Note: Descriptions are shown in the official language in which they were submitted.
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A TELESCOPIC CONDUCTOR CASING FOR A WELL INSTALLATION AND A
METHOD OF DRIVING SAME INTO THE UNDERGROUND
The invention regards a telescopic conductor casing for a
well installation, preferably a sub sea hydrocarbon well,
s more particularly a telescopic conductor casing in which an
outer pipe is releasably coupled to an inner pipe, the lower
end of which comprises means of cooperating with a driving
mechanism. When the conductor casing has been driven far
enough into the unconsolidated sediments so as to project a
to prescribed distance above the surface of the unconsolidated
sediments, the outer pipe is separated from the inner pipe.
The inner pipe is driven further into the unconsolidated
sediments until it encounters so lid sediments or reaches the
planned driving depth. A device by the lower end of the outer
15 pipe ensures that the outer pipe cannot be pushed down on the
outside the inner pipe. The invention also comprises a method
of driving a telescopic conductor casing into the ground.
When establishing a well such as a hydrocarbon well in an
area with unconsolidated sediments above the rock structures,
zo it is necessary to insert a con~.uctor casing through the
unconsolidated sediments. The conductor casing separates the
wellbore from the unconsolidatec7. sediments and acts as a
foundation for installations (wallhead, BOP etc.) at the
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surface of the unconsolidated sediments. The installations
will, in accordance with regulations, be placed at a certain
height relative to the surface, i.e. ground surface or
seabed. Analyses of the unconsolidated sediments form the
s basis for the selection of a conductor casing length, which
in all probability can be driven far enough down for the
upper end of the conductor casing to attain a prescribed
height above the unconsolidated sediments. When there is
uncertainty with regards to the condition of the
to unconsolidated sediments, the length of the conductor casing
may be to great or too small, and it becomes necessary,
particularly when establishing a sub sea well, to carry out
complicated operations to lengthen or shorten the conductor
casing so as to achieve the correct height for the upper end
is of the casing.
The object of the invention is to remedy the disadvantages of
prior art. In particular, the object is to reduce the cost
and practical effects of the uncertainty involved in
estimating how far the conductor casing can be driven.
~o The invention also allows the installation of long conductor
casings without requiring additional conductor casing
sections to be added during the driving.
The object is achieved by the characteristics given in the
description below and in the following claims.
2s A telescopic conductor casing according to the invention is
arranged in a known manner to be driven into unconsolidated
sediments by means of axially directed impulses against
internally placed impact surfaces, preferably in the lower
portion of an inner pipe. The inner pipe is removably coupled
so to an outer pipe, preferably by an upper portion of the inner
pipe being coupled to an upper portion of the outer pipe.
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In the lower portion of the outer pipe there is provided, in
a non-displaceable manner, one or more locking members
abutting the outside wall of the inner pipe. The locking
elements) is/are arranged to allow an inner pipe released
from the outer pipe to move axially away from the upper
portion of the outer pipe. The locking elements) is/are
furthermore arranged to prevent an outer pipe released from
the inner pipe to move axially towards the lower portion of
the inner pipe.
to Preferably, the outer pipe is arranged to receive one or more
known stabilizers located externally. This is particularly
relevant when the conductor casing is to be placed in
unstable unconsolidated sediments. The stabilizers causes the
conductor casing to present a greater abutment surface to the
unconsolidated sediments, whereby the unconsolidated
sediments can accommodate a greater load directed radially of
the pipe.
Preferably, the outer pipe is provided with one or more stops
arranged to abut an upper portion of the stabilizer(s). This
2o makes it possible to place the stabilizers) at a predefined
level relative to the surface of the unconsolidated sediments
when they are driven into the unconsolidated sediments along
with the outer pipe.
The invention further comprises a method of driving a
a5 conductor casing into unconsolidated sediments in order to
line a wellbore, the conductor casing being arranged to be
driven into the unconsolidated sediments by axially directed
impulses against an internal abutment in the lower portion of
the conductor casing, where:
so - an outer pipe is removably coupled to the upper portion
of an inner pipe;
- the compound telescopic conductor casing is driven into
the unconsolidated sediments until the upper portion of the
outer pipe assumes a prescribed distance from the surface of
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the unconsolidated sediments;
- the outer pipe is released from the inner pipe;
- the inner pipe is driven further into the unconsolidated
sediments until it reaches the planned driving depth or until
s no further driving is possible, the inner pipe moving away
from the upper portion of the outer pipe in the axial
direction.
Preferably, the method comprises the provision of one or more
stabilizers on the outer pipe prior to driving this into the
to unconsolidated sediments.
The following describes a non-limiting example of a preferred
embodiment illustrated in the accompanying drawings, in
which:
Figure 1 shows a longitudinal section through an assembled
15 to lescopic conductor casing according to the invention;
Figure 2 shows a longitudinal section, on a smaller scale,
through an assembled telescopic conductor casing being driven
into unconsolidated sediments;
Figure 3 shows a longitudinal section through the telescopic
~o conductor casing being driven into unconsolidated sediments,
with an inner pipe sliding in a disconnected outer pipe;
Figure 4 shows a side view of a conductor casing
corresponding to the longitudinal section of figure 3, but
where the outer pipe is provided with a stabilizer; and
z5 Figure 5 shows a top view of the conductor casing in figure
4.
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Reference is first made figure 1, in which a telescopic
conductor casing 1 comprises an inner pipe 3, an outer pipe
5, an annular coupling device 7 and also an annular locking
member 9.
s The upper portion 11 of the inner pipe 3 is provided with an
annular coupling groove 13. A lower portion 15 of the inner
pipe 3 is provided with a driving shoe 17 with an internal
striking surface 19.
An upper portion 21 of the outer pipe 5 is provided with an
so external coupling section 23 capable of receiving and
retaining a well installation (not shown). The outside of a
central portion 25 of the outer pipe has annular stabilizing
stops 27. A lower portion 28 of the outer pipe is provided
with an internal annular locking groove 29.
is The coupling device 7 has an internal coupling section 31
that extends from a lower central opening 33. The threaded
portion 31 of the coupling device 7 is a complementary fit to
the coupling section 23 on the outer pipe 5. An upper bore 35
is a complementary fit to the outer diameter of the inner
ao pipe 3. An annular shoulder 37 is a complementary fit to the
coupling groove 13 on the inner pipe 3. The coupling device
is removable, being divisible (not shown) by means of a tool-
bearing remote operated vehicle (not shown).
The locking element 9 is shaped like an annular disk spring
as with a convex ring surface 41 facing the lower end 15 of the
outer pipe 5. An internal lip 43 tightly abuts the outer wall
of the inner pipe 3.
Reference is now made essentially to figures 2 and 3. The
conductor casing 1 has been driven into unconsolidated
3o sediments 51 by means of an internally placed hammer 61, 63
connected to a driving and control mechanism (not shown) via
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a cable 65. The hammer 61, 63 can transmit driving impulses
to the conductor casing via the impact surface 19.
In an alternative embodiment the conductor casing 1 is
provided with a cylindrical stabilizer 71 enclosing portions
of the outer pipe 5. A central pipe 73 encloses the outer
pipe 5 coaxially and abuts the stabilizer stop 27 when in the
active position. A cylindrical jacket 77 is coaxial with the
central pipe 73 and is rigidly connected to this by several
supporting ribs 75 that project in the radial direction from
to the central pipe 73 and extend along the entire axial length
of the stabilize r 71.
Prior to driving a conductor casing 1 into the ground, the
unconsolidated sediments 51 are analysed to find out how far
the conductor ca sing 1 can be driven and how much uncertainty
exists around this analysis, i.e. what is the expected
maximum driving depth and what is the estimated minimum
driving depth. Then a length of inner pipe 3 is selected
which under no circumstances will cause the inner pipe 3 to
protrude above the unconsolidated sediments by more than what
zo is prescribed for a well installation which is subsequently
to be installed on the conductor casing 1. Also, the length
of the outer pipe 5 is selected to be such that the outer
pipe 5, when pro truding above the unconsolidated sediments 51
as prescribed with regard to the well installation, overlaps
as the inner pipe when this has been driven down to the maximum
depth.
The conductor casing 1 is driven into the unconsolidated
sediments 51 in a manner that is known per se, by the hammer
61, 63 partly making a hole by penetrating into the
3o unconsolidated sediments 51 and forcing them aside and partly
hammering the conductor casing into the unconsolidated
sediments 51 through impacts against the impact surface 19 on
the driving shoe 17. During the first part of the driving,
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the coupling device 7 interconnects the inner and outer pipes
3, 5 of the conductor casing 1.
When the outer pipe 5 has reached a prescribed depth, i.e. it
protrudes above the unc onsolidated sediments 51 at a
s prescribed height, the coupling device 7 is removed; at a sub
sea installation preferably through use of tools on a remote
operated vehicle (ROV).
The driving then continues, the inner pipe 3 moving axially
through the outer pipe 5 by sliding through the locking
so member 9. When the inner pipe 3 has reached its maximum depth
the hammer 61, 63 is retrieved from the conductor casing 1.
In the alternative embodiment where the outer pipe 5 has a
stabilizer 71, this is driven into the unconsolidated
sediments together with the outer pipe 5, the central pipe 73
i5 of the stabilizer 71 abutting the stabilizer stop 27. The
large surface area of the jacket 77 ensures, in a manner that
is known per se, an increase in the lateral stability of the
conductor casing 1 when placed in unstable unconsolidated
sediments 51.
2o The conical shape of the locking member 9 ensures that the
outer pipe 5 will not s lip down the inner pipe 3 under
stress, as the internal lip 43 of the locking member 9 will
seize against the surface of the inner pipe 3.
The conductor casing 1 according the invention can assume a
z.s wide range of dimensions, as the inner pipe can assume all
relevant dimensions according to industrial practice.
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