Abstract:
A lock assembly for locking an outer tubular element to an inner tubular element extending through the outer tubular element for holding loads between the tubular member when lowered downhole. The assembly includes a lock mandrel connected to one of the tubular elements and the other tubular element having a recess with at least one inwardly converging side surface. A lock member, having a retracted and an expanded mode, is arranged between the first and second tubular elements. The lock member is movable relative to the recess in the retracted mode and locks against the inwardly diverging side surface when in the expanded mode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a lock assembly for locking an outer tubular element to an inner tubular element extending through the outer tubular element. Such lock assemblies are, for example, applied in a wellbore for the production of hydrocarbon fluid from an earth formation. In such application the outer tubular element can be connected to (or integrally formed with) the wellbore casing or a wellbore production tubing, and the inner tubular element is adapted to receive a wellbore device (e.g. a valve). 
     (2) Background of the Invention 
     A problem with such applications comes to light when the lock assembly is subjected to longitudinal forces. For example, when the inner element is subjected to a longitudinal force due to fluid pressure of produced hydrocarbon fluid, such force can lead to relative movement between the two elements leading to loosening of the lock connection. Furthermore, such relative movement prevents adequate transmission of signals, e.g. acoustic or electric signals, between the inner and outer tubular elements. A further problem occurs with applications involving conventional dog and lock shoulders whereby the inner tubular element is subjected to radially inward forces upon application of a pulling force, thus requiring an increased wall thickness of the inner tubular element. 
     Accordingly it is an object of the invention to provide an improved lock assembly which overcomes the problems of the conventional lock assemblies. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a lock assembly for locking an outer tubular element to an inner tubular element extending through the outer tubular element, the assembly comprising a lock mandrel connected to one of said tubular elements and being provided with a recess facing the other one of said tubular elements, the recess having at least one inwardly diverging side surface, a lock member arranged between the first and second tubular elements in a locking relationship with the other one of the tubular elements, the lock member extending into said recess and being operable between a retracted mode in which the lock member is movable relative to the recess and an expanded mode in which the lock member is expanded against the inwardly diverging side surface, the assembly further comprising an actuator means for expanding the lock member in said recess against said diverging side surface. 
     It is thereby achieved that when the lock member is in the expanded mode, a load applied to the lock assembly, e.g. a longitudinal pulling force, induces the lock member to become even more firmly locked in the recess due to the inwardly diverging side surface of the recess. Thereby the locking action of the assembly is enhanced. Furthermore, it is thereby ensured that the inner and outer elements are in firm contact with each other allowing adequate transmission of electric or acoustic signals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described hereinafter in more detail with reference to the accompanying drawings in which: 
     FIG. 1 schematically shows a first embodiment of a wellbore assembly according to the invention; 
     FIG. 2 shows detail A of FIG. 1 in a first mode of operation; 
     FIG. 3 shows detail A of FIG. 1 in a second mode of operation; 
     FIG. 4 schematically shows a lock member for use in the first and second embodiments; 
     FIG. 5 shows the lock member of FIG. 4 in another mode of operation; and 
     FIG. 6 schematically shows a second embodiment of a wellbore assembly according to the invention; 
    
    
     In the detailed description below like reference numerals relate to like components. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 there is shown a lock assembly  1  extending in a wellbore (not shown) formed in an earth formation, the assembly  1  having a central longitudinal axis  2  substantially coinciding with the with the longitudinal axis of the wellbore. The lock assembly is symmetrical with respect to axis  2 , therefore only one half of the lock assembly is shown in FIG.  1 . The lock assembly includes an outer tubular element in the form of a wellbore casing  3  arranged in the wellbore. A lock mandrel  5  is connected to the casing  3  by welds  7 ,  8  so as to form an integral part of the casing  3 . 
     Referring in more detail to FIG. 2, an annular recesses  10  is formed in the casing  3  at the inner surface thereof, the recess  10  having outwardly diverging side surfaces  12 ,  14  arranged opposite each other and an end surface  15  extending parallel to the longitudinal axis  2 . 
     An inner tubular element  16  is concentrically arranged within the casing  3 , the inner tubular element  16  including a first actuating member  18 , a second actuating member  20 , and a rotatable sleeve  22  in co-operating arrangement with the first actuating member by means of a left hand threaded connection  24  and in co-operating arrangement with the second actuating member  20  by means of a right hand threaded connection  26 . As shown more clearly in FIG. 2, an annular space  28  of variable length is thereby defined between the actuating members  18 ,  20 . Thus upon rotation of the sleeve  22 , the actuating members  18 ,  20  move relative to each other in longitudinal direction between an extended mode in which the space  28  is relatively long and a retracted mode in which the space  28  is relatively short. The location of the inner tubular element  16  relative to the recess  10  is such that the centre of space  28  is located opposite the centre of recess  10 . The ends of the actuating members  18 ,  20  facing the space  28  have end surfaces  30 ,  32  diverging in outward direction. 
     Two or more lock members  34  (only one of which is shown) are arranged in the annular space  28 , the lock members  34  being interconnected by one or more circular springs  35  acting as retracting springs keeping the lock members in place against actuating members  18 ,  20 . 
     As shown in more detail in FIGS. 4 and 5, each lock member  34  includes a first part  36  and a second part  38 , the parts  36 ,  38  being mutually rotatable about a rod  40  extending in circumferential direction. The rod  40  can be an integral part of one of the lock members  34 . Part  36  has an outer surface  41   a,  an outer side surface  41   b,  and an inner side surface  41   c.  Part  38  has an outer surface  42   a,  an outer side surface  42   b,  and an inner side surface  42   c.    
     The parts are held together by a leaf spring  44  biasing the parts  36 ,  38  to a retracted position in which the outer surfaces  41   a,    42   a  extend at an angle so as to form a concave radially outer end of the lock member  34 . The dimensions of the lock member  34  are such that the lock member is capable of passing into the recess  10  when the parts  36 ,  38  are in the retracted position. 
     Referring to FIG. 3, the orientation of the outer side surfaces  41   b,    42   b  is such that when the parts  36 ,  38  are rotated to an expanded position (shown in FIG. 5) in which the outer surfaces  41   a,    42   a  are aligned, the lock member  34  fits in the recess  10  whereby the outer surfaces  41   a,    42   a  are in contact with the radially outer surface  15  of the recess, and wherein the outer side surfaces  41   b,    42   b  are in contact with the respective side surfaces  12 ,  14  of the recess  10 . Furthermore, the orientation of the inner side surfaces  41   c,    42   c  is such that when the parts  36 ,  38  are rotated to the expanded position the inner side surfaces  41   c,    42   c  are in contact with the respective end surfaces  30 ,  32  of the actuating members  18 ,  20 . 
     The second actuating member  20  is provided with an orienting/holding slot  50  (FIG. 1) for orienting and holding an actuator (not shown) in the inner tubular element  16 . A wellbore tool (not shown), for example a downhole production valve or a downhole safety valve, is connected to the actuating member  18 . The first actuating member  18  is internally provided with a set of primary slots  54  and the sleeve  22  is provided with a set of secondary slots  56 . The actuator is adapted to engage the slot  50  and includes two parts rotatable relative to each other, each part having a set of fingers capable of gripping into the respective sets of slots  54 ,  56 . 
     During normal operation the inner tubular element  16  is lowered into the wellbore casing  3  with the actuator attached thereto, and whereby the actuating members  18 ,  20  are in the extended mode thereby allowing the leaf spring  44  of each lock member  34  to retract the lock member parts  36 ,  38  to their retracted position. Lowering is stopped when the lock members  34  are positioned opposite the annular recess  10 , as shown in FIG.  2 . The actuator is then activated whereby the sets of fingers of the actuator grip into the respective sets of slots  54 ,  56 . The two actuator parts are then rotated relative to each other so as to rotate the sleeve  22  in a direction that the first and second actuating members  18 ,  20  move relative to each other to the retracted mode. As a result the diverging end surfaces  30 ,  32  of the actuating members push each lock member  34  into the recess  10  whereby the outer surfaces  41   a,    42   a  of the respective lock member parts  36 ,  38  contact the end surface  15  of the recess  10 . Upon further rotation of the sleeve  22  the parts  36 ,  38  rotate relative to each other around the rod  40  until the lock member  34  becomes in the expanded position in which the outer surfaces  41   a,    42   a  are aligned and in full contact with the end surface  15 , and the outer side surfaces  41   b,    42   b  are in full contact with the respective side surfaces  12 ,  14  of the recess  10 . In this position the lock members  34  are locked into the recess  10 . 
     It is thus achieved that a form fit connection between the inner tubular  16  and the casing  3  is created, which provides an excellent acoustic or electrical link. In case the wellbore tool or the inner tubular element  16  are subjected to a longitudinal force, for example due to pressure of hydrocarbon fluid flowing through the wellbore, the lock members  34  become even more firmly locked into the recess  10  due to the outwardly diverging shape of the recess  10  and lock member  34 . It is thereby prevented that the connection between inner tubular element  16  and casing becomes loose or that the inner tubular element  16  collapses due to inward movement of the lock members. Furthermore, the tight connection ensures that acoustic signals for wellbore control or information transfer are adequately transferred between the inner tubular element  16  and the casing  3 . 
     Reference is further made to the second embodiment of the lock assembly according to the invention, as shown in FIG.  6 . The lock assembly is symmetrical with respect to longitudinal axis  58 , therefore only one half of the lock assembly is shown in FIG.  6 . The second embodiment is largely similar to the first embodiment, except that the sleeve for moving the actuating members  18 ,  20  relative to each other has been replaced by a set of shaped memory alloy actuators  60  (hereinafter referred to as SMA actuators), whereby one end of each SMA actuator  60  is fixedly connected to actuating member  18  by fasteners  62 , and the other end of the SMA actuator is fixedly connected to actuating member  20  by fasteners  64 . Each SMA actuator  60  has a transition temperature above which the SMA actuator has an increased length, and below which the SMA actuator has a reduced length. The sets of slots  54 ,  56  of the first embodiment are absent in the second embodiment. 
     Normal operation of the second embodiment is similar to normal operation of the first embodiment, except that instead of using the actuator tool to move the actuating members  18 ,  20  relative to each other, such movement is induced by contraction of the SMA actuators. This is achieved by installing a heater (not shown) in the inner tubular element  16  and operating the heater during lowering of the inner tubular element  16  into the casing so that the temperature of the SMA actuators is above the transition temperature. Thereafter the heater is turned off so that the temperature of the SMA actuators drops below the transition temperature whereby the SMA actuators contract and thereby move the actuating members  18 ,  20  to their retracted mode.