This Application Claims Priority from Provisional Application No. 60/736,891 filed Oct. 15, 2005 for Packing Assembly For Rotary Drilling Swivels, the disclosure of which is incorporated herein by reference for all purposes
1. Field of the Invention
The present invention relates to a stuffing box and a sealing assembly for use in effecting fluid sealing between a fixed body and a rotating body and, in particular around the wash pipe of a rotary drilling swivel.
2. Description of Prior Art
In the drilling of oil and gas wells, a drill bit is rotated in a borehole by means of a string of drill pipe. The drill pipe is rotated on the surface mechanically by a rotating table mounted on a drilling platform or by a hydraulic motor, commonly referred to as a top drive. As is common in such oil and gas well drilling, drilling fluid or mud is circulated through the drill pipe and the drill bit to cool the drill bit and remove the cuttings, the mud being recirculated to the surface and the cuttings removed from the drilling fluid/mud so it can be reused.
The rotary drilling swivel commonly used in the drilling of oil and gas wells provides rotating support for the drill string suspended from it and a sealed passageway for circulating drilling fluids into the drill string. The drill pipe is in open-flow communication with a wash pipe, through which the drilling fluid flows, the wash pipe usually being stationary. A packing assembly forming part of the swivel rotates with the drill pipe, and is in sealing engagement with the wash pipe to prevent loss of drilling fluid out of the swivel assembly.
Depending on the depth of the well and/or well conditions, drilling fluid pressures can reach several thousand psi, and at these high pressures, conventional, prior art packing assemblies used to seal between the wash pipe and the rotary head to which the drill pipe is secured have reduced life, resulting in leaking.
In particular, as deeper wells are drilled at higher mud pressures, e.g., 6,000 psi, turning rates of 220 rpm and high flow rates of drilling mud, the wearing problem on the seals between the wash pipe and the rotary head to which the drill pipe is secured is exacerbated. For example, the wash pipe for a 3″ bore wash pipe may have a 3.65″ OD and rotate at 120 rpm at a maximum pressure of 3,500 psi. This calculates to PV of 398,565 psi-fpm. In contrast, when a 4″ bore wash pipe (OD=4,875″), typically used in deep, high-speed drilling, is employed at pressures of 6,000 psi and a turning rate of 220 rpm, a PV of 1,684,575 psi-fpm is reached. This PV value is typically more than four times more severe than that usually encountered in conventional drilling operations. Presently, packing materials used to seal between the wash pipe and the rotary head, under the severe conditions noted, have an expected life of from 20 hours to a maximum of several hundred hours. As is well known to those skilled in the art, once the packing fails, it is necessary to stop the drilling and replace the packing, an operation that in and of itself can take eight to ten hours. Furthermore, this is not the total downtime before drilling can be resumed. It will be appreciated that on a deepwater drill ship or rig, this amount of downtime translates to thousands of dollars and penalties.
Typical prior packings now used in rotary drilling swivels are usually made from molded rubber and fabric composites and in this regard, a number of combinations of various fabrics and elastomers can be employed depending upon the operating conditions. For example, a common elastomer is Buna-n rubber and a common fabric is cotton. To these composites can be added lubricating materials such as graphite, molybdemum disulfide, PTFE resins, etc.
It is becoming increasingly apparent that these typical prior art packings made from the materials described above do not have sufficient lifetime when operating under severe conditions of high mud pressures, high turning rates and high flow rates.
Presently, there are materials that can be used to make packings or seals for these systems that can withstand these higher PV's, as well as the high heat loads generated at the interface of the packing or seal lip and the wash pipe surface. Thus, while more sophisticated materials such as PTFE, PTFE alloys, high temperature plastics and rigid elastomers/rubber composites can withstand these harsh operating conditions, they have disadvantages which affect their sealing ability. These materials, while they perform well initially, lose their sealing ability once the drilling is stopped and/or the mud pressure is reduced, e.g., when it is necessary to add a new joint of drill string or for some other reason encountered in the drilling operation. The reason that seals of these more sophisticated materials fail to seal under these conditions, i.e., moving from high PV's to low PV's, is because of their material make-up. Typically these materials are generally hard or rigid elastomers, plastics, etc., and generally yield under the initial stress and accordingly, lose their interference engagement with the wash pipe, such that when mud pressure is brought back up to operating conditions leakage occurs. As noted above, conventional packing materials of softer elastomers/rubber composites have sufficient elasticity to maintain a sealing force under high or low PV's, but they have poor wear characteristics.
In one embodiment the present invention provides a sealing assembly for use in sealing between a relatively rotatable housing and a member extending through the housing. The sealing assembly includes an annular seal ring carrier; an annular seal ring carried by the carrier, the seal ring having an annular, radially outer portion and an annular, radially inner portion; an annular seal ring spreader operatively engaged with the seal ring; an elastic biasing member operatively engaged with the seal ring spreader; and an annular follower. The spreader exerts a greater force on one of the radially inner or outer portions than the other of the radially inner or outer portions when the spreader is biased toward the seal ring.
In another embodiment, the present invention provides a stuffing box or packing assembly for use in sealing between a fixed housing and a rotatable member extending into the fixed housing, the stuffing box assembly including a housing having a bore for receipt of a rotatable shaft, the housing forming a sealing assembly chamber, and a sealing assembly as described above received in the sealing assembly chamber in the housing.
Referring first to
Referring now to
Adapter 45 engages a second annular, spacer 60 which in turn engages a wave spring 62 which is spaced from another wave spring 64 by annular spacer 66. Wave spring 64 in turn engages a second, annular seal ring spreader 66. A second O-ring keeper 65 holds spacer 60 in place. A second seal ring 68 is carried in an annular notch 70 of a second seal ring carrier 72, seal ring 68 having an annular, radially inwardly extending sealing lip 74 which is engaged by spreader 67 and an annular, radially outer portion 69 that also forms a sealing lip. The seal ring 68 is nested in a second annular adapter 76 which in turn is nested in end wall 28 of packing gland 24.
It will be appreciated that when threaded follower 32 is tightened such that it is moved in the direction of arrow A, wave springs 50, 52, 62 and 64 will all be compressed. In this regard, the sizing of the spacers, the seal ring carriers, adapters, etc. is such that when the wave springs are in the relaxed position, i.e., not under compression, their axial extent would be greater than as shown in
As can be seen from
Turning now to
Positioned in the annulus surrounding wash pipe 98 is a sealing assembly having a seal ring carrier 106, seal ring carrier 106 having an axially extending annular skirt 108 and a radially inwardly extending annular flange 110. An O-ring 112 provides sealing between a threaded follower 104 and seal ring carrier 106. Skirt 108 and flange 110 cooperate to form an axially extending, radially opening recess 114. Received in recess 114 is a spacer 116 that is engaged by seal ring 118 having a radially inwardly extending, annular sealing lip 120. Seal ring 118 also has an annular, radially outwardly extending sealing lip 122. An annular spreader 124 engages sealing lip 120 in a manner described more fully hereafter. A wave spring 126 engages spreader 124. A second wave spring 128 is nested between flange 110 and a spacer 130.
The assembly shown in
As in the case described in
The seal rings can be made from a large variety of materials which are wear and heat resistant. Non-limiting examples of materials which can be employed are PTFE alloys, high temperature plastics, rigid elastomer/rubber fabric composites, engineered plastics, and other materials that are capable of withstanding high temperatures and pressures but which can plastically yield or take a permanent set. Accordingly, the seal rings can be made of any plastic, elastomeric or composite materials which can withstand high temperatures, e.g., greater than about 300° F., and high pressures, e.g., greater than about 3,000 psi. The seal rings can be constructed in a variety of ways. Thus, the seal ring can be made of a single material, e.g., thermoplastic or thermosetting resin including such materials as nylon, polyesters, aramids, acrylics, glass, carbon and the like and can also incorporate reinforcements as, for example, a composite of a thermoplastic or thermosetting resin incorporating braided metal wire, fibrous materials such as fiberglass, carbon fibers, etc. Further, seal rings can be constructed such that the body of the seal and the sealing lip are made of one construction and there is a reinforcing heel bonded to the body of the seal to prevent extrusion. Such reinforcing or anti-extrusion sections are particularly desirable when the fluids being handled, e.g., drilling mud, contains abrasives or other solid materials.
As noted above, these more sophisticated materials and seal constructions for the most part have a tendency to plastically yield or take a permanent set when under load and/or high temperatures for extended periods of time and accordingly loose at least some of their sealing capabilities over time. However, the sealing assembly of the present invention compensates for this yield by utilizing the stored energy of the wave springs in combination with the seal ring spreaders to urge the sealing lips into sealing engagement with the wash pipe.
Although the seal ring is shown as being of the V- or Chevron type, the seal rings can have any cross-sectional configuration provided they have at least one annular, radially inwardly extending sealing lip which can sealingly engage the wash pipe in fluid-tight engagement and which can be urged radially inwardly under the action of the seal ring spreaders from force exerted by the wave spring(s).
In the description above, reference has been made to a seal ring carrier. The term carrier is intended to mean any body of whatever shape in or on which the seal rings can be nested, carried, positioned, housed or supported.
It will be appreciated that while two sealing assemblies of seal rings have been shown in
While the invention has been described with respect to wave springs, it will be appreciated that Belville springs and other annular-type springs can be used as well. It is also possible to employ compression-type coil springs, e.g., a compression-type coil spring having an ID greater than the OD of the wash pipe such that it can encircle the wash pipe or a series of small coil springs circumferentially arranged around the wash pipe and carried by a spring holder. However, washer-type springs such as Belville springs and wave springs are preferred because of more even force distribution exerted by such springs around their circumference.
While the invention has been specifically described with respect to a radially inwardly extending sealing lip, it will be appreciated, that the sealing lip could be radially outwardly extending. In circumstances where the sealing lip was radially outwardly extending, a seal ring carrier would be employed, albeit though in this circumstances seal ring carrier would be radially inwardly of the radially outwardly extending portion of the seal ring. Also, in cases where the sealing lip was radially outwardly extending, the seal ring spreader would be positioned radially outwardly of the seal ring carrier but would still serve the purpose of cooperating with a suitably disposed spring such as a wave spring, Belville spring, etc. to urge the radially outwardly extending sealing lip in a radially outwardly direction.
The seal ring spreaders can take many shapes. It is only necessary that the seal ring spreader be operatively engageable with the seal ring or a portion thereof, such that when an axial force is exerted on the portion of the seal ring spreader that engages the seal ring, it preferentially acts either on the radially inner portion of the seal ring or the radially outer portion of the seal ring. Stated differently, the seal ring spreader should be of a size and shape such that it operatively acts upon the seal ring to exert a greater force on one or the other of the radially inner portion of the seal ring or the radially outer portion of the seal ring when the spreader is biased towards the seal ring by the biasing members, e.g., the wave springs. It will, thus, be appreciated that various combinations of shapes of the seal ring and the seal ring spreader can be employed provided they cooperate to impart a force vector on the seal ring that urges either the outer portion of the seal ring in a generally radially outward direction or the inner portion of the seal ring in a generally radially inward direction.
In cases where both the outer and inner portions of the seal ring form sealing lips, i.e., an annular, radially outwardly extending sealing lip and an annular, radially inwardly extending sealing lip, then the spreader will be of a type that engages one or the other of the sealing lips preferentially with a greater force than any force that might be exerted on the other of the sealing lips, albeit minimal.
It is also to be understood that the fact that the seal ring spreader cooperates with the seal ring to selectively exert a greater force on either the radially inner portion or the radially outer portion does not preclude some engagement of the seal ring spreader with both the inner and outer portions, provided that a greater force is exerted on either the inner or outer portion of the seal ring relative to the other portion of the seal ring. Furthermore, the seal rings of the type used in the assemblies of the present invention, of their very nature, wear with time. Accordingly, it will be recognized that when a sealing assembly of the present invention is initially installed and, by way of example, if the seal ring spreader is exerting a greater force on an annular, radially inwardly extending sealing lip with essentially no force being exerted on the radially outer portion of the seal ring, whether that outer portion be another sealing lip or not, as the seal ring wears, the seal ring spreader may well engage the radially outer portion of the seal ring to some extent, albeit with still a lesser force than that exerted on the radially inwardly extending sealing lip.
While the invention has been described above with respect to sealing between a stuffing box and the wash pipe of a rotary drilling swivel, it is to be understood that it is not limited. The packing assembly can be used between any two relatively moveable bodies to effect fluid-type sealing between the bodies and is particularly applicable to environments which require that the seal ring be made of a material which can withstand high pressures, temperatures and is wear resistant but which has a tendency to undergo plastic yield or permanent set when under load, particularly for extended periods of time and/or at elevated temperatures.
Also, while the invention has been described with respect to a member, e.g., a wash pipe, extending through a housing, it will be apparent that the member could extend into the housing rather than through the housing.
Number | Date | Country | |
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60736891 | Nov 2005 | US |