Abstract:
The present invention provides for a rotary fluid-sealing structure for a harsh environment which reduces the PV pressure (×velocity) that a sealing system may be exposed through the use of a rotary speed reducing planetary gear system. The system may have multiple stages with the amount of velocity reduction produced by the system being determined by the number of stages and the planetary gear ratios. Several alternatives are presented for the sealing under extreme conditions such as found in the interface between a wash-pipe and a rotary drilling string in a drilling rig.

Description:
[0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/756,781 filed Jan. 6, 2006. This document is to be expressly incorporated herein in its entirety by this specific reference thereto. 
     
    
       [0002]    The present invention generally relates to sealing devices which require added sealing performance and as such particularly applies to severe fluid sealing applications such as, for example, a sealing system or structure for a wash-pipe rotary swivel joint used in oil drilling rig top drives. 
         [0003]    The present invention is particularly applicable for rotary sealing systems for sealing drilling mud on land or sea-based drilling platforms. The conditions in this operation include a combination of extremely high pressure, up to 7,500 psi, high-speed up to 2000 fpm and high temperature to 350° Fahrenheit or higher. 
         [0004]    Drilling pipe diameters are generally from 3 to 5 inches and as a result of high pressure×velocity (PV) conditions, the life of the sealing system is relatively short and unpredictable. 
         [0005]    The present invention includes a sealing structure which provides predictability in seal service life which, in turn, prevents costly unplanned downtime and longer sealing system life by useful factors. 
       SUMMARY OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
       [0006]    A rotary fluid-sealing structure using speed reduction stages in accordance with the present invention generally includes a rotatable lower member, a fixed upper member, and an intermediate rotatable member disposed between the lower and upper members. 
         [0007]    A first sealing system is disposed between the lower member and the intermediate member and a second sealing system is disposed between the intermediate member and the upper member. 
         [0008]    Means, coupling the lower member and the intermediate member, is provided for causing the intermediate member to have a rotational speed lower than a rotational speed of the lower member in order to reduce speed differential across each of the sealing systems. 
         [0009]    In accordance with aspects of the present invention, a plurality of intermediate rotatable members may be sequentially disposed between the lower member and the upper member. Thus, sealing systems disposed between adjacent lower intermediate and upper members are provided with lower or reduced speed differentials there across. 
         [0010]    In other aspects of the present invention, a fluid-sealing structure may include a spline driven rotatable lower wash pipe, a fixed upper wash pipe, and an intermediate rotatable wash pipe concentrically disposed with the lower wash pipe and having one end thereof disposed over an end of the lower wash pipe and another end thereof abutting a face of the upper wash pipe. 
         [0011]    In yet other aspects of the present invention, a rotary fluid-sealing system is disposed between the lower wash pipe and the intermediate wash pipe and a pressure sealing system is disposed between the intermediate wash pipe and the upper wash pipe. 
         [0012]    The pressure sealing systems for the reduced-speed stages could use either of several types of fluid seals including an elastrometric V-type packing or an energized lip-seal of a polymeric type plastic material, etc. For this example, the figure shows a pressure seal-system innovation. At each pressure-seal location is a seal system consisting of two pressure-seals separated by a grease-pack. This configuration provides a means of isolating the harsh sealing challenges of both the abrasive media and the high differential pressure. 
         [0013]    In certain preferred embodiments, a sun driving gear is disposed on an outer circumference of the lower wash pipe along with a fixed ring gear and a plurality of planetary spur gears, coupled to the intermediate wash pipe, are disposed between the lower wash pipe driving gear and the ring gear in order to cause the intermediate wash pipe to have a rotational speed lower than a rotational speed of the lower wash pipe to reduce speed differentials across each of the sealing systems. Preferably, a rotational speed experienced by each of the sealing systems is half the rotational speed of the lower wash pipe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The advantages and features of the present invention may be more clearly understood by the following detailed description when considered in conjunction with the appended drawings of which: 
           [0015]      FIG. 1  is a cross sectional view of a rotary fluid-sealing structure using space-reductions stages in accordance with the present invention generally showing a lower member, and intermediate member, and an upper member along with two sealing systems and a sun-driving gear, ring gear with planetary spur gears disposed therebetween; 
           [0016]      FIG. 2  is a cross sectional view taken along the line  2 - 2  of  FIG. 1  showing the planetary gear system; and 
           [0017]      FIG. 3  is a view taken along the line  3  of  FIG. 2  illustrating an individual planetary gear engaging the sun-driving gear and the ring gear. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    With reference to  FIG. 1 , a rotary fluid-sealing structure  10  provided in accordance with aspects of the present invention is shown, which includes a rotatable lower member, or wash pipe,  12  which is driven by a shaft spline  14  for a lower drive collar (not shown) along with a fixed upper member, or wash pipe  20 , with an intermediate rotatable member, or wash pipe  24 , disposed between the lower wash pipe  12  and upper wash pipe  20  as will be hereinafter described in greater detail. The fluid-sealing structure  10  may be useable with a land or sea-based drilling platform comprising drivers, such as motors and pumps, a rotating drill string, a hoisting structure, and means for circulating drilling fluid. 
         [0019]    A first pressure sealing system  28  is disposed between the lower member, or wash pipe,  12  and the intermediate member, or wash pipe,  24 . The first sealing system  28 , is a media-isolation sealing system and is configured to isolate two harsh conditions of a hard to seal media, i.e. drilling mud that is both abrasive and non-lubricating and a high-pressure differential. The components of the sealing system  28 , namely the floating seal  30 , the rear seal  32  and the grease pack  34 , are preferably selected to withstand adverse conditions. In operation, the media isolation system functions as follows: 
         [0020]    The media pushes on the floating barrier lip seal  30 , which is typically a U-cup lip seal that can be spring and media pressure energized. Behind the floating seal  30  is a lubricating fluid  34 , usually grease, that transfers pressure to the rear seal  32  and provides lubrication for the sealing system  28  to increase surface life. The floating seal  30  then floats a small distance to maintain the pressure on the grease pack, or lubricating fluid,  34 . 
         [0021]    A second sealing system  38  is disposed between the intermediate wash pipe  24  and a face  40  of the upper wash pipe  20  and includes a floating seal  44 , a rear seal  46 , and a grease pack, or lubricating fluid,  48  disposed there between. The second sealing system  38 , is a media-isolation sealing system similar to the sealing system  28  described above. The two seal system may be known as pressure seals in the relevant art. 
         [0022]    It should be appreciated that while the wash pipe drive system, or structure,  10  is shown with one intermediate wash pipe member  24 , an arrangement with multiple identical or similar intermediate wash pipes may be incorporated to further reduce PV values on the seal systems to provide a longer service life, only two seal systems  28 ,  38  being shown. As further discussed below, a respective epicyclic gearing or planetary gearing system would further reduce the rotational velocity of each successive intermediate wash pipe to thereby reduce the PV values and therefore increase seal performance and seal life. 
         [0023]    With reference also to  FIG. 2 , a sun-driving gear  52  is disposed on a circumference  54  of the lower wash pipe  12  along with a fixed ring gear  58  and a plurality of planetary spur gears  60  provide a means, coupling the lower wash pipe  12  and the intermediate member pipe  24 , for causing the intermediate wash pipe  24  to have a lower rotational speed than a rotational speed of the lower wash pipe in order to reduce speed differentiation across each of the sealing systems  28 ,  38 . 
         [0024]    It should be appreciated that while a geared system is provided for coupling the lower wash pipe  12  and the intermediate wash pipe  24  for exemplary purposes, the drive system could incorporate any of several drive mechanisms or means (not shown) such as chains, belts, other mechanical drive systems, an electric motor system, a hydraulic motor system or pneumatic motor system. All of these couplings for reducing the speed between the lower wash pipe  12  and intermediate wash pipe  24  are to be considered within the scope of the invention. 
         [0025]    In accordance with the present invention, the intermediate wash pipe  24  rotates at a reduced speed, perhaps 50 percent, relative to the lower wash pipe rotation and thus the two sealing systems  28 ,  38  will experience lower speed differential there across, which provides for reduced PV values and therefore an increase in seal service life. 
         [0026]    In operation, the sun-drive gear  52  meshes with the planetary spur gear  60 , which in turn meshes with the fixed ring gear  58  to obtain a speed reduction that is determined by the gear ratios. The spur gear  60  may be coupled with the intermediate wash pipe  24  by pins  64 . 
         [0027]    More particularly, the intermediate wash pipe  24  may be supported at an upper end  66  by a bushing  68  and a plurality of spring energized lip seals  72 ,  74 ,  76  Lubricating oil is provided in a cavity  78  for lubricating the drive gear  52 , ring gear  58 , and plurality of planetary gears  60 . 
         [0028]    The sealing system  28  bears against a retaining ring  82  which provides a fixture for supporting a bushing  84  for a lower portion  88  of the intermediate wash pipe  24 . Similarly, a retaining ring  92  supports a bushing  68 , and retaining ring  119  supports a bushing  94 . 
         [0029]    The structure  10  is assembled with a wash pipe top nut  96  screwed to threads  100  on the fixed upper wash pipe  20  along with bolts  102 ,  104 ,  106 ,  108 ,  110 . Relief ports  114 ,  116  are provided to divert any media leakage, which eventually migrates past the pressure seals, away from any critical components such as the centering bushings  68 ,  84  and the planetary gear  60 . Spring energized low friction lip seals  72 ,  74 ,  118  are placed, as shown, to confine any leakage from the sealing system to the relief ports  114 ,  116 . 
         [0030]    Although there has been hereinabove described a specific rotary fluid-sealing structure using speed-reduction stages in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims. As examples, grease ports may be incorporated to replenish the grease packs, each sealing system may include multiple seals having multiple grease packs positioned there between to gradually reduce the seal back pressure for the subsequent seal stages, and using split-housings where applicable for ease of maintenance and repairs, just to name a few.