This invention relates generally to an¬ nular blowout preventers and more particularly to a packing unit and insert for such packing unit.

For many years the design of blowout pre- venter packing units has followed the principles described in U.S. Patent No. 2,609,836. Such packing units incorporate metal inserts equally spaced about the packer longitudinal axis and embedded in an elas¬ tomeric material. Upon inward constriction or clo- sure of the unit about a well drill pipe, the elas¬ tomeric material is anchored by the insert webs as it produces vertical folds stretching radially in¬ wardly to seal the pipe. When the packer unit closes on itself as in the case when no pipe is present in the longitudinal bore of the unit, elastomeric ma¬ terial of the folds advancing toward the axis must at certain times stretch or extend as much as 350 to 400%. Repeated closures produce excessive wear and fatigue of the elastomeric or rubber material, reducing the ^" useful life of the packer due to such extreme stretching.

U.S. Patent Nos. 3,958,808 and 3,917,293 disclose a packing unit and inserts for such a pack¬ ing unit which significantly increase the packing unit cycle lifetime. The increase in cycle life¬ time results from locating the insert webs in the elastomeric material with spacing from the central

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longitudinal axis and from each other in a dif¬ ferential manner in order to provide differential anchoring about the axis of circularly spaced por¬ tions of the elastomeric material subject to inward displacement. Rubber flow paths are opened between the inserts.

In one form of the invention disclosed in the above referenced patents, the anchoring of the rubber by certain webs is closer to the central axis than anchoring of the material by other webs. In other words, webs effectively closer to and f rther from the axis may alternate about the axis. In other forms of the invention, the webs are general¬ ly equally spaced from the axis but certain pairs of the webs have closer circular spacing about that axis than other pairs of webs. Significant increases in packer cycle life are achieved by the invention disclosed in the above referenced patents. A con¬ tinuing need exists, however, for increases in packer cycle life over and above those achieved by the above referenced inventions.

Thus, the object of the present invention is to provide a packer and an insert designed for the packer which produces increased packer unit cycle life.

Accordingly, the present invention provides in an insert adapted for use in an annular blowout preventer packing unit and having top and bottom plates interconnected by a generally longitudinal web, the improvement.wherein the inward edge of the web slopes generally radially inward to radially out¬ ward from the connection to the top plate to the bottom plate.

The present invention also provides a packer unit adapted for use in an annular blowout preventer

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having an axial bore, the packer unit adapted for compressive inward radial, displacement toward the axis of the bore, ^' the packer unit comprising metal¬ lic inserts generally spaced circularly about the axis, the inserts having webs which extend generally longitudinally, the inward edge of the webs sloping generally downwardly in an outward radial direction from the axis of the bore, and an annulus of elas¬ tomeric material extending about the axis and embed- ding the webs so that the webs anchor the material during inward compressive displacement of the packer.

The insert of the present invention pro¬ duces a reversing of the pressure profile on the pipe moving the peak pressure to the lower end of the packing unit thereby producing less extrusion about the top plate of the packing unit, with re¬ sulting increase -j_ _{n C} y _C ι _e life of the packer unit. Further, the elastomeric material in which the in¬ sert is embedded is placed in compression at the top portion of the web thereby reducing tearing and extrusion above the top plate of the packing unit. In the drawings:

Figure 1 illustrates in a top cross-section view an annular packer constructed generally ac- cording to one embodiment of a long life packing unit illustrated in U.S. Patent Nos. 3,958,808 and 3,917,293;

Figure 2 illustrates the novel shape of the webs of the inserts used in the packing unit of Figure 1;

Figure 3 illustrates the novel insert and the integral web and resulting pressure profile of a packing unit of an annular blowout preventer closed about a pipe according to the invention; and Figure 4 illustrates the web shape of a prior art insert and a corresponding pressure profile

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resulting from its use in a packing unit of an ^' an¬ nular blowout preventer.

Figure 1 illustrates in a cross-section view a packing unit disclosed in U.S. Patent Nos. 3,958,808 and 3,917,293. The invention to be de¬ scribed in detail below is related to the ones dis¬ closed in such U.S. patents which are owned by the same assignee which owns the subject invention. Referring to Figures 1 and 2, a blowout preventer 10 includes a metallic housing 11 which may be bolted to wellhead casing and other well equipment. The housing contains a piston 15 movable upward in chamber 16 in response to fluid pressure exertion upwardly against the piston for constrict- ing an annular packer unit 18 via pressure exertion from piston cam surface 22 against packer exterior surface 23. Surfaces 22 and 23 are frustro-conical and flared upwardly. The packer when sufficiently radially inwardly displaced seals off about a well pipe 19 shown extending axially vertically through the preventer 10 in Figure 2 and in the absence of a pipe, the packer unit 18 will completely close off the vertical passage 20 through the preventer when the unit is sufficiently constricted by piston 15. Upon downward movement of the piston, the packer expands radially outward to the open position. The packer unit 18 is normally confined vertically un¬ der a housing cap, the lower interior surface 27 of which is illustrated in Figure 2. In accordance with the disclosure of the above-mentioned U.S. patents, the packer unit com¬ prises metal inserts 51 and 50 ^' generally circularly spaced about the longitudinal central axis of the unit 40. The inserts including webs 31 and 33 that extend generally longitudinally. An annulus of elastomeric

material 34 extending about the packer axis embeds the webs so that they anchor the material toward in¬ ward compressive displacement for constriction of the packer. The spacing of the webs from the axis and from each other creates differential anchoring about the axis of circularly spaced portions of the elas¬ tomeric material subject to inward displacement about the axis. As indicated in the above-mentioned U.S. patents such differential anchoring facilitates dif- ferential inward flow or extrusion of circularly spaced portions of the elastomeric material to the end that maximum stretching of the material is min¬ imized and maximum stresses are correspondingly min¬ imized. Turning now to Figure 4, a prior art in¬ sert 51 (of alternatively 50) is illustrated as the packer unit in which it is a part is being closed about pipe 19. The web 60 of insert 51 is integral with a top. plate 61 and a bottom plate 62. The shape of the top plate 61 and bottom plate 62 may be as those illustrated in Figure 1 and Figure 4 but are not important to this invention which is related to the inward edge shape of the web 60.

The prior art web 60 is characterized by a inward edge which slopes downwardly from a greater radius 63 to a smaller radius 68. In other words, the inward dge slopes downwardly from out to in. The prior art insert 60 illustrated in Figure 4 is illustrated in the condition of upward well pressure tending to force the elastomeric material 34 upward thereby extruding it past the upper plate 61. The pressure profile of the prior art packing unit embedding a prior art insert 51 as shown to the right of Figure 4 illustrates that the downwardly inwardly sloping web 60 places the maximum point of pressure of the elastomeric material 34 against pipe

19 relatively high along the pipe. The arrows 64 showing the elastomeric material 34 along the upper part of the inner edge of the insert 60 indicate that the elastomeric material is in tension tending to force the elastomeric material away from the embedded insert 60, as the packer unit is closing about pipe 19. Such tension is believed to contri¬ bute to the tearing about the upper ridge 66 of upper plate 61 during repetitive opening and closing of the packer, thereby contributing to a tearing off of the upper part of the elastomeric material 34 as shown by dotted lines 67.

According to Figure 3, an insert 51* or alternatively an insert 50 ' which may replace in- serts 51 or 50 of the packer unit illustrated in Figure 1 is illustrated having a top plate 61' and a bottom plate 62' but with an integral web 60' constructed according to the invention. According to the invention, the inward edge-of web 60' slopes downwardly from a smaller upward radius 64' to a larger downward radius 68'. In other words, the slope slope of the inward edge of the insert slopes down¬ wardly from a smaller radius to a larger radius. Another -way to characterize the novel slope of the in- ner edge of web 60 * is that it is sloped creating a positive angle (+£) with respect to the longitudinal axis of the packing unit in which it is embedded. The shape of the inner edge of web 60' is distinguish¬ ed from the inner edge of web 60 of prior art in- sert 51 which slopes at a negative angle (-Θ) with respect to the longitudinal axis of the packing unit in which it is embedded.

As illustrated in Figure 3, the effect of the slope of the inward edge of web 60' causes relatively more of the elastomeric material 34 to be

trapped in the lower part of the inner edge of web 60*. Such slope on the inner edge of the web- 60' causes a lowering of the maximum point of the pres¬ sure profile against the pipe 19 about which the 5 packer unit is closing as seen on the right hand side of Figure 3. It is believed that the down¬ wardly outwardly sloping inner edge of the web 60' causes the elastomeric material to be placed in com¬ pression against the inner edge of the web 60' as Q illustrated at arrows 65. Even though the entire packing element is placed in tension because of the upward force of the well pressure below the packing unit tending to cause separation of the elastomeric material 34 from pipe 19 during pack-off about pipe 19, the elastomeric material bonded to the inner edge of web 60' is placed in compression. Less tearing at the upper edge 66 ' at the top plate re¬ sults from the compressive effect of the elastomeric material 34 at the top inner edge of web 60'. Figure 2 shows a preferred embodiment of the invention in which the inner webs 60' of two different kinds of inserts 50' and 51' are illustrat¬ ed in the packer unit of Figure 1 in which the inserts 50' and 51' are substituted for the prior art in- serts 50 and 51. Figure 2 is a section of the pre¬ venter 10 taken through the cross-section lines 2-2. Figure 2 illustrates the downward sloping inner edge from the smaller topmost inner radius to a larger lowermost inner radius of the inner edges of the webs of inserts 50' or 51*.

Thus, the packer unit of elastomeric ma¬ terial with the novel inserts according to the in¬ vention is characterized by relatively more elasto¬ meric material lower in the packer unit with more metal higher in the packer unit. The preferred range

of internal angles of the leading edge of the webs of the inserts' according to the invention is from a positive six (6) ^' to twelve (12) degrees, depending on the geometry of the packer, causing the elasto- meric material to move up into the"upward part of the web (as illustrated in Figure 3) , rather than pulling away (as illustrated in the prior art insert of Figure 4) .

It should be emphasized that although the inserts are illustrated as being of the differential insert type as illustrated in Figures 1 and 2, the inserts may all be of identical shape equally spaced about the radius of the packer unit like those, for example, of U.S. Patent No. 2,609,836. Thus, according to the invention, an in¬ sert and packer embedding one or more of such inserts is provided in which the inner edge of the web slopes downwardly from a relatively smaller inner radius to a relatively greater radius. The shape of the in- ward edge of the web causes the rubber to be placed in relative compression at the upper inner edge of the web and thereby reduces tearing at its upper plate and places the pressure profile relatively lower along the pipe or other object in the bore of the packer unit during pack-off. Such lower pres¬ sure profile causes less tendency for tearing at the upper plate of the elastomeric material and contri¬ butes to a longer cycle life.

Various modifications and alterations in the described apparatus will be apparent to those skilled in the art from the foregoing description which does not depart from the spirit of the in¬ vention. The foregoing disclosure and description of the invention are illustrative and explanatory thereof and details of the illustrative embodiment may be made without departing from the spirit of the invention.