Note: Descriptions are shown in the official language in which they were submitted.
OMsoo3/~r 2 ~ ~ ~ 7 5 8 PATEN~
GLB:es
~PPLICA~ION FOR P~TENT
INVENTORS: Thomas E. Winship
Edmond I. Bailey
TITLE: Variable Depth Grooved Drill
String Member
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to drill string
members used in the rotary drilling art of the oil and gas
industry. In particular the invention relates to an intermediate
weight member adapted for placement between relatively lighter
weight drill pipe and heavier weight drill collars.
2. Description of Prior art
Intermediate weight members have been used in the art
of rotary drilling as a transition member between stiff drilling
collars and standard drill pipe. Such intermediate weight
members reduce fatigue in the stress-susceptible transition zone
between drill pipe and drilling collars.
2~ A prior art intermediate weight member sold by OMSCO
Industries, the assignee of the invention described herein,
includes a relatively heavy weight tubular member having upper
and lower sections separated by a short center wear pad. The
member has a constant inner diameter along its entire length.
The upper and lower sections are of constant outer diameter. The
wear pad has an outer diameter which is slightly less than about
one-half inch lar~er than the outer diameter of the upper and
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lower sections. The outer diameter of the upper section is
small enough to enable handling by standard slips and
elevators of a drilling rig. The cross-section moment of
inertia of the OMSCO intermediate weight member is
significantly greater at the center wear pad from that at the
upper and lower constant outer diameter sections.
Accordingly, the OMSCO intermediate weight member, because of
its construction, can be characterized by upper and lower
relatively limber sections separated by a relatively stiff
center section.
Another intermediate weight drill string member is
described in U.S. patent 4,460,202 to Chance et al. The
chance drill string member includes an upper relatively short
slip and elevator section and a lower grooved section which
extends substantially the remaining length of the member.
The grooved section is of an outer diameter which is larger
than the outer diameter of the slip and elevator section, but
has spiral grooves formed therein of a number and depth such
that the bending moment of inertia along the entire length of
the member is substantially constant. In other words, the
cross-section moment of inertia anywhere along the spiral
section is substantially equal to the cross-section moment of
inertia in the slip and elevator area. As a consequence, the
Chance member can be characterized as having a single bending
pattern which is substantially constant from one end of the
member to the other. In addition, the spiralled grooved
section provides advantages, like other spiralled members, of
reduced potential for differential sticking in the hole,
aiding in the removal of drilling chips up the annulus
between the drill string and the borehole, and possible
forward thrusting effect during drilling.
3. Identification of objects of the invention
It is a primary object of the invention to provide
certain advantages of the two prior art intermediate weight
members described above with a unique mechanical structure.
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It is another object of the invention to provide an
intermediate weight member which includes not only a slip and
elevator section and spiralled sections, but may also include
a center wear pad section.
It is still another object of the invention to provide
a drill string member of intermediate weight having a
structure such that the cross-section moment of inertia of
the member gradually changes a significant amount as a
function of length along the member so as to reduce bending
stresses inherent in regions where bending moments abruptly
change.
SUMMARY OF THE INVENTION
The objects identified above as well as other advantages
and features of the invention are incorporated in a drill
string member which is an integral elongate tubular member
having tool joints placed at each end for screwing to other
drill string members above and below. Typically a plurality
of the members constructed according to the invention are
screwed end to end and form an intermediate weight assembly
between drill pipe above and drill collars below. The
member, of substantially constant inner diameter along its
entire length, includes an upper slip and elevator section of
a first outer diameter of a dimension substantially the same
as the outer diameter of drill pipe for which it is adapted
to connect.
In a preferred embodiment of the invention, the member
includes a partially grooved section placed downwardly of the
slip and elevator section. The outer diameter of the grooved
section is greater than the outer diameter of the slip and
elevator section. The grooved section includes first and
second grooved sections separated by an ungrooved section.
The ungrooved section is a relatively short section
which may include hardbanding rings. Such rings are
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typically welded on strips that include granulated tungsten
carbide particles which inhibit wear. The first and second
grooved sections include grooves which vary in depth as a
function of the length of the respective section. The first
grooved section between the slip and elevator section and the
ungrooved section is characterized by spiral grooves which
are cut deeply into the outer diameter of the section at its
slip and elevator end. Such grooves are cut progressively
less deeply as the length of the first section approaches the
ungrooved section.
The second grooved section between the ungrooved section
and the lower end of the member likewise has grooves cut into
the outer diameter. The depth of such grooves also varies as
a function of length. Such grooves are shallow at the
ungrooved section end of the second grooved section and are
progressively deeper as the length of the section approaches
the lower end of the member.
As a result of the grooved sections which have groove
depths which vary as a function of length of the member, the
bending or cross-section moment of inertia of the member
makes a relatively smooth transition from the slip and
elevator section to the first grooved section as the length
of the member increases from top to bottom. The term
"bending moment" as used in the specification and claims
shall be interpreted as the moment of inertia of a cross
section where the deflection is calculated. With the depth
of the grooves being cut progressively shallower, and then
progressively deeper as a function of length along the
member, the bending moment of inertia as a function of length
increases approximately linearly from the slip and elevator
section to the ungrooved section and thence decreases
approximately linearly from the ungrooved section toward the
lower end of the member. A relatively short reduced diameter
section is provided at the lower end of the member. Tool
joints are attached e.g., by welding to the top and bottom
ends of the member.
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The shape of the cross-section moment of inertia as a
function of length along the member provides an intermediate
heavy wall tool which is relatively more stiff at a short
center section, yet is relatively more flexible at its ends.
Such characteristics are advantageous in horizontal and
directional drilling where the member is likely to be put
under compression and a central, relatively more stiff and
rugged region provides enhanced life and drilling
performance. The spiralled sections of the first and second
grooved sections not only provide the advantages of a
smoothly varying cross-section moment of inertia of the
member as a function of length, but also provide advantages
of reducing possible differential sticking problems in the
borehole. The novel structure also results in an
intermediate weight drill string member of greater weight of
the entire member as compared with prior art members. Such
greater weight is advantageous in providing more weight on
the drilling bit below. The novel structure also provides a
greater wear surface toward the center of the member as
compared with prior art members.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects, advantages and features of the invention
will become more apparent by reference to the drawings which
are appended hereto and wherein like numerals indicate like
parts and wherein an illustrative embodiment of the invention
is shown, of which:
Figure 1 is an illustration of the intermediate weight
member of the invention with a graphical illustration of its
bending moment of inertia as a function of length along the
member;
Figure 2 is a more detailed illustration of the
intermediate weight member of the invention showing tool
joints provided at its upper and lower ends and grooved
sections having grooves of varying depth provided below a
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slip and elevator section; and
Figure 3, 4 and 5 are cross-section illustrations taken
along section lines 3-3, 4-4, and 5-5 of Figure 2, which show
the depth of grooves varying as a function of length along
the member.
DESCRIPTION OF THE INVENTION
The preferred embodiment of the invention as defined by
the claims below is illustrated in Figures 1 through 5 below.
Figures 1 and 2 illustrate the elongated integral drill
string member 10 having tool joints 11 and 12 provided (as by
welding) to its upper and lower ends. The tool joint 11 is
provided with box threads to releasably join member 10 with
other members 10 or with a string of drill pipe above. The
tool joint 12 is provided with pin threads to releasably join
member 10 with other members 10 or with a bottom hole
assembly including drill collars below.
The drill string member 10 has a internal bore of a
substantially constant inside diameter along its entire
length. It includes a slip and elevator section 14 having a
diameter small enough to accommodate slip and elevator
equipment of the drilling rig. Such diameter is typically
matched to the outside diameter of drill pipe to which it is
adapted to connect. The purpose of the drill string member
10 is to provide a thick or heavy wall drill pipe which can
tolerate compression and tension forces between the thinner
walled drill pipe above and the thicker walled drill collars
below. A larger diameter for almost the entire remainder of
drill string member 10 is advantageous.
Accordingly, the partially grooved section 16 is
characterized by a diameter D which may be about five and
one-half inches for a three inch inner diameter and a five
inch outer diameter for slip and elevator section 14. These
dimensions for other sizes of intermediate weight members are
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scaled depending on the drill pipe size, drill collars, and
particular drilling application.
The partially grooved section 16 extends from the lowér
end of slip and elevator section 14 to a relatively short
reduced diameter section 24 of a diameter d2. For example,
for five inch drill pipe diameter d2 of reduced diameter
section 24 is preferably five and one-eighth inches for an
outside diameter D of about five and one-half inches of a
partially grooved section 16. Diameter d2 could of course be
a smaller diameter. For example, it could match the diameter
of the slip and elevator section. Diameter d1 is the size
typically used to describe the drill string member, e.g.,
five inch pipe. Alternatively, it need not be reduced in
diameter from the diameter of partially grooved section 16,
but providing a reduced diameter for section 24 increases the
flexibility at the lower end of the drill string member 10,
and as a consequence, reduces the bending stress of the drill
string member 10.
The partially grooved section 16 includes first grooved
section 18 disposed between slip and elevator section 14 and
ungrooved section 22. A second grooved section 20 is
provided between ungrooved section 22 and reduced diameter
section 24 at the lower end of drill string member 10.
The first grooved section 18 preferably includes three
right hand spiral grooves 30A, 30B, 30C, the depth of each of
which varies progressively with increasing length from the
lower end of slip and elevator section 14 to the upper end of
ungrooved section 22. Figures 3, 4 and 5 taken at upper,
middle and lower section lines 3-3, 4-4 and 5-5 of upper
grooved section 18 illustrate that grooves 30A, 30B, and 30C
become more and more shallow toward the ungrooved section 22
end, and yet are relatively deep at the upper end of grooved
section 18. The depth of the grooves 30A, 30B, 30C at the
slip and elevator section is such that the bending moment of
inertia at the upper end of first grooved section 18 is
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approximately the same as that of the slip and elevator
section 14.
To illustrate such feature, the graph of Figure 1 below
the illustration of drill string member 10 shows that the
cross-section moment of inertia at P1, where grooves 30A, 30B,
30C begin in first grooved section 18, makes a relatively
smooth transition from the slip and elevator section 14 to
the first grooved section 18. This graph depicts typical
values for a five inch size intermediate weight member. The
grooves 30A, 30B, and 30C are progressively shallower with
increasing length along grooved section 18 until such grooves
vanish at the lower or ungrooved section end of first grooved
section 18.
As illustrated by the region L22 of the graph of figure
1, the bending moment of inertia of the ungrooved section 22
is approximately fifty percent greater than that of the slip
and elevator section 14.
The grooves 30A, 30B, 30C of second grooved section 20
are shallow cut at the upper or ungrooved section end and are
cut progressively more deeply with increasing length as
illustrated in Figures 1 and 2 and especially in Figures 5,
4 and 3. Preferably such grooves have a depth at the lower
end of second grooved section 20 such that the bending moment
of inertia at point P2 approximately matches that of reduced
diameter section 24.
The drill string member 10 of the invention may also
include one or more hardbanding rings 26 and 28 about
ungrooved section 22. Such rings enhance the wear
characteristics of the member where the ungrooved section 22
scrapes against the borehole.
The drill string member 10 of the invention may also
include one or more regions of the member which are cold
worked to increase fatigue resistance at highly stressed
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areas. Regions L~ and Lp where the upper and lower tool
joints 11 and 12 are joined with drill string member 10 are
such high stress areas where cold working of the steel
material may be beneficial.
The drill string member 10 including upper and lower
tool joints 11 and 12 produces advantages of relatively
flexible ends with a relatively stiff center section. The
center section 22 also functions as a wear region which may
be hardbanded.
An integral slip and elevator section 14 provides
flexibility at one end. Varying depth grooves 30A, 30B, 30C
in first grooved section 18 and second grooved section 20
allow gradual transition of flexibility or cross-section
moment of inertia as a function of length over a magnitude
ratio of one to about one and one-half.
One of ordinary skill in the drilling art will
preferably use the drill string member 10 as an intermediate
weight member between drill pipe and drill collars.
A modification of the structure of Figures 1 and 2 may
be advantageous where handbanding between grooved section 18
and grooved section 20 is not necessary. For such a case,
the length of ungrooved section 22 maybe reduced to zero such
that the grooves of grooved section 18 become very shallow at
its lower end and actually become continuous with the shallow
grooves of grooved section 20. In other words, the shallow
grooves of grooved section 18 at its lower end can be
continuous with shallow grooves of grooved section 20 at its
upper end.
Still another modification of the structure of Figures
1 and 2 may be advantageous, like that above, where the
length of ungrooved section 22 may be reduced to zero.
Rather than the shallow grooves of grooved section 18 being
continuous with the shallow grooves of grooved section 20,
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- 10 -
such grooves may simply vanish in an alternating or
interleaving manner at the point along the length of member
10 where the two grooved sections 18 and 20 come together.
In other words, the two sets of groove patterns are not
continuous at the intersection point, but rather are spaced
from each other at sixty degree intervals, for example, about
the periphery of the member 10 at the intersection of grooved
section 18 and grooved section 20.
The drill string member 10 is manufactured from a steel
bar or tube of outside diameter D. A bore of diameter do is
formed in the bar or tube. Slip and elevator section 14,
reduced diameter section 24, and first and second grooved
sections 18 and 20 are formed by conventional mach;n;ng
techniques. Grooves 30A, 30B and 30C are formed with a
grooving machine having a flat bottomed cutter. Other groove
shapes may be used by those of skill in the machining art
without varying from the scope of the invention. Any grooves
formed as a function of length in first and second grooved
sections 18 and 20 which produce a cross-section moment of
inertia versus length profile similar to that of Figure 1 is
within the scope of the invention described herein.
Various modifications and alterations in the described
methods and apparatus will be apparent to those skilled in
the art of the foregoing description which does not depart
from the spirit of the invention. For this reason, these
changes are desired to be included in the appended claims.
The appended claims recite the only limitation to the present
invention. The descriptive manner which is employed for
setting forth the embodiments is to be interpreted as
illustrative but not limitative.
