Abstract:
A lock assembly including a mandrel having one or more windows arranged alternatingly with one or more struts. One or more dogs are included corresponding to the one or more windows and are radially extendable therethrough. A member is operatively arranged for radially extending each of the one or more dogs. Each of the one or more dogs is operatively coupled between the member and the mandrel when fully radially extended by the member for bypassing loading in the one or more struts during loading of the assembly.

Description:
BACKGROUND 
     Lock assemblies are ubiquitous in the downhole drilling and completions industry. One common type of lock assembly involves locking a plug, choke, pressure holding device, tool, etc., in place by radially extending a plurality of dogs into engagement with corresponding features of a radially disposed tubular. In order to accommodate the dogs, windows must be formed in a mandrel or other component of the tubular string, with relatively narrow struts located between each window presenting likely failure points when the string experiences high pressure situations. This results in the need to balance the width of the dogs and the width of the struts, as making either too small can result in failure of the system (e.g., inability of the dogs to lock the string in place and/or fracture of the struts due to heavy loading). In view of these issues and the prevalence of dog type locking systems in the industry, advances and alternatives in the field of lock assemblies are always well received. 
     BRIEF DESCRIPTION 
     A lock assembly including a mandrel having one or more windows arranged alternatingly with one or more struts, one or more dogs corresponding to the one or more windows and radially extendable therethrough, and a member operatively arranged for radially extending each of the one or more dogs, each of the one or more dogs operatively coupled between the member and the mandrel when fully radially extended by the member for bypassing loading in the one or more struts during loading of the assembly. 
     A method of locking an assembly including causing relative movement between an extender member and a mandrel, the mandrel including one or more windows arranged alternatingly with one or more struts, extending one or more dogs with the extender member through the one or more windows due to the relative movement, landing the one or more dogs at a landing feature, and bypassing loading the in the one or more struts during loading of the assembly due to the one or more dogs being operatively coupled between the mandrel and the member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a cross-sectional view of a lock assembly having dogs in a retracted state; 
         FIG. 2  is a cross-sectional view of the lock assembly of  FIG. 1  with the dogs in an extended state; and 
         FIG. 3  is an enlarged view of one of the dogs of  FIG. 2  showing a radial overlap between the dog and an extender for the dog. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring now to  FIG. 1 , a locking assembly  10  is shown having a mandrel  12  and an extender  14 . The mandrel  12  includes plurality of windows  16  for accommodating a plurality of locking dogs  18  therein, with one dog  18  in each window  16 . The mandrel  12  further includes struts  20 , with one strut  20  located adjacently between each pair of the windows  16 . The mandrel  12  and the extender  14  are, for example, part of a tubular string runnable downhole in a borehole. 
     The extender  14  is arranged to radially extend dogs  18 , either radially inwardly or outwardly, through respective ones of the windows  16 . For example, the dogs  18  include a surface  22  that is arranged to correspondingly engage with another surface, e.g., a landing nipple, recess, radial restriction or other engagement surface in a tubular radially disposed with the assembly  10 . For example, the assembly  10  could be run inside of a production tubing string, with the production tubing string including recesses or a landing nipple for receiving the surface  22  of the dogs  18 . For the sake of discussion, a landing nipple  23  of a radially disposed tubular is shown in  FIG. 1  (the rest of the tubular including the landing nipple  23  being truncated for clarity of the assembly  10 ). Of course, this is just one example and other arrangements are possible and will be recognized by one of ordinary skill in the art in view of the description of the embodiments herein. 
     In the illustrated embodiment, the extender  14  includes a plurality of steps (or tiers, ramps, etc.)  24   a - 24   c . Each step  24   a - 24   c  is formed as a portion of the extender  14  having a different radial dimension than the other steps for enabling the dogs  18  to progressively extend from the mandrel  12  as the dogs  18  are successively engaged with each step  24   a - 24   c . Any suitable number of steps, ramps or tiers, including just one, could be utilized in other embodiments for extending the dogs  18  to any desired degree. Thus, in the illustrated embodiment, by axially moving the extender  14  with respect to the dogs  18 , the dogs  18  engage successively with each of the ramps  24   a - 24   c , resulting in the dogs  18  extending incrementally further through the windows  16  of the mandrel  12 . The dogs  18  are shown fully retracted in  FIG. 1  and fully deployed in  FIG. 2 . 
     In the illustrated embodiment, a threaded connection  26  enables axial movement of the extender  14  with respect to the mandrel  12 , and therefore the dogs  18 , which are held in the windows  16 . Once fully threadingly engaged, a lock mechanism  28 , e.g., a radially compressed ring or c-ring, is arranged to spring outwardly into a corresponding recess  29  for preventing any further relative movement between the extender  14  and the mandrel  12 . Other devices for enabling, and then restricting, relative movement between the mandrel  12  and extender  14  could be used, e.g., a ratcheting device or body lock ring between the mandrel  12  and the extender  14 , etc. It is also to be recognized that non-axial movement of the extender  14  could cause extension of the dogs  18 , e.g., the extender  14  could be a cam (e.g., with ramps of different dimensions arranged circumferentially as opposed to longitudinally) for enabling rotation of the extender  14  to selectively deploy the dogs  18 . 
     Since the struts  20  are of a narrowed circumferential width (in order to form the windows  16 ), the struts  20  present relatively weak sections of the mandrel  12  that are more likely to fail if the mandrel  12  is subjected to high forces. That is, as the assembly  10  is a locking assembly, it will inevitably be loaded in one or both directions, e.g., by weight of the string with which the assembly  10  is run, pressuring up chambers on either axial side of the assembly, etc. 
     Accordingly, it is one purpose of the current invention as described herein to avoid loading of, or stress in, the struts  20  during loading of the assembly  10  in or from either axial direction. As discussed above, the extender  14  includes a plurality of ramps  24   a - 24   c . In the illustrated embodiment, the ramps  24   b  and  24   c  define a set of radial dimensions x 1  and x 2 . The dogs  18  include a surface  30  having a projection  32  therefrom, which respectively share the dimensions x 1  and x 2  when the dogs  18  are engaged with the ramps  24   b  and  24   c , and are therefore fully extended by the extender  14 . The radial difference between the two dimensions x 1  and x 2  creates a radial overlap x 3  between the projection  32  of the dogs  18  and the step  24   c  of the extender  14 . It is noted that a similar overlap is formed by the step  24   a  in order to stabilize the dogs  18  in their run-in positions shown in  FIG. 1 . 
     The overlap x 3  is shown most clearly in  FIG. 3 . When the extender  14  becomes fully actuated, e.g., by fully threading the connection  26  between the extender  14  and the mandrel  12 , the step  24   c  of the extender  14  will bottom out on the projections  32  of the dogs  18 . In turn, the dogs  18  will bottom out on an edge  34  of the windows  16  of the mandrel  12 . Since movement of the extender  14  is prevented by the lock device  28 , each of the dogs  18  becomes axially locked between the step  24   c  of the extender  14  and the edge  34  of each of the windows  16 . Effectively, this makes the dogs  18  a fixed part of the mandrel  12 . In this way, any pressure on the mandrel  12  (e.g., due to a pressure event downhole of the mandrel  12 ) will transfer through the threaded connection  26  to the extender  14 , where it will transfer from the step  24   c  of the extender  14  to the projection  32  of the dogs  18  (due to the radial overlap x 3 ), and from the dogs  18  to the landing nipple  23 . In the opposite direction, weight down on the extender  14  will transfer directly through the step  24   c  to the dogs  18  to the landing nipple  23 . Advantageously, the radial overlap x 3  enables a bypass of the struts  20  so that they are not stressed during loading (e.g., without the overlap x 3 , the dogs  18  would shift to the edges of the windows  16  opposite from the edges  34 , thereby putting the struts  20  into tension). 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.