Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2012/010480
CA 02805848 2013-01-171
PCT/EP2011/061963
Title: Drill Pipe
Description of Invention
The present invention relates to a drill pipe, particularly, but not
exclusively to
a drill pipe for use in drilling an oil or gas well.
The drilling of a borehole or well is typically carried out using a steel pipe
known as a drill pipe or drill string with a drill bit on the lowermost end.
The drill
string comprises a series of tubular sections, which are connected end to end.
The entire drill pipe may be rotated using a rotary table, or using an over-
ground drilling motor mounted on top of the drill pipe, typically known as a
'top
-
drive', or the drill bit may be rotated independently of the drill pipe using
a fluid
powered motor or motors mounted in the drill string just above the drill bit.
As
drilling progresses, a flow of mud is used to carry the debris created by the
drilling process out of the borehole. Mud is pumped down the drill pipe to
pass
through the drill bit, and returns to the surface via the annular space
between
the outer diameter of the drill pipe and the borehole (generally referred to
as
the annulus). The mud flow also serves to cool the drill bit, and to
pressurise
the borehole, thus substantially preventing inflow of fluids from formations
penetrated by the drill pipe from entering into the borehole. Mud is a very
broad drilling term and in this context it is used to describe any fluid or
fluid
mixture used during drilling and covers a broad spectrum from air, nitrogen,
misted fluids in air or nitrogen, foamed fluids with air or nitrogen, aerated
or
nitrified fluids to heavily weighted mixtures of oil and or water with solid
particles.
Significant pressure is required to drive the mud along this flow path, and to
achieve this, the mud is typically pumped into the drill pipe using one or
more
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positive displacement pumps which are connected to the top of the drill pipe
via a pipe and manifold.
Whilst the main mud flow into the well bore is achieved by pumping mud into
the main bore at the very top end of the drill pipe, it is also known to
provide
the drill pipe with a side bore which extends into the main bore from a port
provided in the side of the drill pipe, so that mud can be pumped into the
main
bore at an alternative location to the top of the drill pipe.
For example, as drilling progresses, and the bore hole becomes deeper and
deeper, it is necessary to increase the length of the drill pipe, and this is
typically achieved by disengaging the top drive from the top of the drill
pipe,
adding a new section of tubing to the drill pipe, engaging the top drive with
the
free end of the new tubing section, and then recommencing drilling.
To facilitate the connection of the new length of tubing to the top of the
drill
pipe, each end of each section of drill pipe is provided with what is known as
a
"tool joint" which comprises a portion of the drill pipe with a greater wall
thickness than the central portion of the drill pipe. The increased wall
thickness is achieved by providing a taper which increases the outer diameter
of the drill pipe, whilst the internal diameter of the drill pipe is
substantially
constant along the entire length of the drill pipe including the tool joint.
The
tool joint at one end of each length of drill pipe is typically provided with
a male
threaded connector portion, whilst the tool joint at the other end is provided
with a female threaded connector portion. Two adjacent sections of drill pipe
may therefore be joined by screwing the male connector portion of one into the
female connector portion of the other. Such a tool joint is illustrated in US
6,244,631, for example.
It will, therefore, be appreciated that pumping of mud down the drill pipe
ceases during this process. Stopping mud flow in the middle of the drilling
process is problematic for a number of reasons, and it has been proposed to
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facilitate continuous pumping of mud through the drill string by the provision
of
a side bore in each section of drill string. This means that mud can be pumped
into the drill string via the side bore whilst the top of the drill string is
closed,
the top drive disconnected and the new section of drill string being
connected.
In one such system, disclosed in US Patent 3,298,385, at the top of each
section of drill string, there is provided a side bore which is closed using a
plug, and a valve member which is pivotable between a first position in which
the side bore is closed whilst the main bore of the drill string is open, and
a
second position in which the side bore is open whilst the main bore is closed.
During drilling, the valve is retained in the first position, but when it is
time to
increase the length of the drill string, the plug is removed from the side
bore,
and a hose, which extends from the pump, connected to the side bore, and a
valve in the hose opened so that pumping of mud into the drill string via the
side bore commences. A valve in the main hose from the pump to the top of
the drill string is then closed, and the pressure of the mud at the side bore
causes the valve member to move from the first position to the second
position, and hence to close the main bore of the drill string.
The main hose is then disconnected, the new section of tubing mounted on the
drill string, and the main hose connected to the top of the new section. The
valve in the main hose is opened so that pumping of mud into the top of the
drill string is recommenced, and the valve in the hose to the side bore
closed.
The resulting pressure of mud entering the top of the drill string causes the
valve member to return to its first position, which allows the hose to be
removed from the side bore, without substantial leakage of mud from the drill
string. The side bore may then be sealed permanently, for example by welding
a plug onto the side bore, before this section of drill string is lowered into
the
well.
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According to a first aspect of the invention we provide a drill pipe having an
elongate tubular body with an interior surface enclosing a main bore which
extends generally parallel to a longitudinal axis of the tubular body from a
first
end to a second end of the tubular body, a side port provided in an exterior
surface of the tubular body, a side bore extending through the body from the
main bore to the side port, and a valve assembly which is operable to
substantially prevent flow of fluid along the main bore and to substantially
prevent flow of fluid along the side bore, wherein the valve assembly, side
port
and side bore are provided in a first connection portion of the drill pipe at
the
first end thereof, the first connection portion comprising a thickened portion
of
the tubular body in which the separation of the interior surface and the
exterior
surface is substantially greater than the adjacent portion of the tubular
body,
the length of the connection portion parallel to the longitudinal axis of the
tubular body being less than 64 cm.
Well bore are not always completely straight, and in directional drilling it
is
common to drill curved sections of well bore. To achieve this, it is necessary
for the drill pipe to be sufficiently flexible to allow it to bend around the
curved
sections of well bore as drilling progresses. By incorporating the valve
assembly required for continuous mud circulation into the tool joint, and by
minimising the length of the tool joint, the stresses experienced by the drill
pipe
when it is bent around a curved section of well bore can be more evenly
distributed along the length of the drill pipe, and the maximum stress
experienced can be reduced. This may assist in improving the fatigue
resistance of the drill pipe.
Preferably the valve assembly includes a first valve member which is movable
between an open position, in which flow of fluid along the main bore is
permitted, and a closed position, in which flow of fluid along the main bore
is
substantially prevented, and a second, separate, valve member which is
movable between an open position, in which flow of fluid along the side bore
is
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permitted, and a closed position, in which flow of fluid along the side bore
is
substantially prevented.
The first valve member may comprise a ball which is rotatable between the
open position and the closed position.
The second valve member may be mounted at least predominantly within the
side bore, and may be slidable in the side bore between the open position and
the closed position.
Preferably the first connection portion is provided with a first threaded
portion.
Preferably there is a second connection portion at the second end of the
tubular body, the second connection portion also comprising a thickened
portion of the tubular body in which the separation of the interior surface
and
the exterior surface is substantially greater than the adjacent portion of the
tubular body. In this case, preferably the second connection portion is
provided with a second threaded portion which is a mate for the first threaded
portion. This means that the drill pipe can be connected to another identical
drill pipe by mating of the first threaded portion of one drill pipe with the
second
threaded portion of the other drill pipe. The first threaded portion may be
provided in the interior surface of the drill pipe, i.e. the first connection
portion
may be the female connector, and the second threaded portion may be
provided in the exterior surface of the drill pipe, i.e. the second connection
portion is the male connector.
An embodiment of the invention will now be described, by way of example
only, with reference to the accompanying drawings, of which,
FIGURE 1 shows a schematic illustration of a cross-section through end
portions of two interconnected drill pipes according to the invention,
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FIGURE 2 shows a cross-section through an end portion of a drill pipe
according to the invention, the valve assembly having been omitted from the
drawing for clarity,
FIGURE 3 shows a perspective view of a section through part of the valve
assembly of the drill pipe illustrated in Figure 1,
FIGURE 4 shows a cross-section through the portion of the drill pipe labelled
X
in Figure 1,
FIGURE 5 is a detailed cross-section through the part of the valve assembly
illustrated in Figure 4,
FIGURE 6 is a detailed cross-section through the part of the valve assembly
shown in Figure 5 without the cap, and
FIGURES 7a and 7b are schematic illustrations of two different configurations
of drill pipe in a curved section of well bore.
Referring now to Figure 1, there is shown a section of drill pipe 10, having a
tubular body 12 through which is provided a main bore 14 which extends
generally parallel to a longitudinal axis A of the tubular body from a first
end to
a second end of the tubular body 12. As is typical for drill pipes, in this
example, the exterior surface of the tubular body 12 is generally circular in
transverse cross-section, and the main bore 14 is cylindrical and extends
axially through the tubular body 14 from a first end 12a to a second end of
the
tubular body 12. A side port 16 is provided in the exterior surface of the
tubular body 12, and a side bore 18 extends through the tubular body 12 from
the main bore 14 to the side port 16, in this example, generally perpendicular
to the main bore 14.
The drill pipe 10 is provided with a valve assembly which is operable to
substantially prevent flow of fluid along the main bore 14 and to
substantially
prevent flow of fluid along the side bore 18. In this example, the valve
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assembly comprises two separate valve members ¨ a first valve member 20
which is movable between an open position, in which flow of fluid along the
main bore 14 is permitted, and a closed position, in which flow of fluid along
the main bore 14 is substantially prevented, and a second valve member 22
which is movable between an open position, in which flow of fluid along the
side bore 18 is permitted, and a closed position, in which flow of fluid along
the
side bore 18 is substantially prevented.
In this example, the first valve member 20 is a conventional Kelly valve which
comprises a ball which is rotatable about an axis B generally perpendicular to
the longitudinal axis A by means of a pin 24 which extends from the main bore
14 through a further bore 25 to the exterior surface of the tubular body 12.
The pin 24 has a head 26 which is shaped to be engagable with a tool such as
a spanner or Allan key, and the tool used to rotate the ball between the open
position and the closed position. The ball is provided with a central bore 20a
which lies parallel to the longitudinal axis A of the tubular body 12 when the
valve member 20 is in the open position, and which lies generally
perpendicular to the longitudinal axis A when the valve member 20 is in the
closed position. It will be appreciated that the valve member 20 is shown in
the open position in Figure 1, and that flow of fluid along the main bore 14
of
the drill pipe 10 can occur via the central bore in the ball 20 when in this
position. In contrast, as the ball is rotated about axis B, the ball blocks
flow of
fluid along the main bore 14.
In this example, the second valve member 22 is mounted at least
predominantly within the side bore, and is slidable in the side bore 18
between
the open position and the closed position. In this example, the second valve
member 22 comprises a poppet check valve which is mounted in a generally
cylindrical valve housing 28 which is retained in a corresponding recess at
the
side port 16 in the exterior surface of the drill pipe 10. In this example,
one
side bore 18 is provided in the drill pipe 10, although it should be
appreciated
that more than one may be included to increase the cross-section available for
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flow of mud of the drill pipe 10 via the side bore 18. The valve housing 28 is
retained by means of a screw thread (not shown) which engages with a
corresponding screw thread in the side bore 18, but it will be appreciated
that
bolts, or any other appropriate fastening means could be used. Alternatively
the valve housing 28 could be integral with the tubular body 12 of the drill
pipe
10.
Two 0-rings 30 are mounted each in a circumferential groove provided in the
exterior surface of the valve housing 28 and provide a fluid tight seal
between
the valve housing 28 and the tubular body 12 of the drill pipe 10. The valve
housing 28 is also provided with a central bore 32 which is generally parallel
to
the side bore 18 in the drill pipe 10 and in which is located the valve member
22. The valve member 22 includes a stem 34 one end of which is mounted
centrally on a disc 36 so that the stem 34 extends generally normal to the
disc
36 to a free end of the stem. A circular valve seat 38 is provided at the
interior
end of the valve housing 28 which is adjacent the main bore 14 of the drill
pipe
10. The valve member 22 is located such that the stem 34 extends into the
central bore 32 of the valve housing 28 from the interior end thereof, whilst
the
disc 36 lies in the side bore 18 without protruding into the main bore 14 of
the
drill pipe 10, outside the valve housing 28 and adjacent the interior end
thereof. The diameter of the disc 36 is greater than the diameter of the
central
bore 32 and of the valve seat diameter of the valve seat 38, so when the valve
member 22 is in the closed position, the disc 36 engages with the valve seat
38, providing a generally fluid tight seal which substantially prevents fluid
flow
along the side bore 18 in the drill pipe 10.
In order to locate the valve member 22 radially within the central bore 32 of
the
valve housing 28, an annular flange 40 is provided which extends from the
valve housing 28 into the central bore 32. The flange 40 includes a central
aperture which is just slightly larger in diameter than the stem 34 of the
valve
member 22, and the stem 34 of the valve member 22 extends through this
aperture. The valve member 22 is biased into the closed position by means of
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a helical spring 42 which extends between a generally circular groove provided
in the flange 42 and a collar 46 fixed to the free end of the stem 34. It is
therefore necessary to move the valve member 22 against the biasing force of
the spring 42 in order to move it out of the closed position to the open
position,
in which fluid can flow through the central bore 32 via the space between the
valve seat 38 and disc 36. The valve member 22 is configured such that this
may be achieved by the supply of pressurised fluid to a hose connected to the
side bore 18 of the drill pipe 10.
The central bore 32 of the valve housing 28 is threaded so that a cap 48 can
be provided as illustrated in Figures 4, and 5. The cap 48 is provided with a
generally circular top part 48a from which extends a generally cylindrical
wall
48b of smaller diameter than the top part 48a. The wall 48b extends into the
central bore 32 of the valve housing 28, and is provided with two 0-rings 50
each of which is located in a circumferential groove around the exterior
surface
of the wall 48b. The screw thread by means of which the cap 48 is retained in
the valve housing 28 is provided on the exterior surface of the wall 48a
between the top part 48a and the 0-rings 50.
The 0-rings 50 engage with the central bore 32 of the valve housing 28 to
provide a substantially fluid tight seal. This ensures that the cap 48
provides a
secondary seal preventing fluid flow through the side bore 18 in the drill
pipe
10 in case the seal provided by the valve member 22 fails.
Other fastening means may be used to retain the cap 48 in the valve housing
28. For example, a bayonet lock or similar type of quick connection methods
may be used instead of the thread.
During the usual operational mode of the drill pipe there exists a pressure
inside the main bore 14 that forces the valve member 22 against the seat 38.
To use the second valve, during the connection of a new length of drill pipe,
the cap 48 is removed. The cap 48 may also be provided with a relief slot (not
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shown) to allow safe venting of any pressure trapped in the central bore 32.
Once the cap 48 is removed an adapter (not shown) can be threaded into the
thread, with similar 0-rings to the 0-rings 50 on the cap 48 being provided to
ensure a substantially fluid tight seal between the valve housing 28 and the
adapter. Fluid pressure can then be supplied through this adapter which will
start lifting the disc 36 from the seat 38 once the applied pressure is
sufficient
to overcome the biasing force of the spring 42 and exceeds the internal
pressure in the bore 14 of the drill pipe 10. At this point the second valve
22 is
opened and flow will pass through the circumferential clearance into the main
bore 14 of the drill pipe 10.
Once the flow is stopped, and the pressure in the adapter is reduced below the
pressure in the drill pipe10, the second valve 22 will close. The spring 42
will
always ensure that the valve 22 is held in a closed position at all times when
there is no pressure applied from the internal bore of the drill pipe 10 and
there
is no pressure applied externally.
It should be appreciated that the invention is not restricted to this
configuration
of valve assembly, and the second valve 22 may, advantageously, be as
described in our co-pending patent application WO 2010/046653.
The first and second valves 20, 22, side port 16 and side bore 18 are all
provided in a first connection portion 10a of the drill pipe 10 at the first
end
thereof, the first connection portion 10a comprising a thickened portion of
the
tubular body 12 in which the separation of the interior surface and the
exterior
surface is substantially greater than the adjacent portion of the tubular body
12.
The thickening may be achieved by maintaining the internal diameter of the
drill pipe 10 constant along its entire length, the outer diameter increasing
at
the first end 10a, as illustrated in Figure 1. Alternatively, in addition to
the
increase in the outer diameter, further thickening may be provided by
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decreasing the internal diameter over at least a portion of the connection
portion 10a, as illustrated in Figure 2. In the embodiment of the invention
shown in Figure 2, the internal diameter of the drill pipe 10 decreases in
stages from the very end of the drill pipe 10. First, there is provided a
first
tapered portion 52 in which the internal diameter decreases linearly and
which,
in this example is threaded, then there is a portion of constant internal
diameter 54 through which the pin receiving bore 25 extends, followed by a
step 56 in which the internal diameter is reduced further in two stages to a
second portion of constant internal diameter 58, through which the side bore
18 extends. Finally, there is a second tapered portion 60 in which the
internal
diameter increases slightly. The first constant internal diameter portion 54
is
provided with a circumferential internal groove 62 which in use, receives a
retainer ring that holds the ball valve 20 in place.
There is a second connection portion at the second end of the tubular body 12,
the second connection portion 10b also comprising a thickened portion of the
tubular body 12 in which the separation of the interior surface and the
exterior
surface is substantially greater than the adjacent portion of the tubular body
12. In this example, the second connection portion 10b is provided with a
second threaded portion 64 which is a mate for the first threaded portion 52.
The first threaded portion 52 is provided in the interior surface of the drill
pipe
10, i.e. the first connection portion is the female connector, and the second
threaded portion 64 is provided in the exterior surface of the drill pipe 10,
i.e.
the second connection portion 10b is the male connector. This means that the
drill pipe 10 can be connected to another identical drill pipe 10' by mating
of
the first threaded portion 52 of one drill pipe 10 with the second threaded
portion 64' of the other drill pipe 10', as illustrated in Figure 1.
The length of the first connection portion 10a parallel to the longitudinal
axis of
the tubular body is between 19 inches (48 cm) and 25 inches (64 cm). Ideally
it is less than 24 inches long, and in this example is 23.85 inches long.
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By incorporating the valve assembly required for continuous mud circulation
into the tool joint, and by minimising the length of the tool joint, the
stresses
experienced by the drill pipe when it is bent around a curved section of well
bore can be more evenly distributed along the length of the drill pipe 10.
This
is illustrated in Figures 7a and 7b, which show a curved portion of well bore
66
containing two different configurations of drill pipe 10. In Figure 7a, the
first
and second connection portions 10a, 10b are relatively long, whilst in Figure
7b, the first and second connection portions 10a, 10b are relatively short. It
can be seen that in Figure 7a there is a sharper bend at the transition
between
the thicker, and therefore stiffer, connection portions and the thinner, and
therefore more flexible, central portion of the drill pipe, than there is in
Figure
7b. In this way, the maximum stress experienced by the drill pipe can be
reduced, and this may assist in improving the fatigue resistance of the drill
pipe 10.
When used in this specification and claims, the terms "comprises" and
"comprising" and variations thereof mean that the specified features, steps or
integers are included. The terms are not to be interpreted to exclude the
presence of other features, steps or components.
The features disclosed in the foregoing description, or the following claims,
or
the accompanying drawings, expressed in their specific forms or in terms of a
means for performing the disclosed function, or a method or process for
attaining the disclosed result, as appropriate, may, separately, or in any
combination of such features, be utilised for realising the invention in
diverse
forms thereof.
