Blow-out protector packer element

A packer element for a blow-out protector comprising a body of an elastomeric packing material interposed between a pair of opposed reinforcing plates wherein a slight pre-load compression is imparted to the working surface with which the packer element seals off the annular space around a drill pipe. The pre-load compression is achieved by forming the packing body with top and bottom surfaces which diverge in the direction of the working surface and compressing the packing body between the reinforcing plates such that in the blow-out protector the reinforcing plates sit in substantially planar parallel relation. By building pre-load compression into the packer element, it has been found that the useful life of the element is enhanced.

BACKGROUND OF THE INVENTION 
The present invention relates to a ram-type packer element for use in a 
blow-out protector and, more particularly, to a packer element which is 
designed to be useful as a stripping tool and provide good shear-resisting 
properties. 
Blow-out protectors are well known. In general, they are valve devices 
which are designed to pack off the annular space between the drill pipe 
and the well casing in the event of a blow-out. A typical blow-out 
protector comprises, as its essential components, a packing element and an 
exteriorly operated actuator means which acts on the packing element and 
forces it into sealing engagement with the drill pipe. Usually, the 
blow-out protector includes or is associated with some means of sensing or 
reacting to an increase of pressure in the well hole and is designed such 
that the protector is actuated and the well pressure is controlled before 
the well pressure can do substantial damage to the drilling equipment or 
cause injury at the drilling site. 
One example of a blow-out protector is illustrated in U.S. Pat. No. 
2,231,221. In that protector, the packing element is carried on an 
elongated actuator sleeve provided with a plurality of annular gear teeth. 
In the event of a blow-out, the packing element is driven by the sleeve 
into abutment with a shoulder located internally in the well hole 
whereupon the packing element is compressed and the packing extrudes or 
bulges from the element and into sealing engagement with the drill pipe. 
There are numerous other examples of blow-out protectors in the art which 
differ in the design of the packing element and the means whereby the 
element is forced into sealing engagement with the drill pipe. A few 
examples of the other drill pipe protectors that have been known are 
disclosed in U.S. Pat. Nos. 2,375,432; 2,139,526; and 1,963,683. 
A frequent design used for the packing element, or "gate" as it is 
sometimes referred, is a generally semi-circular structure in which an 
elastomeric packing is interposed between two semi-circular reinforcing 
elements. The structure is formed with a semi-cylindrical cut out or arch 
in its diametric side which receives the drill pipe. The packing which 
faces on this cut out defines a work surface which packs off the well 
casing. The elastomeric packing is usually a block of a high strength 
wear-resistant rubber compound. Packing elements are used in pairs with 
one element positioned diametrically opposite the other on each side of 
the drill pipe such that the drill pipe extends through the circular 
aperture formed by the interfacing semi-cylindrical arches. In the 
blow-out protector, the elements function as a packer valve. Pressure is 
applied to each element of the pair whereby the element is compressed or 
deformed and the packing extrudes from the element and engages the drill 
pipe to seal off the annular space around the pipe in the well. 
One problem which blow-out protector packer elements have faced is a 
tendency for the elements to wear out and fail in use. A major source of 
wear occurs when the drill pipe is pulled out of the well to replace 
damaged pipe or a worn drill bit. As the drill pipe is withdrawn from of 
the well, it is coated with the drilling fluids which carry suspended bits 
of cut rock and the like. As the surface of the pipe slides across the 
packing element in the blow-out protector, the packing element is 
subjected to elongational shear along the working face. This forceably 
elongates the working surface and gradually mechanically degrades the 
packing element to the point that it can no longer function 
satisfactorily. One practice that is frequently adopted which intensifies 
abrasion and wear is to partially close the blow-out protector as the 
drill pipe is removed from the well in order to use the packing element as 
a stripping tool to remove mud and drilling fluids from the drill pipe 
surface. This operation prevents even greater abrasion and wear problems 
since the packing element is positively biased against the surface of the 
drill pipe as it is removed. Under the applied pressure of the blow-out 
protector, the packing element is subjected to higher shearing forces 
which enhances mechanical degradation. As the packing element is worn and 
degraded it becomes unable to deliver a uniform sealing action around the 
circumference of the drill pipe in the event of a blow-out. 
Several attempts have previously been made to overcome the wear-resistance 
and abrasion-resistance problems and to improve the useful service life of 
blow-out protector packing elements. Efforts have particularly 
concentrated on developing elastomeric compositions and elastomeric 
composites which resist the wear and abrasion caused by the drill pipe. 
Relatively little attention has been directed to the packing element 
design itself. 
SUMMARY OF THE INVENTION 
A principal object of the present invention is to provide a blow-out 
protector packing element having improved abrasion and wear resistance. 
Another object of the present invention is to provide a packing element 
which can be used as a stripping tool to remove mud and drilling fluids 
from the surface of the drill pipe as it is withdrawn from the well 
without impairing the ability of the packing element to seal off the well 
in the event of a blow-out. 
Still another object of the invention is to provide a packing element which 
neutralizes or reduces the surface elongational mechanical degradation 
which occurs when a drill pipe slides across the working surface of the 
packing element. 
These and other objects of the present invention are attained by a blow-out 
protector packing element in which a body of elastomeric packing material 
is maintained under a slight localized, pre-load compression in the 
vicinity of the work surface with which the packing element grips the 
drill pipe in the event of a blow-out or when used as a stripper tool. The 
term "pre-load compression" as used herein designates an in situ 
compression which is built into the packing element by dimensioning the 
packing element larger along its work surface and compressing it between a 
pair of reinforcing plates as described below. In accordance with the 
present invention, it has been found that elongational shear of the 
working surface caused by the drill pipe as it slides across the work 
surface is at least partially neutralized or compensated by 
pre-compressing the elastomeric packing. The pre-load compression built 
into the invention packing element offsets the initial shearing caused 
when the drill pipe slides along the work surface of the packing. Thus, 
the invention element may be considered as having a built-in reserve of 
compression which is gradually exhausted as the element is used as a 
stripper tool but which extends its useful service life. It has been found 
that the invention element is degraded less by the 
precompression-elongation cycle than by the compression-relaxation cycle 
which occurs with conventional elements. Thus, the packing elements of the 
present invention have a longer useful life and can be used to strip drill 
mud from the drill pipe as it is removed from the well. 
In accordance with the present invention, a pre-load compression is built 
into the packing element by molding the elastomeric body with top and 
bottom surfaces which diverge in the direction of the working surface. In 
the completely uncompressed element, the reinforcing plates which bracket 
the elastomeric body are offset approximately 1.degree. to 10.degree. 
preferably 2.degree. to 7.degree. and in the most typical case about 
5.degree.. (The angle between one plate and and a horizontal line when the 
other plate is horizontal.) By applying a clamping pressure to the offset 
reinforcing plates the plates are drawn into a substantially planar 
parallel relation and the work surface is maintained under a slight 
pre-load compression. 
Clamping pressure can be applied to the packing element by various means of 
which probably the simplest to effect is to tie the plates with a tie bolt 
which is counter-sunk in one of the plates and extends through a channel 
in the elastomeric body to a threaded hole in the other plate. Of course, 
the tie bolts can be replaced by functionally equivalent fastening means. 
Another means of imparting pre-load compression is to provide mounting 
means for the packing element in the blow-out protector in which 
converging cam surfaces are appropriately positioned relative to the 
divergence in the packing element such that in receiving the packing 
element the reinforcing plates are forced into a parallel relation. 
For purposes of the discussion herein, pre-loaded compression is described 
with reference to the planar parallel relationship of the reinforcing 
plates, however, those skilled in the art will appreciate that pre-loaded 
compression can be achieved when the plates are not perfectly parallel; 
accordingly, the reinforcing plates in the pre-compressed element are 
sometimes described herein as being in "substantially planar parallel 
relation". 
The angle of offset between the reinforcing plates in an uncompressed 
element in accordance with the invention may vary from approximately 
1.degree. to 10.degree. with 5.degree. offset being representative. 
Theoretically, some benefit is achieved in the invention with even the 
slightest compression of the working surface. Hence, offsets greater than 
0.degree. can be used in the invention. As a practical matter, the 
improvement in wear resistance is not appreciable until the plates are 
offset 1.degree. to 2.degree.. In terms of the change in the thickness of 
the working surface side of the packing element, pre-load compression may 
range from approximately 2.5% to 5.0% when calculated as the percent 
difference between the width of the working surface side of the packing 
element in the pre-compressed and the uncompressed state based on the 
final pre-compressed width. Again, however, some improvement in wear 
resistance is achieved at percent compressions less than 2.5%. 
Packing elements fabricated in accordance with the present invention can be 
used in conjunction with various blow-out protector devices; the present 
invention does not reside in the particular blow-out protector device 
used. Generally, the invention element can be used in conjunction with any 
blow-out protector in which the blow-out protector is closed by applying 
pressure to the work surface through parallel opposed major surfaces of 
the packing element. The packing element of the invention can be used in 
conjunction with blow-out protectors, such as those illustrated in U.S. 
Pat. Nos. 2,139,526 and 2,231,221.

DETAILED DESCRIPTION OF A WORKING EMBODIMENT 
FIG. 1 illustrates the orientation of the packing elements of the present 
invention with respect to the drill pipe. In FIG. 1, packing elements 10 
and 12 are opposed about the drill pipe 14 such that the semi-cylindrical 
arches 16 and 17 form a cylindrical channel through which the drill pipe 
14 extends. FIG. 1 is only for illustration, in actuality packing elements 
10 and 12 would be mounted in a blow-out protector device capable of 
applying a pressure to the opposed major surfaces of the element in the 
event of a blow-out or when using the element as a stripping tool. In both 
events, pressure on the packing elements causes the elastomer to extrude 
around the drill pipe 14 and close off the space between the pipe and the 
packing elements. 
Referring to FIGS. 2 and 3, the packing element of the present invention 
comprises a pair of horizontally oriented reinforcing plates 18 and 20 
respectively positioned on the top and bottom of an elastomeric body or 
block 22. 
Various commercially available elastomers can be used in forming the 
elastomeric body 22. Elastomeric compounds which exhibit high wear and 
abrasion resistance are preferred. One technique frequently used to 
improve the wear resistance of the elastomer is to incorporate into the 
elastomer a fibrous and/or particulate reinforcing material such as fiber 
glass, nylon fiber, carbon black, etc. One composition that has been used 
effectively is shown below. 
______________________________________ 
Parts 
______________________________________ 
HYCAR 1000 .times. 225 (acrylonitrile- 
100.0 
butadien rubber 41% ACN) 
Zinc oxide 5.0 
Stearic acid 1.0 
SRF N-762 (carbon black) 56.0 
Sulfur 0.1 
VULTROL (REDAX)(N--Nitroso diphenyl amine) 
1.0 
Ethyl tuads (tetraethyl thiuram disulfide) 
2.5 
Hycor 505 glass (PPG fiberglass 1/4 inch 
20.0 
chopped strand) 
______________________________________ 
The external shape of the packing element is designed to accomodate the 
particular blow-out protector with which the elements are employed. In the 
embodiment illustrated, plates 18 and 20 and elastomeric body 22 have a 
generally rectangular layout in which the corners are truncated. For some 
types of blow-out protector, the packing elements must be 
semi-cylindrical. The reinforcing plates may extend commensurate with the 
surface of the elastomeric block, however, it is generally preferred to 
inset the plates a small distance (about 1/2") on the back side. On the 
other hand, the plates are preferably co-extensive with the rubber around 
the arch 24 so as to direct the extrusion of the rubber against the drill 
pipe when the element is under compression. 
The packing element is formed with a semi-cylindrical arch 24 which is 
centrally located on one of its major sides. Arch 24 is defined by 
corresponding aligned semi-circular cut outs in the reinforcing plates 18 
and 20 and the elastomeric body 22. The cut-outs are sized to have a 
radius of curvature larger than that of the drill pipe such that by 
applying pressure to the plates the space around the drill pipe is sealed 
off. Arch 24 defines a working surface 26 which grips the drill pipe 14 
when the packing element is under the exteriorly applied pressure of the 
blow-out protector. 
The elastomeric body 22 is best seen in FIG. 4 where it is shown in an 
uncompressed state. Body 22 is formed with top and bottom surfaces 28 and 
30 which diverge toward the working surface side 32 of the packing 
element. When placed on the elastomeric body, plates 18 and 20 abutt 
shoulders 34 and 36 respectively positioned at the back side of the upper 
and lower surfaces of the packing element. Elastomeric body 22 is 
dimensioned such that plates 18 and 20 are offset 5.degree. from 
horizontal in the embodiment illustrated. 
In the embodiment which has been illustrated, a pre-load compression is 
applied to the working side of the packing element by tieing plates 18 and 
20 with counter-sunk tie bolts 38 and 40. Two or more bolts are 
appropriately located in the packing element to provide uniform 
compression along the working surface side 32 of the element as described 
next. Tie bolt 40 extends through a bore 42 in the elastomeric body and 
screws into a threaded hole 44 in the base plate 20 as seen in FIGS. 4 and 
5. A similar arrangement is provided on the opposite side of the packing 
element for the tie bolt 38. Pre-load compression is applied to the 
packing element by tightening the bolts 38 and 40. Pivot bolts 46 and 48 
are provided in the element displaced slightly rearward of bolts 38 and 40 
so that as bolts 38 and 40 are tightened, plates 18 and 20 pivot about 
pivot bolts 46 and 48 and assume a planar parallel relationship as shown 
in FIG. 5. This has the effect of building in compression on the working 
surface side 32 of the packing element. 
Having described the invention in detail and with reference to a specific 
embodiment thereof, those skilled in the art will appreciate that numerous 
modifications and variations therein are possible without departing from 
the invention defined by the following claims: