Abstract:
An anchor assembly for a downhole tool has upper and lower frictional engagement member for engaging with an inner wall of the casing. The upper frictional members are spring-tensioned, while the lower frictional engagement members slide, to certain degrees, in relation to a longitudinal axis of the anchor assembly. At the same time conical engagement between the lower frictional members and the supporting surface causes the lower frictional members to extend outwardly and engage the inner surface of the casing. As a result, the working tool, for instance a sand cutter secured to the anchor assembly is stabilized in the casing, and an even cut may be performed.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to downhole anchoring tools, and more particularly to a well bore anchor that may be used for stabilizing a sand cutter and similar equipment in the well bore during a cutting operation. 
   In well operations, sometimes a well must be abandoned and plugged. The government regulations require that a casing be cut at a certain depth below the surface. Sand cutters have been conventionally used for performing the cutting operation. It was noted that when the cutting is performed at the depth of about 100 feet, the pressures downhole tend to push and excite the nozzle of the sand cutter and move it out of alignment by a small distance, such as a quarter of an inch. However, this small distance is critical in the tight confines of a casing. The string supporting the cutter is energized and causes it to move from the required alignment. As a result, the cut created by the sand cutter is no longer circular but rather resembles a spiral, such that the end of the cut does not necessary meet the beginning of the cut. 
   The deeper the casing cutting operations are performed, the more pronounced the problem becomes. With deeper wells, more hydraulic lines need to be run, more feed of the pipes downhole, and more possibility of misalignment. One of the solutions was to place a centralizing plate around the cutting tool to keep the cutter from moving into misalignment. However, the centralizing plate has to be carefully inserted and then properly aligned at the desired depth. Even then, a possibility exists for the hydraulic force imparted on the cutter to unseat the plate, which will result in an uneven cut. 
   The present invention contemplates elimination of drawbacks associated with the prior art and provision of an anchoring tool, which positively engages the inner walls of the casing allowing a cutting tool, or other necessary equipment to be securely connected to the top or bottom of the tool for performing the required operations in the well bore. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a well bore anchor tool, which is adapted for engaging the inner wall of the casing, and stabilize any attached equipment within the well bore. 
   It is another object of the present invention to provide a well bore anchor tool, which frictionally engages the inner wall of the casing by slidable expanding slips once the anchoring tool reaches the desired depth. 
   These and other objects of the present invention are achieved through a provision of a well bore anchor tool, which comprises an elongated hollow mandrel, an upper sub carried by the mandrel, a plurality of upper frictional members secured on the upper sub for frictionally engaging an inner wall of a casing within the well bore, a bottom sub carried by the mandrel, and a plurality of lower frictional members detachably engageable with the bottom sub. Each of the bottom frictional members has an inclined inner surface matching an inclined surface of recesses formed along an upper exterior portion of the bottom sub. A downward movement of the mandrel causes the bottom frictional member to move outwardly in relation to the bottom sub and frictionally engage the casing inner wall. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made to the drawings, wherein like parts are designed by like numerals, and wherein 
       FIG. 1  is a perspective view of the anchor tool in accordance with the present invention. 
       FIG. 2  is a perspective detail view of a mandrel showing an upper sub and a wicker sleeve. 
       FIG. 3  is a detail front view of an upper sub. 
       FIG. 4  is a top view of the bottom sub showing dovetail-shaped tracks for receiving bottom frictional members, or slips. 
       FIG. 5  is a detail view illustrating a side view of the bottom sub, or cone. 
       FIG. 6  is a detail front view of an upper frictional member, or wiper block. 
       FIG. 7  is a detail side view of a wiper block showing compression springs. 
       FIG. 8  is a detail view of a slip showing dovetail-shaped channel formed on the inner surface of the slip. 
       FIG. 9  is a detail front view of the slip. 
       FIG. 10  is a detail side view of the slip. 
       FIG. 11  is a cross-sectional view of a wicker dog. 
       FIG. 12  is a detail bottom view of the wicker dog. 
       FIG. 13  is a detail front view of the wicker dog. 
       FIG. 14  is cross-sectional view of a leaf, or drag spring. 
       FIG. 15  is a detail top view of a main spring stop. 
       FIG. 16  is a detail top view of a split thrust. 
       FIG. 17  is a perspective view of a main spring and FIG  18  is a cross-sectional view of a wicker dog retainer ring. 
       FIG. 19  is a detail perspective view of the wicker dog retainer ring. 
       FIG. 20  is a detail sectional view of a wicker sleeve, wicker dog and the drag spring mounted in the upper sub. 
       FIG. 21  is a cross-sectional view of the upper sub. 
       FIG. 22  is a detail perspective view showing engagement of the inner casing wall by the upper and bottom frictional engagement members. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Turning now to the drawings in more detail, numeral  10  designates the well bore anchor tool in accordance with the present invention. The anchor tool  10  comprises an elongated central mandrel  12  having an upper sub  14  and a bottom sub  16  secured thereto. A top sub  15  has exterior threads  18  which allow securing of a work string thereto. A lower sub  17  is similarly provided with exterior threads  20  that allow securing of a downhole tool, for instance a sand cutter thereto. 
   A wicker sleeve  24  is mounted in a threadable engagement with the upper part of the mandrel  12 . The wicker sleeve has exterior threads  22  formed along at least a lower portion the wicker sleeve  24 . The upper part of the wicker sleeve  24  has a smooth exterior surface. A plurality of wicker dogs  94  is threadably engaged with the threads  22 , as will be explained in more detail hereinafter. 
   An annular collar  26  is secured about a lower portion of the mandrel  12 . A split thrust  28  rests with its bottom surface on the collar  26 . The split thrust  28  has a threaded portion, which is threadably engaged with the bottom sub  16  when the bottom frictional members  42  are in their extended position engaging the inner casing wall. A main compression spring  30  urges against the top surface of the split thrust  28 . A spring stop  32  is mounted in a surrounding relationship over the mandrel body  12  and provides an upper stop for the main spring  30 . 
   The bottom sub  16  has an upper part  34 , which extends above the spring stop  32 , and a lower cylindrical portion  36 . The upper part  34  is provided with a plurality, for instance three, recesses  38 . Each recess  38  has a dovetail-shaped cross section and a bottom surface  40 . Each of the recesses  38  defines a dovetail-shaped track for receiving a bottom frictional member, or slip  42  in a sliding engagement therein. As shown in  FIGS. 8–10 , each slip  42  comprises a bottom part  44  and a T-shaped upper securing member  46 . A dovetail-shaped cutout  48  is formed in an inner surface  50  of each slip  42 . The cutout  48  matches the recess  38  in the lower sub  16 , allowing the slip  42  to move up and down, to some degree, along the track  38 . 
   The exterior surface of each slip  42  is provided with a plurality of projections, or serrations  54  which facilitate frictional engagement of the slip  42  within a casing. The T-shaped securing member  46  fits into a matchingly profiled cutout  56  formed adjacent a lower edge of the upper sub  14  ( FIGS. 1 and 3 ). 
   The upper sub  14  wiper is formed as a cylindrical member with a plurality of rectangularly-shaped slots  62  for receiving an upper frictional engagement member, or wiper block  70  therein. A pair of openings  64  are formed in the top and bottom of the slot  62  for receiving retainer screws therein. The upper sub  14  may have three or four such slots  62 , each adapted for receiving a wiper block  70  in a detachable engagement therein. 
   As can be better seen in  FIGS. 6 and 7 , each wiper block  70  comprises a main body  72 , which has a generally trapezoidal cross-section. An inner surface  74  of the body  72  carries a plurality of compression springs  76 , which extend outwardly from the base  74  and can be three or four in number. An outer surface  78  of the body  72  is provided with projections  80 , which facilitate frictional engagement of the wiper blocks  70  with the inner wall of the casing. Each wiper block  70  has an upper retaining plate  82  and a lower retaining plate  84 . A retainer screw  86  extends through the retainer plate  82  and an opposing retainer screw  88  extends through a retainer plate  84 . The screws  86  and  88  engage within respective openings  64 . 
   As can be better seen in  FIG. 19 , the wicker sleeve  24  has exterior threads  22  which extend along the bottom portion of the wicker sleeve  24 . Matching threads  92  are formed on a wicker dog  94 . A drag spring, or leaf spring  96  is mounted in contact with an exterior surface  98  of the wicker dog  94 . The upper sub  14  is formed as a hollow cylinder with a plurality of recesses formed on the interior wall thereof. Each wicker dog  94  fits into a respective recess by sliding the wicker dog  94  vertically from the top of the sub  14  into a respective recess such that a bottom  100  of the wicker dog  94  rests on an internal shoulder  102  formed along the inner wall of the upper sub  14 . 
   A retainer ring  104  is positioned on top of the wicker dogs  94  and rests on top of an upper shoulder  106  formed inside the retainer member  60 . The retainer ring  104  is retained in place by a plurality of screws  108 , which pass through the wall of the upper sub  14 , as can be seen in  FIG. 19 and 20 . The head of the screw  108  is positioned outside of the upper sub  14 . If desired, the exterior surface of the upper sub  14  can be provided with recesses  110  to allow the heads of the screws  108  to be recessed and not contact the inner wall of a casing. 
   In operation, if the anchor tool  10  is to be used with a sand cutter, the sand cutting head is made up to the bottom of the tool  10  by engaging with the threads  20 . The anchor tool assembly with the sand cutter is lowered into the well bore on a connected work string. Once the cutting depth has been achieved, right hand rotation is applied to the string while slowly lowering the work string downhole. The wiper blocks  70  and the leaf springs  96  resist rotation by maintaining friction on the inner wall  111  of the casing  112 . The wicker sleeve  24  eventually disengages from the wicker dogs  94 . Continued lowering of the work string allows the slips  42  to move downward and out to anchor the tool  10  inside the inner wall  111  of the casing  112 . 
   The main spring  30  is partially compressed to maintain a uniform pressure on the assembly while the sand cut is being made from the inside of the casing  112 . Normally one rotation per hour is applied to the work string. It may take two or three rotations to complete the cut to the casing cylinder. After the cut has been made, the anchor assembly  10  is released by picking up on the work string and retrieving the tool from the well bore. The upward movement allows the slips  42  to shift into a release position out of a frictional engagement with the casing inner wall  111 . 
   If desired, the anchor tool  10  can be run in an upside down position. The sand cutter will then be attached to the threads  18 . Once the cutting depth is achieved, left hand rotation is applied while the work string is slowly raised. The wiper blocks  70  and the leaf springs  96  resist rotation and lifting while maintaining friction on the wall of the casing  112 . The upward movement disengages the wicker sleeve  24  from the wicker dogs  94 . A continued raising of the work string allows the slips  42  to move downward and outward to anchor the tool  10  firmly to the inside wall  111  of the casing  112 . An upward pull of 5,000 to 10,000 pounds is to be applied and maintained to the work string throughout the cutting procedure. The main spring  30  is partially compressed to maintain uniform pressure on the assembly while the cut is being made. Normally one rotation per hour is applied to the work string. It may take two to three rotations to complete the sand cut once the cut has been performed, the tool  10  is released by simply lowering the work string. This allows the slips  42  to shift into a release position and the tool  10  can be retrieved from the well bore together with the sand cutter attached thereto. 
   The tool  10  may be successfully used for aligning and stabilizing a variety of downhole equipment during wellbore operations. It will be understood that the exemplary application of the apparatus for use with a sand cutter is but of many potential applications where anchoring of a tool at a certain depth is required. 
   Many changes and modifications can be made in the design of the present invention without departing from the spirit thereof. We, therefore pray that our rights to the present invention be limited only by the scope of the appended claims.