Patent Publication Number: US-7900708-B2

Title: Multiple-block downhole anchors and anchor assemblies

Description:
FIELD OF THE INVENTION 
     This invention relates generally to downhole equipment for production wells and, in particular, to downhole anchors and anchor assemblies for such equipment. 
     BACKGROUND 
     Torque anchor assemblies are used in applications where rotation of tubular elements or tools in a downhole well environment is not desirable and is to be prevented. One primary application of such anchor assemblies is in conjunction with Progressive Cavity (PC) pumps, to prevent a tubing string from rotating in a certain direction when a pump is working. In some production wells, for example, if a PC pump&#39;s stator or the tubing string is allowed to turn to the right, joints in the tubing string can be loosened and the pump and/or the tubing can be lost in the well. 
     A torque anchor assembly is typically run in a well to the depth where it is required, and set by applying either right- or left-hand torque to a mandrel through the tubing string. Some sort of anchor element is pushed outward by the mandrel, to contact the well bore or casing. Many different types of torque anchor assemblies are currently available. However, the actual anchor elements tend to be substantially unprotected from the casing or well bore during positioning of a torque anchor assembly and are thus subject to wear. 
     SUMMARY OF THE INVENTION 
     Some embodiments of the invention provide a protected torque anchor assembly having one or more anchors which are set by applying right hand torque to a mandrel and prevent right hand rotation. When the torque is released, each anchor automatically disengages the casing and re-sets itself in a run position to be moved in a well or pulled to the surface. 
     According to one aspect of the invention, a downhole anchor assembly for a tubing string is provided. The anchor assembly includes a mandrel to be coupled to the tubing string; an anchor block coupled to move, with rotation of the mandrel, between a run position out of contact with a well bore and a set position in contact with the well bore to set the downhole anchor assembly in the well bore; a drag block, coupled to the mandrel, to contact the well bore at least when the anchor block is out of contact with the well bore; and a biasing arrangement to bias the anchor block away from the well bore and the drag block toward the well bore. 
     The anchor block may be coupled to move from the run position toward the set position with rotation of the mandrel in a predetermined direction. 
     In some embodiments, the mandrel is rotated in the predetermined direction by applying a torque to the mandrel, and the biasing arrangement is coupled to move the anchor block from the set position toward the run position when the torque is removed from the mandrel. 
     The drag block and the anchor block may include respective spring seat surfaces, in which case the biasing arrangement may include at least one spring, such as a coil spring or a leaf spring, positioned between the spring seat surfaces. 
     Where the drag block includes multiple spring seat surfaces and the anchor block includes a plurality of spring seat surfaces opposed to the plurality of spring seat surfaces of the drag block, the biasing arrangement may include multiple springs respectively positioned between opposed pairs of the plurality of spring seat surfaces of drag block and the plurality of spring seat surfaces of the anchor block. 
     The anchor block includes a structure to engage a shoulder on the mandrel in some embodiments. The shoulder moves the anchor block from the run position toward the set position with rotation of the mandrel in a predetermined direction and allows the biasing arrangement to move the anchor block from the set position toward the run position with rotation of the mandrel in a direction opposite to the predetermined direction. 
     The structure of the anchor block and the shoulder of the mandrel may be shaped to limit movement of the anchor block with rotation of the mandrel in the predetermined direction. 
     In some embodiments, the downhole anchor assembly includes multiple anchors. Each anchor includes a drag block coupled to the mandrel, an anchor block coupled to move between the run position and the set position with rotation of the mandrel, and a biasing arrangement to bias the drag block toward the well bore and the anchor block away from the well bore. 
     A housing may also be provided to at least partially enclose the mandrel, the drag block, and the anchor block. The mandrel is rotatable relative to the housing, and the drag block is coupled to the mandrel by the housing. The drag block and the biasing arrangement may then retain the anchor block in contact with the mandrel. 
     The downhole anchor assembly may also include bearings positioned between the housing and the mandrel. The bearings connect the housing to the mandrel and allow the mandrel to rotate relative to the housing. A guide screw may be installed in a bore in the mandrel to engage a slot in the housing, such that the guide screw and the slot limit an extent of relative rotation between the mandrel and the housing. 
     In some embodiments, the downhole anchor assembly includes a pair of retaining rings coupled to the mandrel. The drag block is coupled to the mandrel by the pair of retaining rings, and the drag block and the biasing arrangement retain the anchor block in contact with the mandrel. 
     A method is also provided, and includes connecting a mandrel of an anchor assembly to a tubing string of a production well, the anchor assembly further comprising an anchor block coupled to move, with rotation of the mandrel, between a run position out of contact with a well bore of the production well and a set position in contact with the well bore to set the downhole anchor assembly in the well bore; a drag block, coupled to the mandrel, to contact the well bore at least when the anchor block is out of contact with the well bore; and a biasing arrangement to bias the anchor block away from the well bore and the drag block toward the well bore; moving the anchor assembly, with the anchor block in the run position, to a desired downhole location; and rotating the tubing string to move the anchor block into the set position to set the anchor assembly at the desired downhole location. 
     Rotating may involve rotating the tubing string to apply a torque to rotate the mandrel in a predetermined direction. The method may also include removing the torque from the mandrel, to thereby allow the biasing arrangement to move the anchor block from the set position to the run position and release the anchor assembly. 
     In some embodiments, the method also includes moving the anchor assembly, with the anchor block in the run position, to a second desired downhole location; and rotating the tubing string in the predetermined direction to move the anchor block into the set position to set the anchor assembly at the second desired downhole location. 
     A downhole anchor is also provided, and includes an anchor block for moving, with rotation of a mandrel, between a run position out of contact with a well bore and a set position in contact with the well bore to set the downhole anchor assembly in the well bore; a drag block, coupled to the anchor block, for contacting the well bore at least when the anchor block is out of contact with the well bore; and a biasing arrangement to bias the anchor block away from the well bore and the drag block toward the well bore. 
     The drag block and the anchor block may include respective spring seats, in which case the biasing arrangement may include at least one spring, illustratively a coil spring or a leaf spring, positioned between the spring seats. 
     Other aspects and features of embodiments of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of embodiments of the invention will now be described in greater detail with reference to the accompanying drawings. 
         FIG. 1  is a side view of an example anchor assembly according to an embodiment of the invention. 
         FIG. 2  is an isometric view of the example anchor assembly of  FIG. 1 . 
         FIG. 3  includes end and side views of the example anchor assembly of  FIG. 1  in a well bore. 
         FIG. 4  is a cross-sectional view of the example anchor assembly of  FIG. 1  along line A-A of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the example anchor assembly of  FIG. 1  along line B-B of  FIG. 3 . 
         FIG. 6  is a cross-sectional view of the example anchor assembly of  FIG. 1  along line C-C of  FIG. 3 . 
         FIG. 7  is an exploded view of the example anchor assembly of  FIG. 1 . 
         FIG. 8  is a front view of an example dual-block anchor. 
         FIG. 9  is an exploded view of the example dual-block anchor of  FIG. 8 . 
         FIG. 10A  is a side view of the example anchor assembly of  FIG. 1 . 
         FIGS. 10B through 10E  include cross-sectional views of the example anchor assembly of  FIG. 1  along lines D-D and E-E of  FIG. 10A , for different positions of the dual-block anchors. 
         FIGS. 11A and 11B  include isometric and cross-sectional views of the example dual-block anchor of  FIG. 8  in different positions. 
         FIG. 12  is a side view of an example anchor assembly according to another embodiment of the invention. 
         FIG. 13  is an isometric view of the example anchor assembly of  FIG. 12 . 
         FIG. 14  includes end and side views of the example anchor assembly of  FIG. 12  in a well bore. 
         FIG. 15  is a cross-sectional view of the example anchor assembly of  FIG. 12  along line F-F of  FIG. 14 . 
         FIG. 16  is a cross-sectional view of the example anchor assembly of  FIG. 12  along line G-G of  FIG. 14 . 
         FIG. 17  is a cross-sectional view of the example anchor assembly of  FIG. 12  along line H-H of  FIG. 14 . 
         FIG. 18  is an exploded view of the example anchor assembly of  FIG. 12 . 
         FIG. 19A  is a side view of the example anchor assembly of  FIG. 12 . 
         FIGS. 19B through 19E  include cross-sectional views of the example anchor assembly of  FIG. 12  along lines J-J and K-K of  FIG. 19A , for different positions of the dual-block anchors. 
         FIG. 20  is a side view of an example anchor assembly according to a further embodiment of the invention. 
         FIG. 21  is an isometric view of the example anchor assembly of  FIG. 20 . 
         FIG. 22  includes end and side views of the example anchor assembly of  FIG. 20  in a well bore. 
         FIG. 23  is a cross-sectional view of the example anchor assembly of  FIG. 20  along line L-L of  FIG. 22 . 
         FIG. 24  is a cross-sectional view of the example anchor assembly of  FIG. 20  along line M-M of  FIG. 22 . 
         FIG. 25  is a cross-sectional view of the example anchor assembly of  FIG. 20  along line N-N of  FIG. 22 . 
         FIG. 26  is a cross-sectional view of the example anchor assembly of  FIG. 20  along line O-O of  FIG. 22 . 
         FIG. 27  is an exploded view of the example anchor assembly of  FIG. 20 . 
         FIG. 28A  is a side view of the example anchor assembly of  FIG. 20 . 
         FIGS. 28B through 28E  include cross-sectional views of the example anchor assembly of  FIG. 20  along lines P-P and Q-Q of  FIG. 28A , for different positions of the dual-block anchors. 
         FIG. 29  is a side view of an example anchor assembly according to yet another embodiment of the invention. 
         FIG. 30  is an isometric view of the example anchor assembly of  FIG. 29 . 
         FIG. 31  includes end and side views of the example anchor assembly of  FIG. 29  in a well bore. 
         FIG. 32  is a cross-sectional view of the example anchor assembly of  FIG. 29  along line R-R of  FIG. 31 . 
         FIG. 33  is a cross-sectional view of the example anchor assembly of  FIG. 29  along line S-S of  FIG. 31 . 
         FIG. 34  is a cross-sectional view of the example anchor assembly of  FIG. 29  along line T-T of  FIG. 31 . 
         FIG. 35  is a cross-sectional view of the example anchor assembly of  FIG. 29  along line U-U of  FIG. 31 . 
         FIG. 36  is an exploded view of the example anchor assembly of  FIG. 29 . 
         FIG. 37A  is a side view of the example anchor assembly of  FIG. 29 . 
         FIGS. 37B through 37E  include cross-sectional views of the example anchor assembly of  FIG. 29  along lines V-V and W-W of  FIG. 37A , for different positions of the dual-block anchors. 
         FIG. 38  is a flow diagram illustrating a method of operating an anchor assembly. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As noted above, anchor elements in currently available torque anchor assemblies tend to be substantially unprotected from a casing or well bore during positioning the anchor. A dual-block anchor configuration, including an anchor block and a drag block which work together, protects the anchor block and may also provide further advantages, such as an automatic release function. 
     A dual-block anchor according to embodiments of the invention includes a drag block, an anchor block, and a biasing arrangement. In one embodiment, the biasing arrangement includes springs and a spring retaining plate. 
     Those skilled in the art will appreciate that production wells may include a casing that is constructed inside a well bore. Although features of embodiments of the present invention are disclosed and claimed herein primarily with reference to a well bore, it is to be appreciated that such references are intended to include well bores that have casings. References herein to well bores should be interpreted accordingly. For example, references to contact with a well bore are intended to include contact with the inside wall of the well bore or with the inside wall of a casing in the well bore if a casing is provided. 
     One function of the drag block is to protect the anchor block, while running the tool in and out of a well. The biasing arrangement, illustratively one or more springs, pushes the anchor block inwards, away from the well bore and toward a mandrel, and also pushes the drag block outwards, toward the well bore and away from the mandrel. Where a spring retaining plate is provided, this plate retains the springs, illustratively in cavities in the anchor block and the drag block, and prevents sand and other materials that may be present in a well from getting into the spring cavities. 
     The anchor block, which is biased away from the well bore and toward the mandrel by the biasing arrangement, is pushed outwards by the rotation of the mandrel, to contact the well bore, and to prevent rotation of the anchor assembly. 
     While the anchor assembly is being run in or out of a well, the drag block, which is being pushed outwards and is in constant contact with the well bore, does not allow engagement of the anchor block with the well bore. While the anchor assembly is travelling into or out of the well, top and bottom tapered shoulders on the drag block allow the drag block to remain a run position. At the same time, the anchor block is being pushed inwards, and the combined action of the anchor block, the drag block, and the biasing arrangement keep the anchor assembly in the run or “un-set” position, with the anchor block protected. The drag block is thus in contact with the well bore at least when the anchor block is out of contact with the well bore, i.e., while the anchor assembly is being run in or out of a well or even when the anchor assembly is not being moved but is also not set. The drag block also need not necessarily be moved out of contact with the well bore when the anchor assembly is set. In this case, the drag block may remain in contact with the well bore even when the anchor block is also in contact with the well bore. 
     When the anchor assembly has reached a desired location in the well, torque is applied to the mandrel through a tubing string. The drag block will remain in stationary contact with the well bore and the rotation of the mandrel will cause the anchor block to emerge into its set position, in which it contacts the well bore. At this point, relative rotation between the anchor assembly and the well bore is stopped. The anchor block will remain in the set (engaged) position as long as torque is applied to the mandrel. When the torque is released, the biasing arrangement will push the anchor block inward, toward the mandrel, the drag block will be pushed outward, against the well bore, and the tool is automatically released (un-set). 
     Illustrative embodiments of the invention are described in further detail below with reference to the drawings. The illustrative embodiments include the following four different configurations: a multiple anchor or “multi set” assembly with housing ( FIGS. 1 to 10E ), a multi set assembly with no housing ( FIGS. 12 to 19E ), a single anchor or “single set” assembly with bearings ( FIGS. 20 to 28E ), and a single set assembly with no bearings ( FIGS. 29 to 37E ). Other embodiments are also contemplated. 
     The multi set configurations are centralizing type tools that might be used mainly in vertical wells, and the single set configurations are de-centralized type tools that would likely be used mainly in horizontal wells and applications where large volumes of sand produced from a formation could build up around downhole equipment and “trap” it. The de-centralized position of a single set anchor assembly allows coiled tubing to be run downhole through a larger open portion of a well bore, for example, to wash sand out and free trapped downhole equipment. 
     The illustrative embodiments will now be discussed in further detail, in terms of structure and then function. 
     An example anchor assembly  10  according to a first embodiment of the invention is shown in  FIGS. 1 to 7 .  FIG. 1  is a side view,  FIG. 2  is an isometric view,  FIG. 3  includes end and side views of the example anchor assembly  10  in a well bore  36 ,  FIGS. 4 to 6  are respective cross-sectional views along lines A-A, B-B, C-C of  FIG. 3 , and  FIG. 7  is an exploded view. 
     The example anchor assembly  10  includes a mandrel  12 , which would be coupled to a tubing string, a drag block  14 , and an anchor block  16 . The anchor block  16  may include an insert  18 , illustratively a carbide insert, in some embodiments for contacting a well bore when the anchor block is in its set position. A spring retaining plate  20  is attached to the drag block  14  using fasteners  22 , illustratively screws, to retain springs  15  between the drag block  14  and the anchor block  16 . 
     A sleeve or housing  24  at least partially encloses the mandrel  12 , the drag block  14 , and the anchor block  16 , and retains or couples the dual block anchor assembly  50  including the drag block, the anchor block, and the springs  15  to the mandrel  12 . The housing  24  also includes openings  25  through which the drag block  14  and the anchor block  16  extend. 
     In the example shown, two bearing rings  28 ,  30  are positioned between the housing  24  and the mandrel  12 , and are secured to the inside of the housing with fasteners  29 ,  31 , which are screws in the example anchor assembly  10 . The bearing rings, also referred to herein as bearings, have three functions: to provide easy rotation between the mandrel  12  and the housing  24 , to retain the housing on the mandrel, and to provide a shoulder for the drag block  14  to sit and push against, as described in further detail below. 
     A guide screw  32  installed in a bore  46  of the mandrel  12  engages a slot  34  in the housing  24  to limit an extent of relative rotation between the mandrel and the housing. 
     The mandrel  12  includes a groove  40  for receiving a structure on the anchor block  16 . The groove  40  provides a shoulder for pushing the anchor block  16  from its run or un-set position to its set position, when torque is applied to the mandrel  12 . The slots  42 ,  44  in the mandrel  12  and the slots  43 ,  45  in the bearings  30 ,  28  receive structures on the drag block  14 , to thereby retain the drag block. The slots  43 ,  45  in the bearings  30 ,  28  have slanted shoulders to bias the drag blocks  14  to extend outwards. The slots  42 ,  44  in the mandrel  12  create free space for extensions  52  ( FIG. 8 ) of the drag blocks  14 . As the mandrel  12  rotates to set (push outwards) the anchor blocks  16 , the drag blocks  14  are already in contact with the well bore, such that the bottom of the slots  42 ,  44  in the mandrel are moving closer to the drag block extensions  52 . 
     In some embodiments, the drag blocks  14  may be accommodated in slots provided only on the mandrel  12  or only in the bearings  28 ,  30 . Where bearings have a greater radial dimension or thickness, bearing slots might provide sufficient space for the drag blocks  14 , for example. Thinner bearings without slots and/or larger drag blocks having a greater dimension between their extensions  52  and the faces which contact the well bore could be used in conjunction with deeper slots in the mandrel  12 . In this case, slots in the mandrel  12  might have slanted shoulders in order to bias the drag blocks  14  outwards. 
       FIG. 7  shows an exploded view of one of the three dual-block anchors  50  in the example anchor assembly  10 . An example dual-block anchor is shown more clearly in  FIGS. 8 and 9 .  FIG. 8  is a front view and  FIG. 9  is an exploded view of an example dual-block anchor  50 . 
     The example dual-block anchor  50  includes a drag block  14 , an anchor block  16 , and a biasing arrangement including springs  15 . Although shown as compression springs, the springs  15  may instead be implemented using other types of springs or biasing elements, such as leaf springs, for example. The spring retaining plate  20  is attached to the drag block  14  with fasteners  22 , illustratively screws, to retain the springs  15  between the drag block  14  and the anchor block  16 , and partially within the anchor block recesses  54 . 
     Extensions  57  of the top of the anchor block  16  are received in grooves that are formed by shoulders  59  on the drag block  14  when the dual-block anchor  50  is assembled, and allow the anchor block and the drag block to slide relative to each other without separating, thereby retaining the springs  15  between the drag block and the anchor block. During assembly, the springs  15  can be placed in the cavities  54  in the anchor block  16 , the drag block  14  can then be slid onto the anchor block with the extensions  57  in the grooves formed by the shoulders  59 , and the spring retaining plate  20  is then attached to the drag block. The springs  15  are retained between the drag block  14 , the anchor block  16 , and the spring retaining plate  20 . This can perhaps be appreciated most clearly with reference to  FIGS. 11A and 11B . 
     Referring again to  FIG. 9 , both the drag block  14  and the anchor block  16  also include structures which cooperate with other components of an anchor assembly. The extensions  52  at each end of the drag block  14  are received in the slots  42 ,  44  in the mandrel  12  and the slots  43 ,  45  in the bearings  30 ,  28  and retained by the housing  24 . A rear tapered surface  53  of the drag block  14  may contact an edge of the opening  25  in the housing  24  in some embodiments. The structure  55  on the anchor block  16  is received in the groove  40  on the mandrel. The dual block anchor  50  is thus located between the slots  42 / 43 ,  44 / 45  in the mandrel  12  and the bearings  30 ,  28  which receive the extensions  52  of the drag block  14 , the housing  24  which covers those slots, and the groove  40  in the mandrel  12  which receives the structure  55  of the anchor block  16 . 
       FIGS. 8 and 9  also illustrate tapered shoulders  51 , which allow the drag block  14  to remain in a run position during movement in a well bore. These tapered shoulders  51  enable the drag block  14  to slide over any irregularities in a well bore, thereby facilitating movement of an anchor assembly with the drag block  14  in contact with the well bore. Although referred to above as top and bottom tapered shoulders, it should be appreciated that the shoulders  51  would be in a top and bottom orientation in a vertical well bore. Other orientations during movement of an anchor assembly are also possible, depending on the path of a well bore. For example, in a horizontal well, the tapered shoulders  51  would not strictly be oriented as top and bottom shoulders, but would still facilitate movement of an anchor assembly with any drag blocks  14  in contact with the well bore. 
     Operation of the example anchor assembly will now be considered in detail primarily with reference to  FIGS. 10 and 11 .  FIG. 10A  is a side view of the example anchor assembly  10 ,  FIGS. 10B through 10E  include cross-sectional views of the example anchor assembly along lines D-D and E-E of  FIG. 10A , for different positions of the dual-block anchors, and FIGS.  11 A and  11 B include isometric and cross-sectional views of the example dual-block anchor  50  in different positions. Although only one spring  15  is shown in  FIGS. 11A and 11B  and described below, it will be apparent from  FIG. 9 , for example, that multiple springs may be provided. 
       FIG. 10B  shows a collapsed position of the dual-block anchors in which the anchor blocks  16  are flat on respective surfaces  56  of the mandrel  12 . A dual-block anchor might be in this position, for example, when the anchor assembly is being run in a horizontal well bore and a drag block  14  is bearing the weight of the anchor assembly. 
     With reference also to  FIGS. 11A and 11B , which respectively show the dual-block anchor  50  in a rest position and a set position, it can be seen that the dual-block anchors are not in the rest position of  FIG. 11A  when collapsed as shown in  FIG. 10B . The anchor block  16  is actually extended when a dual-block anchor  50  is collapsed. This compresses the spring  15  between a spring seat surface  66  of the anchor block  16  and an opposed spring seat surface  64  of the drag block  14 , which biases the anchor block to the left and the drag block to the right in the drawing. This in turn exerts forces on a surface of the groove  40  in which the structure  55  of the anchor block  16  is received, and side surfaces of the slots  43 ,  45  in which the extensions  52  of the drag block  14  are received. 
     It should be noted that references herein to spring seat surfaces of a drag block and/or an anchor block are intended to encompass spring seat surfaces through which spring forces are applied to those blocks. For example, although a spring retaining plate is used in some embodiments to retain one or more springs, references to spring seat surfaces of a drag block are intended to encompass spring seat surfaces of a spring retaining plate that is attached to the drag block. Thus, spring seat surfaces of a drag block or an anchor block need not necessarily be integrated into a single block component. 
     As shown perhaps most clearly in  FIG. 11B , the force on the drag block  14  is applied at the surface  64 , which is above the extensions  52  of the drag block. Since the housing  24  and the side walls of the slots  43 ,  45  retain the extensions  52  of the drag block  14 , the rightward force on the surface  64  would tend to rotate the drag block  14  in a counter-clockwise direction, away from the surface  56  of the mandrel  12 . In a similar manner, the spring  15  exerts a force on the spring seat surface  66  of the anchor block  16  in a direction above the structure  55 , which contacts the surface or shoulder  58  of the groove  40  on the mandrel  12 . This would also tend to rotate the anchor block  16  in a counter-clockwise direction, away from the surface  56  of the mandrel. 
     Thus, the dual-block anchors  50  in the example anchor assembly  10  would not normally remain in the collapsed position shown in  FIG. 10B .  FIG. 10C  shows a free position of the dual-block anchors  50 . 
     In the free position of the dual-block anchors  50 , the spring  15  in each anchor block may remain compressed or be at rest. As noted above, the guide screw  32  and the slot  34  limit the extent of relative rotation between the mandrel  12  and the housing  24 . In some embodiments, the opening  25  in the housing  24  through which the dual-block anchor  50  extends also limits the outward rotation of the dual-block anchor, such that the spring  15  remains compressed between the spring seat surfaces  64 ,  66 . For example, the rear surface  53  of the drag block  14  may come into contact with one side of the opening  25  before the spring  15  is fully extended, and accordingly the spring remains in compression. 
     Other embodiments, such as those without a housing  24 , may enable the spring  15  to be at rest, as shown in  FIG. 11A , when the dual-block anchors  50  are in the free position. If the dual-block anchor  50  is rotated any further in the outward direction, the spring  15  is compressed between the spring seat surfaces  62 ,  68 , and pushes the dual-block anchor toward the rest position shown in  FIG. 11A . The size of each opening  25  in the housing  24 , the distances between the spring seat surfaces  62 ,  64 ,  66 ,  68 , and/or the dimensions of each spring  15  may be determined in accordance with a well bore size in order to ensure that that the drag blocks  14  remain in contact with the well bore, or at least protect the anchor blocks  16  from the well bore, when the dual-block anchors  50  are in an un-set position. 
     The run position of the dual-anchor blocks  50  is shown in  FIG. 10D . In this position, when the anchor assembly  10  is being run in or out of a well, the dual-block anchors  50  maintain the anchor assembly  10  in an un-set state. With reference also to  FIG. 6 , it can be seen that in the run position, the spring  15  is compressed between the spring seat surface  64  of the drag block  14  and the opposing spring seat surface  66  of the anchor block  16 . As noted above, this would tend to rotate the entire dual-block assembly outward, away from the mandrel  12 . The compressed spring  15  biases the drag block  14  into contact with the well bore  36  and biases the anchor block  16  away from the well bore. 
     With the force exerted on the drag block  14  by the spring  15 , and given the fact that movement of the drag block away from the mandrel  12  is constrained by the well bore  36 , the drag block would effectively be pushing shoulders of the bearing slots  43 ,  45  in which the extensions  52  are received (and thus the housing  24 ) in a clockwise direction in  FIG. 10D . The tapered shoulders of the bearing slots  43 ,  45  bias the drag block  14  toward the well bore  36 . At the same time, the spring  15  causes the anchor block  16  to exert a force on the shoulder  58  of the mandrel  12  in the counter-clockwise direction, maintaining the anchor assembly  10  in the un-set position. 
     The drag block  14  is thus pushed outward by the spring  15  and kept in contact with the well bore  36 , and both protects the anchor block  16  and prevents the anchor block from contacting the well bore. The anchor block  16  is biased away from the well bore  36 , providing a further assurance of protection and prevention of contact with the well bore. 
     When the anchor assembly  10  is to be set, the drag block  14  and the housing  24  are stationary with the well bore  36 , since the drag block is in contact with the well bore and stops the housing from rotating. Rotation of the mandrel  12  in a clockwise direction in  FIG. 10D  relative to the housing  24  pushes the structure  55 , moving the anchor block  16  toward the set position shown in  FIG. 11B . Since the drag block  14  is in contact with the well bore  36 , the anchor block  16  rotates in the groove  40  of the mandrel  12  and extends beyond the drag block  14 , until it contacts the well bore  36 . The anchor assembly is now set. In the example shown in  FIGS. 10D and 10E , the anchor block  16  rotates by about 5° between the run and set positions. In other embodiments, more, less, or substantially the same amount of rotation may be sufficient to set the anchor assembly. 
     In addition to locating the anchor block  16  and providing a shoulder  58  for moving the anchor block from a run position to a set position, the groove  40  in the mandrel  12  may also limit the “back rotation” of the anchor block. As shown in  FIG. 10E , the structure  55  of the anchor block  16  is seated in the groove  40  of the mandrel  12  and cannot be rotated further, since it is fully in contact with the shoulder  58 . 
     Rotation between the housing  24  and the mandrel  12  can also be limited by the guide screw  32  and the housing slot  34 , as noted above. 
       FIG. 10E  also illustrates how the slots  42 ,  44  provide additional room to accommodate the extensions  52  of the drag blocks  14  when the dual-block anchors  50  are moved into the set position. 
     When the torque is released from the mandrel  12 , the force exerted by the spring  15  on the spring seat surface  66  of the anchor block  16  will rotate the anchor block in a clockwise direction and push the mandrel shoulder  58  counter-clockwise. At the same time, the force exerted by the spring  15  on the spring seat surface  64  of the drag block  14  will push the bearing slots  43 ,  45  and thus the housing  24  in a clockwise direction, since rotation of the drag block is limited by the well bore  36 . This automatically moves the anchor block  16  from its set position toward its run position, allowing the anchor assembly  10  to be moved in the well bore  36  or pulled to the surface. 
     An example anchor assembly according to another embodiment of the invention is shown in  FIGS. 12 to 19E .  FIG. 12  is a side view,  FIG. 13  is an isometric view,  FIG. 14  includes end and side views of the example anchor assembly of  FIG. 12  in a well bore,  FIGS. 15 to 17  are respective cross-sectional views of the example anchor assembly of  FIG. 12  along lines F-F, G-G, H-H of  FIG. 14 ,  FIG. 18  is an exploded view,  FIG. 19A  is a side view, and  FIGS. 19B through 19E  include cross-sectional views along lines J-J and K-K of  FIG. 19A , for different positions of the dual-block anchors. 
     In the example anchor assembly  110 , which is a multi set assembly without a housing, there are no bearings and the housing and bearings have been replaced with two retaining rings  128 ,  130 . The slots and shoulders in the bearings  30 ,  28  of the anchor assembly  10  have been replaced with slots  142 ,  144  in the mandrel  112 , under the retaining rings  130 ,  128 . Thus, the anchor assembly  110  represents one example of an implementation in which extensions of drag blocks  114  are accommodated by slots in the mandrel  112 . 
     As shown, the example anchor assembly  110  includes a drag block  114 , an anchor block  116 , and a mandrel  112  which would be coupled to a tubing string. An insert  118 , illustratively a carbide insert, may be provided in the anchor block  116  in some embodiments for contacting a well bore  136  when the anchor block is in its set position. A spring retaining plate  120  is attached to the drag block  114  using fasteners  122 , and retains springs  115  between the drag block  114  and the anchor block  116 . 
     The retaining rings  128 ,  130  are attached to the mandrel  112  using fasteners  129 ,  131  such as screws. The retaining rings retain the dual-block anchors  150  on the mandrel  112  by retaining extensions of the drag block  114  in slots  142 ,  144  in the mandrel  112 . The mandrel  112 , as in the first embodiment described above, includes a groove  140  which locates the anchor block  116  and provides a shoulder  158  for moving the anchor block into contact with the well bore  136 . 
     The dual-block anchors  150  may be the same as the dual-block anchors  50  described above. The function of the example anchor assembly  110  is also substantially the same as the anchor assembly  10 , except that the drag block  114  bears on the mandrel slots  142 ,  144 , and that when torque is released from the mandrel  112 , the drag block will push against the well bore  136 , and the anchor block  116  will push against the mandrel  112  to un-set the anchor assembly. Otherwise, operation of the anchor assembly  110  may be as described above, and is illustrated in  FIGS. 19B to 19E , which respectively show a collapsed position of the dual-block anchors  150  on the surface  156  of the mandrel  112 , the free position of the anchors, a run position of the anchors, and a set position of the anchors. 
     As noted above, embodiments of the invention having only a single anchor are also contemplated. An example anchor assembly  210  according to one such embodiment is shown in  FIGS. 20 to 28E .  FIG. 20  is a side view,  FIG. 21  is an isometric view,  FIG. 22  includes end and side views of the example anchor assembly  210  in a well bore,  FIGS. 23 to 26  are respective cross-sectional views of the example anchor assembly  210  along lines L-L, M-M, N-N, O-O of  FIG. 22 ,  FIG. 27  is an exploded view,  FIG. 28A  is a side view, and  FIGS. 28B through 28E  include cross-sectional views along lines P-P and Q-Q of  FIG. 28A , for different positions of the dual-block anchor. 
     The example anchor assembly  210  includes a drag block  214 , an anchor block  216  with an insert  218 , and a mandrel  212  which would be coupled to a tubing string. Bearings  228 ,  230  are located between a housing  224  and the mandrel  212 , and are attached to the housing with fasteners  229 ,  231 , illustratively screws. As described above for the example multi set assembly  10 , the housing  224  includes an opening  225  through which the dual-block anchor  250  extends, and the housing and the bearings  228 ,  230  enable relative rotation between the mandrel  212  and the housing and also retain the dual-block anchor  250 . The extent of rotation between the housing  224  and the mandrel  212  is limited by the guide screw  232  and the slot  234  in the housing. The mandrel  212 , as in the first embodiment described above, includes a groove  240  which locates the anchor block  216  and provides a shoulder  258  for moving the anchor block into contact with the well bore  236 , and slots, one of which is shown at  242  in  FIG. 27 , for receiving extensions of the drag block  214 . The bearings  228 ,  230  also include slots for receiving the drag block extensions, and one of those slots is shown at  243  in  FIG. 27 . 
     The dual-block anchor  250  may be the same as the dual-block anchors  50  described above. The function of the example anchor assembly  210  is also substantially the same as the anchor assembly  10 , with the exception that only a single dual-block anchor is provided. In the example single set anchor assembly  210 , the housing  224  rests against the well bore  236 , while the mandrel  212  is pushing the anchor block  216  into its set position. The housing  224  is then in stationary contact with the well bore  236  when the anchor assembly  210  is set, and will prevent wear of the well bore caused by vibrations and oscillations of the mandrel  212 . 
     Operation of the anchor assembly  210  may otherwise be as described above, as will be apparent from  FIGS. 28B to 28E , which show a collapsed position of the dual-block anchor  250  on the surface  256  of the mandrel  212 , a free position of the anchor, a run position of the anchor, and a set position of the anchor. 
     The physical dimensions of the anchor  250  may be different than in multi set embodiments. For example, since only one anchor is provided in the single set case, longer drag and anchor blocks may be used to ensure proper contact with the well bore  236 . 
     As noted above, a configuration having a single anchor and no bearings is also contemplated. An example anchor assembly  310  according to one such embodiment is shown in  FIGS. 29 to 37E .  FIG. 29  is a side view,  FIG. 30  is an isometric view,  FIG. 31  includes end and side views of the example anchor assembly  310  in a well bore,  FIGS. 32 to 35  are respective cross-sectional views of the example anchor assembly  310  along lines R-R, S-S, T-T, U-U of  FIG. 31 ,  FIG. 36  is an exploded view,  FIG. 37A  is a side view, and  FIGS. 37B through 37E  include cross-sectional views along lines V-V and W-W of  FIG. 37A , for different positions of the dual-block anchor. 
     The example anchor assembly  310  includes a drag block  314 , an anchor block  316  with an insert  318 , and a mandrel  312  which would be coupled to a tubing string. A housing  324  is retained on the mandrel  312  with fasteners, illustratively guide screws  332 , which are installed in bores  346  in the mandrel and engage slots  334  in the housing. The housing  324  includes an opening  325  through which the dual-block anchor  350  extends, and also retains the dual-block anchor. The guide screws  332  and the slots  334  enable limited relative rotation between the mandrel  312  and the housing  324 . The mandrel  312 , as in previously described embodiments, includes a groove  340  which locates the anchor block  316  and provides a shoulder  358  for moving the anchor block into contact with the well bore  336 , and slots, one of which is shown at  342  in  FIG. 36 , for receiving extensions of the drag block  314 . The anchor assembly  310  is thus another example of an implementation in which slots are provided only in the mandrel  312  to accommodate the drag block extensions. 
     This configuration is substantially similar to the example anchor assembly  210 , although with no bearings  228 ,  230 . The housing  324  is used to retain the drag block  314  and the slots in the mandrel are used to guide the drag block. The mandrel  312  is still free to rotate inside the housing  324 , as in the single set with bearings case, with the extent of rotation being limited in the example anchor assembly  310  by the guide screws  332  and the slots  334 . 
     The dual-block anchor  350  may be the same as the dual-block anchor  250  described above. The function of the example anchor assembly  310  is also substantially the same as the anchor assembly  210 . The housing  324  rests against the well bore  336 , while the mandrel  312  is pushing the anchor block  316  into its set position. The housing  324  is then in stationary contact with the well bore  336  when the anchor assembly  310  is set, and will prevent wear of the well bore caused by vibrations and oscillations of the mandrel  312 . 
     Operation of the anchor assembly  310  may otherwise be as described above, as will be apparent from  FIGS. 37B to 37E , which show a collapsed position of the dual-block anchor  350  on the surface  356  of the mandrel  312 , a free position of the anchor, a run position of the anchor, and a set position of the anchor. 
     Although described above primarily in terms of anchors and anchor assemblies, aspects of the invention may also or instead be embodied in other forms, such as methods.  FIG. 38  is a flow diagram illustrating a method of operating an anchor assembly. 
     The example method  400  involves an operation  402  of connecting a mandrel of an anchor assembly to a tubing string of a production well. The anchor assembly also includes an anchor block, a drag block, and a biasing arrangement. The anchor block is coupled to move, with rotation of the mandrel, between a run position out of contact with a well bore of the production well and a set position in contact with the well bore to set the downhole anchor assembly in the well bore. The drag block is coupled to the mandrel to contact the well bore at least when the anchor block is out of contact with the well bore. The biasing arrangement is provided to bias the anchor block away from the well bore and the drag block toward the well bore. 
     At  404 , the anchor assembly is run into a well bore. When the anchor assembly has been moved, with the anchor block in the run position, to a desired downhole location, the tubing string is rotated at  406 , to move the anchor block into the set position to set the anchor assembly at that downhole location. 
     Rotation of the tubing string at  406  applies and maintains a torque on the mandrel to keep the anchor assembly set at the desired location. Removing the torque from the mandrel, as shown at  408 , allows the biasing arrangement to move the anchor block from the set position to the run position and thereby release the anchor assembly. The anchor assembly can then be moved at  409 , either to the surface or to a second desired downhole location. The dashed line in  FIG. 38  illustrates that the anchor assembly can be set at the second desired downhole location and subsequently released and moved. 
     Variations of the example method  400  may be or become apparent to those skilled in the art, from the foregoing description of anchors and anchor assemblies, for instance. 
     What has been described is merely illustrative of the application of principles of embodiments of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the scope of the present invention. 
     For example, other embodiments may employ two dual-block anchors or more than three dual-block anchors, depending on the amount of support required. A desired amount of free space to be provided in a well bore may also influence a decision as to the number of anchors to use and/or their placement. An anchor assembly might employ two anchors toward one side of a housing, for instance, to provide additional support over the single set configuration while still providing a larger open area in a well bore to accommodate coiled tubing to free trapped downhole equipment. 
     Embodiments of the invention may also be used under any of various conditions. For example, anchor assemblies may be used in conjunction with different casing weights. 
     More generally, embodiments of the invention are in no way limited to the specific examples shown in the drawings and described above. Numbers, types, shapes, and/or relative locations of various elements may vary, for instance.