Patent Publication Number: US-2015069752-A1

Title: Modular Tubing Seal Bore System

Description:
FIELD OF THE INVENTION 
     The field of the invention is seal bores and more particularly where the needed space out variation is longer than the length of a standard tubular so that a modular design makes a seal bore to a desired length beyond the length of a standard tubular. 
     BACKGROUND OF THE INVENTION 
     In certain deep completions of over 7,000 meters there exists a need for component space out that exceeds the capability of honing equipment with regard to producing an integral seal bore that can accommodate space out requirements of over 20 meters. Current honing equipment can reach 20 meters by honing the limit of about 10 meters from opposed ends of a tubular. Stock lengths of oilfield tubulars are in the order of 10 to 12 meters. To date the operating premise of those skilled in the art has been that the seal bore that can be reliably produced and operated should not have any connections because the inserted seal assembly would snag in the vicinity of where the pin nose contacts the box. 
     Prior art relating generally to seal bores can be found at U.S. Pat. No. 7,621,327, U.S. Pat. No. 7,516,791 (see  FIG. 3 ) and U.S. Pat. No. 7,905,279. 
     The present invention comprises the concept of a modular seal bore that allows attainment of any desired length as the seal bore is assembled and run in the hole. A variety of connection designs are contemplated to be able to join the modules and get the target length. The inside dimension where the modules contact comes in for special treatment to ensure that even if there is a dimensional difference across the contact location of adjacent modules that such difference is positioned sufficiently far from the seal assembly that can pass by in either direction so that there is no seal assembly damage or in the differential pressure capacity of the connection. In a preferred design the adjoining seal bore surfaces across the connection have a taper so that there is a smooth transition in the seal bore wall and that even if the pin and box tolerances all add up in the same direction that any such dimensional difference is spaced sufficiently far from the outside dimension of the seal assembly that there is no physical damage to the seal assembly. Generally the length of the seal assembly exceeds the length of the tapered surfaces so that sealing integrity is maintained as the seal assembly moves relative to the seal bore. Those skilled in the art will more readily appreciate these and other features of the present invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims. 
     SUMMARY OF THE INVENTION 
     A seal bore is provided in a modular form so that a desired length of continuous seal bore can be provided with modules that are preferably secured to each other with threads. The modular concept allows overall seal bore lengths to go beyond the 20 meter limit that previously existing that could be attained with honing equipment entering opposed ends of a tubular. The modules abut each other as the threaded connection is made up. A transition zone extends in opposed direction on opposed sides of a connection that retracts the contact location between modules far enough so that even if the dimensional tolerances all go to the extreme in the pin and box that make the connection, a surface irregularity will be sufficiently small as to avoid seal stack contact that can result in potential seal damage. The seal stack length spans the transition zone to preserve sealing integrity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of modules of different size assembled into a single seal bore; 
         FIG. 2  is a detailed view at a connection between modules showing opposing tapers to a connection contact location at the seal bore; 
         FIG. 3  is an alternative to the opposing tapers of  FIG. 2  showing adjacent arcuate surfaces. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A modular seal bore assembly is illustrated in  FIG. 1 . It has modules  10  and  12  that can be of the same or different lengths. The modules connect with a thread form and design  14  that is known in the art to form a continuous polished bore surface generally designated as  16 . 
       FIG. 2  shows in more detail what occurs at the thread  14  between a pin  18  and a box  20  on connected modules  10  and  12 . The thread  14  in the preferred embodiment is a two-step thread where the pin nose  22  contacts a shoulder  24  on the box  20  marking a transition line  26  at the seal bore surface  16  that extends over as many modules as the application requires. Depending on the tolerances on the pin  18  and the box  20  there can be a radial offset at transition line  26  that can potentially snag a seal or seals  28  of an assembly on mandrel  30  that is insertable or removable from the seal bore  16  defined by modules  10  and/or  12 . 
     One way to address this potential problem that can damage the seals  28  is to provide tapers  32  and  34  in mirror image that extend to the transition line but can also transition to a parallel orientation with the seal bore  16  short of transition line  26 . In this manner the transition line  26  is at a greater diameter than the seal bore  16  on either side of the tapers  32  and  34 . The preferred taper angle is 2 degrees however larger or smaller angles can be used depending on the inside diameter of seal bore  16  and the amount of anticipated potential radial offset at the transition line  26  from the manufacturing process of a pin  18  and a box  20  that may be assembled to each other. The object is to recess the radial offset from the manufacturing process sufficiently that at the greatest envisioned offset there will not be a protrusion into the nominal seal bore  16  dimension taken outside the transition portions such as tapers  32  and  34 . While the preferred angle for the tapers  32  and  34  is 2 degrees a range of 0.5 degrees to about 5 degrees is contemplated. It is also contemplated that at the top of the ramp, furthest from transition line  26  be rounded to avoid a line transition that could potentially do harm to a seal  28 . 
       FIG. 3  illustrates an alternative embodiment showing the transition line  26  put in a recessed configuration with mirror image transitions  40  and  42 . There are adjoining arcuate surfaces  44  and  46  that can have a constant radius with the curve transitioning at locations  44  and  46  respectively. The radius can also vary for one or both segments of transitions  40  and  42 . The objective is to retract any ledge at the transition line  26  sufficiently far so that any part of the seals  28  will not snag on the ledge and rip or otherwise fail or get stuck. 
     Those skilled in the art will appreciate that the present invention presents an ability to assembly seal bores at the surface to a desired length using modules of the same or different sizes that can be attached together, preferably with standard thread forms and more preferably a two-step thread. To make the modular concept operative at the transition lines the shape of the seal bore is altered on opposed sides so that any ledges caused by machining tolerances is within the recess so that movement of seals in either direction past the transition line will not damage the seal assembly or cause loss of sealing as the seal stack is longer than the mirror image transition segments. The transitions can be planar or arcuate or combinations thereof or can be other configurations that get the transition line out of contact with the passing seal assembly in opposed directions. 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: