pipes would be used to make up a
portion of the drill string, with at least one of the
flexible drill pipes being received and housed within the
bore of the drill guide. The drill pipe terminating in the
drill guide carries a drill bit for cutting the bore hole.
The drill guide is adapted for guiding the direction of
drilling and does not rotate with the flexible drill pipe of
the present invention.
Referring now to Figure 1, there is illustrated per-
spectively a portion of a flexible drill pipe 10 comprising
an elongated tubular member subdivided into a plurality of
segments 14, 16 and 18. The drill pipe 10 is preferably of
rigid construction having a substantial wall thickness to
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withstand the compressive, bending and torque stresses
encountered in drilling bore holes.
The segments 14, 16 and 18 are representative of the
drill pipe lO which has means 12 on each end thereof for
connection with another drill pipe. The connection means 12
shown in Figure 1 is a threaded pin end portion. A threaded
box end portion would normally be provided on the opposite
end of the pipe. The threaded segments of the drill pipe
10, such as the pin end segment 14, are interconnected to a
plurality of intermediate segments, such as segment 16,
which is representative of all other intermediate segments,
and which are arranged in end-to-end relationship.
Each end of each intermediate segment 16 has a plur-
ality of teeth 22 and complementary recesses 24. The teeth
22 of one segment 16 being positioned in the recesses 26 and
interlocking the teeth 27 of the adjacent segment 18 with
sufficient clearance to form a joint permitting relative
movement in any direction between the segments 16 and 18.
The width of the cut forming the teeth 22 and recesses
24 confiyuration is preferably sufficient to permit the
segments of the flexible drill pipe 10 to have radial and
axial relative movement with each other. As torque is
applied to the drill pipe 10 in drilling, one side of the
teeth of one section of the pipe will move into contact with
the sides of the teeth in the next axially adjacent segment
and so on to transmit the torque through the length of the
drill pipe while the gaps or clearances between the segments
will permit limited bending or flexing of the overall pipe
to accommodate a relatively sharp bend in the well bore. It
will be apparent to one skilled in the art that the amount
of overall bending of the pipe 10 will be determined by the
number of individual segments, as well as the size of, and
clearances between, the interlocking teeth forming the
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segments. These parameters therefore may be varied to
accomplish the result desired by the designer of the pipe.
Preferably, the flexible drill pipe 10 of the invention
is manufactured by cutting through the wall thickness of a
conventional drill pipe to form the interlocking teeth and
segments of the flexible drill pipe. While other methods of
manufacture may be available in the industry, it has been
found that by using a commercially available drill pipe as
the basic tubular member, the desired end product is
achieved. This also provides a tubular member having
sufficient wall thickness to give the teeth the strength to
resist the stresses that will be placed on them in drilling.
The present invention particularly resides in the novel
configuration of the means for interlocking the adjacent
segments 16 and 18 of the drill pipe 10. The teeth 22 and
recesses 24 are formed by a cut through the wall thickness
of the pipe 10, which cut is made so as to form the teeth
34, 36, 38 and 40, as illustrated in Figure 3, and comple-
mentary recesses.
As shown most clearly in Figure 3, each of the teeth
34, 36, 38 and 40 is identical, comprising a semicircular
crown portion 42, two substantially flat shoulders 44 and 46
lying along the circumferential direction of the drill pipe
10, and a tapered base 48 which extends downwardly in the
axial direction and outwardly in the circumferential direc-
tion from the tooth crown 42. The diameter of the semi-
circular crown 42 is disposed in a direction generally
circumferential of the pipe 10, while the arc forming the
semicircle extends in a direction generally axial of the
pipe 10. The shoulders 44 and 46 lie along the outer ends
of the diameter of the semicircle forming the crown portion
42 with the top of the base 48 comprising the remainder of
the diameter.
Tapered sides 50 and 52 of the base 48 comprise op-
posed, approximately 90, arcs, so that the ad~acent tapered
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sides 52 and 54 of circumferentially adjacent teeth 34 and
36 on one segment form a continuous semicircular recess for
receiving the semicircular crown portion of the opposed
tooth 38 on the next axially adjacent pipe segment. There-
fore, upon axial compression of the segmented pipe, each of
the semicircular tooth crowns will be in engagement with a
corresponding semicircular recess on the next axially
adjacent pipe segment to provide a ball and socket-type of
bearing surface and distribute the compressive forces over a
relatively large area. Since most of the ~70rk performed
with the segmented drill pipe during drilling activity
occurs under compression, this configuration greatly reduces
the wear on the teeth by providing a smooth bearing surface
and maximizing the area over which the compressive and
sliding forces are distributed.
The configuration of the present invention also elim-
inates the possibility of undue elongation of the drill pipe
10 under tension, which could result in jamming of the teeth
between adjacent segments, or separation between segments.
When the drill pipe 10 is under tension, the opposed essen-
tially flat shoulders 44 and 46 on tooth 34 are adapted to
engage the opposed shoulders S6 on tooth 38 and 58 on tooth
40, to provide a positive stop against excessive further
axial displacement of the pipe segments relative to each
other. It will be appreciated that the clearance between
the opposed shoulder portions will limit the relative
pivotal movement of adjacent pipe segments and thereby the
overall curvature which the pipe 10 may achieve in use.
Therefore, the clearance between the teeth and complementary
recesses is preferably substantially greater in the direc-
tion axial to the pipe, than in the direction circumfer-
ential of the pipe, the difference being represented by the
gap G formed between opposed tooth shoulder areas. The
dimension of the gap G will control the amount of elongation
of the segmented pipe under tension, as well as the relative
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pivotal movement of adjacent pipe segments, and thereby the
overall curvature of the entire segmented drill pipe.
In order to avoid the concentration of large forces in
a small area, it is preferable that the clearances between
the teeth and recesses, including the dimension of the gap
G, be such that the opposed shoulders 44 and 56, or 46 and
50, do not engage during the maximum curvature which the
drill pipe 10 is expected to attain during drilling opera-
tions. Rather, it is desired that essentially all of the
compressive and torque forces generated during use of the
drill pipe 10 be carried along the smooth semicircular
interfaces between the tooth crowns and the complementary
recesses formed by the tapered bases of circumferentially
adjacent teeth on the axially adjacent segments.
As shown most clearly in Figure 3, it is also desirable
to round the edges of the teeth at the junctures between the
shoulder and crown portions, and between shoulder and
tapered base portions, to provide for smooth flexing action
and to minimize the possibility of point-type force concen-
trations which could damage the structure.
The configuration of the improved teeth of the pipe
also provides increased resistance to tooth breakage. It
will be appreciated that the bending moment forces exerted
on the teeth as the pipe segments pivot relative to each
other, will have a substantial circumferential component.
Similarly, the torque transmitted through the drill pipe in
order to rotate the drill bit at the end of the pipe string
will exert a circumferential force on the individual teeth
of the pipe segments. These forces, represented by the
arrow F in Figure 3, will be greater near the base of the
tooth because of the elongation of the moment arm M.
However, with the present configuration, the thickness of
the tooth base increases as the moment arm elongates because
of the tapered base configuration, thereby providing great-
est structural strength at the base of the tooth rather than
1;~34~5
at its crown as shown in prior art configurations such as
U.S. Patents 2,515,366 and 4,328,839.
When the ends of the templated Figure 3 are joined,
there is formed a tubular section representative of the
generally circumferential interlocking connection between
adjacent segments of the flexible drill pipe 10. In the
preferred embodiment of the invention, each end of each
segment of the flexible drill pipe has two teeth 34 and 36
and two complementary recesses separating the teeth 34 and
36 from each other. It has been found that this two-teeth
configuration, with the complementary semicircular recesses
between the teeth, permits a ball and socket-type action on
compressive flexing, which permits maximum deflection while
also maximizing strength and durability of the pipe.
To further distribute the working forces in the seg-
mented pipe, it is preferable that the two teeth formed on
one end of a pipe segment be offset in either direction from
the complementary recesses on the opposite end of the drill
pipe segment. In the preferred embodiment, the teeth and
recesses in each segment are offset in a counterclockwise
direction by approximately 12 for each pipe segment. This
is particularly illustrated in Figure 2, where there are
shown four interconnections of segments of the flexible
drill pipe 10 with each of the interconnections of teeth and
recesses 28, 30 and 32 being offset, in counterclockwise
rotation, from the next preceding interconnection.
The foregoing description and disclosure of the inven-
tion is by way of example only, and various changes may be
made in the size and shape of parts, materials of construc-
tion and other details within the scope of the appended
claims without departing from the spirit of the invention.
