Retrievable bridge plug

A retrievable bridge plug of the type having upper and lower anchors and an elastomeric packer for sealing a well casing. Drill string manipulation of the plug body effects packer compression and sealing. A ratchet maintains packer compression when engaged and permits packer expansion when disengaged. A cam surface on the plug body engages and disengages the ratchet responsive to longitudinal movement of the plug body.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to retrievable bridge plugs for use in sealing a 
casing in a well, and more particularly to such plugs of the type using an 
elastomeric packer to effect sealing. 
The bridge plug of the present invention is of the type having upper and 
lower anchors with the elastomeric packer positioned about a mandrel 
therebetween. Drill string manipulation is used to set the anchors and 
compress the packer thus sealing the casing at a selected location. 
Such plugs, when so set, can be subject to large hydraulic pressures from 
either below or above the plug. Even slight slippage of the anchors 
against the well casing can cause a reduction of the packer-compressing 
force and the seal formed by the packer may be lost. 
In the past, plugs have been provided with means for maintaining 
packer-compression force independent of that provided by the anchors. Such 
past plugs include ratchet mechanisms which are actuated by drill string 
manipulation and when so actuated, maintain the packer in a compressed 
condition. 
One such past ratchet mechanism is formed on facing radially inward and 
outward surfaces. Each ratchet surface is helically formed, in the manner 
of a screw thread. Disengaging the ratchet mechanism requires rotation of 
the drill string to unscrew it. Such rotation requires a tremendous amount 
of torque in view of the force required to properly set the packer. 
Another past mechanism uses a ratchet to maintain packer compression and a 
system of shear pins and retaining rings to relieve packer-deforming 
pressure as well as release the anchors. This permits only one setting of 
the plug, since if it is desired to reset the plug, it must be withdrawn 
and the rings reset with new shear pins. 
It is an object of the present invention to provide a retrievable bridge 
plug which overcomes the above-mentioned problems which exist in past 
plugs. 
It is a more specific object of the invention to provide a retrievable 
bridge plug in which an elastomeric packer can be set or released in 
response to longitudinal movement of the plug body. 
The instant embodiment of the invention includes a center mandrel having a 
packer mandrel concentrically mounted thereover. A packer carried about 
the packer mandrel, is compressed responsive to downward movement of the 
packer mandrel. Cooperating ratchet surfaces are provided about a portion 
of the packer mandrel and on the radially inward faces of collar segments 
which are fixedly disposed about the mandrel. A tang on the radial inward 
face of each collar segment extends through a longitudinal slot in the 
packer mandrel and contacts the center mandrel. The collar segments are 
all radially biased inwardly and each tang abuts against the center 
mandrel. A cam surface on the center mandrel causes radial inward and 
outward movement of the segments, dependent upon longitudinal center 
mandrel position, thus engaging and disengaging the ratchet surfaces. When 
engaged, the ratchet action between the two surfaces permits movement of 
the packer mandrel only in a packer-compressing direction. 
These and other attendant objects and advantages of the invention will 
become more apparent in view of the drawings and following detailed 
description of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawings, and particularly to FIGS. 1a-1d, a 
conventional retrieving head 10 is provided at the top of a preferred 
embodiment of the retrievable bridge plug of the invention. A lug 11 on 
retrieving head 10 cooperates with an overshot or running tool (not shown) 
mounted on the end of a drill string. As will later be more fully 
explained, the plug is suspended on the overshot from a drill string, 
lowered into a well casing (not shown), and by means of rotation and 
longitudinal movement of the drill string is set at a desired position in 
the casing to form a seal. 
Retrieving head 10 is fixedly secured to a center mandrel 12 by means of a 
key 14. Center mandrel 12 extends downwardly to a mandrel cap 17 (FIG. 
1d). The mandrel cap is attached to center mandrel 12 via a threaded 
connection 19 and dog 21. The dog is threaded into cap 17 and protrudes 
into a hole 23 in the center mandrel thus preventing relative rotation 
between mandrel cap 17 and center mandrel 12. A total of four dogs and 
holes, including dog 21 and hole 23, are positioned at 90.degree. 
intervals around the circumference of the plug. The center mandrel 
includes a bore 16 which extends from the bottom of the plug to just above 
a bypass port 18 which permits fluid communication between the top and 
bottom of the plug as it is being moved. A plurality of ports (not 
visible) are formed about the circumference of center mandrel 12 opposite 
port 18. 
Mounted over center mandrel 12 and concentric therewith is a packer mandrel 
20. Mandrel 20 is cylindrically shaped and is of a size suitable to permit 
longitudinal motion relative to the center mandrel. Mandrel 20 is fixedly 
secured to a cylindrical upper slip body 22 via a threaded connection 24. 
The upper portion of slip body 22 includes four inclined surfaces, like 
surface 29, which are formed at 90.degree. intervals about the 
circumference of the slip body. The uppor portion of slip body 22 includes 
a shoulder 23 formed about the circumference of the slip body. An undercut 
about the inner circumference of slip body 22 is provided, as shown, in 
which resides a seal 19 that is engaged about the circumference of mandrel 
12 and is held in place by a spacer 27. 
Indicated generally at 25 is what is referred to herein as upper anchor 
means. Included therein are carbide slips 26, 28, 30, such being suspended 
from a retainer 32. A fourth carbide slip (not visible) is suspended from 
retainer 32 at the rear of the plug, 180.degree. opposite slip 28. Slip 30 
includes a flat, inclined surface 34 which is in flush contact with 
surface 29 of slip body 22. A plurality of carbide disks, like disk 36 are 
mounted on the side of the slip. Each of the other four slips are 
identical in structure to slip 30. 
Retainer 32 is downwardly biased via spring 38. A spring centralizer 40 is 
generally cylindrically shaped and has a common axis with the center 
mandrel. The spring centralizer is threadably secured to retainer 32. 
Spring centralizer 40 includes des, about its circumference, a downwardly 
facing shoulder 42 which abuts against an upwardly facing shoulder 44 
formed about the circumference of center mandrel 12. Beneath shoulder 44 
on the center mandrel is a downwardly facing shoulder 45. Spring 38 is 
prevented from upward motion by means of a stop 46 on retrieving head 10 
which is fixedly secured to the center mandrel by key 14. Thus, spring 38 
is in a compressed condition between the stop and retainer 32 and is 
restrained from downward motion by shoulder 44. 
Indicated generally at 48 (in FIG. 1c) are what are referred to herein as 
lower anchor means. Included in lower the anchor means are six carbide 
slips, like slip 49. The slips are equally spaced about the circumference 
of the plug and each includes a plurality of carbide disks. Each slip 
includes a surface which is in flush contact with a lower slip body 50. 
Like the upper slip body, the lower slip body is generally cylindrically 
shaped except for the plane inclined surfaces against which the slips 
abut. 
Each of the carbide slips are attached at their lower end to a split ring 
collar 52 which is in turn attached, at its lower end, to a drag block 
assembly indicated generally at 54. Collar 52 is of conventional 
construction and extends about the circumference of the plug. 
Included within drag block assembly 54 is a drag block 58, springs 60, and 
a retainer 64. A drag block sleeve 56 is generally cylindrically shaped 
and is mounted over packer mandrel 20 concentric therewith. Drag block 58 
is spring biased outwardly from the sleeve by means of springs 60. A lip 
62, formed in the sleeve, and retainer 64 limit the radially-outward range 
of travel of the drag block. Retainer 64 is secured to the drag block 
sleeve by a bolt 71. Three other drag block assemblies, like assembly 54 
are similarly mounted at 90.degree. intervals about the drag block sleeve. 
The radially outward surface of each drag block is formed to create a 
selected, relatively high level of friction between the blocks and a 
casing into which the plug is lowered. 
A J-slot 66 is formed on the radially-inward surface of drag block sleeve 
56. A lug 68 extends from the radially-outward side of packer mandrel 20 
into the J-slot. The development of the J-slot and position of the lug is 
illustrated in FIG. 2. 
Beneath lug 68, a second J-slot 70 is formed in packer mandrel 20. A lug 72 
is mounted on the radially-outward surface of mandrel cap 17 and extends 
into slot 70. The development of J-slot 70 and the relationship of lug 72 
thereto is illustrated in FIG. 3. 
Each of the lug and J-slot combinations described above are symmetric with 
a second lug and J-slot combination (not visible) formed in the 
corresponding structure 180.degree. opposite the above-described lugs and 
slots. 
Turning now to FIG. 1c, lower slip body 50 is threadably secured to a 
ratchet cover 74. Cover 74 is substantially cylindrically shaped and is 
concentric with the plug axis. A cylindrical packer 76 extends about the 
circumference of mandrel 20 above cover 74. Packer 76 is formed from a 
conventional elastomeric material, and as later will be explained in the 
operation of the bridge plug, is compressible between cover 74 and lower 
shoe 75 and upper slip body 22 (acting through a disk-shaped upper shoe 
78). Mandrel 20 together with upper slip body 22 and shoes 75, 78 are 
referred to herein as packer compression means. 
Indicated generally at 80 in FIGS. 1c and 4, is packer compression locking 
means. Included therein are four collar segments spaced 90.degree. apart 
about mandrel 20, segments 82, 84 being the only two visible in the view 
of FIG. 1c. The segments are restrained from vertical movement by four 
windows, one window being associated with each segment, in slip body 50. 
Segment 82 is substantially contained within window 89. Each segment has a 
tang 86, 88 which extends therefrom through a slot 90, 92, respectively, 
in mandrel 20. Slot 90 includes a top 94 and a bottom 96. There are two 
other slots in mandrel 20 in addition to slots 90, 92, each of the four 
slots being spaced at 90.degree. intervals about the mandrel and each 
slot being substantially the same length and at the same vertical position 
as the others. 
Center mandrel 12, against which tangs 86, 88 abut, includes a sloping 
shoulder 98 which joins to a narrowed or cam portion 100. Ratchets 102 
(best seen in FIG. 5) are formed about the circumference of packer mandrel 
20 along substantially all the length of slots 90, 92. Ratchets 103 (FIG. 
5) are formed on the radially-inner side of each segment. All of the 
segments are radially biased inwardly by resilient bands 104 which extend 
about the circumference of both the collar segments and slip body 50. The 
bands are constrained within grooves, like groove 106 (FIG. 1c) in segment 
84, in each of the segments. 
As can be best viewed in FIG. 4, bands 104 encircle the segments (as well 
as the intervening portions of slip body 50). Each intervening segment of 
slip body 50 has a groove, like groove 108, to restrain movement of band 
104 and to permit necessary radially-inward movement of the band. 
OPERATION 
When it is desired to plug the well casing at a selected location, the 
bridge plug is suspended on the end of a drill string from a conventional 
overshot or running tool which cooperates with lug 11 on retrieving head 
10. During the running-in process, the movable elements of the plug are in 
the positions illustrated in FIGS. 1a-1d. The upper carbide slips 26, 28, 
30 (and one not visible) are in their most radially-inward position as 
shown. Likewise, all of the lower carbide slips are in the same 
(contracted) position. Ratchets 103 on each of the four collar segments, 
two of which being 80, 82, are in a disengaged condition with respect to 
ratchets 102 on mandrel 20. As can be seen in FIGS. 4 and 5, the four 
tangs, including tangs 86, 88, on each of the collar segments are in 
contact with center mandrel 12 at the position shown in FIG. 1c and thus 
maintain the collar segments radially-outwardly spaced to the point where 
ratchets 102, 103 are not in contact. Thus, packer mandrel 20 is free for 
longitudinal movement in either direction. Lugs 68, 72 on packer mandrel 
20 and mandrel cap 17, respectively, are positioned in their associated 
J-slots as shown in FIG. 1d and in solid-line figures in FIGS. 2 and 3. 
During the running-in process, fluid flows upwardly through center mandrel 
12 in bore 16, exiting the bore through bypass port 18 and through the 
opposing bypass bore (not visible). When the location at which the plug is 
to be set is reached, the running-in process is stopped and the drill 
string is lifted a short distance. Since the drill string is coupled 
directly to center mandrel 12 via retrieving head 10, such lifting moves 
lugs 68, 72 upwardly in J-slots 66, 70, respectively. Drag block 58 is 
biased outwardly by springs 60 and is pressed against the well casing. 
Thus, when the lifting occurs the drag block remains stationary at least 
until lug 68 is moved to its uppermost position in the slot. After the 
short upward movement, left-hand rotation (with reference to a view 
directly down the casing) is applied to the drill string. Thus, each of 
the lugs are moved to the right (with reference to the view in FIGS. 2 and 
3), in position for movement down the length of each slot. 
With the continued application of left-hand rotation, the drill string is 
moved downwardly thus moving the lugs down the length of each slot and 
ultimately to the dashed-line positions illustrated in FIGS. 2 and 3. It 
is to be appreciated that the lugs and associated structure (not visible) 
located 180.degree. about the plug from lugs 68, 72 are moving in a 
similar complimentary fashion. Since the drag blocks are in frictional 
engagement with the casing, the drag blocks remain stationary with respect 
to packer mandrel 20 and center mandrel 12 at least until each of the lugs 
is at its lowermost position in its associated slot. During downward 
travel of the lugs in their slots, the lower carbide slips, one of which 
is slip 49, are forced outwardly by virtue of the downward movement of 
slip body 50 with respect to the carbide slips (the carbide slips being 
held at their vertical location through split ring collar 52, by the 
above-described action of the drag blocks). As the slips move outward, the 
carbide disks on each slip grab the well casing and prevent further 
downward movement of lower body slip 50 and of body slip mandrel 74. 
As the drill string continues its downward travel, center mandrel 12 
likewise continues its longitudinal downward motion with respect to the 
anchored portion of the plug. As can be seen in FIG. 1b, such further 
downward motion moves shoulder 44 on the center mandrel downward with 
respect to shoulder 42 on spring centralizer 40. This action permits the 
compressive force in the spring to move retainer 32 downwardly thus 
setting carbide slips 26, 28, 30 and the fourth slip (not visible). 
Downward movement of the retainer causes the carbide slips to move 
outwardly along the inclined surfaces, like surface 29, of upper slip body 
22. Such outward movement permits each of the carbide disks on the slips 
to bite into the well casing and thus prevents upward movement. 
During the downward movement of the plug body, the bypass ports (port 18 
being one) move beneath seal 19 thus preventing fluid from passing into or 
out of bore 16 via either port. At the same time, shoulder 45 moves 
downwardly and abuts shoulder 23 on slip body 22. The action of shoulder 
45 against shoulder 23 moves slip body 22, upper shoe 78 and packer 
mandrel 20 downwardly. Since ratchet cover 74 and lower shoe 75 are 
anchored due to the action of the lower carbide slips, packer 76 deforms 
due to the action of the lower carbide slips, packer 76 deforms into 
sealing engagement with the casing. 
Also during downward movement of center mandrel 12, narrowed portion 100 of 
the mandrel moves to the level of collar segments 82, 84. Since all of the 
collar segments are radially biased inward by virtue of bands 104, each of 
the segments "rides" on their associated tangs down shoulder 98 until 
ratchets 103 on the radially inward side of each segment engage with 
ratchets 102 on packer mandrel 20. In view of FIG. 5, ratchets 102, 103 
move together so that their complimentary surfaces are in contact with 
each other. Such engagement prevents any upward movement by the mandrel 
since the segments are restrained from vertical movement in their 
respective windows in slip body 50. The ratchet action does, however, 
permit downward movement of packer mandrel 20 and such continues until 
packer 76 completely seals the casing. 
At this point the plug is set and the drill string can be lifted since the 
leftward rotation which set the plug likewise disconnected the 
conventional overshot from retrieving head 10. If high pressures from 
either above or below the plug should cause any slippage of the upper or 
lower carbide slips, the seal will not break because the ratchets maintain 
packer mandrel 20 in a compressed condition. 
When it is desired to retrieve the plug, the drill string and overshot are 
run in and set on to retrieving head 10. Right-hand rotation of the drill 
string engages the head with the overshot as well as moving lug 72 (in 
FIG. 3) into position for upward longitudinal movement in its J-slot. 
After the right-hand rotation, the drill string is moved upward, 
disengaging the plug as follows: center mandrel 12 again moves into the 
position illustrated in FIGS. 1a-1d thus forcing the collar segment tangs 
up shoulder 98 and disengaging ratchets 102, 103 from each other. Shoulder 
44 (in FIG. 1b) moves upwardly, and lifts spring centralizer 40 by way of 
upward action against shoulder 42. When retainer 32 is lifted by such 
action, all of the upper carbide slips disengage and return to the 
position illustrated in FIG. 1b. The packer decompresses because shoulder 
45 moves upwardly thus releasing the downward force applied to the packer 
via slip body 22 on shoulder 23. Packer mandrel 20 is free to move upward 
because of the above-described disengagement of ratchets 102, 103 caused 
by upward travel of center mandrel 12. Thus, after disengagement, the 
bridge plug resumes the positional configuration shown in FIGS 1a-1d and 
may be run out of the casing on the drill string. 
While the invention has been particularly shown and described with 
reference to the foregoing preferred embodiment, it will be understood by 
those skilled in the art that other changes in form or detail may be made 
therein without departing from the spirit and scope of the invention as 
clarified in the appended claims.