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FIELD OF THE INVENTION  
         [0001]    The invention relates to liner hanger apparatus used for carrying and anchoring a casing liner in a wellbore casing.  
         BACKGROUND OF THE INVENTION  
         [0002]    Liner hangers are well known in wellbore drilling and completion operations. Following drilling of at least a segment of a wellbore, a metallic casing is positioned into the open hole and cemented into place. Drilling is continued below the cemented casing to extend the depth of the wellbore. At least a second length of smaller diameter casing is lowered into the extended wellbore on a tubular workstring equipped with a liner hanger and is positioned near a bottom end of the existing cemented casing. Typically, liner hangers are equipped with mechanically or hydraulically actuated slips which, when actuated downhole, act to grip the walls of the existing casing and support the substantial weight of the depending liner until such time as the new liner can be cemented into place. This procedure may be repeated more than once, until the wellbore has reached an effective depth, the diameter of each subsequent length of liner being smaller than the previous.  
           [0003]    Hanger capacity, the amount of weight the hanger can support, is of great concern. Ideally, in order to keep the effective diameter of the wellbore within acceptable limits, it is desirable to hang as long a length of liner as can be supported by the liner hanger.  
           [0004]    Attempts have been made to improve hanger capacity by increasing the number of slips and their arrangement in the tool. U.S. Pat. No. 4,926,936 to Braddick teaches a liner hanger having a plurality of circumferentially and vertically spaced slips. Cones for actuation of a plurality of slips are attached to a tubular body using rings and are positioned relative to slips which are attached by arms to a sleeve which overlies the body and is axially moveable thereon, the entirety of the arms and slips being vulnerable to mechanical contact as the hanger is run into the wellbore. Axial movement of the sleeve, either mechanically or hydraulically, engages the slips with the cones causing the slips to engage the casing. The number of vertical sets of slips which equates to the liner hanger&#39;s support capability is limited by the space between the lower circumferentially spaced slips which is required to accommodate the arms extending vertically from the sleeve. Further, fluid passage in the annular space between the casing and the liner hanger is impeded as the number of slip arms increases. Typically, there is little clearance between the outer surfaces of the liner hanger wall and the casing so as to permit the largest possible bore through the center of the liner hanger.  
           [0005]    U.S. Pat. No. 4,603,743 to Lindsey Jr. teaches a hydraulically or mechanically set liner hanger having tandem, longitudinally spaced slips extending on straps from a tubular cage member, which is axially moveable on a tool body. The slips are held in a retracted position by a running tool as the liner hanger is run into the wellbore. A pressure housing on the running tool is axially moveable on the running tool&#39;s mandrel and is actuated to shift, causing the cage on the liner hanger to shift, engaging cam faces on a slip expander housing and causing the slips to move outwards into engagement with the casing. The expander housing has rectangular openings which extend through the wall of the housing. A tieback sleeve is located below the liner hanger and above the liner. The position of the tieback sleeve, in combination with the rectangular openings in the housing, prevents its use for incorporating a liner top packer into Lindsey&#39;s liner hanger system.  
           [0006]    Liner hangers are known wherein the liner can be rotated, not only during insertion into the wellbore, but also during cementing following setting of the liner hanger slips. Depending upon the circumstances, it may be advantageous to rotate the liner during cementing such as to ensure a uniform distribution of cement in the casing annulus as well as proper displacement of the drilling mud, without channeling of the cement through the mud. U.S. Pat. No. 5,181,570 to Allwin et al., U.S. Pat. No. 5,048,612 to Cochran and U.S. Pat. No. 4,848,462 to Allwin, teach rotatable liner hangers.  
           [0007]    During cementing excess drilling fluid is displaced upwardly between the liner hanger and the cemented casing. Restriction in the fluid flow is undesirable.  
           [0008]    There is a need for a liner hanger system having a large hanging capacity to permit hanging of long or heavy lengths of liner and maximum fluid bypass to eliminate any problems with fluid flow during cementing. Preferably, the slips should be protected from damage as a result of irregularities in the borehole. Ideally, the liner hanger should have a simplified manufacture. Ideally, liner hangers having these characteristics should be available in both non-rotating and rotating configurations for use in a wide variety of cementing operations.  
         SUMMARY OF THE INVENTION  
         [0009]    Generally, a liner hanger comprises a slip housing axially moveable over a mandrel. The slip housing has a plurality of slip openings which contain slips. Relative axial movement of the slip housing over the mandrel cause actuation of the slips over cams supported on the mandrel. Fluid flow bypass is increased between the hanger and the casing by implementing additional bypass between the mandrel and the slip housing in an annular space formed therebetween. Bypass is unimpeded therein due to the circumferential arrangement of spaced slips. Sets of slips can be positioned axially along the length of the slip housing. The plurality of sets of slips results in an increased hanging capacity. The number of sets that can be applied is limited only by the length of the slip housing itself. Preferably, fluid bypass is further increased by profiling an inner surface of the housing.  
           [0010]    In one broad aspect of the invention, a non-rotatable liner hanger comprises: a tubular mandrel having a slip housing axially moveable thereon and defining an annular space therebetween, the slip housing having an inlet and an outlet for permitting the flow of fluids through the annular space; one or more sets of slips housed in a plurality of openings in the slip housing and more preferably two or more sets of slips, each slip in each set of slips being spaced circumferentially for passage of fluids therebetween, each of the one or more sets of slips being spaced axially along the slip housing, preferably biased into the slip housing in a stowed position during running of the tool; cam surfaces extending radially outward from the mandrel and corresponding with each slip; and an actuator attached to the mandrel for axially moving the slip housing for engaging the slips with the cam surfaces and causing the slips to move from the stowed position to a radially extended position for engaging the existing casing.  
           [0011]    The cam surfaces are supported by the mandrel and extend radially therefrom, preferably machined from an external surface of the mandrel to improve structural rigidity. The cam surfaces can alternatively extend from a cam sleeve positioned rotationally between the slip housing and the mandrel.  
           [0012]    In a second broad aspect of the invention, a rotatable liner hanger comprises incorporation of the cams on a sleeve between the slip housing and the mandrel. Accordingly the rotatable liner hanger comprises: a tubular mandrel having a slip housing axially moveable thereon and defining an annular space therebetween, the slip housing having an inlet and an outlet for permitting the flow of fluids through the annular space; one or more sets of slips housed in a plurality of openings in the slip housing and more preferably two or more sets, each slip in a set of slips being spaced circumferentially for passage of fluids therebetween, each of the one or more sets of slips being spaced axially along the slip housing; a cam sleeve rotationally supported in the annular space, the cam sleeve having cam surfaces extending radially outward for urging the slips on the slip housing to a radially extended position while permitting the mandrel to rotate freely when the slips engage the casing; and hydraulic means attached to the mandrel for axially moving the slip housing for engaging the slips with the cam surfaces and causing the slips to move to a radially extended position for engaging the existing casing.  
           [0013]    In both the rotating and non-rotating embodiments, the means acting between the slips and the slip housing to bias the slips into the slip housing during running in of the tool are springs attached to the slips and extending laterally therefrom between the slip housing and the mandrel.  
           [0014]    Preferably, the hydraulic means or actuator for actuating the slip housing to move axially to set the slips is a piston in fluid communication with the bore of the mandrel, such that pressure in the bore to causes the piston to move uphole and actuate the slip housing.  
           [0015]    Optionally, both rotating and non-rotating embodiments may have a collet system which acts to prevent premature axial movement of the slip housing while running in the tool. The collet system is positioned between the hydraulic section and the slip housing. A shear screw acts to retain a collet retainer between a collet housing and collet fingers to prevent the collet from releasing from a profile in the mandrel until such time as the mandrel&#39;s bore is pressurized sufficiently to actuate the piston in the hydraulic section. Both the retainer shear screw and a main shear screw between the collet housing and the mandrel must be sheared to permit actuation of the slips.  
           [0016]    Further, in the rotating embodiment, so as to avoid imparting rotational energy to the hydraulic section, the piston is preferably formed in two sections, a lower section carrying seals which can rotate with the hydraulic section and an upper section which bears against the non-rotating collet retainer.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a longitudinal partial sectional view of a liner hanger of the present invention;  
         [0018]    [0018]FIG. 2 is a cross-sectional view according to FIG. 1, sectioned along lines A-A and showing the slips in a retracted position;  
         [0019]    [0019]FIG. 3 is a cross-sectional view according to FIG. 1, sectioned along lines A-A and showing the slips in an extended position;  
         [0020]    [0020]FIG. 4 a  is a front perspective view of a slip removed from the slip housing;  
         [0021]    [0021]FIG. 4 b  is a rear perspective view of the slip according to FIG. 4 a , illustrating the positioning of a laterally extending spring connected to the slip;  
         [0022]    [0022]FIG. 5 a  is a rollout view of a slip housing having two sets of vertically positioned slips and illustrating, in dashed lines, a pattern of a flow of fluids between the plurality of slips;  
         [0023]    [0023]FIG. 5 b  is a rollout view of a slip housing having two tiers of vertically positioned slips and option flow openings and illustrating, in dashed lines, a pattern of flow of fluids between the plurality of slips;  
         [0024]    [0024]FIG. 6 a  is a longitudinal sectional view of a hydraulic portion of the liner hanger according to FIG. 1, the right side illustrating a non-actuated position and the left side illustrating an actuated position;  
         [0025]    [0025]FIG. 6 b  is a sectional view of an optional collet system the right side illustrating a non-actuated position and the left side illustrating an actuated position;  
         [0026]    [0026]FIGS. 7 a - c  are partial longitudinal sectional views of a second embodiment of the invention in which the casing can be rotated during cementing, illustrated in sections, FIG. 7 a  being an uphole section, FIG. 7 b  being an intermediate section and FIG. 7 c  being a downhole section, all of which are shown in a non-actuated position;  
         [0027]    [0027]FIG. 8 is a partial longitudinal view illustrating embodiments of the liner hanger according to FIGS. 1 and 7 a - c  and optionally having either a single set of slips, two sets of slips or three sets of slips; and  
         [0028]    [0028]FIG. 9 is a longitudinal, partially sectioned view of a liner hanger assembly including the liner hanger according to FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    Having reference to FIGS. 1-3, a first non-rotating embodiment of a liner hanger  10  of the present invention is shown in a wellbore casing  11 . The liner hanger  10  comprises an uphole slip portion S and a downhole hydraulic portion H for actuating the slip portion S. The liner hanger  10  has a tubular mandrel  12  having cam faces  13  supported by and extending radially outward therefrom. For additional structural integrity, the cam faces  13  are machined integral from the mandrel.  
         [0030]    A slip housing  14  is mounted on the mandrel  12  and is axially moveable thereon. A plurality of openings  15  are formed in the slip housing  14  to accommodate a plurality of slips  16 . The slips  16  are pivotally retained within the slip housing  14  and are normally retracted within the openings  15 . A slip housing/mandrel annulus  18  is formed between the slip housing  14  and the mandrel  12 . The slip housing/mandrel annulus  18  acts to provide additional fluid bypass for the flow of drilling fluids, displaced upwardly, during cementing.  
         [0031]    Laterally extending biasing means  17 , shown in greater detail in FIGS. 4 a - 4   b , are connected between the slips  16  and the slip housing  14 , extending across and beyond each opening  15 . The biasing means  17  act to normally retract the slips  16  into a radially stowed position in the openings  15  in the slip housing  14 , during insertion of the liner hanger  10  into the casing  11 . In operation, the slip housing  14  is caused to move axially on the mandrel  12  so as to engage the slips  16  with the cam faces  13  resulting in extension of the slips  16  into engagement with the casing  11  for gripping the casing  11  and supporting a liner (not shown) extending therefrom.  
         [0032]    In a preferred embodiment, as shown in FIGS. 4 a ,  4   b  and  5 , the laterally extending biasing means  17  is a flat spring  19  and each slip  16  is attached to the corresponding spring  19  using a fastener  20 , such as a screw. Additionally, as shown in FIG. 5 a , mechanical, cantilevered supports, formed as tabs  21 , extend from the slip housing  14  into opposing sides of each opening  15  at a downhole end  22  of each slip  16  to ensure the slips  16  remain biased to slip housing  14  and to assist in supporting the slips  16  when extended to grip the casing  11 . The supports are formed as tabs  21  on either side of the opening  15 , rather than as a solid bar across the opening  15 , to ensure that the support will bend rather than break under stress should the casing  11  be oversized and the slips  16  over-extend to grip the casing  11 .  
         [0033]    Preferably, the slip housing  14  is assembled as two or more clam-shell portions assembled over the mandrel  12  and welded together, such as through section ring portion at the uphole and downhole ends of the slip housing.  
         [0034]    Further, as shown in FIG. 5 a , the slip housing  14  is slit, above and below each tab  21  at an interface  34  between the tab  21  and the slip housing  14 , to decrease bending stress rather than risk breaking of the tab  21  under undue stress. The slit  35  is locally widened at a distal end  36  to avoid a stress concentration.  
         [0035]    The slip housing  14  has a plurality of fluid inlet ports  30  formed at a downhole end  31  of the slip housing  14  and a substantially circumferential outlet  32  formed at an uphole end of the slip housing  14 .  
         [0036]    As shown in FIGS. 2, 3 and  5   a , the annulus  18  can be further increased in cross-sectional area to provide increased fluid bypass. The slip housing  14  is profiled on an inner surface  33  to provide the increased fluid flow bypass F by creating the enlarged annular space  18  between the mandrel  12  and the slip housing  14 . The profiling can be a simple concavity resulting in a thinning of the wall of the slip housing  14 .  
         [0037]    The fluid flow bypass aids in passing well fluids during operations for cementing the newly hung liner into the wellbore. Cement is pumped through a bore in a liner hanger system, which simplistically includes a running tool suspended from a tubing string to surface and connected at a downhole end to the liner hanger, the depending liner and at a distal end to a float shoe. As cement exits the float shoe and rises to fill an annulus between the casing  11  and the open wellbore (not shown), drilling fluid is displaced upwards and must pass by the liner hanger  10 . When the drilling fluid reaches the cemented casing  11 , the fluid is forced between the liner hanger  10  and the casing  11 . The displaced fluid enters the casing annulus  40  between the casing  11  and the liner hanger  10  and also enters the annulus  18  through the inlet port  30  between the slip housing  14  and the mandrel  12 . Accordingly, displaced fluid can flow through a large cross-sectional area, including both the casing annulus  40  and the slip housing/mandrel annulus  18 . The profiling of the inner surface  33  of the slip housing  14  further increases the annular  18  flow area.  
         [0038]    As shown in greater detail in FIG. 5 a , the slips  16  are positioned circumferentially and vertically about the slip housing  14 . The number of slips  16  that can be positioned vertically, in tiers, is only limited by the length of the slip housing  14 . The more slips  16  present, the more the load from the depending liner is distributed, thus increasing hanger capacity. Flow of drilling fluids F continues substantially unimpeded through the slip housing/mandrel annulus  18  regardless of the number of tiers of sets of slips  16 .  
         [0039]    Optionally, as shown in FIG. 5 b , a plurality of additional openings  15  are formed in the slip housing  14  to further improve fluid access to the annulus  18  and improve fluid flow bypass.  
         [0040]    Referring again to FIG. 1, the hydraulic section H of the liner hanger  10  is located on the mandrel  12  adjacent the downhole end  31  of the slip housing  14  and is adapted to actuate the slip housing  14 .  
         [0041]    As shown in greater detail in FIG. 6, a tubular piston housing  50  is formed around the mandrel  12  creating a cylindrical space  51  therebetween that is in fluid communication with a bore  52  of the mandrel  12  through a port  53 . A piston  54  is positioned within and extends above the cylindrical space  51  and is axially moveable therein. During operation, an increase in pressure within the mandrel bore  52  which acts on a distal end  55  of the piston  54  moves the piston  54  to an uphole actuated position. A shear screw  56  between the slip housing  14  and the mandrel  12  acts to prevent actuation of the piston  54  until such time as the bore pressure acting upon the piston  54  creates a force sufficient to overcome the shear screw  56 . The piston  54  acts on the downhole end  31  of the slip housing  14  to shift the slip housing  14  axially uphole, causing the slips  16  to extend and engage the casing  11 .  
         [0042]    In a preferred embodiment of the invention, the piston housing  50  is retained on the mandrel  12  using a split ring  57  and a ring retainer  58 . The piston housing  50  is further secured to the ring retainer  58  using a set screw  59 .  
         [0043]    Having reference to FIGS. 6 a - 6   b  and more preferably, the slip housing  14  is further temporarily restrained from axial movement during running into the wellbore by a collet system  60 . The collet system  60  comprises a tubular collet housing  61 , a collet  63  and a profile  66  in the mandrel  12 . The tubular collet housing  61  is formed over the mandrel  12  immediately adjacent to and engaging the downhole end  31  of the slip housing  14 , forming a downhole-facing annular space  62  therebetween. Shear screw  56  connects the collet housing  61  to the mandrel  12  thereby restraining the slip housing  14 . The collet  63  is connected, preferably by threads  64 , to the collect housing  61  in the annular space  62 .  
         [0044]    In a non-actuated position, a plurality of shaped distal ends  65  of the collet  63  reside in the profile  66  in the mandrel  12 , locking the collet  63  and slip housing  14  to the mandrel  12 . A tubular collet retainer  67  temporarily resides between the distal ends  65  and the collet housing  61  to retain the collet&#39;s distal ends  65  in the profile  66  and lock the collet housing  61  and slip housing  14 .  
         [0045]    The collet retainer  67  extends from an upper end  68  of the piston  54  to the collet  63 . The retainer  67  is profiled forming an annulus  69  between the collet retainer  67  and the mandrel  12 . An uphole end  70  of the retainer  67  protrudes between the collet housing  61  and the distal end  65  of the collet  63 , for retaining the shaped end  65  of the collet in the profile  66 . Shear screw  71  connects between the collet housing  61  and the collet retainer  67  to prevent the collet  63  from moving out of the profile  66  enabling axial movement of the piston  54  resulting in accidental setting of the slips  16 .  
         [0046]    In operation, uphole, axial movement of the piston  54  causes the piston  54  to bear upon the collet retainer  67 , shearing the collet shear screw  71 . The collet retainer  67  moves axially uphole into the annular space  63  between the collet housing  61  and the collet  63 . An enlarged, shaped inner surface  72  of the collet retainer  67  permits the distal end  65  of the collet  63  to release from the profile  66  and move into the annular space  69 . The uphole end of the retainer  69  acts upon the collet housing  61  causing shear screw  56  to shear and enabling the collet housing  61  to shift the slip housing  14  to the actuated position.  
         [0047]    Having reference to FIGS. 7 a - c , a second, rotating embodiment of the present invention is shown. The uphole slip portion S comprises a tubular mandrel  112 , connectable at a top end  113  to a tubing string (not shown) and at a lower end  114  to a liner (not shown). A slip housing  115  is mounted on the mandrel  112  and as axially moveable thereon and forms an annular space  116  therebetween. The slip housing  115  supports slips  16  as detailed in the previous embodiment. A cam sleeve  117 , having cam surfaces  118  extending radially outward, is positioned within the annular space  116 . Openings or windows  119  are formed in the cam sleeve  117  below the cam surfaces  118  to permit the slips  16  to recess deeper in the radially stowed position. The mandrel  112  and the depending liner are supported on an upper bearing  120  positioned at a shoulder  131  on the mandrel  112  and an uphole end  132  of the cam sleeve. Preferably, the upper bearing  120  is a tapered roller thrust bearing. An uphole facing shoulder  121  on the mandrel  112  supports a lower end  122  of the cam sleeve  117 .  
         [0048]    The slip housing  115  and mandrel  112  are connected for co-axial movement by a shear screw  130  located in a groove  131  on the mandrel  112  permitting the slip housing  115  to rotate independent of the mandrel  112  prior to setting of the slips  16 . The hydraulic section H is as described in the previous embodiment. Once the shear screw  130  has been sheared for actuation of the slips  16 , the mandrel  112  and the connected, depending liner (not shown) are rotationally supported on the cam sleeve  117  through bearing  119 . The mandrel  112  can be freely rotated within the cam sleeve  117 , while the cam sleeve  117  and slip housing  115  are held stationary in the casing  11 .  
         [0049]    Preferably, to avoid imparting rotational or torsional energy to the hydraulic section H, the piston  54  is formed in two sections, a lower section  132  carrying seals  133  which rotates with the mandrel  12  and an upper section  134  which bears upon the non-rotating collet retainer  67 .  
         [0050]    As shown in FIG. 8, the liner hanger  10  is preferably available having one, two or three sets of slips  16  in either a rotating or a non-rotating embodiment. The hanging capacity is increased with the increasing number of sets of slips  16 . The liner hanger having three sets of slips is better seen in FIGS. 7 a - c.    
         [0051]    In Use:  
         [0052]    In a preferred arrangement, as shown in FIG. 9, a liner hanger assembly  100  typically comprises, listed from an uphole end  101 , a tieback receptacle  102  or optionally a liner top packer  103 , a liner hanger  104 , a depending liner  105  containing a hydraulically actuated landing collar  106 , and, at a downhole distal end  107 , a liner float shoe  108  forming a contiguous bore  109 . The assembly  100  is attached to a running tool fluidly connected to a tubing string (not shown) for insertion into a previously cemented wellbore casing  11  (FIG. 1). During insertion, the slips  16  are held in the retracted or stowed and protected position as a result of the laterally extending springs  19 . The piston  54 , in the hydraulic section H, is in the non-actuated downhole position. The collet system  60  prevents premature actuation of the slips  16 , which could otherwise result from mechanical interference in wellbore or as a result of minor pressure increases.  
         [0053]    The liner hanger system  100  is lowered through the cemented casing  11  to a position near a lower end of the casing  11 . A ball  110  is dropped through the contiguous bore  109  and is caught in the landing collar  106 . Once caught, the ball  110  blocks the bore  109 , permitting pressure to be applied above the ball  110  to shear the shear screws  71 ,  56  and actuate the hydraulic portion H of the liner hanger to move the slip housing  14  axially uphole to the actuated position causing the slips  16  to set and grip the casing  11 .  
         [0054]    To begin cementing, the bore  109  is pressured in excess of the slip actuation pressure to blow the ball  110  in landing collar  106  and re-establish fluid communication in the bore  109  with the float shoe  108 . A pre-determined volume of cement is pumped through the bore  109  and out float shoe  108 . As cement fills the annulus between casing and the borehole (not shown), drilling fluid is displaced up the annulus and into the casing annulus  40  and through the mandrel annulus  18  (FIGS. 2-3) at a joint between the old cemented casing  11  and new liner  105 . The displaced fluid flows into the inlet ports  30  in the slip housing  14 , between the slips  16  in the enlarged annulus  18  and exits through the outlet port  32  at the top of the slip housing  14 .  
         [0055]    In the case of the second embodiment described above for the rotating liner hanger, the mandrel  112  and depending liner can be freely rotated during placement of the cement.  
         [0056]    To conclude the cementing operation, a drill pipe wiper (not shown) is dropped from surface into the bore  109  to follow the cement. The drill pipe wiper mates with a liner wiper at a bottom end of a running tool (not shown). The mated wipers are sheared under pressure to drop from the bottom of the running tool to latch into a landing collar  106  which results in a pressure spike indicating latching has occurred. Cementing is then stopped, after which the running tool is removed from the bore  109  and the top packer  103  is set.

Summary:
A liner hanger, in either a non-rotating or rotating format, has a large hanging capacity due to a one or more axially spaced sets of circumferentially spaced slips housed in openings in a slip housing, the slip housing being moveable axially relative to a mandrel for actuating the slips over cams supported by the mandrel. One or more sets of sets of slips are spaced axially along the slip housing. An annular space is formed between the mandrel and slip housing for maximizing fluid bypass through the annular space. Bypass is further improved by profiling the slip housing. In the rotating version, a separate sleeve is positioned between the mandrel and the slip housing for supporting the cams and the mandrel is supported on the cam sleeve through an upper bearing which permits the mandrel to rotate on the cam sleeve when the slips are set.