US3363695A

US3363695A - Hydraulic anchor

Info

Publication number: US3363695A
Application number: US506664A
Authority: US
Inventors: Howard L Mcgill
Original assignee: Schlumberger Well Surveying Corp
Current assignee: Schlumberger Well Surveying Corp
Priority date: 1965-11-08
Filing date: 1965-11-08
Publication date: 1968-01-16
Anticipated expiration: 1985-01-16

Description

Jan. 16, 1968 H. L. MOGILL 3,363,695

HYDRAULIC ANCHOR Filed Nov. 8, 1965 2 Sheets-Sheet l Howard Z. We 6/// INVENTOR.

ATTO/P/V Filed Nov.

H. 1.. M GILL 3,363,695

HYDRAULIC ANCHOR 2 Sheets-Sheet 2 J m L 57 43 Howard 1. Mr

INVENTOR. 45

United States Patent 3,363,695 HYDRAULIC ANCHOR Howard L. McGill, Houston, Tex., assignor to Schlumberger Well Surveying Corporation, Houston, Tex, a corporation of Texas Filed Nov. 8, 1965, Ser. No. 506,664 13 Claims. (Cl. 166120) ABSTRACT OF THE DISCLOSURE As one embodiment of the invention disclosed herein, a pressure-responsive anchor is coupled to a well packer that is adapted for actuation by movement of a tubing string. Selectively-operable valve means are arranged for actuation by movement of the tubing string so that until the packer is set, the anchor is isolated from actuating fluid pressures. Once the packer is set, however, the valve means are opened to admit fluid pressures in the tubing string to the anchor.

Accordingly, as will subsequently become apparent, this invention relates to apparatus adapted for anchoring a well tool in place within the well bore; and, more particularly, to hydraulically actuated anchors which are normally disabled and selectively actuatable to be secured against hydraulic pressures in the well by an anchoring force proportionately related to the acting pressure.

In conducting such well-completion operations as acidizing, cementing, or fracturing, a full-opening Well packer dependently coupled from a tubing string is positioned at a particular depth in a cased well and the packer set to isolate the formation interval to be treated from the remainder of the Well bore thereabove. Treating fluids are then pumped downwardly at high pressure through the tubing and full-bore packer and introduced into the formation being treated through perforations appropriately located in the casing.

It will be appreciated that after the packer is set, whatever fluids there may be in the tubing string ahead of the treating fluid will be displaced therefrom by the treating fluids. With the packer set, these fluids must, of course, be forced into the formation ahead of the treating fluids. Accordingly, in a typical cementing operation, for example, it is customary to fill as much as practical of the tubing string with cement before the packer is set to minimize the volume of unwanted fluids that would otherwise be displaced into the formation. To accomplish this, the tubing string is filled to within a few hundreds of feet above the retracted packer and pressure is applied to the well annulus to maintain the cement up within the tubing. Then, by careful coordination, the packer is set at a predetermined depth as the pressure in the annulus above the packer is reduced and pressure applied to the tubing string to force the cement downwardly at high pressure. By carefully controlling the sequence of these operations, the cement is hopefully discharged from the lower end of the tubing below the packer almost immediately after the packer has been firmly set. In this manner, the volume of unwanted fluids in the tubing string that must be displaced into the formation ahead of the cement is held to a minimum.

Once the packer is set, it will be recognized that it will be subjected to a high, upwardly directed pressure ditlerential from the cement and must, therefore, be securely anchored against upward movement. Heretofore, it has been customary to employ movable anchoring members which are hydraulically extended against the casing by the fluid passing through the tubing to secure the packer against such upward movement.

Typical of such anchors is the one described in Patent No. 2,792,063. Although anchors such as this are being successfully employed in these completion operations, it is recognized that they can be prematurely actuated before the packer has been fully set. For example, in a cementing operation as just described, as the column of cement is first pumped downwardly, its greater density can cause the anchoring elements to extend before the packer has been firmly set. Although such anchoring elements are typically arranged to prevent only upward movement of the tubing string, they can, however, engage the casing wall with such force that further downward travel of the string will be either retarded or totally halted. Should this occur, it is quite possible that suflicient downward travel of the tubing string will not be obtained to fully set the packer. Obviously, unless the packer is fully set, it will be incapable of providing a fluid-tight seal; and is very likely that cement will flow up around the packer element and result in an inadequate cementing job.

Accordingly, it is an object of the present invention to provide new and improved anchoring apparatus for well packers, which apparatus has hydraulically actuated wall-engaging members that are normally disabled and selectively releasable only after the packer is firmly set for anchoring engagement with a well bore with a force proportionately related to the pressure of fluids in the tubing.

This and other objects of the present invention are attained by providing a well packer that is operated in response to a force through the tubing string for packing off a Well bore with anchoring means that are responsive to fluid pressure to secure the packer to the wall of the well bore and means for selectively applying such fluid pressure to the anchoring means in response to a greater force on the tubing string to secure the packer only after the well bore has been packed-off.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation together with further objects and advantages thereof, may best be understood by way of illustration and example of a certain embodiment when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view of a full-bore packer having an anchor thereon employing principles of the present invention and depicted as they would appear within a well bore;

FIG. 2 is a detailed cross-sectional view in elevation of the anchor depicted in FIG. 1 in its retracted position;

FIG. 3 is a cross-sectional view taken along the lines 3-3 of FIG. 2; and

FIG. 4 is a view similar to FIG. 2, but showing the anchor as it will appear when anchoringly engaged.

As seen in FIG. 1, a typical so-called compressionset full-bore packer 10 is dependently connected in a tubing string 11 and positioned within a well bore 12 having a casing 13 set therein and secured by a column of cement 14. A hold-down or anchor 15 incorporating the principles of the present invention is serially coupled between the upper end of the tubular mandrel 16 of the full-bore packer 10 and the lower end of a typical valve 17, which is, in turn, connected to the lower end of the tubing spring 11. As is conventional in the art, the bypass valve 17 is opened to divert some of the fluids therein through the central bore 18 of the packer mandrel 16 whenever the full-bore packer 10 is being shifted 3 within a fluid-filled well. After the packer has been set, the bypass valve 17 is, of course, closed to prevent fluid communication between the tubing string 11 and the well annulus above the sealingly engaged packer.

The typical full-bore packer 10 shown in FIG. 1 includes a tubular housing 19 through which the mandrel 16 is slidably disposed. An elastomeric packing element 20 is mounted above the housing shoulder 21 and a slidably disposed slip bowl 22 on the mandrel 16. Normally retracted slip members 23 are operatively mounted around the housing 19 and cooperatively engaged with the slip bowl 22 in the well-known manner. Conventional drag blocks 24 are arranged to secure the housing 19 to the casing 13 as the mandrel 16 is manipulated relative to the housing to extend the packing means 20 and slips 23 against the casing. A system of conventionally arranged so-callcd Jslots and J-pins (not shown) selectively latch the mandrel 16 relative to the housing 19 to keep the packer 10 retracted.

Accordingly, when the packer 10 is to be set, the tubing string 11 is picked up slightly and then manipulated as required by the arrangement of ]-slots to free the mandrel 16 for downward travel. As the mandrel 16 is lowered, the drag blocks 24 restrain the housing 19 against downward movement as the mandrel successively drives the slip bowl 22 downwardly to extend the slips 23 and foreshortens the packing means 20. By the time the mandrel 16 has reached its lower limit of travel, the slips 23 will be engaged against the casing 13 and the packing means 20 displaced into sealing engagement therewith. To ensure that the packing means 20 are fully displaced, at least part of the weight of the tubing string 11 is slackedoff to impose a substantial downward force through the packer mandrel 16 and shoulder 21 to the packing element. It will be appreciated of course that, once set, the slips 23 will prevent the packer 16 from. being moved further downwardly within the casing 13 by such downward forces. It should also be noted that the bypass valve 17 is typically arranged to be closed as the packer 10' is being set. Thus, once the packer 10 is set, the bypass valve 17 will also be closed and block fluid communication from below the packer and the annulus above the packer.

As will be subsequently explained, a self-contained hydraulic system within the anchor is arranged to operatively actuate the anchor in response to a pressure below the packing means that is greater than that above. Thus, whenever the bypass valve 17 is closed and the packing means 20 set, an increased pressure below the packer 10 will be elfective to anchoringly engage the anchor 15 with the casing 13 to secure the packer mandrel 16 against upward shifting.

Turning now to FIG. 2, the anchor 15 is comprised of a tubular mandrel 25 having anchoring means 26 around the upper portion and its lower portion telescopically received within and extending substantially through a tubular housing 27 to define an annular space 28 between the two members. Coupling means, such as threads 29 and 30, are provided at the upper and lower ends of the mandrel 25 and housing 27, respectively, for coupling the anchor 15 into a string of tools as shown in FIG. 1. A longitudinal bore 31 of uniform diameter extends through the mandrel 25.

A central portion 32 of the mandrel 25 is enlarged and fluidly sealed within the upper end of the housing 27 by an O-ring 33. To limit the downward travel of the mandrel 25 relative to the housing 27, shoulder 34 is provided by the upper end of the housing and normally spaced below an external mandrel shoulder 35. Complementary splines and grooves, as at 36, on the mandrel 25 and in an internal housing shoulder 37 co-rotatively secure the members to one another. An external mandrel shoulder 38 spaced below the splines and grooves 36 is adapted to engage the lower face of housing shoulder 37 to limit the upward travel of the mandrel 25.

The mandrel 25 is normally supported in an elevated position (as seen in FIG. 2) relative to the housing 27 by an exceptionally heavy compression spring 39 confined within the annular space 28 and engaged between the lower face of the mandrel shoulder 38 and a retaining ring 41) resting on an internal housing shoulder 41 therebelow. A second and much weaker compression spring 42 is also arranged within the annular space 28 and engaged between the retaining ring 46 and the upper face of an annular floating piston member 43 that is fluidly sealed to the mandrel 25 and housing 27 by O-rings 44 and 4 5.

The anchoring means 15 mounted around the upper portion of the mandrel 25 are comprised of an expansible elastomeric sleeve 46 encircling the mandrel and a plurality of elongated wall-engaging

members

47 and 48 mounted longitudinally and spaced uniformly around the periphery of the sleeve. The enlarged upper and lower ends 49 and 5% of the elastomeric sleeve 46 are secured by slidable

annular retainers

51 and 52 within opposed

peripheral recesses

53 and 54 around the mandrel 25. 0-

rings

55 and 56 fluidly seal the sleeve ends 49 and 51) within the

recesses

53 and 54 to provide a fluid-tight space 57 between the sleeve 46 and mandrel 25.

Each of the casing-engaging

members

47 and 48 is elongated and has a thick, arcuate cross-section (FIG. 3). Alternate ones 47 of the casing-engaging members are centrally aligned and mounted on the outer convex surface of relatively thin, elongated, arcuate backing members 58. A suflicient number of these mounted members 47 are disposed uniformly around the periphery of the elastomeric sleeve 46 that the backing members 58 substantially encompass the sleeve. The remaining casingengaging members 48 are unmounted and alternately disposed between the mounted casing-engaging members 47 in such a manner that the unmounted members 48 straddle adjacent backing members 58 and cover the gaps 59 therebetween.

The ends of the

casingengaging members

47 and 43 are beveled, as 60 (FIG. 2), for reception within the opposed annular mandrel recesses 53 and 54.

Springs

61 and 62 are operatively engaged at opposite ends of each of the

members

47 and 48 to bias the members inwardly. It will be appreciated, therefore, that although the

casingengaging members

47 and 4 8 will be moved radially outwardly against the

springs

61 and 62 whenever the elastomeric sleeve 46 is inflated, the beveled ends of the members cannot escape from the mandrel recesses 53 and 54.

Turning now to the hydraulic actuating means of the anchor 15. The fluid-tight space 57 between the elastomeric sleeve 46 and mandrel 25 is connected, by way of a longitudinal passage 63 through the enlarged mandrel portion 32, to the upper end of the annular space 64 below the O-ring 33 and above the upper housing shoulder 37. Although there is fluid communication through the clearance between the splines and grooves 36, an O-ring 65 around the lower portion of the upper housing shoulder 37 fluidly seals the housing 27 relative to the mandrel 25 at this point to prevent fluid communication into the annular space 28 therebelow.

Thus, it will be appreciated that so long as the mandrel 25 is elevated with respect to the housing 27 as illustrated in FIG. 2-, the O-ring 65 prevents fluid communication between the two

annular spaces

64 and 28 respectively above and below the O-ring 65. The hydraulic system is, therefore, divided into upper 66 and lower 67 portions. The upper fluid-tight portion 65 is comprised of the fluidtight space 57 inside of the elastomeric sleeve 46, the longitudinal passage 63 and the upper annular space 64 between O-

rings

33 and 65; and the lower hydraulic portion 67 is comprised of the intermediate portion of the annular space 28 below the O-ring 65 and above the annular piston member 43. To provide means for selectively controlling communication between the two above-described

portions

66 and 67 of the hydraulic system, the mandrel 25 is slightly reduced in diameter, as at 68, im-

mediately above where it is sealingly engaged with O-ring 65 whenever the mandrel is elevated.

Accordingly, whenever the fiuid-tight

hydraulic portions

66 and 67 are filled with a suitable hydraulic tluid through conveniently located filling ports (not shown), it will be understood that there is no fluid communication therebetween so long as the mandrel 25 remains in its elevated position (FIG. 2) relative to the housing 27. When, however, the mandrel 25 is shifted downwardly relative to the housing 27, communication will be established between the two fluid-tilled

portions

66 and 67 whenever the reduced mandrel portion 68 is shifted below the O-ring 65 a suflicient distance to permit hydraulic fluid to pass between the O-ring 65 and mandrel.

Thus, by shifting the mandrel 25 downwardly relative to the housing 27, it will be understood that whatever pressure is acting within the lowermost portion of the annular space 28 below the piston 43 will urge the piston upwardly to develop a corresponding hydraulic pressure throughout both of the

hydraulic system portions

66 and 67 and, most particularly, in the fluid-tight space 57 under the elastomeric sleeve 46. The pressure below the annular piston 43 is, of course, the same as that within the tubing string 11 in view of the clearance 69 at the lower end of the mandrel 25 and housing 27. Moreover, it will be appreciated that whenever the packer is set, the pressure in the tubing string 11 and below the packer will be actmg upwardly on the piston 43 and the hydrostatic pressure above the packer will be acting inwardly on the elastomeric sleeve 46.

Turning now to the operational relationship of the anchor 15 and the full-bore packer 10. When the string of tools shown in FIG. 1 are being positioned in a well bore, the heavy spring 39 will hold the mandrel elevated relative to the housing 27 and the full-bore packer 10. It will be appreciated therefore, that before the packer 10 has been set, the upper portion 66 of the hydraulic system will be closed-oil from the lower portion 67 by the sealing engagement of O-ring 65 with the mandrel 25. The hydraulic pressure in each of the

portions

66 and 67 of the hydraulic system will, however, be substantially equal to the hydrostatic pressure of the fluids in the well since both the expansible sleeve 46 and annular piston 43 will be exposed thereto. Inasmuch as the pressures inside and outside of the sleeve 46 are substantially equal, the casing-engaging

members

47 and 48 will be held by

springs

61 and 62 in their retracted positions as shown in FIG. 2.

To set the packer 10, the weight of the tubing string 11 is gradually slacked-off in the usual manner to move the anchor 15 and packer mandrel 16 downwardly relative to the packer housing 19 which is frictionally secured relative to the casing 13 by the drag blocks 24. It will be realized, however, that so long as the heavy spring 43 is not fully compressed, it will support the slacked-oit weight of the tubing string 11 and the anchor mandrel 25 can move downwardly with respect to the housing 27 only as the spring 43 contracts. Nevertheless, a downward force equivalent to this slacked-off weight will, of course, be transmitted by the spring 43 to the packer mandrel 16. Then, once the

shoulders

34 and 35 are engaged, the slacked-oit weight of the tubing string 11 will be transmitted directly from the mandrel 25 through these shoulders to the anchor housing 27 and packer mandrel 16. Thus, although an effective downward force equivalent to the amount of slacked-oif weight is continually applied to the packer mandrel 16, the anchor mandrel 25 is delayed from shifting relative to the anchor housing 27 until sufficient weight has been slacked-ofl to begin compressing the heavy spring 39. It will be recalled, of course, that so long as the anchor mandrel 25 has not shifted sufliciently for the reduced mandrel portion 68 to move under the O-ring 65, the two

portions

66 and 67 of the hydraulic system will remain isolated from one another.

Accordingly, it will be appreciated that by selecting a heavy spring 39 that is sufliciently strong to keep the mandrel 25 substantially elevated until enough weight has been slacked-ofi to displace the packer element 20 against the casing 13, the anchor 15 will be disabled until the packer 10 is sealingly engaged with the casing. Then, whenever sufiicient weight has been slacked-ofi on the tubing string 11 to compress the heavy spring 39, the anchor mandrel 25 will move downwardly relative to the anchor housing 27 a sufficient distance to bring the reduced mandrel portion 68 into register with the O-ring 65. Once this occurs, fluid communication is established between the two

portions

66 and 67 of the hydraulic system so as to enable the pressure within the anchor mandrel bore 31 to develop a corresponding hydraulic pressure therein. Whenever the pressure within the mandrel bore 31 is increased above the hydrostatic pressure of the well annulus, the annular piston 43 will be urged upwardly and develop a hydraulic pressure equal to the tubing pressure less whatever pressure is required to overcome the lighter spring 42.

It will be seen, therefore, that the anchor 15 is positively disabled until enough weight of the tubing string 11 has been applied on the packer mandrel 25 to sealingly engage the packing element 20 with the casing 13. Thus, for example, should a column of cement in the tubing string 11 develop a sufficient hydrostatic pressure within the mandrel bore 31 that would otherwise be suflicient to actuate a typical hydraulic anchor, the casing-engaging

members

47 and 46 will be maintained in a fully retracted position until a substantial force has been imparted to the packer mandrel 16. Once, however, the casing-engaging

members

47 and 48 have been urged into anchoring engagement with the adjacent casing 13, it will be appreciated that they will be continually pressed against the casing with the force that is proportionately related to the pressure differential between the internal mandrel bore 31 and the well annulus at any given moment.

To release the anchor 15, it is necessary only to pick up the tubing string 11 to open the bypass valve 17 and thereby relieve any pressure difiterential across the packing element 20. Once this pressure differential is relieved, the lighter spring 42 will return the piston member 43 to its initial position to relieve the pressure within the hydraulic system and permit the springs 61 and '62 to retract the casing-engaging

members

47 and 48. Further upward movement of the tubing string 11 will return the anchor mandrel 25 to its original positionand, once the mandrel shoulder 38 has engaged the housing shoulder 37, the packer mandrel 16 can be pulled upwardly to retract the slips 23 and packing element 20.

As the

tools

16, 15 and 17 are being retrieved from the well bore 12, it will be appreciated that the hydrostatic pressure acting on the exterior of the expansible sleeve 46 will begin decreasing as the tubing string 11 is pulled further up the well bore. Since the upper portion 66 of the hydraulic system is now isolated by O-ring 65 from the lower portion 67 of the hydraulic system, the hydraulic pressure in the upper portion 66 of the hydraulic system will remain essentially at the hydrostatic pressure at the depth where the packer 10 was set. Thus, to prevent this entrapped pressure from re-extending the casing-engaging

members

46 and 47, a relief valve, such as that shown at 76, is arranged to bleed-off any excess pressure from the upper portion 66 of the hydraulic system to its lower portion 67.

Accordingly, it will be appreciated that the present invention has provided a new and improved anchoring means that is capable of being selectively disabled to permit application of a substantial force to first set the packer without possible restraint from the anchoring means. Then, when suificient force has been applied to insure the packer has become sealingly engaged, the anchor is made operatively responsive to an increased pressure differential from below the packer to anchoringly secure the packer mandrel against the casing with the force proportionately related to this pressure differential.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspect; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus for packing-01f a well bore comprising: means for packing-01f a well bore including a tubular housing member, a body member telescopically received in said housing member and movable with respect thereto between an expanded position and a contracted position, and expansible packing means operatively disposed between said members and expandable in response to movement of said body member toward said contracted position for packing-off the well bore; anchoring means on said body member and responsive to fluid pressure for anchoring said body member to the wall of a well bore; first means connecting said body member to a tubing string and responsive to a first force on the tubing string for moving said body member toward said contracted position; and second means responsive to a second greater force on the tubing string for admitting fluid pressure in the tubing string to said anchoring means to secure said body member in said contracted position.

2. The apparatus of claim 1 wherein said first means includes spring means cooperatively engaged between said body member and tubing string.

3. The apparatus of claim 1 wherein said second means includes fluid passage means; between said anchoring means and tubing string and normally-closed valve means responsive to movement of said body member into said contracted position for opening fluid communication through said passage means.

4. The apparatus of claim 3 wherein said first means includes spring means cooperatively engaged between said body member and tubing string.

5. The apparatus of claim 1 wherein said first means comprises a tubular body telescopically arranged relative to said body member and adapted for connection to a tubing string, and spring means normally urging said body and body member apart, said spring means being yieldable in response to aid first force to urge said body member toward said contracted position.

6. The apparatus of claim 1 wherein said first means comprises a tubular body telescopically arranged relative to said body member and adapted for connection to a tubing string, and spring means normally urging said body and body member apart, said spring means being yieldable in response to said first force to urge said body member toward said contracted position; and said second means comprises fluid passage means between said anchoring means and tubing string, and normally-closed valve means on said tubular body and responsive to movement thereof as said body member is urged into said contracted position for opening fluid communication through said passage means.

7. The apparatus of claim 1 wherein said first means comprises a tubular body telescopically arranged relative to said body member and adapted for connection to a tubing string, and spring means normally urging said body and body member apart, said spring means being yield able in response to said first force to urge said body member toward said contracted position; means including a floating piston member defining an enclosed piston chamber between said body and body member, and a hydraulic fluid in said chamber; and said second means comprises first fluid passage means communicating fluid pressure within the tubing string to said piston member for developing a hydraulic pressure in said piston chamber related to the tubing string pressure, second fluid passage means between said piston chamber and anchoring means, normally-closed valve means on said tubular body and responsive to movement thereof as said body member is urged into said contracted position for opening fluid communication between said piston chamber and anchoring means.

8. As a sub-combination, apparatus comprising: a tubular housing member adapted for connection to a well packer; a tubular body member telescopically arranged with said housing member and adapted for connection to a tubing string; anchoring means on one of said members and including wall-engaging means extendible in response to fluid pressure; spring means normally urging said members apart and yieldable in response to a force on said body member to allow said body member to move to a contracted position relative to said housing member; and means for selectively cont-rolling pressure communication between said tubing string and anchoring means, said controlling means being operable whenever said body member reaches said contracted position.

9. The apparatus of claim 8 further comprising means including a floating piston member defining an enclosed piston chamber between said housing and body members, and a hydraulic fluid in said chamber; and said pressurecontrolling means comprises first fluid passage means adapted to communicate fluid pressure within said body member to said piston member for developing a hydraulic pressure in said piston chamber related to such fluid pres sure, second fluid passage means between said piston chamber and anchoring means, and normally-closed valve means on said body member and responsive to movement thereof into said contracted position for opening fluid communication between said piston chamber and anchoring means.

10. Apparatus adapted for connection to a tubing string and comprising: means for packing-off a well bore; anchoring means connected to said packing-01f means and responsive to fluid pressure for securing the tubing string to the well bore; and means for selectively admitting fluid pressure to said anchoring means including telescoping members movable in response to movement of the tubing string between a first position isolating said anchoring means from fluid pressure in the tubing string and a second position where said anchoring means is responsive to pressure in the tubing string for securing the tubing string.

11. The apparatus of claim 10 wherein said packingofi means is selectively actuatable in response to movement of the tubing string and further including delay means for retarding movement of said telescoping members from said first position to said second position until said packing-01f means is actuated.

12. The apparatus of claim 10 wherein said pressureadmitting means further includes piston means defining a closed hydraulic system between said telescoping members, first passage means providing fluid communication between said piston means and tubing string, second passage means providing fluid communication between said hydraulic system and anchoring means, and means on said telescoping members for opening fluid communication through one of said passage means as said telescoping members move to said second position.

13. The apparatus of claim 12 wherein said packing-off means is selectively actuatable in response to movement of the tubing string and further including delay means for retarding movement of said telescoping members from said first position to said second position until said packing-off means is actuated.

References Cited UNITED STATES PATENTS 2,854,080 9/1958 Dale et al 166-140 3,094,169 6/1963 Conrad 166-134 3,283,824 11/1966 Hoffman et al. 166-212 3,306,360 2/1967 Young 166-120 3,306,361 2/1967 Lebourg 166-122 ERNEST R. PURSER, Primary Examiner.

DAVID H. BROWN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,363,695 January 16, 1968 Howard L. McGill It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification,

lines

3 and 4 for "assignor to Schlumbeger Well Surveying Corporation" read assignor, by mesne assignments, to Schlumberger Technology Corporation column 1, line 61, after "lower" insert open Signed and sealed this 1st day of April 1969.

SEAL) nttesti dward M. Fletcher, Jr.

Ittesting Officer EDWARD J. BRENNER Commissioner of Patents