WO1992013170A1

WO1992013170A1 - Shear ram apparatus

Info

Publication number: WO1992013170A1
Application number: PCT/US1992/000449
Authority: WO
Inventors: Denzil B. Smith; David L. O'donnell
Original assignee: Baroid Technology Inc
Current assignee: Baroid Technology Inc
Priority date: 1991-01-25
Filing date: 1992-01-17
Publication date: 1992-08-06
Anticipated expiration: 1993-07-25
Also published as: DE4290105T1; GB2257733A; GB9220054D0; CA2079001A1; NO923717L; NO923717D0

Abstract

The present invention is directed to shear ram blowout preventer apparatus for severing and sealing about borehole retrievables, particularly about flexible lines, multi-strand cables. The present invention provides an improved shear ram apparatus including keys (64) and cooperating retainer slots (60) for preventing relative longitudinal movement of the blade member (40) and anvil formation (80) carried on opposable ram assemblies (20, 70) when those assemblies are moved laterally inwardly to their shearing or closed position. In a preferred embodiment the shear ram apparatus of the present invention includes a plurality of keys (64) extending inwardly from the inward face of a first shear ram assembly (70) for cooperation with a plurality of slots (60) on the inward face of a second shear ram assembly (20) wherein the keys (64) engage the slots (60), thus preventing relatively longitudinal movement, particularly separation, before contact of the blade member (40) and anvil formation (80).

Description

SHEAR RAM APPARATUS

Background of the Invention

1. Field of the Invention

The present invention generally relates to shear ram apparatus for use in blowout f preventers used for sealing off oil and gas wells during emergency situations in order to i

5 contain dangerous blowouts. More specifically, the present invention is directed to shear ram apparatus for severing and sealing about a variety of borehole retrievables, more particularly,

flexible lines, and most particularly, multi-strand cable and the like which is often not severed by conventional shear ram apparatus.

2. Description of the Background

10 Several different general types of blowout preventers are known in the art. One of these is the ram type blowout preventer which typically includes a housing having a throughway for the drill pipe. First and second ram assemblies are mounted in the housing

on opposite sides of the throughway. These assemblies are reciprocated laterally inwardly and outwardly, i.e., toward and away from each other. These assemblies are moved

15 inwardly to close the blowout preventer when it becomes necessary to seal off the well.

Ram type blowout preventers are further subdivided into various types. One type is commonly referred to as the pipe ram. In this type of apparatus, the ram assemblies, when moved laterally inwardly to the closed position, simply seal about the outer diameter of the drill pipe, thereby sealing off the annulus between the drill pipe and the walls of the well

20 bore. Exemplary prior pipe ram assemblies are disclosed in U.S. Patent No. 3,434,729. A second ram type blowout preventer is commonly referred to as a shear ram. In this type, the ram assemblies, when reciprocated inwardly, actual sever the drill pipe and subsequently

_* seal against each other in such a way that both the drill pipe itself and the surrounding annulus are sealed off in the sense that the closed shear ram prevents communication from the space below to the space above the blowout preventer. Exemplary shear ram assemblies are disclosed in U.S. Patents Nos. 3,736,982, 4,081,027 and 4,540,046, the disclosures and

drawings of which are incorporated herein by reference. Both pipe rams and shear rams are typically included in a complete blowout preventer stack. The shear ram apparatus disclosed in the above patents were intended to sever and

seal about conventional drill pipe. Rigid, conventional drill pipe is readily severed by the lateral movement of the blade and anvil of the opposed ram assemblies. However, conventional shear ram assemblies have been less successfully used to sever and seal about more flexible lines. In fact, conventional shear ram assemblies have been particularly ineffective in severing and sealing about multi-strand cable which tends to separate and spread out across the blade-anvil interface rather than being neatly severed. Once separated

and spread out, multi-strand cable tends to fold over, causing relative longitudinal movement of the opposed blade and anvil. This movement causes the blade and anvil to ride over each other on the spread out cable resulting in failure to cleanly and completely sever and seal the multi-strand cable. For this reason, the described, conventional shear ram apparatus is inappropriate for use with many borehole retrievables, particularly flexible lines such as coil tubing, slicMines, wirelines and cables, most particularly with multi-strand cables. Accordingly, there has been a long felt but unfulfilled need in the oil and gas industry for improved shear ram apparatus capable of cleanly severing and sealing about flexible lines and, particularly, multi-strand cable. Summary of the Invention

The present invention is directed to shear ram apparatus for severing and sealing about borehole retrievables, particularly about flexible lines, and most particularly about multi-strand cable. The present invention provides an improved shear ram apparatus including means for preventing relative longitudinal movement of the blade member and anvil carried on opposable ram assemblies when those assembles are moved laterally inwardly to

their shearing or closed position. Shear ram apparatus in accord with the present invention offers the significant advantage of being able to shear a variety of flexible lines, most particularly multi-strand cable, which could not be cleanly sheared and sealed by

conventional shear ram apparatus.

Shear ram apparatus in accord with the present invention includes a housing body

having a throughway for receipt of the borehole retrievable, particularly a flexible line, and most particularly a multi-strand cable. The apparatus further includes opposed first and second ram assemblies mounted in the housing on opposite sides of the throughway for

reciprocation laterally inwardly and outwardly. Connected to the first and second ram

assemblies, respectively, are first and second drive means for effecting the desired reciprocation. The shear ram apparatus further includes a blade member carried on the

laterally inward side of the first ram assembly and an anvil formation on the laterally inward side of the second ram assembly and positioned for cooperation with the blade member to apply a shearing force to the multi-strand cable or other borehole retrievable when the ram assemblies are moved laterally inwardly. Also included are first and second seal means carried, respectively, in the first and second ram assemblies for sealing the throughway

against longitudinal flow when the ram assemblies have been reciprocated inwardly to their shearing and sealing position. Finally, the shear ram apparatus of the present invention includes means for preventing relative longitudinal movement of the blade member and anvil when the ram assemblies are moved laterally inwardly. The preferred means comprises a plurality of keys projecting laterally inwardly from the inward side of one of the ram assemblies for cooperation with guide means on the inward side of the other ram assembly. In a preferred embodiment the key and guide means are disposed to the side of the blade member and the anvil and engage before the blade member contacts the anvil as the opposed first and second ram assemblies are moved laterally inward to shear and seal.

The opposable shear ram assemblies and the shear ram apparatus of the present invention provide an improved apparatus for severing and sealing about flexible lines and particularly about multi-strand cables. By preventing relative longitudinal movement, i.e., longitudinal separation, of the blade member and anvil during the lateral movement of the closing operation, the improved shear ram apparatus of the present invention prevents flexible lines, and particularly multi-strand cable, from guiding and longitudinally separating the blade member and anvil which would prevent clean shearing and sealing by the shear ram apparatus. This improved feature solves the long felt but unfulfilled need in the oil and gas industry for a rugged, shear ram device capable of severing all borehole retrievables, from rigid drill pipe to highly flexible lines, including multi-strand cables. These and other meritorious features and advantages of the present invention will be more fully appreciated from the following detailed description and claims. Brief Description of the Drawings Other features and intended advantages of the present invention will be more readily apparent by the references to the following detailed description in connection with the accompanying drawings, wherein: Fig. 1 is a cross-sectional illustration of a prior art shear ram blowout preventer apparatus illustrating separation of the blade and anvil by a multi-strand cable and the

resulting failure to sever and seal;

Fig. 2 is a top plan illustration of the prior art shear ram blowout preventer apparatus of Fig. 1 illustrating in cross-section the separated and unsevered multi-strand cable;

Fig. 3 is a cross-sectional illustration through a shear ram blowout preventer apparatus in accord with the present invention with the ram assemblies in the open position;

Fig. 4 is a top plan illustration viewed from the line 4-4 of Fig. 3 of the shear ram blowout preventer apparatus in accord with the present invention illustrating the ram assemblies in the open position; Fig. 5 is a cross-sectional illustration of the shear ram blowout preventer apparatus of the present invention illustrating the ram assemblies in the closed, sealing position with the key and guide means engaged to prevent relative longitudinal movement of the blade and anvil;

Fig. 6 is a front elevational view of the laterally inward side of the first ram assembly along the line 6-6 of Fig. 3 illustrating a blade and guide means in accord with the present invention; and

Fig. 7 is a front elevational view of the laterally inward side of the second ram assembly through the line 7-7 of Fig. 5 and including the blade and guide means of the first

ram assembly in cross-section engaged with the keys of the second ram assembly in accord with the present invention.

While the invention will be described in connection with the presently preferred embodiment, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included in the spirit of the invention as defined in the appended claims.

Detailed Description of the Preferred Embodiment The present invention provides shear ram apparatus for use in blowout preventers for severing and sealing about a borehole retrievable and, particularly, a flexible line. Exemplary of a rigid borehole retrievable is a string of drill pipe or a sinker bar. Exemplary

of flexible borehole retrievables are coil tubing, slicklines, wirelines and multi-strand cables. The shear ram apparatus of the present invention is particularly useful in severing and sealing

about flexible borehole retrievables and, particularly, multi-strand cable. Conventional shear ram apparatus is characterized by a blade member and an anvil formation carried on the laterally inward side of opposed first and second ram assemblies. In conventional shear ram apparatus the blade member and anvil formation are moved laterally inwardly to sever and seal. However, the blade and anvil may be guided into longitudinal movement and

separation by multi-strand cable and other flexible lines, thus preventing the apparatus from cleanly severing and sealing such flexible lines.

Figs. 1 and 2 illustrate prior art shear ram blowout preventer apparatus. These figures illustrate the undesirable longitudinal separation of the blade member and the anvil

formation when the ram assemblies have been moved laterally inwardly in an unsuccessful attempt to sever and seal about a multi-strand cable. The shear ram apparatus of the present invention is distinguishable over such conventional apparatus in that the opposable first and second ram assemblies include means for preventing relative longitudinal movement and undesirable separation of the blade member and anvil formation when the ram assemblies are moved laterally inwardly.

Referring to Figs. 1 and 2, there is shown a ram-type blowout preventer, more specifically, a shear ram apparatus comprising a housing 100. Housing 100 defines a central throughway 112, disposed generally vertically in use, for receipt of a borehole retrievable, typically a string of drill pipe or other flexible line, e.g., coil tubing, slicklme, wireline or multi-strand cable 114. As used herein, terms such as "longitudinally" and "laterally" should be construed with reference to the centerline of throughway 112 unless otherwise indicated. For convenience, it is noted that the centerline of throughway 112 is generally coincident with that of the drill pipe or cable 114 in use. Also, for convenience, terms such as

"vertically" and "horizontally" will be used with reference to the positions normally assumed by various parts of the apparatus in use, and should not be construed in a limiting sense.

Housing 100 defines a pair of chambers 116 and 118 on laterally opposite sides of and

communicating with throughway 112. Chambers 116 and 118 are substantially identical and

house, respectively, first and second ram assemblies.

The first ram assembly, housed in chamber 116, comprises lower ram block 120 having laterally inward side 146. The laterally inward side 146 of ram block 120 is inset and chamfered at 146a. Ram block 120 includes cavity 122 having reduced diameter mouth 124 opening laterally outwardly. Cavity 122 receives flange member 126 connected by reduced diameter neck 128 to piston rod 130. Neck 128 extends through mouth 124 of cavity 122 with piston rod 130 being located outwardly thereof. Because of the reduced diameters of mouth 124 and neck 128, flange 126 and piston rod 130 form opposed shoulders abutting laterally outward portion 125 of ram block 120. In a manner well known in the art, piston rod 130 is connected to a piston housed in a cylinder integral with housing 10. Thus, piston rod 130 serves as a drive member whereby first ram block 120 may be reciprocated laterally inwardly and outwardly.

Ram block 120 carries in an undercut formation 136 on its laterally inward side 146 an L-shaped shear blade 132. Shear blade 132 is characterized by projecting cutting portion 134 and is held within undercut formation 136 by horizontally disposed bolts (not shown). Ram block 120 includes an arcuate groove 142 on its upper surface, a transverse groove 144 along undercut formation 136 and vertical grooves (not shown) extending upwardly from the ends of transverse groove 144 to the ends of arcuate groove 142 for receiving a seal. The first ram assembly further comprises a first seal, conveniently in the

form illustrated in Fig. 9 of U.S. Patent No. 4,540,046, previously incorporated herein by reference. This seal is a monolithic elastomeric body comprising an arcuate seal portion 138 connected at its inward ends by vertical seal portions (not shown) to laterally inward, transverse seal portion 140.

The second ram assembly which is housed in chamber 118 comprises upper ram block

150. The main drive means (piston rod 130 ') and its manner of connection to ram block 150 at its laterally outward portion 155 are substantially identical to those for ram block 120.

Therefore, these parts will not be described in detail, but have merely been given like reference numerals plus the symbol " '" (prime).

Upper ram block 150 is characterized further by laterally inner side 148, inset and chamfered 148a and including cutting anvil formation 152 on its lower surface. Behind anvil formation 152, ram block 150 has been undercut to form recess 154. Ram block 150 further includes along its upper surface an arcuate groove 156 connected at its inward ends by vertical grooves (not shown) to the ends of the laterally inward portion of recess 154. The

groove system thus formed is configured to receive a second monolithic elastomeric seal body similar to that previously described and to that illustrated in Fig. 10 of U.S. Patent No. 4,540,046. This second seal includes arcuate portion 158 connected at the inward ends thereof by vertical portions (not shown) to the ends of transverse seal portion 160. Rigid support bar 162 bolted within recess 154 maintains the seal in place.

Figs. 1 and 2 illustrate the longitudinal movement and separation of blade member 132 and anvil formation 152 in a conventional shear ram assembly caused by separation of a multi-strand cable 114 into its individual strands 114a. Shear ram blowout preventer apparatus in accord with the present invention overcomes this problem so that flexible lines,

including multi-strand cables, are easily and cleanly severed and sealed. Shear ram blowout preventer apparatus in accord with the present invention is illustrated in Figs. 3-7. Figs. 3 and 4 illustrate that shear ram apparatus in the open position. Fig. 5 illustrates that apparatus in the closed position. Figs. 6 and 7 illustrate in cross- section the interlocldng keys and slots which prevent relative longitudinal movement of the blade member and anvil formation in accord with the present invention. Housing 10 defines a central throughway 12, disposed generally vertically in use, for receipt of a borehole retrievable, preferably a multi-strand cable (not illustrated). Housing 10 further defines a pair of chambers 16 and 18 on laterally opposite sides of and

communicating with throughway 12. Chambers 16 and 18 are substantially identical and house, respectively, first and second ram assemblies.

The first ram assembly, housed in chamber 16, comprises ram block 20 having laterally outward portion 22 for connection to the drive means and laterally inward portion 24 for carrying the shear blade 40. Lower ram block 20 includes cavity 26 having reduced diameter mouths 28 opening laterally outwardly. Cavity 26 receives flange members 30 connected by reduced diameter necks 32 to a piston rod 34. Necks 32 extend through

mouths 28 of cavity 26 with piston rod 34 being located outwardly thereof. Because of the reduced diameters of mouths 28 and necks 32, flange members 30 and piston rod 34 form opposed shoulders abutting laterally outward portion 22 of ram block 20. In a manner well known in the art, piston rod 34 is connected to a piston housed in a cylinder integral with housing 10. Thus, piston rod 34 serves as a drive member whereby first ram block 20 may be reciprocated laterally inwardly and outwardly.

On the laterally inward surface of portion 24 of ram block 20 is inset 36 for receiving the borehole retrievable, e.g., pipe, cable or the like, to be sheared. Mounted on the lower portion of the laterally inward surface of ram block 20 is shear blade 40. Blade member 40

is generally L-shaped in cross-section, having a laterally inwardly extending cutting portion 42 and a mounting shank 43 extending downwardly from the laterally outer extremity of the cutting portion 42. As shown in Fig. 4, cutting portion 42, as viewed in plan, has a shallow notch 46 formed by oppositely inclined edges 44 to increase its contact area with the retrievable to be cut. Mounting shank 43 of blade member 40 includes a plurality of counter-

sunk bores 56 for cooperation with a plurality of bores 58 in the laterally inward surface of ram block 20 for mounting of blade member 40 thereon with a plurality of mounting bolts

or screws 38. As is evident from Figs. 3, 4 and 6, the most outwardly portions 96 of mounting shank 43 extend across the depth of cutting portion 42 of blade member 40 while the central portion is inset at 45. Accordingly, outer bores 56a for screws 38a are longer than central bores 56.

Ram block 20 includes a seal means carried in an appropriate groove system. The disposition of the various parts of the groove system and the seal means relative to the remainder of the first ram assembly is readily understood with reference to Figs. 3, 4 and 6. Ram block 20 includes arcuate groove 48 on its upper surface, transverse groove 50

along its laterally inward surface and vertical grooves 49 extending upwardly from the ends of transverse groove 50 to the ends of arcuate groove 48 for receiving a first seal means.

The first ram assembly further comprises a first seal, preferably in the form illustrated in Fig. 9 of U.S. Patent No. 4,540,046. The seal is a monolithic elastomeric body comprising

an arcuate seal portion 52 connected at its inward ends by vertical seal portions 53 to laterally inward, transverse seal portion 54.

The second ram assembly which is housed in chamber 10 comprises upper ram block

70. The main drive means (piston rod 34 ') and its manner of connection to ram block 70 at its laterally outward portion 72 are substantially identical to those for ram block 20. Therefore, these parts and their cooperation will not be described in detail, but have merely been given like reference numerals plus the symbol " '" (prime).

Upper ram block 70 is characterized by laterally outward portion 72 and laterally

inward portion 74 terminating in laterally inward surface 76. Inward surface 76 is inset at 78 to aid in positioning a borehole retrievable, e.g., a multi-strand cable, for cutting relative to notch 46 of blade member 40. Inward surface 76 is inset and chamfered 82 along its top side and provides anvil formation 80 along its lower leading edge for cooperation with cutting portion 42 of blade member 40. Ram block 70 is undercut 94 for receiving blade member 42 and the severed cable or other borehole retrievable in the closed position.

Ram block 70 includes arcuate groove 84 on its upper surface, transverse groove 86 along undercut formation 94 and vertical grooves 85 extending upwardly from the ends of transverse groove 86 to the ends of arcuate groove 84 for receiving a second seal means. The second ram assembly further comprises a second seal, preferably similar to that

previously described above and illustrated in Fig. 10 of U.S. Patent No. 4,540,046. This seal is a monolithic elastomeric body comprising an arcuate seal portion 88 connected at its inward ends by vertical seal portions 89 to laterally inward, transverse seal portion 90. Rigid support bar 92 is disposed within recess 86 behind transverse seal portion 90 to maintain the seal in place.

Longitudinal or vertical, as typically disposed, relative movement of blade 40 on first ram block 20 with respect to anvil formation 80 on second ram block 70 is prevented by cooperating keys 64 extending inwardly from the inward surface of ram block 70 for cooperation with retaining means or slots 60 along the outer edges of extended outer portions 96 of mounting shank 43 of blade member 40. Cooperation of keys 64 with slots 60 is shown in Fig. 7 where keys 64 extend inwardly below upper retaining surfaces 62 toward vertical surfaces 63 of retaining slots 60 to prevent keys 64 and anvil formation 80 from relative upward or longitudinal movement with respect to and away from blade member 40.

In Figs. 3 and 4 it is seen that leading edges 66 of keys 64 preferably extend beyond the

laterally inward surface 76 and anvil formation 80 of ram assembly 70. Accordingly, leading edges 66 of keys 64 engage retaining slots 60 before anvil formation 80 contacts cutting portion 42 of blade member 40. Thus, keys 64 are engaged with retaining slots 60 to prevent relative longitudinal movement of anvil formation 80 relative to blade member 40

before contact with multi-strand cables and other small retrievables could produce unwanted relative vertical or longitudinal movement. The inwardly inclined surfaces 44 toward notch 46 of blade member 40 further enhance this last feature. The foregoing description of the invention has been directed in primary part to a particular embodiment in accordance with the requirements of the patent statutes and for purposes of explanation and illustration. It will be apparent, however, to those skilled in the art that many modifications and changes in the specifically described shear ram apparatus may be made without departing from the scope and spirit of the invention. For example, while the illustrated embodiment includes a pair of keys 64 disposed on one ram assembly for cooperation with a pair of retaining slots 60 on the other assembly, other configurations are readily apparent. For example, each assembly might include a key and retaining slot for cooperation with, respectively, a retaining slot and key on the other assembly. Further, keys 64 might extend inwardly further than those illustrated to engage deeper retaining slots 60 in both the open and closed positions of the ram assemblies ensuring no possible relative longitudinal movement of the blade member and anvil formation. Therefore, the invention is not restricted to the preferred embodiment illustrated but covers all modifications which may fall within the scope of the following claims.

Claims

What Is Claimed Is:

1. Shear ram apparatus for severing and sealing borehole retrievables such as multi-strand cable, wireline, slickline, coil tubing, drill pipe, sinker bar and other said retrievables, comprising:

a housing body having a throughway for receipt of a borehole retrievable; opposed first and second ram assemblies mounted in said housing on opposite sides of said throughway for reciprocation laterally inwardly and outwardly; first and second drive means for effecting said reciprocation connected, respectively, to said first and second ram assemblies; a blade member carried on the laterally inward side of said first ram assembly; an anvil formation on the laterally inward side of said second ram assembly and

positioned for cooperation with said blade member to apply a shearing force to said borehole retrievable when said ram assemblies are moved laterally inwardly; first and second seal means carried, respectively, in said first and second ram

assemblies for sealing said throughway against longitudinal flow when said ram assemblies have been reciprocated inwardly shearing said borehole retrievable; and means carried on said ram assemblies for preventing relative longitudinal movement

of said blade member and anvil formation when said ram assemblies are moved laterally inwardly and before said blade member contacts said anvil formation.

2. The opposable ram assemblies in accord with Claim 1 wherein said means for

preventing relative longitudinal movement comprises key means projecting laterally inwardly from said inward side of one of said ram assemblies for cooperation with guide means on said inward side of the other of said ram assemblies.

3. The opposable ram assemblies in accord with Claim 2 comprising a plurality of said cooperating key and guide means.

4. The opposable ram assemblies in accord with Claim 2 wherein said cooperating key and guide means are disposed to the side of said blade member and anvil formation.

5. The opposable ram assemblies in accord with Claim 2 wherein lateral inward movement of said ram assemblies causes said key means to engage said guide means before said blade member contacts said anvil formation.

6. Opposable shear ram assemblies for mounting in a housing on opposite sides of a throughway in a shear ram apparatus for severing and sealing a borehole retrievable such as multi-strand cable, wireline, slickline, coil tubing, drill pipe, sinker bar and other said

retrievable, comprising: opposable first and second ram blocks for mounting in said housing on opposite sides of said throughway for reciprocation laterally inwardly and outwardly;

a blade member carried on the laterally inward side of said first ram block; an anvil formation on the laterally inward side of said second ram block and positioned for cooperation with said blade member to apply a shearing force to said borehole

retrievable when said ram blocks are moved laterally inwardly; first and second groove systems, respectively, in said first and second ram blocks for

carrying first and second seal means for sealing said throughway against longitudinal flow when said ram blocks have been reciprocated inwardly shearing said borehole retrievable; and

means carried on said ram blocks for preventing relative longitudinal movement of said blade member and anvil formation when said ram blocks are moved laterally inwardly and before said blade member contacts said anvil formation.

7. The ram assemblies of Claim 6 wherein said means for preventing relative

longitudinal movement comprises key means projecting laterally inwardly from said inward side of one of said ram blocks for cooperation with guide means on said inward side of the other of said ram blocks.

8. The ram assemblies of Claim 7 comprising a plurality of said cooperating key and guide means.

9. The ram assemblies of Claim 7 wherein said cooperating key and guide means are disposed to the side of said blade member and anvil formation.

10. The ram assemblies of Claim 7 wherein lateral inward movement of said ram blocks causes said key means to engage said guide means before said blade member contacts said anvil formation.

11. In a shear ram apparatus for severing and sealing a borehole retrievable such as multi-strand cable, wireline, slickline, coil tubing, drill pipe, sinker bar and other said retrievable, said apparatus comprising a housing body having a throughway for receipt of

said borehole retrievable, opposed first and second ram assemblies mounted in said housing on opposite sides of said throughway for reciprocation laterally inwardly and outwardly, first and second drive means for effecting said reciprocation connected, respectively, to said first and second ram assemblies, a blade member carried on the laterally inwardly side of said first ram assembly, an anvil formation on the laterally inward side of said second ram

assembly and positioned for cooperation with said blade member to apply a shearing force

to said borehole retrievable when said ram assemblies are moved laterally inwardly, and first and second seal means carried, respectively, in said first and second ram assemblies for sealing said throughway against longitudinal flow when said ram assemblies have been reciprocated inwardly shearing said borehole retrievable, the improvement comprising:

means carried on said ram assemblies for preventing relative longitudinal movement of said blade member and anvil formation when said ram assemblies are moved laterally inwardly and before said blade member contacts said anvil formation.

12. The shear ram apparatus of Claim 11 wherein said improvement comprises key means projecting laterally inwardly from said inward side of one of said ram assemblies for cooperation with guide means on said inward side of the other of said ram assemblies.

13. The shear ram apparatus of Claim 12 wherein said improvement comprises a plurality of said cooperating key and guide means.

14. The shear ram apparatus of Claim 12 wherein said cooperating key and guide means are disposed to the side of said blade member and anvil formation.

15. The shear ram apparatus of Claim 12 wherein lateral inward movement of said ram assemblies causes said key means to engage said guide means before said blade member

contacts said anvil formation.