Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ICR-7696
CASING GUIDE FOR WELL TEMPLATE
Field Of The Invention
-
This invention relates generally to offshore hydrocarbon
production, and more particularly, to a casing guide ~ppara-
tus for connecting a well casing to a subsea well gravity
base template.
B ~_ound Of The Inventi__
With the gradual depletion of subterranean and shallow
subsea hydrocarbon reservoirs, the search for additional
petroleum reserves is being extended to deeper and deeper
waters on the outer continential shelves of the world. As
such deeper reservoirs are discovered, incre~singly complex
and sophisticated production systems have been developed.
It is projected that in the near future, offshore explora-
tion and production facilities will be required for probing
depths of 10,000 feet or more. Since bottom founded
compression structures are generally limited to water depths
of no more than about 1,200-1,500 feet because of the sheer
size of structure required, other, so-called compliant
structures have been developed.
One type of compliant structure receiving considerable
attention is a tension leg platform (TLP). A TLP comprises
a semisubmersible-type floating platform anchored to the sea
bed through vertical members or mooring lines called tension
legs. The tension legs are maintained in tension at all
times by insuring that the buoyancy of the TLP exceeds its
operating weight under all environmental conditions. A TLP
is compliantly restrained in the lateral directions allowing
-2~ 8~
sway, surge and yaw while vertical plane movements such as
heave, pitch and roll are stiffly restrained by the tension
legs.
In the first commercially installed TLP built for the
S Hutton Field in the UoK~ North Sea, installed in 485 feet of
water, separate piled anchor templates were provided for
anchoring the tensioned mooring elements extending from each
of the four corner columns of the floating tension leg plat-
form. A separate well template was also provided on the sea
bed.
It has also been proposed to utilize a gravity base well
template for the anchoring of a TLP and to serve as a guide
template for wells located below the TLP. A gravity base
well template is a massive structure which is held in place
on the sea floor by gravity, rather than by anchored
pilings.
one feature of a gravity base subsea well template which
must be accommodated, however, is the tendency of such a
massive gravity structure to gradually settle downward in
the ocean floor throughout the operating life of the gravity
base well template.
Summary Of The Invention
The present invention provides a casing guide par-
ticularly designed for use with a gravity base well template
to permit the gravity base well template to settle downward
relative to the casing extending upward from the well, while
at the same time providing firm lateral support to the
casing where it passes through the well template.
The casing guide includes a bushing means, operatively
associated with the template and the casing, for permitting
relative vertical movement between the template and the
~3~
casing and for preventing relative lateral movement between
the template and the casing at a well opening defined
through the template. This permits the gravity base
template to settle into the ocean floor relative to the
casing without imposing substantial compressive loads on the
upper portion of the casing, thus eliminating a danger of
buckling of the upper portion of the casing upon settling of
the gravity based template.
The bushing means includes a cylindrical bushing member
having a cylindrical inner bushing bore within which the
casing is closely received. The bushing means also includes
a latch means, operatively associated with the bushing
member and the well opening of the template, for latching
the bushing member into a fixed position within the well
opening upon insertion of the casing and bushing means down-
wardly into the well opening of the template.
~umerous objects, features and advantages of the present
invention will be readily apparent to those skilled in the
art upon a reading of the following disclosure when taken in
conjunction with the accompanying drawings.
Brief Description of The Drawings
FIG. 1 is a schematic elevation view of a TLP anchored
to a gravity base well template.
FIG. 2 is a plan view of the gravity base well template.
FIG. 3 is a partly sectioned elevation view of the gra-
vity base well template of FIG. 2, taken along lines 3-3.
FIG. 4 is an enlarged schematic elevation view of a
segment of the gravity base well template with an upper por-
tion of a well casing received therein. The lower portion
of the well casing is received in and cemented in place
within a well bore extending into the ocean floor.
--4--
~3128~
FIG. 5 is an elevation partly sectioned view of the
upper end of the casing as received in the well template,
showing the details of construction of the casing guide of
the present invention.
Detailed Description Of The Preferred Embodiments
Referring now to the drawings, and particularly to FIG.
1, a tension leg platform 10 is anchored to a gravity base
well template ~2 by a plurality of tethers 14.
The gravity base well template 12 sits on an ocean floor
16 defining the bottom of a body of water 18. The TLP 10
floats on the surface 20 of the body of water 18.
The TLP includes a work deck 22 supported on four corner
columns 24 which are connected by horizontal pontoon members
26.
A plurality of production risers 28 extend from subsea
well heads 30 defined on the upper end of well casings 32.
Each of the production risers 28 terminates in a well head
apparatus 34 commonly referred to as a Christmas tree 34
located upon the work deck 22.
FIGS. 2 and 3 are plan and elevation/section views,
respectively, of the gravity base template 12. The par-
ticular form of gravity base template shown in FIGS. 2 and
3 is described in detail in pending United States Patent
4,669,916, issued June 02, 1987, for ~NITIZED TLP ANCHOR
TEMPLATE WITH ELEVATED WELL TEMPLATE of Charles N. White and
Andrew F. Hunter, and assigned to the assignee of the
present invention. The details of construction of the
template 12 as set forth therein.
The template 12 is primarily constructed from reinforced
concrete, and as seen in FIG. 2, includes the four corner
-5- ~ 281
columns 24, eight small storage tanks 36, four larger
storage tanks 38, interconnecting web portions such as 40,
and a structural steel grid work 42 defining a plurality of
well openings such as 44 therein.
The concrete portion of the template 12 includes a skirt
piling 116 which extends downward around the outer perimeter
of template 12 and penetrates the ocean floor 16 upon ini-
tial placement of the gravity base well template 12 on the
ocean floor 16.
On the top of each of the corner columns 24 is an anchor
template 46 to which the tethers 14 are attached.
FIG. 3 is a schematic elevation section view of the gra-
vity base well template 12 of FIG. 2 taken along line 3-3
of FIG. 2.
In FIG. 3, one of the well casings 32 is shown, having
its lower portion 48 cemented in place at 50 within a well
bore 52. An upper portion 54 of casing 32 extends upward
from the well bore 52 above the ocean floor 16 to the struc-
tural grid portion 42 of gravity base well template 12.
The upper portion 54 of casing 32 extends through lower
and intermediate loose-fitting conductor guides 55 and 57,
respectively, which are supported by frame members 59 and
61, respectively, of template 12. The guides 55 and 57 and
frame members 59 and 61 are shown in a schematic fashion in
FIG. 3.
FIG. 4 is an enlarged elevation sectioned schematic view
somewhat similar to FIG. 3, which shows in greater detail
the construction of the grid work 42 of template 12, and the
manner in which the upper portion 54 of casing 32 is
received therein.
The grid work 42 includes a plurality of upper and lower
horizonal members 56 and 58, respectively, connected by ver-
tical members 60.
-6- ~2~81
The well opening 44 is defined within a cylindrical
template housing 62 which is supported from the upper and
lower horizontal members 56 and 58 by smaller horizontal and
diagonal structural members 64 and 66, respectively.
5Each casing housing such as 62 is located in the center
of four guide posts such as 68 to which are connected guide
lines (not shown) for use in guiding tubular members such as
the casing 32 when they are lowered from the TLP 10 to the
template 12.
10FIG. 5 is a still further enlarged section elevation
view of those portions of the grid work 42 of template 12
immediately surrounding one of the template housings 62,
along with the upper end of casing 32 and the apparatus of
the present invention providing for connection between the
15casing 32 and the template 12. The well casing 32 typi-
cally will be a thirty-inch diameter casing.
~ bushing means 68, shown in FIG. 5, is operably asso-
ciated with the template housing 62 of template 12 and the
casing 32, for permitting relative vertical movement between
20the template 12 and the casing 32 and for preventing rela-
tive lateral movement between the template 12 and the casing
32 at well opening 44,
The bushing means ~8 includes a cylindrical bushing
member 70 having a cylindrical inner bushing bore 72 within
which the casing 32 is c~osely received. The bushing member
70 is preferably constructed from two semicylindrical halves
which are connected together about the uppermost section of
casing 32. Bushing member 70 is constructed from a material
which is compatible cathodically with the material of the
template 12.
The bushing member 70 has a tapered lower end 71 to
avoid hanging up of the bushing member 70 as it is inserted
-7~ ~ 8~
downward into template housing 62. 8ushing member 70 also
has a ra~ially outward extending annular lip 73 at its upper
end.
Bushing means 68 further includes a latch means 74
operably associated with the bushing member 70 and with the
well opening 44 of template 12, for latching the bushing
member 70 into a fixed position within the well opening 44
upon insertion of the casing 32 and bushing means 68 down-
wardly into the well opening 44 of template 12.
The well opening 44 is defined by a cylindrical housing
bore 44 of template housing 62.
The latch means 74 includes upper and lower annular
latching grooves 76 and 78, respectively, defined in the
well opening/housing bore 44.
Latch means 74 further includes upper and lower radially
outwardly biased locking means 80 and 82, respectively, con-
nected to the bushing member 70 and extending radially out-
ward from the bushing member 70 for receipt in the upper and
lower latching grooves 76 and 78, respectively, of the well
opening/housing bore 44 of housing 62 of well template 12.
Upper groove 75 is shown as having a tapered lower annu-
lar surface 77 for allowing lower locking means 82 to pass
downward past upper groove 76.
The well template 12 further includes an upwardly open
conical guide means 84 concentrically disposed about the
well opening/housing bore 44 above the well opening/housing
bore 44. A downwardly open conical guide means 85 extends
downward below well opening/housing bore 44 to prevent
hanging up of bits, underreamers and the like which may be
passed upward through well opening/housing bore 44.
The bushing member 70 has a cylindrical outer surface 86
closely received in the well opening/housing bore 44 of
template housing 62.
8~
The upper and lower locking means 80 and 82 shown in
FIG. 5 may be expandable snap rin~s which are carried by
upper and lower grooves 88 and 90 defined in outer surface
86 of bushing member 70.
A releasable connecting means 100 is operably associ-
ated with the casing 32 and bushing member 70 for initially
limiting vertical mo~ement of the bushing member 70 relative
to the casing 32 until the bushing member 70 is latched into
the fixed position illustrated in FIG. 5 within the well
opening/housing bore 44 of well template 62. The releasable
connecting means 100 preferably is a means for initially
preventing any substantial vertical movement OI the bushing
member 70 relative to the casing 32, but could also be
designed to allow some limited movement of the bushing
member 70 relative to the casing 32.
In the preferred embodiment illustrated n FIG. 5, the
releasable connecting means 100 includes a plurality of
shear pins such as 102 and 104 connected between the casing
32 and the bushing member 70.
The casing 32 includes a sleeve 106' fixedly connected
thereto and sleeve 106 snugly but slidably positioned
therebelow, sleeves 106 and 106' together defining outer
cylindrical surface 108. The sleeve 106' is snugly received
in the inner bushing bore 72. Sleeve 106' is stiff enough
to prevent any substantial lateral movement of the casing 32
relative to the bushing member 70. The snug fit of sleeve
106' in bore 72 does, however, permit vertical sliding
motion of casing 32 and the sleeve 106' thereof relative to
bushing member 70.
The sleeve 106' is preferably made from metal or a hard
elastomeric-composite material which is shrink-fitted or
bonded the casing 32, while sleeve 106 which is made of the
same material is simply fit snugly upon casing 32. One
purpose of sleeves 106' and 106 is to provide a more concen-
tric outer surface 108 than is present on typical casing
which may be slightly out-of-round.
The sleeve 106 includes a radially outwardly extending
tapered lip 109, located below tapered lower end 71 of
bushing memb~r 70, to aid in preventing hanging up of
bushing member 70 as it is inserted downward into template
housing 62 and, more importantly, to avoid undesired contact
by an external member with bushing member 70 that might
prematurely shear shear pins 102 and 104.
The shear pins such as 102 and 104 have their radially
inner ends contact-welded to an outer surface 110 of casing
32, and extend through sleeve 106' into engagement with
blind bored drilled radially into the bushing bore 72 as
seen in FIG.5.
The methods of using the present invention may be
generally described as follows.
First, the gravity base well template such as 12 having
a well opening 44 defined therein is placed upGn the subsea
floor 16.
The bushing means 68 is assembled with the well casing
32 which is then lowered from the TLP 10 down through the
well opening/housing bore 44 of template 12 until the lower
portion 48 of casing 32 is received in the well bore 52.
Upon downward insertion of the casing 32 and bushing
means 68 into the well opening/housing bore 44 of template
12, the upper and lower locking means 80 an 82 connectably
engage with the upper and lower grooves 76 and 78 defined in
well opening/housing bore 44 so that the bushing means 68 is
substantially fixed relative to the template 12 for prevent-
ing lateral movement of the casing 32 relative to the
template 12 at the well opening/housing bore 44.
During the period of time that the casing 32 and
bushing means 68 are being lowered into position, the
bushing means 68 is held fixed to the casing 32 by the
releasable connecting means 100.
Once the bushing means 68 is connectably engaged with
the template 12 as illustrated in Fig. 5, the releasable
connecting means 100 may be released by applying a vertical
load to the casing 12 thus shearing the shear pins 102 and
- 1 0 -
81
104 and allowing the casing 12 with its elastomeric sl~eve
106' to slide vertically within the bushing bore 72,
slidable sleeve 10~ can slip down casing 32 as necessaxy
when contacted by bushing 70.
Then the lower portion 48 of casing 32 is fixed in the
well bore 52 by cementing as indicated at 50.
During the operational life of the well template 12, it
will tend to gradually settle into the ocean floor. This
settling in some cases may be up to approximately ten inches
over the operating life of the template 12.
With a gravity base well template 12 line that illus-
trated in FIG. 3, the upp~r unsupported portion 54 of casing
32 extending from the ocean floor 16 to the grid work 42 of
template 123 may have a lengtll on the order of thirty to
fifty meters. Accordingly, if the gravity base template 12
were fixedly attached to the casing 32 at the well open-
ing/housing bore 44, the compressive loads applied to the
unsupported upper portion 54 of casing 32 during settling of
the gravity base well template 12 would present a real
danger of buckling the upper portion 54 of casing 32.
The bushing means 68 of the present invent.ion, however,
allows the gravity base well template 12 to settle downward
into the ocean floor relative to the casing 32 without
imposing substantial compressive loads upon the upper
portion 54 of casing 32 thus eliminating the danger of
buckling of the upper portion 54 of the casing 32.
At the same time, however, it is necessary that a firm
lateral support be provided to the casing 32 at the well
opening/housing bore 44.
As schematically illustrated in FIG. 3, an upper end
112 (see FIG. 5) of casing 32 is connected to one of the
production risers 28 by a connector 114.
As will be appreciated by those skilled in the art, the
production riser 28 is subject to substantial lateral forces
from currents and from movement of the TLP. If the casing
32 is not firmly supported against alteral movement at the
well opening/housing bore 44 defined through the grid work
42 of template 12, the dynamic response o~ the production
riser 28 could result in potentially damaging impacts
between the casing 32 and the template 42. Additionallv,
dynamic forces could be transmitted to the upper portion 54
of the casing 32 and to other tubular members contained
therein which could over a long period of time lead to
fatigue failure of these items.
The bushing means 68 of the present invention provides
the necessary lateral support, while at the same time
allowing the gravity base well template 12 to settle into
the ocean floor without imposing dangerous compressive loads
upon the unsupported upper portion 54 of casing 32.
Thus it is seen that the apparatus and methods of the
present invention readily achieve the ends and advantages
mentioned as well as those inherent therein. While certain
preferred embodiments of the invention have been illustrated
for the purposes of the present disclosure, numerous changes
in the arrangement and construction of parts may be made by
those skilled in the art which changes are encompassed
within the scope and spirit of the present invention as
defined by the appended claims.
