Abstract:
A pressure compensation assembly for a drill bit having a cavity to receive the pressure compensation assembly, a mud port connected to the cavity, and a lubricant passageway connected to the cavity, is disclosed. The pressure compensation assembly includes a relief mechanism having a selected operating pressure. The pressure compensation assembly is movable from a first position to a second position within the cavity. The pressure compensation assembly may receive lubricant at a pressure exceeding the selected operating pressure to permit the flow of lubricant into the lubricant passageway while substantially preventing the release of lubricant into the mud port while in the first position. The pressure compensation assembly is operable to limit a pressure differential within the drill bit while in the second position.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to drill bits and, more particularly, to pressure compensation devices for drill bits. 
     BACKGROUND 
     Sealed bearing roller cone drill bits generally incorporate a compensating mechanism to limit the pressure differential between the lubricant sealed within the drill bit and the well bore fluid. The most common device is a flexible diaphragm separating the two fluids. The diaphragm responds to the conditions in the well to maintain a balanced pressure across the primary dynamic seals in the drill bit. These devices also typically compensate for volumetric changes of the lubricant which occur in the form of leakage or through thermal expansion. 
     Conventional compensators tend to bleed lubricant during lubrication of the drill bit due to the pressure at which lubricant is pumped into the drill bit, among other factors. As a result, a drill bit may have undesirable pressure variation and/or an improper amount of lubricant. Accordingly, it is a desire to provide an apparatus and method for providing a proper quantity of lubricant into a drill bit. 
     SUMMARY OF THE INVENTION 
     A apparatus and method for introducing lubricant into a drill bit is disclosed. 
     In one embodiment, a pressure compensation assembly for a drill bit having a cavity to receive the pressure compensation assembly, a mud port connected to the cavity, and a lubricant passageway connected to the cavity, is disclosed. The pressure compensation assembly includes a relief mechanism having a selected operating pressure. The pressure compensation assembly is movable from a first position to a second position within the cavity. The pressure compensation assembly may receive lubricant at a pressure exceeding the selected operating pressure to permit the flow of lubricant into the lubricant passageway while substantially preventing the release of lubricant into the mud port while in the first position. The pressure compensation assembly is operable to limit a pressure differential within the drill bit while in the second position. 
     In another embodiment, a drill bit having a pressure compensation assembly is disclosed. The pressure compensation assembly includes a relief mechanism having a selected operating pressure, wherein the pressure compensation assembly may receive lubrication at a pressure exceeding the selected operating pressure while substantially preventing the release of lubricant from the pressure compensation assembly. 
     In another embodiment, a method for lubricating a drill bit having a pressure compensation assembly comprising a relief mechanism having a selected operating pressure, is disclosed. The method includes the steps of providing lubricant to the drill bit at a selected pressure greater than the selected operating pressure; and substantially preventing lubricant from leaking from the pressure compensation assembly during the step of providing lubricant. 
     The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  is a partial, cross-sectional view of an arm of a roller cone drill bit having an embodiment of the pressure compensating apparatus; 
         FIG. 2  is an enlarged partial cross-sectional view of a portion of  FIG. 1 , illustrating the pressure compensating apparatus in more detail in the fill position; 
         FIG. 3  is a cross-sectional view taken generally along the line  3 - 3  of  FIG. 2  showing the pressure compensating apparatus in a fill position; 
         FIG. 4  is an enlarged partial cross-sectional view of a portion of  FIG. 1 , illustrating the pressure compensating apparatus in more detail in the operating position; 
         FIG. 5  is a cross-sectional view taken generally along the line  5 - 5  of  FIG. 4  showing the pressure compensating apparatus in a operating position; 
         FIG. 6  is a partial cross-sectional view of another embodiment of the pressure compensating apparatus, illustrating the pressure compensating apparatus in the fill position; and 
         FIG. 7  is a partial cross-sectional view of the embodiment of  FIG. 6 , illustrating the pressure compensating apparatus in the operating position. 
     
    
    
     DETAILED DESCRIPTION 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     As used herein, the terms “up” and “down”; “upper” and “lower”; “uphole” and “downhole” and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point. 
       FIG. 1  shows a partial cross sectional view of a section of a drill bit  10  suitable for an embodiment of the disclosed pressure compensator. Drill bit  10  includes a threaded body portion  12 , a cone support arm  14 , and a cutting cone  16  that is rotatably supported by the arm  14 . The cone  16  is rotatably supported on the arm  14  by ball bearings  18 , a bushing  20 , and a thrust button  22 . The cone  16  includes on its outer periphery several cutting elements  24 . The cutting elements  24  engage the wall and bottom of a formation. The application of the rotation of and the application of weight to the bit  10  forms a well bore. Although  FIG. 1  shows drill bit  10  as a roller cone drill bit, other types of earth boring bits may include embodiments of the disclosed pressure compensator. 
     Lubricant is located within the cone  16  to lubricate the bearings  18 , bushing  20 , and thrust button  22  and extend the useful life of the bit  10 . Arm  14  includes a lubricant passageway  26  and a cavity  28 . As shown in  FIGS. 1 and 2 , the cavity  28  is configured to receive an embodiment of pressure compensating cartridge or assembly  30 . Cavity  28  includes counterbore  72  positioned at the base of cavity  28  at an offset distance  68  from centerline  70  of cavity  28 . Plug  74  is positioned within counterbore  72 . Plug  74  may comprise a rubber plug or metal spring, for example, such that plug  74  may compress when pressure compensating assembly  30  is captured within cavity  28 . Plug  74  may also absorb shock to protect the components of assembly  30 . 
     Pressure compensating assembly  30  includes a flexible, cup-shaped diaphragm  32  exposed on one side to fluid pressure in the well bore (not shown) through a dome vent or mud port  36  formed in the arm  14  and on the other side to lubricant pressure. Mud port  36  intersects cavity  28  at the offset distance  68  from centerline  70 , at a different point than counterbore  72 . Bit seals  37  and  39  encircle the arm  14  within the cone  12  to retain the lubricant in the cone  16  and around the bushing  20 , bearings  18 , and thrust button  22 . The seals  37  and/or  39  also prevent deleterious materials from entering into the cone  16  and causing premature bit failure due to bearing failure. 
       FIG. 2  is an enlarged partial cross-sectional view of a portion of  FIG. 1 , illustrating the embodiment of pressure compensating assembly  30  in more detail. Referring to  FIGS. 1 and 2 , pressure compensating assembly  30  includes reservoir cap or body  38 . O-rings  40  and  42  encircle the exterior of body  38  to seal the lubricant from the downhole environment. Cone support arm  14  comprises annular O-ring grooves  80  to house and secure O-rings  40  and  42 . Body  38  includes several radial perforations  46  to provide fluid communication between lubricant located in a hollow interior  48  of body  38  and the lubricant passageway  26 . The interior  48  is exposed to the interior of diaphragm  32 , which is also initially filled with lubricant. The diaphragm  32  has an annular lip or rim  50  that is disposed between lip  52  that is formed in the interior of the body  38  and piston disk  54  to retain diaphragm within interior  48   
     The body  38  has a fill passageway  64  extending axially through the body  38  and intersecting the interior  48 . A removable plug  62  may be positioned into the fill passageway  64 . 
     Pressure compensating assembly  30  includes snap ring  56  encircling the exterior of body  38  to capture the assembly  30  within cavity  28 . Plug  74  may secure assembly  30  tightly against snap ring  56 . Assembly  30  includes end cap  58  coupled to body  38  to contain the components of assembly  30  within interior  48 . End cap  58  includes an offset end cap hole  66  positioned at a selected offset distance  68  from the centerline  70  of assembly  30  and cavity  28 . The diameter of offset hole  66  may be equal to or smaller than that of plug  74 . 
     Pressure compensation assembly  30  includes spring  60 , such as a Belleville spring, to seal assembly  30  and allow release of excess pressure within assembly  30 . For example, Belleville spring  60  may have an operating pressure of about 60 to 80 p.s.i. Assembly  30  may include piston disk  54  positioned between diaphragm  32  and Belleville spring  60 . Piston disk  54  increases the effective surface area of diaphragm  32 , to increase its pressure relieving force which corresponds to an increase in sealing force. Bellevelle spring  60  and piston disk  54  include passageways  76  and  78 , respectively. 
       FIGS. 2 and 3  show pressure compensation assembly  30  in a “fill position”.  FIG. 3  is a cross-sectional view taken generally along the line  3 - 3  of  FIG. 2 . While assembly  30  is in the fill position, offset hole  66  of end cap  58  is positioned proximate to plug  74 . In the fill position, assembly  30  may pull vacuum and allow lubricant to be pumped into assembly  30 . Because offset hole  66  is positioned proximate to plug  74 , a user may introduce lubricant into lubricant passageway  26  of drill bit  10  at a selected pressure exceeding the operating pressure of the relief mechanism, e.g., Belleville spring  60 , without causing lubricant to leak into mud port  36 . Once assembly  30  has been filled with lubricant, assembly  30  may be rotated within cavity  28  about centerline  70  to an “operating position”, at which point plug  62  may be positioned into fill passageway  64  and snap ring  56  coupled to assembly  30  to capture it in the operating position. 
       FIGS. 4 and 5  show pressure compensation assembly  30  in the operating position.  FIG. 5  is a cross-sectional view taken generally along the line  5 - 5  of  FIG. 4 . While assembly  30  is in the operating position, offset hole  66  of end cap  58  is positioned proximate to mud port  36 , providing a open channel between the two. In the operating position, assembly  30  may limit the pressure differential between the lubricant sealed within drill bit  10  and the well bore fluid. 
     As shown in  FIGS. 3 and 5 , pressure compensation assembly  30  may include a locking mechanism to selectively secure assembly  30  in the fill position or the operating position. Assembly  30  may include locking pin  88  positioned in end cap  58 . Cavity  28  may include pin holes  90  and  92  to receive locking pin  88 . As shown in  FIG. 3 , when assembly  30  is positioned into the fill position, a user may engage locking pin  88  to pin hole  92  to prevent assembly  30  from moving into the operating position. Once lubrication is completed, a user may disengage locking pin  88  from pin hole  92 , position assembly  30  into the operating position shown in  FIG. 5  and engage locking pin  88  to pin hole  90  to secure assembly  30  in the operating position. 
       FIGS. 6 and 7  show another embodiment of pressure compensation assembly  30   a . Arm  14   a  also includes side counterbore  82  positioned on a side wall of cavity  28  to allow plug  74  to be positioned therein. Arm  14   a  also includes side passageway  84  positioned on a side wall of cavity  28  and connected to mud port  36 . End cap  58   a  of assembly  30   a  includes side end cap hole  86 . 
       FIG. 6  shows assembly  30   a  in the fill position. When assembly  30   a  is in the fill position, side hole  86  of end cap  58   a  is positioned proximate to plug  74 , which is positioned in side counterbore  82 . Because side hole  86  is positioned proximate to plug  74 , a user may introduce lubricant into drill bit  10  at a selected pressure exceeding the operating pressure of the relief mechanism. Once assembly  30   a  has been filled with lubricant, assembly  30   a  may be rotated within cavity  28   a  about centerline  70  to an operating position, at which point plug  62  may be positioned into fill passageway  64  and snap ring  56  coupled to assembly  30   a  to capture it in the operating position. 
       FIG. 7  shows assembly  30   a  in the operating position. While assembly  30   a  is in the operating position, side hole  86  of end cap  58   a  is positioned proximate to side passageway  84  which is connected to mud port  36 , providing a open channel. In the operating position, assembly  30   a  may limit the pressure differential between the lubricant sealed within drill bit  10  and the well bore fluid. 
     From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a pressure compensation assembly for a drill bit that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.