US 3653671 A
A well packoff for installing in the annulus between a well casing head and an inner concentric pipe to establish and maintain a fluid-tight seal therebetween, regardless of the well pressures to which the tool is subjected. The packoff includes a pair of resiliently deformable seal rings arranged to receive an axially directed pressure, significantly increase it to a predetermined degree, and then exert that increased pressure against the casing head and pipe.
Claims available in
Description (OCR text may contain errors)
United States Patent Shipes SELF -ENERGIZING WELL PACKOFF Kelly V. Shipes, Houston, Tex.
FMC Corporation, San Jose, Calif.
Oct. 23, 1968 Inventor:
U.S. Cl ..277/l03, 166/88 Int. Cl ..E21b 33/02, F16j 15/02 Field of Search ..277/102, 103, 114; 166/88 References Cited UNlTED STATES PATENTS 11/1922 Newkirk ..277/102 5/1956 Brown ..277/l02X [451 Apr. 4, 1972 3,438,654 4/1969 Jackson et a1 ..166/88 X Primary Examiner-Laverne D. Geiger Assistant Examiner-Robert 1. Smith Atmrney--F. W. Anderson and C. E. Tripp [5 7] ABSTRACT A well packoff for installing in the annulus between a well casing head and an inner concentric pipe to establish and maintain a fluid-tight seal therebetween, regardless of the well pressures to which the tool is subjected. The packoff includes a pair of resiliently deformable seal rings arranged to receive an axially directed pressure, significantly increase it to a predetermined degree, and then exert that increased pressure against the casing head and pipe.
13 Claims, 4 Drawing Figures PATENTEDAPR 4 I972 SHEET 1 OF 2 INVENTOR KELLY V. SHIPES ATTORNEYS PATENTED R 4 I972 SHEET 2 0F 2 INVENTOR. KELLY v. SHIPES ATTORNEYS BACKGROUND OF THE INVENTION The field of art to which this invention pertains includes tools for use in drilling wells, and in a more particular sense to well tools for sealing or packing off the annular space between the well bore and the casing at the wellhead.
In the process of drilling a well for petroleum or other fluids, the hole or bore normally is lined with pipe to prevent it from caving, preclude migration of fluids from one earth stratum to another, and avoid erosion of the bore surface by the fluids used in drilling as well as the petroleum or other fluids that are ultimately produced. This lining, called casing, is suspended or hung from a casing head at the top of the well, and is secured at its lower end to the well bore by cement. For one reason or another, practically all wells of this type are lined with two or more concentric strings of casing, the outermost or surface casing extending perhaps but a few hundred feet and the inner string or strings extending consecutively further. Each of these casing strings must be sealed fluid-tight to the casing head, and to accomplish this a well tool, called a packoff and having one or more seal rings of rubber or other resiliently deformable material is positioned or set in the head surrounding the string and then forced axially by tightening a series of lockdown screws until the seal rings exert apressure against the head and easing greater than that of the fluid to be contained.
Although the prior art is replete with various types of packoffs, including some that function quite satisfactorily where well pressures of average magnitude are involved, the pressures encountered in the deep wells now being drilled often are so high, such as 10,000 p.s.i. or more, as to be beyond the sealing capabilities of the conventional devices. The ability to generate adequate force on the packoff by means of the lockdown screws is limited, and attempting to exceed this limit in order to control these higher pressures by further turning the screws merely embeds them in the packoff or destroys them.
It was primarily to solve these problems that the efforts leading to the present invention were put forth, which efforts have resulted in a new type of packoff that not only will readily seal these very high pressures, but will do so in a safe manner avoiding any danger of impairing the integrity both of the lockdown screws and the packoff itself.
SUMMARY OF THE INVENTION Broadly considered, the present invention involves a compression-type packoff with annular-shaped seals that are selfenergized by the fluid pressure in the well in such a manner that they always exert a sealing pressure greater than the prevailing well pressure, and therefore always maintain a fluid-tight barrier between the casing head and the casing with which they are in contact. This packoff comprises axially spaced primary and secondary annular body portions, a pair of resiliently deformable annular seal rings disposed between these body portions, a pair of rigid annular junk rings intermediate the seal rings, and a number of pin-like pistons that extend from the junk rings axially and freely through the seal rings. The junk rings are axially opposed, and each is adjacent one of the seal rings. The pistons are spaced circumferentially around the junk rings and seal rings, and means are provided to retain the pistons with the junk rings. Since the pistons can move freely in an axial direction with respect to the seal rings, when pressure is applied against the junk rings and the pistons in an axial direction tending to compress the seal rings between the junk rings and the body portions, this pressure is opposed by a seal ring surface of less area than the surface against which the pressure is applied, and the seal rings exert a proportionately greater pressure against the casing head and the casing. Hence, when the applied pressure is that of the well itself, the seal rings establish a fluid-tight barrier regardless of the pressure magnitude.
All of this is accomplished automatically in a self-energizing manner, and with greatly less pressure requirements on the lockdown screws. In fact, with this packofl it is only necessary to apply sufficient initial force with the lockdown screws to establish a pressure differential across the seal rings. This force has been found to be approximately 5 percent of the lockdown screw force normally required by other types of packoffs. Furthermore, once the seal is established, any increase in well pressure will act through this unique junk ringpiston-seal ring combination to proportionately increase the sealing pressure, thereby assuring that the seal between the casing head and the casing remains intact.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of an embodiment of the invention in a well packoff, with a portion of the packoff broken away to show the arrangement of the parts more clearly.
FIG. 2 is a view in diametric section through the packoff of FIG. 1, installed between a casing head and casing string with the lockdown screws applying sufficient force to establish an initial seal between the seal rings, the casing head, and the casing string.
FIG. 3 is an enlarged fragmentary view of the right hand portion of FIG. 2.
FIG. 4 is a view like FIG. 3, but showing the condition of the packoff when both seal rings are compressed.
DESCRIPTION OF THE PREFERRED EMBODIMENT Broadly considered, and with reference to the drawings, a preferred embodiment of this invention comprises a packoff 10 with a primary or upper body portion 12, a secondary or lower body portion 14, a pair of annular rubber or otherwise resiliently deformable seal rings 16, 18 adjacent the body portions 12, 14, respectively, a pair of annular rigid junk rings 20, 22 intermediate the seal rings 16, 18, a number of pin-like pistons 24 extending from the junk ring 20 freely through the seal ring 16, and an equal number of pin-like pistons 26 extending from the junk ring 22 freely through the seal ring 18. These elements are held together in their illustrated assembled relationship by a plurality of circumferentially spaced cap screws 27 that slidably extend through aligned holes in the lower body portion 14, the seal rings l6, l8 and the junk rings 20, 22, into threaded engagement with the upper body portion 12.
As is conventional, the packoffs upper body 12 has an external annular groove 28 with a lower surface 30 that provides a bearing for lockdown screws 32 (FIGS. 2, 3 and 4) that extend through the side wall of the well casing head 34 to hold the packoff in the casing head. A lateral port 36 extends through the upper body 12 between the groove 28 and the packofis bore 38, and another port 40 extends through the casing head 34, to provide fluid communication between the interior of the packoff and the outside of the casing head, such as for circulation of well drilling fluid.
When the packoff 10 is in place in a casing head such as 34 (FIG. 2), it surrounds the top of a casing string 42 that is hung in the usual manner in the casing head by a hanger 44 with slips 46. The packoffs lower body portion 14 rests upon the hanger 44, so that when the lockdown screws 32 are threaded inwardly, thereby applying a downward force on the packoff, the seal rings 16, 18 are pressured and deformed outwardly into tight engagement with the casing head 34 and the casing 42, establishing a fluid-tight seal therebetween. This is the condition, indicated in FIGS. 2 and 3, that is established prior to subjecting the packoff 10 to greater pressures sufficient to activate its self-energizing function.
The pistons 24 extend through the upper junk ring 20 and the seal ring 16 into bores 48 in the packoff's upper body 12, and in like manner the pistons 26 extend in the opposite direction through lower junk ring 22 and the lower seal ring 18 into bores 50 in the packoffs lower body 14. The pistons 24 preferably are spaced uniformly around the packoff, thereby distributing their effect evenly, and in similar fashion the pistons 26 are spaced directly opposite the pistons 24. The opposed ends of the pistons 24, 26 are diametrically enlarged to provide flangeilike heads 24a, 26a, respectively, and these heads are countersunk into the junk rings 22, 20, so that they do not conflict when the junk rings are abutting (FIGS. 1-3). When the junk rings 20, 22 have substantially the same outer and inner diameters, respectively, as those of the seal rings 16, 18, such as is illustrated in the drawings, there is a significant difference between the size of the annular area made up of a junk ring and its pistons compared with the area of the seal ring against which the junk ring abuts, and this difference is the sum of the cross-sectional area of the pistons. Pressure acting on a piston exerts an axial force proportional to the crosssectional area of the piston body, which force is transferred to the junk ring by means of the piston retaining flange. Since this axial force is transferred from the junk ring to the seal ring, the force per unit area, or pressure at the junk ring-seal ring interface, and hence the pressure exerted by the seal rings against the casing head 34 and the casing 42, is significantly greater than the pressure applied to the piston.
In other words, when an axial force towards the seal rings is applied to the junk rings and their pistons, this force will not be increased, but will be opposed by an equal and opposite axial force exerted by the seal rings on the junk rings. However, since the surface of the seal rings that receives this force is less in area size, by virtue of the piston area, than the area of the junk rings and their pistons, the force per unit area (or pressure) on the seal rings is greater than the force per unit area (or pressure) which generates the axial force on the junk rings and their pistons. Thus, it can be said that a truly selfenergizing action is achieved by the junk ring-pistons-seal ring assembly.
FIG. 4 illustrates the effect on the packoff when a pressure P1 is introduced through the casing head 34 via a lateral port 52, as is commonly done in testing after the packoff is set in the casing head. The pressure P1, of course, acts equally on both junk rings 20, 22 in an axial direction towards the seal rings l6, l8, and likewise on the pistons 24, 26, forcing the junk rings and their pistons apart axially, and thereby compressing and deforming the seal rings into tighter engagement with the casing head 34 and the casing string 42. If, for example, the effective exposed radial surface area of the junk rings 20, 22 and the heads 24a, 26a of the pistons 24, 26, were 104 square inches, and the resisting surface area of the seal rings were 95 square inches, the resultant seal ring pressure would be greater than the applied pressure P1 by a factor of 104/95, or 1.095/l. This has been found to be a highly effective ratio for very high well pressures. However, it should be understood that other ratios are also within the scope of this invention, dependent among other things upon the nature of the composition of the seal rings, the size of the packoff, and the well pressure which is to be controlled. Lower ratios, such as l.05 to I, also have been found quite satisfactory for certain conditions. The point to be realized is that the invention does not depend upon a specific ratio for operation, but rather upon the unique combination of junk ring-pistons-seal ring as described above.
The unique self-energizing action of this invention works equally well if axial pressure is applied to just one of the junk rings, i.e., in either a downward direction as P2 (FIG. 4) against thejunk ring 22 and pistons 26, or an upward direction as P3 against the junk ring and its pistons 24. In the case of pressure P2, the seal ring 16 derives no benefit from the pistons 24 since the pressure P2 would also be exerted against the pistons end faces 24b through port 54 to equalize the pressure exerted against the heads 24a. However, since pistons 26 would be exposed to the pressure P2 only at their heads 26a, the pistons 26, the junk ring 22, and the seal ring 18 would respond to this pressure in the same way as they respond to the pressure Pl. Hence, under the influence of the pressure P2 the seal ring 18 will deform as represented in FIG. 4 to establish a fluid-tight barrier between the casing head 34 and the casing 42, thereby preventing the pressure P2 from passing by the packoff 10.
In the same manner, when a pressure P3 (FIG. 4) is applied in an axially upward direction, such as a pressure in the annulus between the casing head 34 and the casing 42, the seal ring 18 would derive no benefit from the pistons 26 since the pressure P3 is exerted equally against the piston heads 26a and their opposite end surfaces 26b, whereas the seal ring 16 is self-energized just as when the pressure P1 is applied thereto. This results in a fluid-tight barrier between the casing head 34 and the casing 42 at the seal ring 16 to effectively contain the pressure P3 below the seal ring 16.
Among the several advantages of this invention is that of the force required of the lockdown screws to set the packoff in the casing head, it being necessary only to apply enough initial force to effect a pressure differential across the seal rings 16, 18. In fact, a force ofas little as 500 p.s.i., or as low as 5 percent of that normally required with other packoffs, has been found to be quite adequate to set the packoff herein disclosed. This in turn substantially eliminates the extensive deformation of the packoff shoulders which occurs when the lockdown screws must be turned in to generate seal pressure greater than the liquid to be contained.
Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as set forth in the appended claims.
Having completed a detailed description of the invention so that those skilled in the art could practice the same, I claim:
1. A well tool for controlling fluid flow between a well head and an inner concentric pipe string, comprising 1. an annular primary body portion,
2. an annular secondary body portion coaxial with and spaced from said primary body portion,
3. a first resiliently deformable seal ring intermediate said primary and secondary body portions,
4. a second resiliently deformable seal ring intermediate said first seal ring and said secondary body portion,
5. a pair of rigid junk rings intermediate said seal rings, and
6. a plurality of pistons each of which is retained with one of said junk rings and extends freely through one of said seal rings,
said pistons, said junk rings, and said seal rings interassociated such that when said pistons and junk rings are pressured toward said seal rings said seal rings are subjected to a pressure greater per unit area than that exerted on said pistons and said junk rings.
2. A well tool according to claim 1 wherein each of said junk rings has a plurality of pistons attached thereto.
3. A well tool according to claim 2 wherein the pistons attached to one junk ring are axially opposed to the pistons attached to the other junk ring.
4. A well tool according to claim 3 wherein said pistons are evenly spaced circumferentially about said junk rings.
5. A well tool according to claim 1 wherein said pistons project through openings in said junk rings, and are retained therein by annular cap-like flanges.
6. A seal assembly for use in packing off the annulus between an outer tubular member and an inner tubular member surrounded thereby, comprising:
1. a first rigid annular support element having inner and outer axial side surfaces and first and second radial end surfaces, said second radial end surface constituting a seal-pressurizing surface, said support element having at least one axial bore intermediate its inner and outer axial side surfaces;
2. a second rigid annular support element having inner and outer axial side surfaces and primary, secondary radial end surfaces and at least one axial bore intermediate its inner and outer surfaces;
3. a resiliently deformable seal ring having inner and outer axial side surfaces, first and second radial end surfaces, and at least one axial bore intermediate its inner and outer axial side surfaces, said first end surface of said seal ring confronting the seal-pressurizing surface of the first support element, and said second end surface of said seal ring confronting the primary end surface of the second support element;
4. a piston freely residing in one of the axial bores of each of the first and second support elements and the seal ring, said piston having a radial end surface and being capable of free longitudinal non-rotative movement with respect to said first and second support elements and said seal ring substituted therefor.; and
. means to limit in one direction only the free longitudinal non-rotative movement of the piston in the axial bore of said first support element,
whereby when the seal assembly is in position in the annulus between the outer and inner tubular members and a force at a first pressure per unit area is exerted axially against the first radial end surface of the first support element and the radial end surface of the piston, the seal-pressurizing surface of the first support element transmits said force to the first end surface of the seal ring at a second pressure per unit area greater than said first pressure per unit area.
7. A seal assembly according to claim 6 wherein the first support element and the seal ring have a like plurality of coaxial bores, and a like plurality of pistons extends into said bores.
8. A seal assembly according to claim 6 including means for holding the first support element and the seal ring together.
9. A seal assembly according to claim 6 wherein said piston retaining means comprises a radial flange-like head of greater cross-sectional area than the bore in the first support element.
10. A seal assembly according to claim 9 wherein the bore in the first support element is counterbored to receive the piston head.
11. A seal assembly according to claim 6 wherein the magnitude X of the area of the first radial end surface of the first support element plus the area of the radial end surface of the piston is greater than the magnitude Y of the area of the end surface of the seal ring.
12. A seal assembly according to claim 11 wherein the ratio of magnitude X to magnitude Y is at least 1.05 to l.
13. A seal assembly according to claim 12 wherein the ratio is 1.095 to 1.
UNITED STATES PATENT OFFICE 1 Fij -1050' (5/69) CERTIFTCATE 0F CORRECTION Patent No. 5 7 Dated April l, 1972 Inventor(s) KELLY V. SHIPES EDWARD M.FLETCHER,JR. Attesting Officer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
061' Q; 'iihe f ter "outer" insert axial side Col 5, line 10, after ring" insert 5 Col 5, line 10 delete "substituted therefor;"
Signed and sealed this 26th day of September 1972.
ROBERT GOTTSCHALK Commissioner of Patents