U.S. patent number 3,705,623 [Application Number 05/151,748] was granted by the patent office on 1972-12-12 for offshore well equipment with pedestal conductor.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Bob E. Busking, Wouter H. van Eek, Adrianus W. VAN Gils.
United States Patent |
3,705,623 |
van Eek , et al. |
December 12, 1972 |
OFFSHORE WELL EQUIPMENT WITH PEDESTAL CONDUCTOR
Abstract
Apparatus and method for drilling and completing subsea wells
using a wellhead mounted on a pedestal conductor supported above a
conductor pipe string by a buoyant member. The conductor string
supports a plurality of casings which are cemented over their
entire lengths. A single small-diameter casing is suspended from
the wellhead and extends over the length of the pedestal
conductor.
Inventors: |
van Eek; Wouter H. (The Hague,
NL), Busking; Bob E. (The Hague, NL), VAN
Gils; Adrianus W. (The Hague, NL) |
Assignee: |
Shell Oil Company (New York,
NY)
|
Family
ID: |
10291361 |
Appl.
No.: |
05/151,748 |
Filed: |
June 10, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jun 17, 1970 [GB] |
|
|
29,424/70 |
|
Current U.S.
Class: |
166/338; 166/353;
166/381; 166/368 |
Current CPC
Class: |
E21B
33/035 (20130101); E21B 7/124 (20130101); E21B
7/128 (20130101) |
Current International
Class: |
E21B
33/035 (20060101); E21B 33/03 (20060101); E21B
7/12 (20060101); E21B 7/128 (20060101); E21B
7/124 (20060101); E21b 007/12 (); E21b
043/01 () |
Field of
Search: |
;166/315,.6
;175/6,7,8,9,10,171 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moore; Richard E.
Claims
We claim as our invention
1. Apparatus for completing a well which penetrates a formation
located below a body of water comprising:
a conductor string arranged for at least the greater part thereof
in the well and cemented to the formation;
a pedestal conductor for providing a wellhead location above the
bottom of the body of water;
at least one buoyancy member connected to the pedestal conductor
near the upper end thereof for supporting the pedestal conductor in
the body of water above the conductor string;
means for sealingly coupling the lower end of the pedestal
conductor to the upper end of conductor string;
a wellhead mounted on the upper end of the pedestal conductor;
pipe suspending means arranged in the conductor string near the
upper end thereof;
at least one string of tubular pipe suspended from the pipe
suspending means in the conductor string and extending into the
well below the lower end of the conductor string; and
a string of tubing suspended from the wellhead and extending
downwardly through the pedestal conductor and into the conductor
string, the string of tubing being connected at its lower end in
communication with the string of tubular pipe suspended in the
conductor string.
2. The apparatus of claim 1 including means for coupling the lower
end of the string of tubing to the upper end of the string of
tubular pipe suspended in the conductor string.
3. The apparatus of claim 1 wherein the means for coupling the
lower end of the pedestal conductor to the upper end of the
conductor string includes a blowout preventor.
4. The apparatus of claim 1 wherein a plurality of strings of
tubular pipe of different diameters are suspended from the
conductor string, and wherein the string of tubing suspended from
the wellhead is connected at its lower end in communication with
the string of tubular pipe of smallest diameter.
5. The apparatus of claim 4 wherein the string of tubing suspended
from the wellhead is of the same diameter as the string of tubular
pipe of smallest diameter.
6. The apparatus of claim 4 wherein there is an annular space
around each of the plurality of strings of tubular pipe and wherein
the annular space around each of the strings of tubular pipe is
filled with solid material around substantially the entire length
of the string of tubular pipe.
7. The apparatus of claim 4 including a production tubing suspended
from the wellhead and extending downwardly into the well through
the string of tubing suspended from the wellhead and through the
string of tubular pipe of smallest diameter.
8. In a well drilled into a formation located below a body of water
and provided with equipment of the type comprising a relatively
large diameter conductor pipe string positioned in the upper part
of the well, at least one string of casing extending to the bottom
of the well, and a wellhead mounted above the conductor pipe string
on a pedestal conductor coupled to the conductor pipe string and at
least in part supported in the water by buoyant support means, an
improved method of equipping the well comprising the steps of:
suspending the string of casing at a point below the upper end of
the conductor pipe string from casing suspension means supported by
the conductor pipe string;
cementing the suspended string of casing in the borehole throughout
substantially the entire length of the suspended string of casing
below the casing suspension means;
extending a string of tubing from the wellhead to the upper end of
the suspended string of casing;
coupling the string of tubing to the suspended string of casing;
and
suspending the string of tubing from the wellhead, thereby
providing a continuous conduit from the wellhead to the bottom of
the string of casing a substantial portion of which is not
supported by the pedestal conductor on which the wellhead is
mounted.
9. The method of claim 8 including the steps of
extending a production tubing string into the well through the
string of tubing and through at least part of the suspended string
of casing; and
suspending the production tubing string from the wellhead.
10. A method of drilling a well into a formation located below a
body of water comprising the steps of:
drilling a borehole into the formation with equipment lowered from
the water surface;
extending a relatively large diameter conductor pipe string into
the bore hole;
cementing the conductor pipe string in the bore hole;
positioning in the water above the conductor pipe string a pedestal
conductor supported by at least one buoyant support means;
coupling the pedestal conductor to the conductor pipe string;
extending drilling equipment from the water surface into the bore
hole through the pedestal conductor and the conductor pipe
string;
drilling the bore hole deeper into the formation with the drilling
equipment to a point below the lower end of the conductor pipe
string;
extending a casing into the deepened bore hole thereby defining an
annular space around the exterior of this casing;
suspending the casing in the conductor pipe string with a pipe
suspension means;
filling the annular space around the suspended casing with cement
along substantially the entire length of the suspended casing;
extending a string of tubing into the well to a point adjacent the
top of the suspended casing;
coupling the lower end of the string of tubing to the upper end of
the suspended casing;
suspending the string of tubing from a wellhead mounted on the top
of the pedestal conductor;
extending drilling equipment from the water surface into the bore
hole through the string of tubing and the suspended casing; and
drilling the bore hole deeper into the formation with the drilling
equipment to a point below the lower end of the suspended casing.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to equipment for a well penetrating a
formation located below a body of water, and more particularly to
well equipment comprising a wellhead mounted on a pedestal
conductor.
2. Description of the Prior Art
Several types of equipment for drilling underwater wells are
already known. Use can be made for instance of a marine structure
supported on the bottom of a body of water and extending with the
upper part thereof above the water level. The drilling installation
is located on this upper part of the marine structure, and a well
is drilled via a conductor string extending from the drilling
installation into the formation to be drilled. Wellhead equipment
typical for land operations is applied above the level of the
water.
In another manner, wells are drilled below a body of water by
special equipment comprising wellheads suitable to be placed on the
bottom of the body of water. The necessary operational techniques
to be carried out at the wellhead may be performed by divers or by
remotely controlled manipulators. This technique is suitable for
application in water which is either too deep for placement of
permanent marine structures of wherein structures above sea level
are not allowed for navigational reasons.
However, in still deeper water, the placement of wellhead equipment
at or near the sea bottom will create problems if repairs to or
substitution of such equipment cannot be carried out or can only be
effected by divers. To solve these problems, it has been proposed
to place the wellhead on a pedestal conductor, which extends from a
level at or below the sea bottom to a level at which divers can
easily operate.
Such a pedestal conductor is kept in an upright position by
guy-lines and/or by a buoyancy member connected to the top of the
conductor and/or by buoyancy members distributed along the length
of the conductor.
SUMMARY OF THE INVENTION
The present invention relates to equipment for underwater wells
which are drilled and completed in subsea formations lying below
very deep water, i.e., waters in which divers cannot actually or
economically operate at or near the bottom thereof. In the new
equipment, the drilling operations take place via the pedestal
conductor, which is kept in an upright position by at least one
buoyancy member connected to the upper part thereof. The coupling
and uncoupling of the various parts of the wellhead during the
drilling operation, as well as the installation of the various
tubular members in the well, may take place either by remote
control or by robot-like equipment. It is also possible, since the
wellhead can be located at diving depth, to carry out such
operations by means of divers.
One object of the present invention is to provide equipment for a
well penetrating a formation located below a body of water, said
equipment comprising a pedestal conductor carrying a wellhead and
suspended by at least one buoyancy member, by means of which
equipment the well can be operated in a very safe manner.
A further object of the present invention is to provide equipment
for a subsea well comprising a pedestal conductor which is of such
a construction that it can be very easily and quickly installed,
thus reducing the possibility of failure during installation
thereof.
A still further object of the invention is to provide equipment for
an underwater well comprising a buoyancy member from which tubular
means are suspended, the tubular means being of minimum weight
without endangering the safety of the operations carried out in the
well.
Another object of the present invention is to provide equipment for
an underwater well comprising a buoyancy member mounted on a
pedestal conductor, wherein the volume of the buoyancy member is as
small as possible.
According to the invention, equipment for a well penetrating a
formation located below a body of water comprises a conductor
string arranged for at least the greater part thereof in the well
and cemented to the formation, said conductor string being provided
with coupling means at its upper end; at least one string of
tubular means arranged in part in the conductor string and
suspended in the conductor string by means arranged near the upper
end of the conductor string; a pedestal conductor provided at the
lower end thereof with coupling means sealingly coupled to the
coupling means of the conductor string; at least one buoyancy
member connected to the pedestal conductor near the upper end
thereof; a wellhead mounted on the upper end of the pedestal
conductor and provided with means from which at least one string of
tubing is suspended, which string of tubing at the lower end
thereof communicates with the upper end of the string of tubular
means arranged in the conductor string.
Coupling means may be provided between the lower end of the string
of tubing and the upper end of the string of tubular means.
The coupling means arranged between the lower end of the pedestal
conductor and the upper end of the conductor string may include
blowout preventer equipment.
The lower end of the string of tubing may be connected to the lower
end of the pedestal conductor.
The coupling means arranged between the conductor string and the
pedestal conductor may be of the automatic type which performs the
coupling action upon relatively longitudinal movement of the
coupling elements.
The pedestal conductor may have a single string of tubing suspended
therein, whereas the conductor string may have suspended therein
several strings of tubular means. The string of tubing suspended in
the pedestal conductor communicates with the string of tubular
means having the smallest diameter and is capable of withstanding
the same pressures as this string of tubular means.
The annular spaces around substantially the entire lengths of the
strings of tubular means suspended from the conductor string are
preferably filled with solid material, such as hardened cement.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a side view partially in cross-section of a well
installation according to the invention.
FIG. 2 shows a longitudinal section of part of the well
installation according to FIG. 1 on a scale larger than that of
FIG. 1.
FIG. 3 shows a longitudinal section over the conductor string
during placement thereof in the formation.
FIG. 4 shows a longitudinal section over the conductor string when
cemented in position in the well.
FIG. 5 shows a side view of the well installation during placement
of the pedestal conductor.
FIG. 6 shows the well installation in longitudinal section during
further deepening of the borehole after the pedestal conductor has
been placed.
FIG. 7 shows in longitudinal section the well equipment arrangement
after a first casing has been placed in the borehole.
FIG. 8 shows in longitudinal section the well equipment arrangement
after a second casing has been placed in the borehole.
FIG. 9 shows in longitudinal section part of the well installation
according to the invention in an embodiment wherein the coupling
between the pedestal conductor and the conductor string includes
blowout preventer equipment.
FIG. 10 shows another embodiment of the well installation according
to the invention in longitudinal section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, we see a drilling ship 1 (partly shown)
provided with a derrick 2 and all other equipment (not shown)
necessary for carrying out drilling operations in wells below the
sea level 3. The ship 1 is kept in the position above a location
where a well 21 is to be drilled by means known per se, such as
dynamic positioning means (not shown) which make use of propulsion
units controlled by position locators. A conductor string 5 is
cemented in the well 21 which is being drilled into a formation 4.
This string 5 is suspended from the sea bottom 6 by a base plate 7
provided with guide line posts 8. A casing 9 is suspended from the
conductor string 5, and a casing 10 is suspended directly from the
casing 9 (and indirectly from the conductor string 5) in a manner
as will be described hereinafter. The lower part 11 of the well 21
can be drilled by a bit 12, which is temporarily retracted from the
well 21 as shown in FIG. 1. The connection between the drilling
ship 1 and the well 21 is formed by a marine conductor 13 (which
may include a telescopic section) which conductor is guided by
means of guide bars 15 via guide lines 14 to a wellhead 16 mounted
on the upper end of a pedestal conductor 17. The pedestal conductor
17 is coupled at its lower end to the conductor string 5 by means
of coupling 18 and is kept in an upright position by a buoyancy
member 19 connected to the upper end of the pedestal conductor 17.
The buoyancy member 19 carries guide line posts 20 to which the
guide lines 14 are connected. The guide line posts 20 are, just as
the guide line posts 8, known per se and will not be described in
detail. The guide lines 14 are kept taut in the usual manner, e.g.,
by constant-tension devices (not shown), such as counter weights or
winches arranged on the ship 1.
Reference is now made to FIG. 2, which shows the characteristic
parts of the well equipment according to FIG. 1 in longitudinal
section, and in greater detail than FIG. 1. Identical parts in
FIGS. 1 and 2, as well as in the other figures, are indicated by
the same reference numerals.
FIG. 2 shows the buoyancy member 19 consisting of metal (preferably
steel) contains at least partially filled with air, and having a
water displacement of at least sufficient magnitude to keep the
pedestal conductor 17 under tensional stress. The design of the
member 19 is such that the walls thereof can withstand any pressure
differences which may exist between the fluids inside and outside
the member.
The buoyancy member 19 carries the guide line posts 20 and the
wellhead 16, which is of a design suitable for submarine
operations. Since a great number of such designs are already known,
no details of the wellhead 16 are given.
The upper end of the pedestal conductor 17 is connected to the
wellhead 16 in a suitable manner. The lower end of the pedestal
conductor 17 is provided with a coupling member 18 suitable to
co-operate with the upper end of the conductor string 15 which is
cemented in the bore hole 21 by a cement layer 22.
The upper end of the conductor string 5 is further provided with a
base plate 7 for supporting the conductor string 5 during cementing
thereof. The base plate 7 carries guide line posts 8 to which guide
lines 23 are connected for guiding the pedestal conductor 17, which
is provided with guide bars 24, downwards to bring the coupling 18
thereof into alignment with the upper end of the conductor string 5
when placing the pedestal conductor. Guide bars 24, guide lines 23
and guide line posts 8 may be of the usual type and in the usual
number and are hence not described in detail.
The casing 9 is suspended from the conductor string 5 by a casing
suspension means such as a hanger 25 which may include pack-off
means and which is preferably provided with fluid by-pass means.
Such hangers are known per se and for the sake of simplicity are
indicated only schematically in the figures.
The casing 9 extends downwards through the conductor string 5 to a
level in the bore hole 21 below the lower end of the conductor
string 5. The casing 5 is surrounded along the entire length
thereof by a cement layer 28, and thus no free annular space is
left around this casing, in which space gas or liquid pressure
might build up which would require the application of venting means
to control the pressure in such space.
The casing 10 is suspended in the casing 9 by suspension means 26
(which can be of the same type as suspension means 25) and provided
with a cement layer 29 arranged along substantially the entire
length thereof, such that no free annular space is left around this
casing. Casing 10 extends downwards through the casing 9 to a level
of the well bore 21 below the lower end of casing 9.
Within the casing 10, the production tubing 30 is suspended from
the casing 10 by the suspension means 27 (which suspension means
can be of the same type as suspension means 25). The production
tubing 30 is cemented by a layer 31 over substantially the entire
length thereof and communicates at or near the lower end thereof
with the oil production layer 32 of the formation 4.
The upper end of the production tubing 30 communicates with a
string of tubular means 33 which is suspended from the wellhead 16
by means suitable for the purpose and known per se. The production
tubing 30 and the string of tubular means 33 communicate via
coupling means 34 which are known per se and therefore shown
schematically only.
The well equipment as shown in the situation according to FIG. 2 is
suitable for the production of fluids from the layer 32. These
fluids are driven out of the layer 32 into the production string 30
and flow upwards through the string of tubular means 33, and via
the wellhead 16 into a flow line (not shown) through which they are
transported to a suitable storage means (not shown).
Since the various casings used in the well 21 extend upwards only
to the sea bottom 6, and are suspended (indirectly) from the
conductor string 5, the buoyancy member 19 has to be designed for
carrying (besides its own weight) only the weight of the wellhead
16, the pedestal conductor 17 and a string of tubular means 33. The
dimensions of the buoyancy member 19 are minimal since the weight
of the casings 9 and 10, as well as of the production tubing 30 is
not carried thereby.
The wall thickness of the string of tubular means 33 suspended from
the buoyancy member 19 is preferably chosen equal to the wall
thickness of the production tubing 30 communicating therewith.
Since this tubing 30 is designed to withstand the maximum pressure
which may be expended at the depth to which it extends, the string
33 will also be capable of withstanding this pressure and thus
prevent damage of the pedestal conductor 17 by such pressure.
The way in which the well 21 is drilled and completed will now be
described in more detail.
As shown in FIG. 3, a drill string 50 is let down from a drilling
ship (not shown) at a location where the well should penetrate into
the formation 4. The drill string 50 carries a coupling member 51
which is suitable for being coupled to the upper end of the
conductor string 5. The coupling member 51 is of a known type and
may comprise an annular piston 52 axially displaceable in an
annular cylinder 53 and capable of actuating locking dogs 54
co-operating with a groove 55 in the upper parts of the outer wall
of the conductor string 5. The piston 52 can be actuated by
hydraulic fluid which is supplied to and drained from the cylinder
parts above and below the piston via suitable conduits (not shown)
leading to the drilling ship. Suitable sealing means (not shown)
may be provided to seal the clearance between the coupling member
51 and the conductor string 5.
The coupling member 51 is provided with guide bars 56 co-operating
with the guide lines 23 and the guide line posts 8 arranged on the
base plate member 7.
The lower end of the drill pipe 50 is connected to a hydraulic
turbine 57 of known design, which is actuated by a flow of fluid
being passed through the drill string 50. The turbine shaft 58
carries a drill bit 59 and is provided with a splined section 60
co-operating with a splined section 61 of a casing shoe 62, which
is rotatably arranged on the lower end of the conductor string 5.
Locking means 64 lock the shoe 62 against longitudinal displacement
with respect to the conductor string 5. This shoe is at the lower
end thereof provided with an annular row of cutting means 63. A
cutting element is thus formed by the bit 59 and the means 63
suitable to drill a hole having a diameter greater than the outer
diameter of the conductor string 5. Thus, the conductor string 5
can be let down in the hole 21 when the drilling operation is being
carried out at the bottom thereof by the bit 59 and the cutting
means 63 arranged on the rotatable casing shoe 62.
The splined section 60 co-operating with the splined section 61 is
arranged such that this section 60 and the bit 59 can, together
with the turbine 57, be retracted from the shoe 62 in axial
direction thereof by lifting the drill string 50 after the coupling
51 has been uncoupled from the conductor string 5. This operation
is carried out when the hole 21 has a depth sufficient to receive
the entire length of the conductor string 5. This string is then
supported by the base member 7 resting on the sea bottom 6.
When the drill string 50, the coupling member 51, the hydraulic
turbine 57 and the bit 59 have been retracted from the conductor
string 5, the string is cemented in the bore hole 21. To this end,
a cementing tube 65 (FIG. 4) provided with a coupling member 66 and
packer means 67 (known per se) is let down in the water. No details
are shown in FIG. 4 of coupling member 66, since this member is of
a construction similar to the construction of the coupling member
51 shown in FIG. 3. The tube 65 is guided from the ship (not shown)
into the conductor string 5 by guide bars 68 (known per se)
co-operating with the guide lines 23 and the guide line posts 8
arranged on the base plate 7. In the position shown in FIG. 4 the
coupling member 66 is coupled to the upper end of the string 5, and
the packer 67 is set to seal off the annular space around the
cementing tube 65 at the level indicated.
Via the cementing tube 65, cement is injected into the bore hole
21, thereby filling the annular space around the conductor string 5
with a cement layer 22. The cement overflowing at the upper end of
the bore hole forms a cake 69. It will be appreciated that the
casing shoe 62 is cemented in the well together with the conductor
string 5.
To minimize the pressure and the velocity at which the cement will
enter the hole 21, a restriction (not shown), such as a
spring-loaded valve, may be arranged at or near the lower end of
the cementing tube 65. Fracturing of the formation 4 can then be
prevented as the high pressure prevailing at the lower end of the
cement column within the tube 65 is decreased by the resistance
which is met by the cement flowing through the restriction.
After the cement has hardened, the packer 67 is loosened and the
coupling member 66 detached from the conductor string 5. Thereafter
the cementing tube 65 is retracted from the string 5 together with
the packer 67.
Subsequently the pedestal conductor 17 is mounted on the conductor
string 5. To describe this operation, reference is first made to
FIG. 5, which shows on a scale similar to FIG. 1 the pedestal
conductor 17 after it has been built from the drilling ship 1.
To assemble the pedestal conductor, the buoyancy member 19, which
is provided with a central opening, is first positioned such that
the central opening is in alignment with the moonpool or well 70
arranged vertically through the ship 1 and having the central axis
thereof coinciding with the axis of the derrick 2 arranged on deck
of the ship 1. Thereafter the coupling 18 provided with guide bars
24 is arranged below the buoyancy member 19 and the pedestal
conductor 17 is assembled by passing the various parts thereof
through the moonpool or well 70 of the ship 1 and through the
central opening of the buoyancy member 19, interconnecting these
parts and connecting the lowest part to the coupling member 18
carrying the guide bars 24. When the pedestal conductor 17 has the
desired length, the upper part thereof is connected to the buoyancy
member 19, whereafter wellhead equipment 16 as is normally used for
underwater drilling, is mounted on the upper part of the pedestal
conductor 17. As the type and size of this equipment 16 vary during
the various stages of the drilling of the well, this equipment is
only schematically indicated. During the various stages of the
drilling and completion of the well, this equipment may, for
example, include blowout preventers and casing suspension means,
both of various sizes.
After the pedestal conductor arrangement comprising the pedestal
conductor 17, the buoyancy member 19 and the equipment 16 has been
completed, the whole system is lowered to a level below the wave
zone by means of a string of tubing 71 attached to the wellhead 16
mounted on the buoyancy member. This is the position shown in FIG.
5. In this position, the lower end of the pedestal conductor 17 is
preferably at a sufficiently great distance from the upper end of
the conductor string 5 to prevent damage thereof by the pedestal
conductor 17 if the ship 1 should be subject to very high
waves.
During a period of low waves, the pedestal assembly is lowered, and
guided by means of the guide bars 24 co-operating with the guide
lines 23 onto the upper end of the conductor 5. Directly after the
coupling member 18, which is of a construction similar to that of
the coupling 51 shown in FIG. 3, is landed on the upper end of the
conductor string 5, the coupling is made in a manner such as
described with reference to coupling 51 and groove 55 shown in FIG.
3. Since high pressure differences may exist between the interior
and the exterior of the pedestal conductor, the coupling 18 is
preferably provided with sealing means.
As the above-mentioned coupling operation can be performed in a
very short time, the chances that deteriorating weather conditions
might influence the coupling operation can be neglected. Thus, the
placement of the pedestal conductor on the well entrance is a very
safe operation.
It will be appreciated that the buoyancy of the member 19 may be
controlled such that the string of tubing 71 is under a small
tensional load. Once the coupling 18 has been coupled to the upper
end of the conductor string 5, the buoyancy of the member 19 is
preferably increased, so as to bring the pedestal conductor 17
under tensional stress.
To control the buoyancy of the member 19 during its descent, the
interior of the member 19 is preferably in open communication with
the exterior near the lower part thereof. Thus, the buoyancy can be
controlled by pumping air into the interior (or venting air
therefrom). To this end, float chambers of the member 19
communicate with air compressors which are mounted on board of the
ship 1 and connected to the float chambers of the member 19 by
flexible conduits.
After the pedestal conductor 17 has been mounted on the conductor
string 5, the marine conductor 13 (FIG. 6) is lowered through the
moonpool 70 of the ship 1, and guided by means of guide bars 15
along guide lines 14 onto the wellhead 16 and connected thereto in
a manner known per se. Thereafter, the drilling operation is
continued by means of a bit 72 connected to a drill string 73. The
diameter of the bit 72 is smaller than the diameter at which the
first part of the hole 21 has been drilled (see FIG. 3). When a
sufficient depth has been reached, the bit 72 is retracted from the
hole, and a casing 9 is lowered into the hole 21 by means known per
se. The casing 9 is suspended (FIG. 7) in the conductor string 5 by
means of a hanger 25 which is also known per se and hence not
described in detail. Thereafter the annular space around
substantially the entire length of the casing 9 is cemented in a
manner similar to that described with reference to FIG. 4, with the
difference, however, that the cementing tube 65 (FIG. 4) is not
provided with a coupling member 66. The cement layer 28
substantially fills the entire volume of the annular space around
the casing 9, thus preventing any build-up of fluid pressure in
this space and eliminating the need for means suitable to measure
such pressure and to vent this space.
After the casing 9 has been set in the bore hole 21, a string of
tubing 75 is suspended from the wellhead 16, the lower end of this
string being sealingly connected by a coupling member 76 to the
upper end of the casing 9. The tubing 75 has substantially the same
diameter and substantially the same wall thickness as the casing 9.
Since the casing 9 is designed to withstand the maximum formation
pressure which may be met during the further drilling of the hole
21 to a depth at which the next casing is to be set, the tubing 75
is advantageously sufficiently strong to withstand such pressure
and protect the pedestal conductor 17 against damage by such
pressure.
Subsequently, the bore hole 21 is deepened further in a manner
similar to that described with reference to FIG. 6. When a
sufficient depth has been reached, a liquid with extremely high
density is circulated into the well. Thereafter the string of
tubing 75 is withdrawn from the pedestal conductor 17, and the
casing 10 (FIG. 8) is introduced via the pedestal conductor 17 into
the well 21 and suspended from the casing 9 by suspension means 26
which are of the same construction as the means 25. This casing 10
is then cemented in such a manner that the cement layer 29 fills
substantially the entire volume of the annular space around the
casing 10.
Either before or after the casing 10 has been cemented, a string of
tubing 77 is suspended from the wellhead 16. The lower end of the
string of tubing 77 is sealingly coupled to the upper end of the
casing 10 by means of a coupling member 78. The diameter and wall
thickness of the tubing 77 are advantageously substantially equal
to the diameter and thickness respectively of the casing 10. Thus
the tubing 77 can withstand the maximum pressure which might be met
during a further deepening of the well, and thus will protect the
pedestal conductor 17 against damage by such pressure.
The borehole 21 is further deepened in a manner similar to that
described with reference to FIG. 6. When the desired depth has been
reached (in this case the oil containing layer 32), the well is
pumped dead by circulating a mud with very high density into the
well. Thereafter the production tubing 30 (FIG. 2) is suspended
from the casing 10 by suspension means 27 which are of a
construction similar to that of the suspension means 25.
Subsequently the tubing 30 is cemented by means of a layer 31
substantially filling the entire volume of the annular space around
the tubing 30.
When the tubing 30 has been set, the string of tubing 77 (FIG. 8)
is retracted from the pedestal conductor 17 and replaced by a
string of tubing 33 (FIG. 2) which is also suspended from the
wellhead 16, but is sealingly connected by means of a coupling
member 34 to the upper end of the production tubing 30. As the
coupling member 34 is known per se, no detailed description will be
given thereof.
Tubing 33 is advantageously as strong as tubing 30, and thus will
withstand all the pressures that the production tubing 30 can
withstand.
Subsequently the well is completed, e.g., by perforating the lower
end of the production tubing 30 where it penetrates the production
zone 32, removing the marine conductor 13 and connecting the
necessary flow lines to the wellhead 16. It will be appreciated
that in case no oil or gas is found, the well 21 can be abandoned
by plugging back of the well, retracting the tubing 33 and removing
the pedestal conductor 17 and buoyancy member 19 after having
uncoupled the coupling 18.
It will be appreciated that during the replacement of the tubing 75
(FIG. 7) by the tubing 77 (FIG. 8), and of the tubing 77 (FIG. 8)
by the tubing 33 (FIG. 2), the buoyancy of the buoyancy member 19
has to be controlled, as otherwise the pedestal conductor 17 would
be overstressed. By replacing the tubing suspended from the
wellhead 16 by a tubing with smaller diameter whenever a new casing
(or the production tubing) is suspended in the bore hole 21, the
weight to be carried by the buoyancy member 19 will be kept as
small as possible. This results in a member 19 which will be easier
to manipulate than a buoyancy member used in combination with a
well system in which each casing extends upwards to the wellhead
16.
It has been remarked already, that the coupling member 18 as
indicated in FIG. 2 for coupling the pedestal conductor 17 to the
conductor string 5, may be of a construction similar to that of the
coupling member 51 shown in FIG. 3. However, any other design of
coupling member may be used for this purpose, such as an automatic
coupling member which can couple the pedestal conductor 17 to the
conductor string 5 by a longitudinal movement of these members
relative to each other.
It will be appreciated that the coupling member 18 shown in FIG. 2
may be combined with blowout preventer equipment and/or with
articulated couplings (for allowing an angular displacement of the
pedestal conductor 17 with respect to the production tubing). A
design of well equipment provided with a blowout preventer included
in the coupling between the conductor string 5 and the pedestal
conductor 17 is schematically shown in FIG. 9. In this design a
blowout preventer 80 provided with shear rams 81 is connected to
the lower end of the pedestal conductor 17 by a coupling member 82
which may be hydraulically actuated in the manner described with
reference to coupling 51 shown in FIG. 3. The housing 83 of the
blowout preventer 80 is designed such that it is able to withstand
the highest pressures which will be met in the well during the
drilling and production of this well.
The shear rams 81 can be actuated by means of the pistons 84
slidably arranged in the cylinders 85 located in the housing 83.
Suitable conduits (not shown) lead to the cylinder spaces to
actuate the shear rams 81 by hydraulic fluid. When actuated, the
rams close off the passage through the housing 83, thereby shearing
any tubular equipment which is caught therebetween.
A coupling member 18, as described hereinbefore, is connected to
the lower end of the housing 83 of the blowout preventer 80. During
placement of the pedestal conductor 17, this conductor 17 is
lowered in combination with the blowout preventer 80 and the
coupling member 18. Subsequent to this placement, the well 21 is
deepened in the same manner as described with reference to FIG. 6
hereinabove. After the desired depth has been reached, a casing 86
can be suspended from the blowout preventer 80 by means of a casing
hanger 87 known per se and cemented therein by a cement layer 88.
Drilling of the hole is continued through casing 86 after a casing
89 having the same thickness and diameter as the casing 86 has been
suspended from the wellhead (not shown) carried on top of the
pedestal conductor 17. The lower end of casing 89 is provided with
a packer 90 for sealing the entrance to the annular space between
the casing 89 and the pedestal conductor 17.
After the desired depth of the borehole 21 has been reached, the
drill bit is retracted from the borehole and a casing 91 is run
into the hole via the casing 89 and suspended in the housing 83 of
the blowout preventer 80 by a casing suspension means 92 known per
se. Thereafter the annular space around the casing 89 is filled
with cement forming a solid layer
Subsequently, the casing 89 suspended by the wellhead is replaced
by a casing 94 provided with a packer 95. By choosing the diameter
and thickness of casing 94 equal to the diameter and thickness of
the casing 91, the pedestal conductor 17 is protected against the
maximum pressures which can be met when the borehole is further
deepened.
It will be appreciated that on further drilling of the hole, the
number of casings suspended therein may be increased. Preferably,
however, only a single casing is suspended from the wellhead, since
this decreases the weight which has to be carried by the buoyancy
member carrying this wellhead. The single string of casing is
preferably of the same type as the casing of smallest diameter
suspended from the blowout preventer 80.
The well may be completed by applying a production string which is
partly suspended from the blowout preventer housing and partly
suspended from the wellhead carried by the buoyancy member. In this
case, the wellhead only supports the part of the production string
located within the pedestal conductor.
However, the well may also be completed by loosening the packers
and suspension means from all the casings ending in the housing 83
of the blowout preventer 80, removing the casing(s) suspended from
the wellhead, and thereafter uncoupling coupling 18 and lifting the
pedestal conductor 17 and the blowout preventer 80 from the upper
part of the conductor string 5. Subsequently a wellhead (not shown)
is lowered onto the upper end of the casing 91 and coupled thereto.
Production tubing suitable for the purpose may be supported by this
wellhead.
It will be appreciated that this latter type of well completion may
also be used in combination with the equipment shown in FIG. 2
after the coupling 18, the pedestal conductor 17, the string of
tubular means 33, and the buoyancy member 19 and the wellhead 16
have been removed.
It will be appreciated that the casing suspension means 87 and 92
shown in FIG. 9 may, if desired, be set in a thickened wall 96 of
the upper portion of the conductor string 5 instead of in the
housing 83 of the blowout preventer 80. In the same manner, the
packers 90 and 95 may be set in a thickened wall 97 of the lower
portion of the pedestal conductor 17.
Although only a single buoyancy member has been shown in the
example of the present invention described hereinabove with
reference to the drawing, it will be understood that the present
invention is not limited thereto. Also the pedestal conductor 17
may be provided with buoyancy means distributed along the length
thereof. Such buoyancy means may be in the form of separate floats,
or may be formed by using double-walled tubing for the pedestal
conductor.
The application of the invention is not limited to the number of
casings used in the example described above. Any desired number of
casing strings may be applied. Moreover, any desired number of
strings of tubular means may be applied within the pedestal
conductor. It will, however, be appreciated that the use of only a
single string of tubular means is to be preferred since this
reduces the size of the buoyancy member considerably.
The tubing 30 (FIG. 2) may be used as a casing as shown in FIG. 10.
In this embodiment a production tubing 30a may be extended from the
top of the pedestal conductor 17 to a level below the lower end of
the conductor string 5. The production tubing 30a may be suspended
from the wellhead 16. The production tubing 30a may extend through
the tubular means 30 and 33. The annular space between the casing
30 and the production tubing 30a is preferably packed off above the
production layer 32 with a packer 100.
The buoyancy member may be of any desired type and be arranged
below the ship or within the moonpool 70 (FIG. 5) thereof in any
desired manner.
The replacement of a string of tubular means suspended from the
wellhead equipment by a string of smaller diameter may either take
place prior to or after cementing of the casing which will have to
communicate with the string of smaller diameter.
It will further be appreciated that the supervising of the well
drilled and completed in accordance with the present invention is
simplified by the fact that all the casing and the production
tubing is cemented along the entire length thereof, thus
eliminating the need for control of fluid pressures which would
otherwise develop in the spaces around the casings or the
production tubing.
Where necessary, the tubular equipment or the couplings may be
provided with a telescopic joint. Thus, by providing the coupling
34 (FIG. 2) with a telescopic joint, expansion and/or contraction
of the string of tubular means 33 can be compensated in a simple
manner.
It will be appreciated that the application of the invention is not
restricted to systems making use of guide cables. If desired, other
types of re-entry systems may be applied as well.
The application of the invention is further not restricted to the
use of the turbine 57 in combination with the rotatable casing shoe
62. If desired, other means for actuating the drilling bit may be
applied, which bit may be of a type permitting a decrease in the
outer cutting diameter when the bit is to be moved through the
conductor string 5.
* * * * *