U.S. patent number 3,552,507 [Application Number 04/778,509] was granted by the patent office on 1971-01-05 for system for rotary drilling of wells using casing as the drill string.
Invention is credited to Cicero C. Brown.
United States Patent |
3,552,507 |
Brown |
January 5, 1971 |
SYSTEM FOR ROTARY DRILLING OF WELLS USING CASING AS THE DRILL
STRING
Abstract
A rotary well drilling system employing well casing as the drill
string; a bit assembly having radially expansible cutters bodily
insertable and removable through the bore of the casing and
releasably connected thereto; and a drive connection means
releasably insertable into the upper end of the casing bore
including casing-gripping means nonthreadedly engageable with the
casing bore wall for transmitting rotational torque to the
casing.
Inventors: |
Brown; Cicero C. (Houston,
TX) |
Family
ID: |
25113586 |
Appl.
No.: |
04/778,509 |
Filed: |
November 25, 1968 |
Current U.S.
Class: |
175/258 |
Current CPC
Class: |
E21B
7/208 (20130101); E21B 19/07 (20130101); E21B
10/64 (20130101); E21B 3/02 (20130101); E21B
10/66 (20130101); E21B 10/34 (20130101) |
Current International
Class: |
E21B
10/26 (20060101); E21B 10/34 (20060101); E21B
3/02 (20060101); E21B 7/20 (20060101); E21B
3/00 (20060101); E21B 19/00 (20060101); E21B
19/07 (20060101); E21B 10/00 (20060101); E21B
10/66 (20060101); E21B 10/64 (20060101); E21b
009/26 () |
Field of
Search: |
;175/258,257,263,274,285,291,286 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Byers, Jr.; Nile C.
Claims
I claim:
1. A system for rotary drilling of wells using casing as the drill
string comprising:
a. a string of well casing;
b. a bit assembly constructed and arranged to be bodily inserted
and removed through the bore of the casing;
c. latch means releasably securing said bit assembly to the lower
end of the casing for rotation thereby;
d. radially expansible and retractible cutter elements carried by
the bit assembly for drilling a well bore to a diameter to receive
said casing; and
e. drive connection means operatively associated with said string
of casing and adapted to be connected to a rotary drive power
source and releasably insertable into the upper end of the bore of
the casing having casing-gripping means nonthreadedly engageable
with the casing bore wall for transmitting rotational torque from
said source to the casing.
2. A system according to claim 1, wherein said bit assembly
includes: means actuated by fluid pressure applied through the
casing for expanding said cutter elements.
3. A system according to claim 1, wherein said bit assembly
includes:
a. a generally tubular body;
b. a pilot bit centrally secured to the lower end of said body;
and
c. fixed radial cutters mounted on the body between said cutter
elements and said pilot bit adapted to drill said well bore to at
least the diameter of said body.
4. A system according to claim 1, wherein said bit assembly
includes:
a. a generally tubular body;
b. pivot means pivotally connecting said cutter elements to said
body;
c. a cylinder in said body;
d. piston means slidable in said cylinder in response to fluid
pressure in said casing; and
e. lever means drivingly connecting said piston means to said
cutter elements for extending and retracting the same.
5. A system according to claim 4 wherein said lever means comprises
toothed rack-and-gear means.
6. A system according to claim 4, wherein said lever means
comprises crank-and-pin connection means.
7. A system according to claim 1, wherein said bit assembly
includes:
a. a tubular housing coaxially connectable to the lower end of said
casing and having an annular latching recess interiorly
thereof;
b. a generally tubular body coaxially insertable in said
housing;
c. latch elements mounted in the wall of said body for radial
movement into and out of latching engagement with said recess;
d. an expander sleeve slidably mounted in the bore of said body for
axial movement therein between positions projecting said latch
elements into said recess and releasing said latch elements for
retraction from said recess; and
e. means normally biasing said expander sleeve toward the
latch-projecting position.
8. A system according to claim 1, wherein said drive connection
means includes:
a. a tubular mandrel adapted to be connected to a rotary drive
power source;
b. a pipe-gripping assembly mounted about the mandrel including
pipe-gripping elements radially movable into and out of gripping
engagement with the casing in response to rotation of said mandrel;
and
c. arcuate shoe elements rockably disposed about said mandrel and
carrying vertically extending teeth movable into and out of
torsion-applying engagement with said casing in response to
relative angular movement between the mandrel and the shoes.
9. A system according to claim 1, wherein said drive connection
means includes:
a. a tubular mandrel adapted to be connected to a rotary drive
power source;
b. stop means on the mandrel engageable with the upper end of the
casing to limit inward movement of the mandrel;
c. pipe-gripping slips mounted on the mandrel for radial movement
into and out of gripping-engagement with the casing;
d. expander means mounted on the mandrel for axial movement into
and out of wedging engagement with said slips in response to
rotation of said mandrel; and
e. pipe-engaging shoes rockably mounted about the mandrel for
movement thereby into said nonthreaded engagement with the
casing.
10. A system according to claim 9 including complementary left-hand
thread means connecting said mandrel to said expander means.
Description
BACKGROUND OF THE INVENTION
In conventional rotary drilling, the drilling string generally
comprises a relatively small diameter string of drill pipe having
the drill bit threadedly connected to the lower end thereof, the
bit size being such as to drill a borehole of substantially larger
diameter than that of the drill string. After drilling the borehole
to a predetermined depth, the drill string is withdrawn and the
borehole lined with casing to support the earth formations defining
the borewall. During drilling, a suitable drilling fluid is
generally circulated down through the drill string, out the bit and
up through the annulus to the surface.
In such conventional drilling procedures, the borewall,
particularly where constituted by relatively soft formations, will
tend to slough off or cave, this action being frequently
accentuated by the washing action of the drilling fluid. This will
often seriously interfere with the drilling operation and may cause
sticking of the drilling string with its many attendant problems.
Also, the operations in the open hole, as when withdrawing the
drill string to change bits and returning it into the borehole, and
the procedure for running casing to line the borehole, are all
subject to many hazards resulting from the fact that the borewall
is exposed during all such operations.
Various efforts have heretofore been made to overcome difficulties
such as those mentioned by procedures in which the well casing is
run closely following the advance of the drill but none of these
earlier procedures have proven to be successful, particularly when
attempts were made to employ them in drilling deep wells where
borehole diameters are relatively large as compared with the size
of the drill string.
SUMMARY OF THE INVENTION
In accordance with the present invention a system is provided which
employs the well casing itself as the drill pipe. A bit assembly
which is bodily insertable and withdrawable through the bore of the
well casing, is releasably secured to the lower end thereof, and
includes radially expansible cutter elements to enable drilling of
a borehole having a diameter such as to freely accommodate the
casing/drill pipe. A drive connection is provided for transmitting
rotational power to the upper end of the casing string and includes
a drive connector means which is slidably insertable into the upper
end of the casing and includes casing-gripping means which are
nonthreadedly engageable with the casing wall for transmitting
rotational torque to the casing.
By means of a system such as described, the borewall will at all
times be fully supported by the casing which will remain in the
wellbore while the bit assembly may be withdrawn for repair or
replacement. Moreover, by the employment of the readily insertable
drive connection, effective rotary torque can be applied to the
casing with minimum manipulative operations for making and
releasing the drive connection.
The system in accordance with this invention will obviate the
difficulties encountered in more conventional rotary drilling
systems; will assure protection for the wall of the wellbore
throughout the drilling; permits ready installation and removal of
the bit assembly through the bore of the casing; and provides
simple means for attaching and releasing the drive connection to
the casing when adding sections thereto.
Other and more specific objects and advantages of this invention
will become more readily apparent from the following detailed
description when read in conjunction with the accompanying drawings
which illustrate useful embodiments in accordance with this
invention.
In the drawings, FIGS. 1A and 1B, together, comprise a
longitudinal, partly sectional view of a drilling system in
accordance with the present invention in place in a wellbore, the
parts being shown in the positions occupied while drilling
proceeds;
FIG. 2 is a longitudinal, partly sectional view on a somewhat
enlarged scale of the lower portion of the drill string and bit
assembly showing the parts of the bit assembly in the released
position preparatory to withdrawing the bit assembly through the
casing;
FIG. 3 is a view similar to FIG. 2 showing the bit assembly in the
drilling position with the expansible cutters extended;
FIG. 4 is a view generally similar to FIGS. 2 and 3, showing a
fishing tool inserted in the bit assembly preparatory to
withdrawing the latter through the casing;
FIG. 5 is a view similar to FIG. 4 showing the bit assembly in
process of being withdrawn through the casing string;
FIGS. 6, 7 and 8 are cross-sectional views taken, respectively,
along lines 6-6, 7-7 and 8-8 of FIG. 2;
FIG. 9 is a cross-sectional view taken along line 9-9 of FIG.
3;
FIG. 10 is a longitudinal, partly sectional view of the drive
connection assembly employed for transmitting rotary drive torque
to the upper end of the casing, the parts being shown in their
nondrive relation;
FIG. 11 is a view similar to FIG. 10 showing the parts in the
casing drive relation;
FIG. 12 is a cross-sectional view taken along line 12-12 of FIG. 10
showing the parts of the torsional drive elements in their
nondriving position;
FIG. 13 is a view similar to FIG. 12 showing the torsional drive
elements in their drive positions;
FIG. 14 is a longitudinal, partly sectional view of a modified form
of the bit assembly with the expansible cutters in retracted
condition;
FIG. 15 is a view similar to FIG. 14 showing the bit assembly
locking into the casing string and with the expansible cutters in
the extended position;
FIG. 16 is a cross-sectional view taken along line 16-16 of FIG.
14; and
FIG. 17 is a cross-sectional view taken along line 17-17 of FIG.
15.
Referring to the drawings, FIGS. 1A and 1B show the assemblage of
apparatus comprising the system, disposed in a wellbore W, the
upper end portion of which is lined with a conventional conductor
casing K surmounted by a wellhead fitting F which includes a
conventional slip bowl H adapted to receive hanger slips G (shown
in broken lines) for supporting the casing string at appropriate
stages of operation.
The drilling system includes a string of casing C which functions
as the drill pipe and which may include one or more centralizer
sections S for maintaining the drill string in substantially axial
alignment in the wellbore. At its lower end the string of casing is
connected to a tubular body 10 forming a part thereof and which
also forms a housing for the bit assembly, designated generally by
the letter A, which is slidably insertable into and removable from
bore 11 of the housing. The overall dimensions of the bit assembly
are such that it is also freely insertable and removable through
the bore of casing C.
The third major element of the drilling system comprises a
connector assembly, designated generally by the letter B, through
which rotary power is transmitted to the casing string for rotating
the bit assembly in a manner to be described subsequently.
The bit assembly comprises a tubular cage 12 having a bore 12a and
provided with a plurality of angularly spaced radial openings 13
therein in which are mounted latching dogs 14 for radial movement
into and out of an annular locking recess 15 provided in the wall
of housing 10. The exterior of cage 12 above openings 13 is
provided with fan-shaped grooves 16 widemouthed and open at their
lower ends and terminating in relatively narrow pockets 17 at their
upper ends. Grooves 16 and pockets 17 cooperate with stop pins 18
extending through the wall of housing 10 and projecting into
grooves 16 to guide the movement of the bit assembly into the
housing, the engagement of pins 16 in pockets 17 limiting the
downward movement of the assembly relative to the housing to a
position placing dogs 14 opposite recess 15. An annular packing,
such as O-ring 19, is mounted about the upper end of cage 12 to
seal with the wall of bore 11 when the bit assembly is fully
inserted in the housing. A tubular dog actuating sleeve 20 having a
bore 20a is slidably mounted in the bore of cage 12 and is provided
at an intermediate point thereon with external enlargements 21
adapted to engage the inner faces of dogs 14 when in registration
therewith to urge the latter outwardly into recess 15 to lock the
cage to housing 10, and to release the dogs when moved out of
registration with the dogs. The portion of latching sleeve 20 above
enlargements 21 is reduced in external diameter to define the
upwardly facing shoulder 29 and defines with cage 12 the annular
space 22. A spacer collar 23 is inserted concentrically between the
upper portion of sleeve 20 and cage 12 and is threadedly secured at
24 to the upper end of the cage. The inner end of spacer collar 23
terminates above the shoulder 29 and a coil spring 25 is mounted in
compression in annular space 22 between the inner end of spacer
collar 23 and shoulder 29. An annular seal 26 is disposed about the
upper end portion of sleeve 20 in slidable sealing engagement with
the bore wall of spacer collar 23. An annular latching groove 27 is
provided in the bore wall of sleeve 20 for purposes to be described
later. Spring 25 functions to normally bias sleeve 20 downwardly
toward the position placing enlargement 21 in registration with
dogs 14.
Sleeve 20 is initially held in retracted position compressing
spring 25, (FIG. 2) by shear pins 60 connecting it to a running
tool R, a part of which is shown in FIG. 2 but which, since it is
generally conventional, does not itself form a part of the present
invention. Running tool R includes an over-shot portion 0 also
initially connected by shear pins 61 to the upper end of collar 23.
The running tool also includes a jarring sleeve J which, when it is
desired to release locking sleeve 20, may be actuated through
manipulation of the running string in the well-known manner to
apply a downwardly directed blow against the upper end of sleeve 20
sufficient to break shear pins 60, whereupon spring 25 will expand
thrusting sleeve 20 downwardly to cause enlargements 21 to engage
the inner faces of dogs 14 and push them outwardly into locking
engagement in recess 15 (FIGS. 1 and 3) effectively locking the bit
assembly to housing 10. Thereupon, upward pull applied to over-shot
0 will act to break shear pins 61, releasing the running tool for
withdrawal from the casing.
The lower end portion of latching sleeve 20 is also reduced in
external diameter to extend slidably into the lower end of cage 12
and an annular seal 28 is provided between the lower end portion of
the latching sleeve and the cage. The lower end portion of cage 12
is provided with an externally threaded pin 30 receivable in the
internally threaded socket 31 of a cylinder 32 which carries an
annular seal element 33 in sealing engagement with the lower end of
bore 11. A piston 35 is slidably mounted in cylinder 32 and is
connected to a piston rod 36 which projects downwardly through an
opening in the lower end of cylinder 32 into an underreamer body 37
which is formed as an extension of cylinder 32. The lower end of
underreamer body 37 is formed to provide a reduced diameter tubular
extension 38 having an internally threaded box 39 at its lower end
into which is screwed a conventional rotary bit 40. Extension 38
and bit 40, together, comprise the pilot bit section of the bit
assembly. Extension 38 carries a plurality of fixed radially
extending under-reaming cutters 41 adapted to cut a hole diameter
to the gage of underreamer body 37. A piston rod 36 extends
slidably through a central bore 42 in extension 38 and bears
against a coil spring 43 disposed in compression between the lower
end of piston rod 46 and the upper end of bit 40. An annular seal
element 44 is arranged to seal between bore 42 and the lower end of
the piston rod.
A plurality of underreamer cutters 45 are pivotally mounted in
longitudinal slots 46 in the wall of body 37 for radial movement
between positions projecting outwardly at right angles to the axis
of the bit assembly and retracted positions generally parallel to
the axis of the assembly. When retracted, the cutters will be
substantially fully enclosed within slots 46 so that the bit
assembly will be freely movable through casing C and into and out
of housing 10. Cutters 45 are rollably mounted on hollow shafts 45a
(FIG. 2) which terminate in flattened heads 47 which extend into
slots 46 and are mounted for pivotal movement about hollow pivot
pins 48 extending transversely of slots 46 (FIGS. 7 and 9). The
inner ends of heads 47 are formed as sector gears 49 each of which
is arranged to mesh with a rack 50 formed on the opposed exterior
face of piston rod 36, which is made generally square in cross
section to accommodate the several racks.
With the cutter arrangement and piston elements described, it will
be seen that when piston 35 is in its elevated position in cylinder
32 (FIG. 2) racks 50 in cooperation with sector gears 49 will move
cutters 45 to their retracted positions (FIGS. 2, 4, 5 and 7). When
piston 35 is moved downwardly to its lowermost position, shown in
FIGS. 1B, the rack and gear cooperation will swing cutters 45 to
their radially outwardly projecting positions (FIGS. 1B, 3 and 9).
Piston 35 and piston rod 36 are formed with an axial passage 51
providing fluid communication with the interior of cylinder 32 at
one end and with the interior of extension 38 at the other. The
latter communicates through passages 52 (FIGS. 2, 3 and 8) which
exit through the outer ends of cutters 41. Other passages 53 (FIGS.
3, 7 and 9) communicate the interior of extension 38 with passages
54 through hollow pivot pins 48 and thence through passages 55 in
shafts 45a exiting through the outer ends of cutters 45. Bit 40 is
provided with fluid jet passages 56 which communicate with the
interior of extension 38. The reciprocating movements of piston 35
in cylinder 32 are limited in one direction by the inner end of pin
30, the fully retracted positions of cutters 45, and at the
opposite end by an internal shoulder 32a in cylinder 32, the fully
extended position of cutters 45.
Drive connector assembly B, illustrated in FIGS. 1 and 10 to 13,
inclusive, includes a tubular mandrel or support member 60 having
an axial bore 60a and provided with a threaded box 61 at its upper
end for connection to a power source. A tubular bushing 62 is
rotatably mounted about the upper portion of the mandrel on
antifriction bearings 63 and has a radially extending flange 64
dimensioned to rest on the upper end of the uppermost section of
casing C which will normally project upwardly above the upper end
of the well bore. Flange 64 forms stop means engageable with the
upper end of the casing section to limit inward movement of the
connection assembly into the bore of the casing. The inner end of
bushing 62 carries an inwardly turned lip 65 on which a plurality
of pipe-gripping wedges or slips 66 are hingedly supported by means
of outwardly projecting hanger lips 67 formed on the upper ends of
the slips. An upwardly and inwardly tapering conical expander 68 is
disposed about mandrel 60 between the latter and slips 66 and is
provided internally with a section of relatively coarse left-hand
threads 69 engageable by a complementary section of threads 70
formed on mandrel 60 intermediate the ends thereof. With this
left-hand threaded connection between the expander and the mandrel
it will be seen that right-hand rotation of the mandrel will cause
expander 68 to move upwardly relative to slips 66, the
complementary tapered surfaces thereof cooperating to move the
slips outwardly into gripping engagement with the wall of casing C.
Reverse rotation of the mandrel will move the expander downwardly
to release the slips from gripping engagement with the casing.
The lower portion of expander 66 is provided with an annular
outwardly opening recess 71 defined by a cylindrical bottom wall 72
and at its outer end by oppositely extending annular lips
73-73.
Pipe-engaging elements, designated generally by the numeral 74, are
mounted in recess 71 and are operable in response to angular
movement of the mandrel to apply torsional force to the casing.
This form of the gripping elements 74 is described in detail in my
U.S. Pat. No. 3,322,006, issued May 30, 1967, and constitute
casing-gripping means which are nonthreadedly engageable with the
casing for transmitting rotational torque thereto. While the
specific details of these casing-gripping elements do not form a
part of the present invention in view of the earlier patent
thereon, a brief description will be helpful in connection with the
present disclosure.
Mounted within recess 71 concentrically with bottom wall 72 is a
pair of generally semicircular pipe-gripping shoes 75 which are
normally urged apart radially by means of relatively light coil
springs 76 seated in suitable sockets 77 in the opposed ends of the
shoes, as best seen in FIGS. 12 and 13, the spacing between the
inner ends of the shoes permitting a limited amount of independent
movement of the shoes. The upper and lower end edges of the shoes
are provided with oppositely extending upper and lower flanges
78-78 which are adapted to engage lips 73-73, whereby the latter
will prevent the shoes from being radially expelled from recess 71.
Each of the shoes is provided centrally on its external surface
with a longitudinally extending convex, generally smooth arcuate
surface portion 79, which has a circular radius adapted to provide
smooth or nongripping engagement with the inner wall of a
surrounding pipe, such as well casing C. Surface portion 79 extends
for a relatively short angular distance about the outer periphery
of the shoes. On each side of surface portion 79 the exterior of
the shoes is offset slightly radially inwardly at 80 and these
radially offset portions are provided with a few parallel,
longitudinally extending, radially projecting teeth 81 which are
normally out of contact with casing C when portion 79 is engaged
with the casing wall. The teeth 81 are adapted, upon relative
rotation or oscillation between the shoes and casing C, to engage
the casing and prevent further relative rotation between the shoes
and the casing, and to then apply a strong torsional force to the
casing in response to rotational force transmitted from the
expander body to the shoes. By reason of the longitudinally
extending form of the teeth, some longitudinal slippage between the
teeth and the casing can occur, even though the torsional force
will prevent relative rotation between the teeth and the casing, as
will appear subsequently. To effect relative rotation or rocking
movement of the shoes, bottom wall 72 is machined to provide
oppositely radially extending lugs 82, the lugs on opposite sides
of recess 71 having openings 83 through which a cylindrical shaft
84 extends. A series of rollers 85 are mounted on each shaft 84 on
opposite sides of the lugs 82 and constitute cam followers, the
sets of the cam followers thus being mounted on diametrically
opposite sides of recess 71. The inner periphery of shoes 75 on
each side of the central portion thereof is provided with a
noncircular cam surface 86 which are engageable by cam followers 85
in response to relative angular movement between expander 68 and
the shoes. As best seen in FIG. 13, cam surfaces 86 are shown
engaged with cooperating cams 85 to rock shoes 75 angularly
relative to casing C, so as to project teeth 81 into torsional
gripping engagement with the wall of casing C.
The lower end portion of expander 60 is provided about the exterior
thereof below recess 71 with an annular seal element 90 arranged
for slidable sealing engagement with casing C and an internal
annular seal element 91 arranged for slidable sealing engagement
with the exterior of mandrel 60. Upper and lower stop collars 92
and 93, respectively, are mounted about mandrel 60 above and below
the ends of the connector assembly to limit the extent of relative
longitudinal movement between the mandrel and the other parts of
the assembly.
Mandrel 60 is adapted to be connected by means of box 61 through a
drive nipple 95 to the tubular drive spindle 96 of a
fluid-pressure-operated rotary power unit 97 of any well-known
construction. Such a unit is described in my copending application,
Ser. No. 736,179, filed June 11, 1968, now U.S. Pat. 3,467,202.
Power unit 97 is carried on a swivel 98 suspended in a well derrick
(not shown) on elevators 99 connected to the conventional drawworks
(not shown) of a drilling rig, by means of which the power unit and
the elements connected thereto may be raised and lowered relative
to the well as required in the course of operations. Swivel 98 is
provided with a goose neck 100 through which drilling fluid may be
circulated through passages communicating with the bores of spindle
96, nipple 95 and bore 60a of mandrel 60 whence the fluid will be
directed through casing C to bit assembly A to the various jet
discharge passages provided therein. The fluid discharging from the
passages in the bit assembly will flow upwardly through the annulus
between the drilling string and the well bore to the surface.
OPERATION OF THE SYSTEM
The apparatus may be assembled by any suitable and known
procedures. Usually a string of casing C carrying housing 10 on its
lower end will be run into conductor casing K and suspended therein
from wellhead fitting F on slips G. Bit assembly A will then be
lowered through the casing on running tool R (FIG. 2) until seated
on pins 18, whereupon a downward jar on latching sleeve 20 will
actuate the anchor dogs to lock them into recess 15 (FIG. 3), after
which the running tool may be released by upward pull as previously
described.
Connector assembly B suspended from power unit 97 will now be
lowered into the upper end of casing C until flange 64 rests on the
upper end of the casing (FIG. 10). Right-hand rotational movement
will now be imparted by the power unit to mandrel 60 causing
expander 68 to move upwardly relative to the mandrel and setting
slips 66 into the wall of casing C (FIGS. 1 and 11). Because of the
longitudinal arrangement of teeth 81 on shoes 75, pipe-gripping
units 74 will slide upwardly on the casing wall for the distance
required to accommodate the slip-setting movement of the expander.
As slips 66 are tightly set, however, further rotational force
applied to mandrel 60 will produce the relative angular movement
operative to rock shoes 75 to positions at which such rotational
force will be transmitted as driving torque to the casing. As soon
as slips 66 are set, the hanger slips G may be removed freeing the
casing string for rotation by power transmitted from power unit 97
to connector assembly B.
Fluid circulation is now begun as the drill string is rotated with
the pilot bit section making the hole. The flow restrictions formed
by the several jet passages through the cutter elements will cause
the fluid pressure to build up in cylinder 32 above piston 35
forcing the latter downwardly and swinging underreamer cutters 45
outwardly to the positions shown in FIGS. 1 and 3. Continued
rotation of the drilling string will now be operative to drill a
well bore having a diameter to freely and continuously accommodate
the casing as the drill progresses downwardly.
To add a casing section to the upper end of the casing string, the
string may again be suspended and anchored in slips G, whereupon
reverse or left-hand rotation of spindle 96 for a few turns will be
sufficient to back expander 68 away from slips 66, releasing the
latter from their gripping engagement with the casing. The
connector assembly can now be pulled out of the top of the casing.
A new section of casing may now be attached to the upper end of the
casing hanging in the wellhead fitting, and connector assembly B
inserted in the upper end of the added casing section, and
reactuated by right-hand rotation of the mandrel. Hanger slips G
may now be removed and drilling continued.
In order to remove the bit assembly, as for repair or replacement
of the cutter elements, without removing the casing string from the
well bore, the casing string will again be hung in hanger slips G
and connector assembly released and removed. A fishing tool D
(FIGS. 4 and 5) of any well-known design is run through the bore of
the casing so that gripping elements E will be caused to latch into
recess 27 of the latching sleeve. Thereupon, upward pull applied
through the fishing tool will retract latching sleeve 20 to the
position shown in FIG. 5, at which dogs 14 will be released for
retraction from anchor recess 15. Upward pull applied to sleeve 20
will be transmitted to cage 12 and the entire bit assembly A may
now be pulled out of housing 10 and upwardly through casing C to
the surface. Casing C being left in the well bore will support and
protect the wall thereof throughout its full length.
With fluid circulation cut off, the pressure on piston 35 will be
relieved sufficiently so that as the bit assembly is pulled
upwardly, the extended underreamers will engage the lower end of
housing 10 and will be forced thereby to swing downwardly, and
sector gears 49 acting through racks 50 will move piston rod 36 and
piston 35 back upwardly to their retracted positions at which the
underreamers will return to their fully retracted positions in
slots 46 (FIG. 5).
FIGS. 14 to 16 illustrate a modification of the bit assembly
portion of the drilling system heretofore described, the other
parts of the system being unchanged.
In this modification the toothed rack-and-sector gear connection
between the underreamer cutters and the actuating piston are
replaced by a cam-and-lever connection. Modification of some of the
other details of the bit assembly are also employed as will appear
hereinafter.
In this modification a tubular housing 110 is secured to the lower
end of casing C and is provided with an anchor recess 115 in the
bore wall thereof. Stop pins 118 are mounted in the housing below
recess 115. The bit assembly includes the tubular cage 112 having
radial windows 113 for the reception of anchor dogs 114. Guide
slots 116 for cooperation with stop pins 118 are provided in the
exterior of cage 112 below windows 113. Cage 112 is made unitary
with underreamer body 137 and is provided with a central bore a
portion of which forms the cylinder 132 in which is slidably
mounted the piston 135 connected to a hollow piston rod 136 which
extends slidably through an opening 130 into a hollow box 138 into
which is screwed the shank of a rotary pilot bit 140.
A latching sleeve 120 carrying external enlargements 121 is
slidably disposed in the bore of cage 112 for axial movement
between an upper position (FIG. 14) releasing dogs 114 and a lower
position (FIG. 15) at which dogs 114 are held in projected
anchoring position in recess 115. Latching sleeve 120 is provided
with an internal latching groove 127 having the same function as
groove 27 of the previously described embodiment. Elongate hanger
bolts 150 having heads 151 extending slidably through perforate
ears 152 carried by the lower end of sleeve 20 and are secured to
piston 135.
Underreamer body 137 is provided with angularly spaced longitudinal
slots 146 for receiving underreamer cutters 145 which are mounted
on shafts 145a terminating in heads 147 mounted for pivotal
movement on pivot pins 148 which extend transversely of slots 146
(FIG. 17). Heads 147 are formed with angularly extending lever arms
149 which extend past the exterior of piston rod 136 and carry
crank pins 160 receivable in cam slots 161 formed in the adjacent
face of piston rod 136.
With this arrangement it will be seen that downward movement of
piston rod 136 to the position shown in FIG. 15 will swing
underreamer cutters 145 outwardly to their projected position.
Retraction of piston rod 136 to the position shown in FIG. 14 will
return the underreamer cutters to their retracted positions.
In this modification gage cutters 41 have been dispensed with, as a
pilot bit 140 is employed dimensioned to cut a bore to the gage of
body 137. It will be understood, however, that radial gage cutters
may be incorporated in the bit assembly as in the previously
described embodiment.
It will be understood that numerous other alterations and
modifications may be made in the details of the illustrative
embodiments within the scope of the appended claims but without
departing from the spirit of this invention.
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