U.S. patent number 3,732,143 [Application Number 05/145,142] was granted by the patent office on 1973-05-08 for method and apparatus for drilling offshore wells.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Cornelis G. Joosse.
United States Patent |
3,732,143 |
Joosse |
May 8, 1973 |
METHOD AND APPARATUS FOR DRILLING OFFSHORE WELLS
Abstract
A method and apparatus for drilling offshore wells wherein a
base unit and conductor string are lowered in the water by a drill
string that is coupled to the conductor string, a rotatable shoe
including cutting means being mounted on the lower end of the
conductor string. A self-contained drilling unit is disposed in the
conductor string below the coupling between the conductor string
and drillstring, the drilling unit being used to drive the
rotatable shoe to install the conductor string. After the conductor
string is installed the drill string and self-contained drilling
unit are withdrawn and the conductor string and base unit cemented
in place.
Inventors: |
Joosse; Cornelis G. (The Hague,
NL) |
Assignee: |
Shell Oil Company (New York,
NY)
|
Family
ID: |
10291344 |
Appl.
No.: |
05/145,142 |
Filed: |
May 20, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jun 17, 1970 [GB] |
|
|
29,423/70 |
|
Current U.S.
Class: |
175/6; 175/171;
175/101 |
Current CPC
Class: |
E21B
7/20 (20130101); E21B 7/124 (20130101); E21B
7/128 (20130101) |
Current International
Class: |
E21B
7/12 (20060101); E21B 7/20 (20060101); E21B
7/128 (20060101); E21B 7/124 (20060101); E21b
043/01 (); E21b 007/12 () |
Field of
Search: |
;175/257,171,173,92,101,202,260,261,103,402,62,386 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Champion; Marvin A.
Assistant Examiner: Favreau; Richard E.
Claims
I claim as my invention:
1. Apparatus for use in drilling offshore wells comprising:
a conductor string;
a base member carried by the conductor string;
a drill string connected to the conductor string by coupling
means;
a self-contained drilling unit carried within the conductor string
at a level below the said coupling means, said drilling unit in
addition having a rotable part with a drill bit attached to the
rotatable part:
a shoe carried by the lower end of the conductor string, said shoe
being rotatably arranged with respect to the central axis of the
conductor string and provided with means to prevent axial
separation between the shoe and the string, the shoe being further
provided at the lower and thereof with cutting means and having a
central passage in which said drill bit is arranged; and
coupling means arranged between the shoe and the rotatable part of
the self-contained drilling unit and suitable for transmitting at
least rotational loads.
2. Apparatus according to claim 1 and in addition a telescopic
joint, said telescopic joint being disposed in the drill string
above said drilling unit and below said coupling means.
3. Apparatus according to claim 1 wherein the base member is
provided with means suitable for connecting at least one guide line
to the base member.
4. Apparatus according to claim 1, wherein the drilling unit is
carried by the conductor string.
5. Apparatus according to claim 4, wherein the drilling unit
comprises a hydraulic motor and a packer is placed to seal the
space between the inner wall of the conductor string and the outer
wall of the hydraulic motor.
6. Apparatus according to claim 1, wherein the drilling unit is
carried by the drill string.
7. Apparatus according to claim 6, wherein the coupling means
between the shoe and the self-contained drilling unit is also
suitable for transmitting axial loads, and in addition a telescopic
joint suitable for transmitting rotational loads, said telescopic
joint being arranged in the drill string between the self-contained
drilling unit and the coupling means between the drill string and
the conductor string.
8. Apparatus according to claim 5, and in addition at least one
drill collar, and drill collar being disposed in the drill string
between the telescopic joint and the self-contained drilling
unit.
9. Apparatus according to claim 1, wherein the base member is
connected near the lower end of the conductor string by coupling
means and provided with downwardly projecting extensions capable of
being inserted into the soil below a body of water to prevent
rotation of the base member.
10. Apparatus according to claim 9, wherein guide bars for guiding
the drill string along the guide lines are rotatably arranged with
respect to the drill string.
11. Apparatus according to claim 10, wherein the extensions project
in a downward direction beyond any other parts of the
apparatus.
12. Apparatus according to claim 11, wherein the coupling means
between the base member and the conductor string are shear
means.
13. Method for use in drilling offshore wells comprising the
following steps:
suspending from a drilling ship the lower part of a conductor
string provided with a rotatable casing shoe with cutting means at
its lower end,
mounting a hydraulic motor having a drill bit connected to the
output shaft thereof at the lower end of the conductor string, such
that the drill bit protrudes through the central opening of the
casing shoe, and coupling the output shaft to the casing shoe,
lowering the conductor string onto the formation surface by adding
conductor pipes to the conductor string,
rotating the drill bit and the casing shoe by supplying pressure
fluid to the hydraulic motor via the conductor string and drilling
a hole into the formation by simultaneously lowering the conductor
string and adding further conductor pipes to the conductor
string,
interrupting the drilling operation and mounting a base member
provided with guide lines on the top of the conductor string, and
coupling a drill string consisting of at least one drill pipe to
the top of the conductor string,
resuming the drilling operation by supplying pressure fluid to the
hydraulic motor via the drill string and the conductor string and
simultaneously lowering the conductor string into the hole by
adding further drill pipes to the drill string,
interrupting the drilling operation when the base rests on the
surface of the formation,
lifting the hydraulic motor together with the drill bit and
suspending it in the conductor string at a higher level, injecting
a solidifiable material through the drill string, the conductor
string, and the casing shoe and into the borehole part around the
conductor string,
uncoupling the drill string from the conductor string and lifting
the drill string, and
lifting the hydraulic motor together with the drill bit from the
conductor string.
14. A method for use in drilling offshore wells comprising the
following steps:
suspending from a drilling ship the lower part of a conductor
string provided at the lower end thereof with a rotatable casing
shoe with cutting teeth, and a base member with downwardly
projecting extension,
mounting a hydraulic motor having a drill bit connected to the
output shaft thereof in the lower end of the conductor string such
that the drill bit protrudes through the central opening of the
casing shoe, and coupling the output shaft to the casing shoe,
lowering the conductor string onto the formation surface by adding
conductor pipes to the conductor string,
uncoupling the base member from the conductor string,
rotating the drill bit and the casing shoe by supplying pressure
fluid to the hydraulic motor via the conductor string and drilling
a hole into the formation by simultaneously lowering the conductor
string and adding further conductor pipes to the conductor
string,
interrupting the drilling operation for coupling a drill string
consisting of at least one drill pipe to the top of the conductor
string,
resuming the drilling operation by supplying pressure fluid to the
hydraulic motor via the drill string and the conductor string and
simultaneously lowering the conductor string into the hole by
adding further drill pipes to the drill string, interrupting the
drilling operation when the hole has reached a sufficient
depth,
lifting the hydraulic motor together with the drill bit and
suspending it in the conductor string at a higher level,
injecting a solidifiable material through the drill string, the
conductor string and the casing shoe and into the borehole part
around the conductor string,
uncoupling the drill string from the conductor string and lifting
the drill string, and
lifting the hydraulic motor together with the drill bit from the
conductor string.
15. Method for use in drilling offshore wells characterized by the
following steps:
suspending a drilling apparatus from a drilling ship, said
apparatus including a conductor string, a base member carried by
said conductor string, a drill string and a self-contained drilling
unit carried by said drill string,
lowering the apparatus onto the surface of the formation,
rotating the self-contained drilling unit comprising a hydraulic
motor by supplying pressure fluid thereto via the drill string, and
drilling a hole into the formation by simultaneously lowering the
conductor string and adding further drill pipes to the drill
string,
interrupting the drilling operation when the hole has a sufficient
depth,
uncoupling the drill string from the conductor string,
lifting the string over a distance, wherein the drilling unit
remains in the conductor string,
sealing the passage through the annular space between the drill
string and the conductor string,
supplying solidifiable material through the drill string, the
hydraulic motor and the conductor string to the annular space
around the conductor string, and
lifting the drill string together with the hydraulic motor and the
drill bit from the conductor string.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for use in
drilling offshore wells, and pertains more particularly to a method
and apparatus for the drilling of offshore wells wherein a
conductor string is lowered into the bottom of a body of water
simultaneously with the drilling of the initial part of the
borehole.
By means of such method and apparatus the conductor string need not
be introduced into the hole after this hole has been drilled to the
required depth, thus obviating possible damage to the hole during
running in of the conductor string, as well as the difficulties
encountered when the entrance to the hole has to be relocated after
retraction of the drill bit and prior to running in of the
conductor string.
A base member is often applied in offshore drilling techniques,
which base member is provided with means suitable for connecting
one or more guide lines to the base member. Such guide lines are at
the upper end thereof connected to the drilling barge, floating
platform or structure supported by the bottom of the body of water,
and are useful in guiding the equipment from the ship, floating
platform or structure to the entrance of the borehole and vice
versa.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus
for use in drilling offshore wells, which comprises a conductor
string which can be introduced into the bottom of a body of water
in a very efficient manner, wherein the required amount of drilling
energy is relatively low.
It is a further object of the present invention to provide a method
and apparatus for use in drilling offshore wells, wherein contact
with the entrance to the hole is not lost during the initial
drilling period.
It is still another object of the present invention to provide a
method for drilling an offshore well, without applying a temporary
guide base, or a permanent guide base provided with a drive
pipe.
It is another object of the present invention to decrease the time
required to place and cement a conductor string provided with a
guide base, as much as possible.
It is a further object of the present invention to provide a method
and an apparatus for use in drilling offshore wells wherein the
guide lines, if applied, cannot become entangled during placement
of the conductor string in the bottom of the body of water wherein
a borehole is being drilled.
According to the invention, an apparatus for use in drilling an
offshore well comprises:
A CONDUCTOR STRING,
A BASE MEMBER CARRIED BY THE CONDUCTOR STRING,
A DRILL STRING CONNECTED TO THE CONDUCTOR STRING BY COUPLING
MEANS,
A SELF-CONTAINED DRILLING UNIT PROVIDED WITH A DRILL BIT AND
CARRIED WITHIN THE CONDUCTOR STRING AT A LEVEL BELOW THE SAID
COUPLING MEANS,
A SHOE CARRIED BY THE LOWER END OF THE CONDUCTOR STRING, WHICH SHOE
IS ROTATABLY ARRANGED WITH RESPECT TO THE CENTRAL AXIS OF THE
CONDUCTOR STRING AND PROVIDED WITH MEANS TO PREVENT AXIAL
SEPARATION BETWEEN THE SHOE AND THE STRING, THE SHOE BEING FURTHER
PROVIDED AT THE LOWER END THEREOF WITH CUTTING MEANS AND HAVING A
CENTRAL PASSAGE IN WHICH THE DRILL BIT IS ARRANGED, AND
COUPLING MEANS ARRANGED BETWEEN THE SHOE AND THE ROTATABLE PART OF
THE SELF-CONTAINED DRILLING UNIT AND SUITABLE FOR TRANSMITTING AT
LEAST ROTATIONAL LOADS.
The drilling unit may either be carried by the conductor string, or
by the drill string.
If the drilling unit is carried by the drill string, the coupling
means between the shoe and the drilling unit may further be
suitable for transmitting axial loads, and a telescopic joint
suitable for transmitting rotational loads may be arranged in the
drill string between the self-contained drilling unit and the
coupling means arranged between the drill string and the conductor
string.
The base member may be provided with means suitable for connecting
at least one guide line to the base member.
The base member may be connected near the lower end of the
conductor string by a coupling means and be provided with
downwardly projecting extensions suitable to be inserted into the
bottom of a body of water to prevent rotation of the base member.
Guidebars may be provided to guide the drill string along the
guidelines, the guidebars being rotably arranged with respect to
the drill string.
A method for using the apparatus according to the invention may
comprise the following steps:
suspending from a drilling ship the lower part of the conductor
string provided with the rotatable casing shoe with cutting means
at its lower end,
mounting the hydraulic motor having the drill bit connected to the
output shaft thereof in the lower end of this part of the conductor
string, such that the drill bit protrudes through the central
opening of the casing show, and coupling the output shaft to the
casing shoe,
lowering the conductor string onto the formation surface by adding
conductor pipes to the conductor string,
rotating the drill bit and the casing shoe by supplying pressure
fluid to the hydraulic motor via the conductor string and drilling
a hole into the formation by simultaneously lowering the conductor
string and adding further conductor pipes to the conductor
string,
interrupting the drilling operation and mounting the base member
provided with guide lines to the top of the conductor string, and
coupling the drill string consisting of at least one drill pipe to
the top of the conductor string,
resuming the drilling operation by supplying pressure fluid to the
hydraulic motor via this drill string and the conductor string and
simultaneously lowering the conductor string into the hole by
adding further drill pipes to the drill string,
interrupting the drilling operation when the base rests on the
surface of the formation,
lifting the hydraulic motor together with the drill bit and
suspending it in the conductor string at a higher level,
injecting a solidifiable material through the drill string, the
conductor string, and the casing shoe and into the borehole part
around the conductor string,
uncoupling the drill string from the conductor string and lifting
the drill string, and
lifting the hydraulic motor together with the drill bit from the
conductor string.
An alternative method for using the apparatus according to the
invention may comprise the following steps:
suspending from a drilling ship the lower part of the conductor
string provided at the lower end thereof with the rotatable casing
shoe with cutting teeth, and with the base member with downwardly
projecting extension,
mounting the hydraulic motor having the drill bit connected to the
output shaft thereof in the lower end of this part of the conductor
string such that the drill bit protrudes through the central
opening of the casing shoe, and coupling the output shaft to the
casing shoe,
lowering the conductor string onto the formation surface by adding
conductor pipes to the conductor string,
uncoupling the base member from the conductor string,
rotating the drill bit and casing shoe by supplying pressure fluid
to the hydraulic motor via the conductor string and drilling a hole
into the formation by simultaneously lowering the conductor string
and adding further conductor pipes to the conductor string,
interrupting the drilling operation for coupling the drill string
consisting of at least one drill pipe to the top of the conductor
string,
resuming the drilling operation by supplying pressure fluid to the
hydraulic motor via this drill string and the conductor string and
simultaneously lowering the conductor string into the hole by
adding further drill pipes to the drill string,
interrupting the drilling operation when the hole has reached a
sufficient depth,
lifting the hydraulic motor together with the drill bit and
suspending it in the conductor string at a higher level,
injecting a solidifiable material through the drill string, the
conductor string and the casing shoe and into the borehole part
around the conductor string,
uncoupling the drill string from the conductor string and lifting
the drill string, and
lifting the hydraulic motor together with the drill bit from the
conductor string.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will, by way of example, by described hereinafter in
more detail with reference to the drawing, wherein
FIG. 1 shows a longitudinal section through one embodiment of the
invention during the placement thereof in the bottom of a body of
water,
FIG. 2 shows a longitudinal section through the same embodiment as
shown in FIG. 1, but in position in a borehole drilled in the
bottom of the body of water and connected to this bottom,
FIG. 3 shows a longitudinal section through another embodiment of
the invention during the placement thereof in the sea or ocean
bottom, and
FIG. 4 shows a longitudinal section through an embodiment according
to the invention, suitable for use in a body of water which has a
depth smaller than the length of the conductor string.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, the drill string 1 carries a coupling
member 4 which is suitable for being coupled to the upper end of
the conductor string 5. This coupling member 4 is of a conventional
type and comprises an annular piston 6 axially displaceable in an
annular cylinder 7 and capable of actuating locking dogs 8 which
cooperate with a groove 9 in the upper part of the outer wall of
the conductor string 5. The piston 6 can be actuated by hydraulic
fluid, which is supplied to and drained from the cylinder parts
above and below the piston 6 via suitable (not shown) flexible
conduits leading to the drilling ship. Suitable sealing means 10
are provided to seal the passage between the coupling member 4 and
the conductor string 5.
The conductor string carries a base member or base plate 11 which,
as will be described hereinafter with reference to FIG. 2, serves
to support the conductor string 5 when the hole 2 is at the
required depth.
The base member 11 is provided with guide posts 12 of a
conventional type, which guide posts have guide cables 13 connected
thereto and running upwards to the drilling ship (not shown).
Guidebars 14 connected to the coupling 4 cooperate with the guide
cables 13 and the guide posts 12.
The lower end of the drill pipe 1 is connected to a hydraulic
turbine 15 of known design, which can be actuated by a flow of
fluid being passed through the drill string 1. The drill motor
shaft 16 carries a drill bit 17 and is provided with a splined
section 18 cooperating with a splined section 19 of a casing shoe
20, which is rotatably arranged on the lower end of the conductor
string 5. Locking and rolling means comprising balls 21 running in
semi-annular grooves arranged in the shoe 20 and the conductor
string 5 lock the shoe 20 against axial displacement with respect
to the conductor string 5.
An annular row of cutting teeth 22 is arranged at the lower end of
the shoe 20. Thus a cutting element is formed by the bit 17 and the
teeth 22 for drilling the hole 2 to a diameter greater than the
outer diameter of the conductor string 5. The conductor string 5
can thus be lowered into the hole 2 when the drilling operation is
being carried out at the bottom thereof by the bit 17 and the teeth
22 arranged on the rotatable casing shoe 20.
When drilling the hole 2, the whole assembly shown in FIG. 1 is
lowered from the ship (not shown) to the surface 23 of the bottom
of a body of water by means of the drill string 1. The guide lines
13 are kept in a vertical position by exerting a substantially
constant force at the top thereof, e.g., by means of constant
tension winches (not shown) mounted on board of the drilling
ship.
Hydraulic fluid is pressurized on board of the ship and injected
into the upper end of the drill string 1 for actuation of the
hydraulic motor 15. As a result, the bit 17 is rotated with respect
to the drill string 1. Since the bit 17 is connected to the shoe 20
via the splines 18 and 19, the shoe 20 is also rotated with respect
to the drill string 1 and in the same sense as the bit 17. Under
influence of the load on the cutting element formed by the teeth 22
and the bit 17, this element enters the formation 3 and drills a
hole 2. The load on the cutting element may be controlled by
controlling the load on the hook in the rig from which the drill
string 1 is suspended.
The drilling operation continues until the depth of the hole 2
equals the distance between the base member 11 and the cutting
teeth 22 of the shoe 20. The assembly is then suspended from the
base member 11 resting on the surface 23 of the sea or ocean bottom
3. Subsequently, the locking dogs 8 are retracted from the groove 9
in the conductor string 5 by displacing the annular piston 6 by
pumping hydraulic fluid below this piston and by lifting the drill
string 1. The hydraulic motor 15, the splined section 18 and the
drill bit 17 are subsequently retracted from the conductor string
5. During this upward displacement, the coupling 4 is guided along
the guide cables 13 by means of the guidebars 14.
Subsequently, a cementing tube 25 is lowered into the conductor
string 5, which tube is provided with a coupling 25 similar to the
coupling 4 shown in FIG. 1. The coupling 26 is provided with
guidebars 26 A cooperating with the guide cables 13 and the guide
posts 12 on the base member 11. The cementing tube 25 carries a
packet element 27 known as cement retainer which in the position
shown in FIG. 2 seals off the annular passage between the cementing
tube 25 and the conductor string 5. Cement is injected into the
borehole 2, thereby filling the annular space around the conductor
string 5 with a cement layer 28. It will be appreciated that the
casing shoe 20 is cemented in the well together with the conductor
string 5.
After cementing of the conductor string 5, the cementing tube 25 is
removed from the conductor string 5 and the cement retainer 27
prevents backflow from the cement 28 into the conductor string 5.
After hardening of the cement, drilling of the borehole proceeds
via the conductor string 5 in one of the known manners. It will be
appreciated that the equipment required for further drilling of the
borehole can be guide along the guide cabels 13 to the entrance of
the conductor string 5 or to any equipment mounted on the string 5
(such as blowout preventers and a conically-shaped funnel).
In an alternative embodiment of the invention, the conductor string
5 may be cemented in the borehole 2 by passing the cement or other
solidifiable compound via the drill string 1 and the hydraulic
motor 15 into the annular space around the conductor string.
Preferably, the hydraulic motor 15 and the bit 17 are lifted over a
distance within the conductor string, which operation can take
place after having uncoupled coupling 4. It will be appreciated
that a packer member closing off the annular space between the
drill string 1 and the conductor string 5 is suitable to prevent
flow of cement through the conductor string 5 in an upward
direction. As hydraulic motor suitable for this purpose, use can,
e.g., be made of the pump known as a "Moyno" pump manufactured by
Robbins and Meyers, Springfield, Ohio. Hydraulic fluid is then
injected into the outlet of this pump, and the shaft of the pump is
used as a drive shaft for actuating the bit 17. The hydraulic motor
and the interior of the conductor string are cleaned of cement
after the cementation process by injecting a displacing fluid
behind the cement and in an amount sufficient to displace the
cement inside the conductor string to the level of the shoe 20. It
will be appreciated that the drill string 1 should be lifted
sufficiently high prior to cementing so that a large volume of
cleaning fluid can pass the hydraulic motor for effective cleaning.
In this method total withdrawal of the drillstring 1 is only
possible after the cement has hardened.
It is one of the advantages of the apparatus according to the
invention, that the conductor string 5 is continuously being
lowered in the hole while the later is being drilled, and that this
operation requires a minimum amount of energy since, although the
conductor string 5 carries rotational cutting members, shoe 20 is
the only member in contact with the borehole wall that is rotated
in the hole. Moreover, the assembly comprising the conductor string
5 with rotatable casing shoe, the drill string 1 with coupling 4
and turbine/bit unit 15, 17 is of compact design and is easy to
operate at large sea depths.
A further advantage is that guide lines 13, if applied, cannot
become twisted or entangled during the drilling operation, since
the application of the hydraulic motor (or any other self-contained
drilling unit such as an electric drill) in combination with the
rotatable casing shoe and the coupling between the non-rotating
drill string and the conductor string prevents rotation of the
guide lines around the drill string. It is true that as a result of
the torsion of the drill 1 caused by the operation of the turbine
15 the guide cables 13 are displaced with respect to the string 1
through a certain angle. However, at shallow waters this angle is
not so great and this torque will be released when the motor is
stopped. At greater depths, however, it may be advisable to prevent
such torsion of the drill string 1 by using the equipment according
to the invention as shown in FIG. 3.
The conductor string 5 as shown in FIG. 3 carries a base member 29,
which is connected thereto by means of shear pins 30 (only one of
which is shown). Extension means 31 projecting downwards from the
base member 29 are partly driven into the sea bottom 32 when the
assembly shown in FIG. 3 is placed on this bottom.
The guide posts 33 having guide cables 34 connected thereto are
mounted on the base member 29. This member 29 is further provided
with an opening 35 allowing (when pin 30 has been sheared) axial
displacement between the base member 29 and the conductor string
5.
The conductor string 5 carries a rotatable shoe 37 at the lower end
thereof. Sealing means 38 are arranged between the shoe 37 and the
string 5 to prevent passage of fluid between these two elements.
Balls 39 are provided between the shoe 37 and the string 5 in
grooves with semi-circular cross-section arranged therein for
locking the shoe 37 and the string 5 in axial direction and
transmitting radial loads exerted on the shoe 37 to the string 5.
Balls 40 are provided to transmit axial loads between the shoe 37
and the string 5. The lower end of the shoe 37 carries cutting
wheels 41 to drill, in combination with the bit 42 arranged in the
central passage 43 of the shoe 37, a hole in the sea bottom 32,
which hole has a diameter sufficiently large to allow the passage
of the conductor string 5 therethrough.
Bit 42 is mounted by screw thread 44 on member 45 which is mounted
on the shaft of the hydraulic motor 46. The member 45 is provided
with splines 47 cooperating with splines 48 arranged at the wall of
the passage 43 of the shoe 37. The splines 47 rest at the lower
ends thereof on the shoulders 49 of the grooves arranged between
the splines 48.
The load required on the cutting element consisting of the central
bit 42 and the annular bit formed by the elements 41 is provided by
the weight of the hydraulic motor 46 and the drill collars 50
arranged on top of the motor 46. The upper end of the string of
drill collars 50 is coupled to one side of a telescopic member (a
so-called bumper sub) comprising a piston rod 51, a piston 52 and a
cylinder 53. To prevent rotation between the piston 51 and the
cylinder 53, the outer surface of the rod is non-circular, the
opening of the cylinder 53 through which the rod 51 is passed
having a corresponding shape.
The upper end of the telescopic member is connected to a coupling
member 54 by a pipe 55. The coupling member 54 is provided with
J-slots (not shown) for cooperation with pins 56, arranged on the
conductor string 5. The coupling member 54, is further provided
with guide bars 57 having guide members 58 attached thereto for
cooperation with the guide cables 34 in a manner known per se. The
guide bars 57 are connected to a ring member 59 which is rotatably
arranged with respect to the coupling member 54 and a drill string
60.
The assembly comprising the coupling member 54, the conductor
string 5, the telescopic member 51-53, the drill collars 50, the
hydraulic motor 46, the bit 42 and the shoe 40 is suspended from
the drill string 60 connected to the coupling member 54. It will be
appreciated that a passageway of sufficient cross-section is
provided through the various elements of the assembly to allow
fluid to flow from the interior of the drilling string 60 to the
hydraulic motor 46 and to the cutting element formed by the bit 42
and the shoe 37.
The operation of the equipment as shown in FIG. 3 is as
follows:
The whole assembly is lowered to the sea bottom 32 by lowering the
drill string 60. The guide cables 34 are kept sufficiently taut to
prevent entanglement thereof.
On being placed on the sea bottom 32, the lower ends of the
extension 31 enter this bottom, and the pins 30 between the base 29
and the conductor string 5 are sheared off when the extensions 31
have entered the bottom 32 over a sufficient distance. When the
hydraulic motor 46 is actuated by the supply of drilling liquid via
the drill string 60, a hole is drilled in the bottom 32 by the
combined action of the bit 42 and the shoe 37. The conductor string
5 is continuously lowered in the borehole, sliding through the
opening 35 provided in the base 29. The drill string is subjected
to torsion, but since the base 29 is anchored to the seabottom 32
by the extensions 31, and the guide bars 57 are rotatably arranged
with respect to the drill string 60, the guide lines 34 cannot be
displaced angularly with respect to the drill string 60.
Consequently, the cables 34 which are kept in constant tension
cannot become entangled during the drilling process.
When the desired borehole depth has been reached, the conductor
string may be cemented in the hole in one of the manners as
hereinbefore described.
When the depth of the body of water overlying the formation in
which a conductor string is to be placed is less than the length of
the conductor string, this string is not suspended from a drill
string during the initial drilling of the hole. The embodiment of
the present invention which enables the placing of a conductor
string under these circumstances will now be described with
reference to FIG. 4.
A part of the conductor string 5 is now suspended by a coupling 70
provided with an eye 71 suitable to cooperate with the hook (not
shown) of a drilling rig. The coupling 70 is provided with a
connection 72 suitable to be connected to a (not shown) mud hose.
The mud supplied via the connection 72 (vide arrow 73) flows via
the coupling 70 into the conductor string 5 (vide arrow 74). The
lower end of the conductor string 5 is provided with a rotatable
casing shoe 75 provided with an annular row of cutting elements 76.
The manner in which the shoe 75 is rotatably connected to the
conductor string 5 is only shown schematically. A locking and
bearing element comprising balls 77 running in grooves of
semi-circular cross-section prevents axial separation between the
shoe 75 and the conductor string 5.
The casing shoe 75 carries at the inner wall thereof a splined
section 78 designed to cooperate with a splined section 79 carried
by the output shaft 80 of the hydraulic motor 81. The shaft 80
carries a drill bit 82 protruding through the central opening of
the shoe 75 and forming a drilling element in combination with the
cutting teeth 76 carried by the shoe 75. The hydraulic motor 81 is
connected to the inner wall of the conductor string 5 by a coupling
83 known per se and suitable to transfer an axial, as well as a
rotational load between the conductor string 5 and the hydraulic
motor 81, and to seal the passage through the annular space 84
between the hydraulic motor 81 and the conductor string 5.
The entrance for the drive fluid to the hydraulic motor 81 is
schematically indicated at 85. The motor 81 is of the type suitable
for passing cement slurry therethrough. To this end use can be made
of a pump known as a Moyno pump, manufactured by Robbins and
Meyers, Springfield, Ohio, by supplying pressure fluid to the
outlet of this pump and connecting the bit 82 to the shaft of this
pump.
In operation, the assembly as shown in FIG. 4 is suspended from the
drilling ship (not shown) and pressure fluid is supplied to the
hydraulic motor 81 via the connection 72, coupling 70 and conductor
string 5 (vide arrows 73, 74 and 86).
Rotation of the shaft 80 activates the bit 82 and the cutting
elements 76 of the casing shoe 75, which cut under axial load a
hole into the formation, into which hole the conductor string 5 is
lowered by adding further conductor pipes between the top of the
conductor string 5 and the coupling 70.
When the length of conductor string suspended from the coupling 70
is sufficiently long for the purpose, the drilling operation is
interrupted and a base member (not shown) as well as a drill pipe
(not shown) is coupled to the top of the conductor string by
coupling means known per se. Thereafter the drilling operation is
resumed by supplying pressure fluid via this drill pipe. From time
to time, as the depth of the hole increases, new drill pipes are
added to the drill string.
When the desired depth of the hole has been reached, the total
length of the conductor string will have been lowered into the hole
and be suspended from the surface of the formation by the base
member resting on this surface.
The drilling operation is then stopped, and the hydraulic motor 81
together with the splined section 79 and the drill bit 82 is
detached from the conductor string 5 by uncoupling the coupling 83
and thereafter again reconnected to the conductor string 5 by
setting this coupling at a higher level. This operation can be
carried out in a manner known per se by means of a (not shown) pipe
string.
Subsequently, a solidifiable material is injected via this pipe
string, the hydraulic motor 81 and the central passage of the
casing shoe 75 into the annular space around the conductor string.
After the material has consolidated the drill is uncoupled from the
conductor string 5 and lifted. Thereafter the pips string carrying
the self-contained drilling unit comprising the hydraulic motor 81,
the splined section 79 and the drill bit 82 is retrieved from the
conductor string 5. Thereafter, the hole is further deepened in a
manner known per se.
If desired, the self-contained drilling unit comprising the
hydraulic motor 81 may be uncoupled from the conductor string when
the drilling operation is stopped and connected to the lower end of
the drill string. The self-contained drilling unit is then removed
together with the drill string from the conductor string after
cementation of this string and solidification of the cement.
In an alternative method, the hydraulic motor 81 is removed
together with the bit 82 from the conductor string, whereafter
cementation takes place in the manner as described with reference
to FIG. 2.
It will be appreciated that at least one telescopic joint (a
so-called casing thumper) may be installed between sections of the
conductor string 5, to compensate for wave action influencing the
distance between the coupling 70 and the surface 87 of the
formation to be drilled. Such telescopic joints may also be
arranged in the drill string.
Although the coupling 83 includes a packer member for sealing the
passage between the outer wall of the hydraulic motor 81 and the
inner wall of the conductor string 5, the invention is not
restricted thereto. If desired, the packer member may be separate
from the coupling 83. The packer member need not be set when the
hydraulic motor 81 is suspended from a higher level during the
cementing operation. The cement will then pass around the hydraulic
motor on its way downward through the conductor string. The the
invention is further not restricted to the use of a base member
connected to the top of the conductor string 5 of the system as
shown in FIG. 4. If desired, the base member may be coupled to the
lower end of this conductor string by means which are uncoupled
when the base member rests on the surface 87 of the formation to be
drilled. This base member is then provided with means preventing
rotation of the member with respect to the central axis of the
conductor string during the drilling operation. In view hereof,
reference is made to the base member 29 as shown in FIG. 3.
If desired, the self-contained drilling units as shown in FIGS. 1
and 3 may be replaced by a self-contained drilling unit as shown in
FIG. 4.
It will be appreciated that the invention is not restricted to the
particular designs as shown in FIGS. 1-4. Thus, the number and
construction of the guide posts may differ from the guide posts
shown. Further, any other type of coupling suitable for the purpose
may be applied instead of the coupling 4 shown, as well as for the
spline construction arranged between the rotatable shoe and the
central bit arranged within the shoe.
Furthermore, the extensions 31 suitable for anchoring the base 29
to the sea bottom to prevent rotation of the base 29 around its
central axis, may be replaced by any other type of anchoring means
suitable for the purpose. If desired, the anchoring means may be
provied with drilling or jetting elements to improved the
penetration.
It will further be appreciated that the hydraulic or electric motor
used for actuating the drill bit may be mounted anywhere between
the coupling used for connecting the drill string to the conductor
string, and the drill bit. Thus, the motor 46 may be mounted just
below the telescopic coupling 51-53.
In the arrangement as shown in FIG. 1, the drill string 1 may be
kept in the center of the conductor string by means of centralizers
known per se.
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