Abstract:
An apparatus and method includes releasably engaging a cementing tool in a casing assembly at a junction of plural wellbores. Cementing slurry is pumped through the cementing tool to fill an annular region around the casing assembly. The cementing tool is retrievable without first milling components at the junction. The cementing tool has an anchoring mechanism adapted to engage a landing profile of the casing assembly. Further, the cementing tool has an external seal adapted to seal inside the casing assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Serial No. 60/263,935, entitled “Cementing Tool,” filed Jan. 24, 2001. This is also a continuation-in-part of U.S. Ser. No. 09/518,365, filed Mar. 3, 2000, which is a continuation of U.S. Pat. No. 6,056,059, which is a continuation-in-part of U.S. Pat. No. 5,944,107, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/013,227, filed Mar. 11, 1996, No. 60/025,033, filed Aug. 27, 1996, and No. 60/022,781, filed Jul. 30, 1996, all hereby incorporated by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates generally to cementing operations for wellbores. More specifically, the invention relates to a method and apparatus for cementing casing in a wellbore.  
         BACKGROUND  
         [0003]    In the petroleum industry, wells are drilled in selected formations in an effort to produce hydrocarbons in commercially feasible quantities. During drilling operations for a typical oil or gas well, various earth formations are penetrated. To complete the well, casing is installed into the drilled wellbore.  
           [0004]    Referring to FIG. 1, an example casing assembly  20  used in some oil and gas wells is shown. The casing assembly  20  for a given well is typically selected with an outer diameter that is small enough to go into the hole and still leave room for a cement layer  22  around the casing assembly  20 , and an inner diameter that is large enough for the passage of downhole tools. Typically, as joints of the casing assembly  20  are connected to form a conventional casing string, the casing string is gradually moved downhole into the well. Once the desired length of a casing assembly  20  is connected, the casing assembly  20  is suspended or “hung” in the well, either from the surface or from the end of a previously cemented casing.  
           [0005]    A casing assembly  20  may include a guide shoe (not shown) at the bottom of the casing assembly  20  to guide the casing assembly  20  as it is lowered into the well. A guide shoe prevents the casing assembly  20  from snagging on the wall of the wellbore  14  as it is lowered into the well. A fluid passage is typically formed through the center of the guide shoe to allow drilling fluid to flow up into the guide shoe as the casing assembly  20  is lowered into the wellbore  14 . The fluid passage also allows cement pumped down the casing assembly  20  to flow downhole and out of the casing assembly  20  during cementing operations.  
           [0006]    Cementing of the casing assembly  20  in the well is typically done by pumping a volume of cement into the casing assembly  20  sufficient to fill the annulus between the casing assembly  20  and the wellbore  14 , followed by pumping displacement fluid on top of the cement to displace the cement down the casing assembly  20  and up the annulus between the casing assembly  20  and wellbore  14 . The volume of cement required to fill the annulus between the casing assembly  20  and the wellbore  14  can be calculated from the geometry of the wellbore  14  and the geometry of the casing assembly  20  inserted in the wellbore  14 .  
           [0007]    Cementing techniques are well developed for single-bore wells. However, multilateral wells are becoming increasingly more desirable to improve production. A bore leading from the surface is referred to as a primary or main wellbore. Each of directional wellbores extending from the primary wellbore is referred to as a lateral wellbore. The junction between a primary wellbore and one or more lateral wellbores is referred to as a wellbore junction.  
           [0008]    Casing and cementing in a multilateral well presents a greater challenge than for uni-bore wells, especially in providing support and pressure integrity at the wellbore junction between the primary wellbore and a lateral wellbore. Existing cementing technology for multilateral wells makes use of hardware components, such as cement retainers, packers, and diverters, which are permanently set in the casing assembly during cementing operations that must be milled to clear the path for subsequent drilling operations. At a wellbore junction, the milling of the hardware components and cement in the internal volume of the wellbore may cause damage at the wellbore junction. This milling operation can also be time consuming and costly because of the number of downhole trips required.  
         SUMMARY  
         [0009]    In general, an improved cementing tool for cementing a casing assembly at a junction of plural wellbores is provided. For example, the cementing tool includes a body, an anchoring mechanism adapted to anchor the body within the casing assembly, and a flow conduit adapted to channel cement flow to an annular region outside the casing assembly. The anchoring mechanism is adapted to be released to enable retrieval of the cementing tool from the casing assembly. 
       
    
    
       [0010]    Other or alternative features will be apparent from the following description, the drawings, and the claims.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a longitudinal sectional view of conventional casing cemented in a wellbore.  
         [0012]    [0012]FIG. 2 illustrates a multilateral well in which a cementing tool according to some embodiments can be installed.  
         [0013]    [0013]FIG. 3 illustrates one embodiment of the cementing tool used to cement a casing assembly at a lateral junction.  
         [0014]    [0014]FIG. 4 is an isolated view of the cementing tool of FIG. 3.  
         [0015]    [0015]FIG. 5 is an isolated view of the casing assembly of FIG. 3.  
         [0016]    [0016]FIG. 6 is an isolated view of another embodiment of a cementing tool configured to cement the casing assembly of FIG. 5.  
         [0017]    [0017]FIG. 7 illustrates the cementing tool of FIG. 6 being used to cement the casing assembly of FIG. 5.  
         [0018]    [0018]FIG. 8 illustrates one example of bypass tubes useable with the cementing tool of FIG. 4 or  6 , the bypass tubes configured to break at selected locations.  
         [0019]    FIGS.  9 A-B are sectional views of one example of a securing mechanism used in the cementing tool of FIG. 4 or  6 .  
         [0020]    FIGS.  10 A- 10 J illustrate a cementing tool according to another embodiment in different positions.  
         [0021]    FIGS.  11 A- 11 D are a longitudinal sectional view of the cementing tool of FIGS.  10 A- 10 J.  
         [0022]    FIGS.  12 A- 12 D are a side view of the cementing tool of FIGS.  11 A- 11 D.  
         [0023]    FIGS.  13 A- 13 B illustrate the detachment of the cementing tool from a hardened block of cement. 
     
    
     DETAILED DESCRIPTION  
       [0024]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.  
         [0025]    As used here, the terms “up” and “down”; “upper” and “lower”; “upwardly” and downwardly”; “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate.  
         [0026]    As shown in FIG. 2, a cementing tool according to some embodiments is positionable at various well junctions  21  in a multilateral well  15 . In the example embodiment shown, a platform  11  is provided at the surface of the well  15 , which is a subsea well. However, in other embodiments, the well  15  can be a land well.  
         [0027]    The well  15  includes a primary wellbore  17  and several lateral wellbores  19 . As used here, the term “wellbore” or “bore” can refer to either the primary wellbore or a lateral wellbore. The multilateral well  15  is completed with a casing assembly, including junction assemblies at respective well junctions  21 . The cementing tool according to some embodiments is designed to cement the casing assembly at the well junctions  21 . The term “casing” is intended to cover both casings and liners, or any other structure designed to line the wall of a wellbore.  
         [0028]    [0028]FIG. 3 shows one embodiment of a cementing tool  110  being used to cement a casing assembly  200 . The casing assembly  200  includes a casing junction assembly  100  that may be installed at each well junction  21  in the well  15 . In the embodiment of FIG. 3, the cementing tool  110  is configured to be retrieved and to prevent the accumulation of cement in an internal volume  100   a  of the casing junction  100  so that the clean up required in the internal volume  100   a  of the junction  100  is minimized. An isolated view of the cementing tool  110  is shown in FIG. 4. An isolated view of the casing junction assembly  100  is shown in FIG. 5.  
         [0029]    Referring now to FIGS. 3 and 5, the casing assembly  200  includes the casing junction assembly  100  coupled to the end of a casing string (not shown) by a coupling section  102 . The casing junction assembly  100  is used to provide support and pressure integrity for the lateral junction  21  defined between the primary wellbore  17  and one or more lateral wellbores  19  to be drilled. According to the guidelines established by the Technological Advancement of Multilaterals (TAML) consortium, this type of multilateral support structure may be classified as a Level  6  TAML Multilateral System. However, other types of casing junction assemblies can be used in other embodiments.  
         [0030]    The casing junction assembly  100  illustrated in FIG. 5 is a deformable casing junction assembly  100 , such as one disclosed in U.S. Pat. No. 5,944,107, which is hereby incorporated by reference. To install the casing junction assembly  100  in a wellbore, the casing junction assembly  100  in its deformed position (not shown) is suspended into a wellbore which has been back-reamed to produce a lower wellbore section with a larger diameter than the wellbore section above it (as shown in FIG. 3). An expansion tool (not shown) is then run into the casing junction assembly  100  and used to expand the casing junction assembly  100  from its deformed position to its reformed (fully opened) position, shown in FIGS. 3 and 5. Once in its opened position, the junction assembly  100  may be cemented in the wellbore and the lateral wells drilled through branches  100   b  defined by the casing junction assembly  100 .  
         [0031]    In this example, the end of the casing assembly  200  includes a guide shoe  108  attached to the bottom of the multilateral casing junction assembly  100  to guide the casing assembly  200  as it descends into the wellbore. The guide shoe  108  includes a fluid channel  109  that allows fluid to pass through the guide shoe  108  and up the annular space between the casing  200  and the wellbore. The fluid channel  109  in the guide shoe  108  includes one or more fluid inlets  109   a  at the upper side of the guide shoe  108  and one or more fluid outlets  109   b  at the lower side of the guide shoe  108 .  
         [0032]    The coupling section  102  has an internal landing profile  102   b  and a casing joint  104 . The coupling section  102  may also include an orienting profile  301 , such as a “muleshoe,” to orient the cementing tool  110 . The casing joint  104  is positioned in the casing to provide a desired spacing between the junction assembly  100  and the landing profile  102   b.  The casing assembly  200  shown in FIG. 5 is only one example of a casing assembly for which a cementing tool may be configured for use in, as other types of casing assemblies can be used in other embodiments.  
         [0033]    [0033]FIGS. 3 and 4 show one embodiment of the cementing tool  110 . FIGS. 6 and 7 show another embodiment of the cementing tool. Referring to FIGS. 3 and 4, the cementing tool  110  is adapted to attach to the end of a work string  112 . The work string  112  includes a string of hollow pipe used to lower the cementing tool  110  into the casing assembly  200 . The work string  112  may also be adapted to channel cement and displacement fluid pumped from the surface down to the cementing tool  110  when positioned in the wellbore.  
         [0034]    The cementing tool  110  includes a generally cylindrical body  111 . The body  111  includes a first member  111   a  slidably coupled with respect to a second member  111   b.  One end of the first member  111   a  is adapted to couple to the work string  112 . The other end of the first member  111   a  operatively couples to the second member  111   b  and is adapted to slide axially to a limited extent with respect to the second member  111   b.  An internal bore  113  extends axially through the first member  111   a  and the second member  111   b  to permit fluid flow through the body  111  of the cementing tool  110 .  
         [0035]    Another embodiment of a cementing tool  110  configured for use in the casing assembly  200  of FIG. 5 is shown in FIG. 6. The body  111  of the cementing tool in this embodiment also includes a first member  111   a  and a second member  111   b  slidably coupled in a manner similar to the embodiment described above. However, in other embodiments, the body  111  may be configured differently than generally cylindrical and may include one member or a plurality of connected members with a fluid passage defined therein, without departing from the spirit of the invention.  
         [0036]    Referring to FIGS. 3 and 7, the cementing tool  110  further includes at least one bypass device  120  for channeling cement from the body  111  of the cementing tool  110  to a desired location to prevent the accumulation of cement in an intermediate volume of the casing junction assembly  100 . The distal end of each bypass device  120  is configured to seat in the fluid channel  109  of the guide shoe  108 . In one embodiment, the bypass device  120  may form a seal with the fluid channel  109  of the guide shoe  108  to prevent cement exiting the bypass device  120  from flowing into the internal volume  100   a  of the casing junction  100 . In the embodiments shown, the at least one bypass device  120  includes a plurality of bypass tubes (or another type of conduit) that extend from the second member  111   b  of the body  111  and are adapted to engage in fluid communication with a corresponding fluid channel  109  in the guide shoe  108 .  
         [0037]    In another embodiment of the invention, the cementing tool  110  does not include a bypass device  120 , and the guide shoe  108  does not include the fluid channel  109 . Instead, the second member  111   b  of the body  111  includes outlets enabling the flow of cement from the interior to the exterior of the cementing tool  110 .  
         [0038]    The cementing tool  110  further includes an anchoring mechanism  114  configured to anchor the cementing tool  110  into place within the casing assembly  200 . In the embodiments shown, the anchoring mechanism  114  includes a plurality of keys  114   a  azimuthally disposed about the body of the cementing tool  110  and configured to engage into a landing profile  102   b  in the casing assembly  200 . In the embodiment shown in FIG. 3, the anchoring keys  114   a  are radially extendable, attached to the second member  111   b , and slidably coupled about an outer surface of the first member  111   a  of the body  111 .  
         [0039]    [0039]FIG. 3 shows the anchoring keys  114   a  in the activated (or expanded) position, and FIG. 4 shows the anchoring keys  114   a  in a deactivated (or retracted) position. In another embodiment, the anchoring mechanism may include a single key, such as a retractable ring-shaped key radially disposed about the body of the cementing tool.  
         [0040]    As shown in FIG. 3, the anchoring mechanism  114  is configured to engage in the landing profile  102   b  provided in the coupling section  102  located above the casing junction assembly  100 . The anchoring keys  114   a  are radially biased outwardly to engage in the annular recess  102   a  of the landing profile  102   b  as the cementing tool  110  descends into position in the casing junction assembly  100 . Alternatively, the anchoring keys  114   a  may be spring loaded to automatically extend outwardly when brought into axial alignment with the landing profile  102   b,  as in the embodiment of FIG. 7.  
         [0041]    Once the anchoring keys  114   a  land in the landing profile  102   b , the lower body  111   b  and the at least one bypass device  120  will be restricted from further axial movement in the casing assembly  200 . Subsequent increase of the axial force on the cementing tool  110  results in the axial downward movement of the first member  111   a  with respect to the second member  111   b  and the anchoring mechanism  114 . With downward movement of the first member  111   a , an enlarged portion  111   c  of the first member  111   a  slides down to engage and lock the keys  114   a  in the landing profile  102   b.    
         [0042]    In one embodiment, the keys  114   a  are configured to withstand axial forces, which may be exerted on the cementing tool  110 , such as forces due to the weight of the tool  110  and work string  112  or buoyancy forces exerted by the cement  124  on the tool  110  during the cementing operation. Those skilled in the art will appreciate that the invention is not limited to an anchoring mechanism  114  with keys  114   a  as described above. Rather, any type of anchoring mechanism suitable for downhole tools may be used in other embodiments without departing from the spirit of the invention.  
         [0043]    The cementing tool  110  may also include at lease one orienting key (not shown) attached to the body  111 . In one embodiment, the orienting key may be one of the anchoring keys  114   a  that is specially adapted and located to mate with orienting profile  301  in the casing assembly  200 . The orienting key cooperates with the orienting profile  301  of the coupling section  102  to orient the cementing tool  110  so that each bypass device  120  lands in an inlet  109   a  of the fluid channel  109  of the guide shoe  108 . It is noted that the orienting key and orienting profile  301  are not required in those embodiments of cementing tool  110  that do not include a bypass device  120 .  
         [0044]    As shown in FIGS. 4 and 6, the body  111  of the cementing tool  110  also includes at least one shear pin  111   e  connecting the first member  111   a  and the second member  111   b  of the body  111  to prevent axial movement of the first member  111   a  with respect to the second member  111   b  until a sufficient shearing force is applied on the pin  111   e.  Once the cementing tool  110  lands and is anchored into the casing assembly  200 , as shown in FIGS. 3 and 7, the shear pin  111   e  connecting the first member  111   a  to the second member  111   b  may be sheared by applying an increased downward force on the tool  110 . Once the pin  111   e  is sheared, the first member  111   a  is permitted to move axially with respect to the second member  111   b  to lock the anchoring keys  114   a  of the tool  110  into the landing profile  102   b  of the casing assembly  200 .  
         [0045]    Once the first member  111   a  of body  111  has concluded its sliding motion, a securing mechanism, such as a ratchet mechanism  450  (see FIGS. 3, 7,  9 ), is activated to secure the first member  111   a  to the second member  111   b  of the body  11 . FIGS. 3 and 7 show the general location of the ratchet mechanism  450 , while FIGS.  9 A-B shows the ratchet mechanism  450  in more detail. FIG. 9A shows the ratchet mechanism  450  prior to the sliding motion of first body member  111   a.  FIG. 9B shows the ratchet mechanism  450  subsequent to the sliding motion of first body member  111   a . The ratchet mechanism  450  comprises teeth  452  on second body member  111   b  that mate with teeth  458  on first body member  111   a  when the first body member  111   a  has concluded its sliding motion (as shown in FIG. 9B). Prior to this, the first body member teeth  458  are located above the second body member teeth  452 . When mated, the teeth  452 ,  458  are configured to prevent upward movement but allow downward movement of first body member  111   a  relative to the second body member  111   b . First body member teeth  458  are, in one embodiment, located on a ratchet key  456  that is attached by a shear pin  460  within a recess  454  of first body member  111   a.  In another embodiment (not shown), it is the second body member teeth  452  that are located on a similar ratchet key attached by a shear pin within a recess of second body member  111   b.    
         [0046]    The cementing tool  110  further includes at least one sealing element  116  disposed about the exterior of the cementing tool  110  to affect a fluid seal between the cementing tool  110  and the casing assembly  200 . Once the cementing tool  110  is in position in the multilateral casing junction assembly  100 , the sealing element  116  may be hydraulically set to seal the volume in the annulus between the work string  112  and the casing string above the sealing element  116  from the volume in the annulus between the multilateral casing junction assembly  100  and the cementing tool  110  below the sealing element  116 . The sealing element  116  may be disposed within a recess in the exterior surface of the second member  111   b  of the body  111 . Those skilled in the art will appreciate that the invention is not limited to using a sealing element or the sealing element described above. Rather any sealing device, including hydraulically, electrically, and mechanically set sealing devices, may be used without departing from the spirit of the invention. Further, it should be understood that the sealing element  116  can be attached to some other component.  
         [0047]    The cementing tool  110  may further include a flow control device  118  disposed within the body  111  of the cementing tool  110  to selectively permit the flow of cement through the cementing tool  110 . In the embodiment shown in FIG. 3, the flow control device  118  is a check valve  119  that permits the downward flow of cement through the cementing tool  110  but prevents the upward flow of cement back up the cementing tool  110  and into the work string  112 .  
         [0048]    In the embodiment shown in FIGS. 6 and 7, a flow control device  118   a  according to another embodiment is a sliding sleeve  121  remotely controlled from the surface. The sliding sleeve  121  includes a cylindrical body having one or more orifices  121   a  through which fluid, such as cement slurry, may flow. The sliding sleeve  121  is integral with the first member  111   a  of the body  111  and thus moves with the first member  111   a  as it is moved from its upper position (FIG. 6), to its lower position (FIG. 7) with respect to the second member  111   b . The orifice(s)  121   a  are positioned within the sliding sleeve  121  such that when the first member  111   a  is in its upper position (FIG. 6) the orifice(s)  121   a  are blocked by the second member  111   b  to prevent fluid flow through the orifice(s)  121   a.  However, when the first member  111   a  is in its lower position (FIG. 7), orifice(s)  121   a  are unobstructed to permit fluid to flow through them. In other embodiments, the flow control device  118  may include any other device that can be used to selectively permit flow through the cementing tool  110 . Further, the location of the flow control device  118  can be varied.  
         [0049]    To permit retrieval of the cementing tool  110  from the casing assembly  200  after the cementing operation, the anchoring mechanism  114  of the cementing tool  110  is configured to be set and released on demand from the surface. In one embodiment, the anchoring mechanism  114  may be released from the surface by pulling up on the first member  111   a  of the body  111 . The pulling motion may be performed by the work string  112 , which may be left downhole throughout the cementing operation, or by a retrieval tool (not shown) attached to the end of another (or the same) work string that is adapted to attach to the first member  111   a . The resulting upward force on the first member  111   a  results in the shearing of the ratchet shear pins  460  (FIGS.  9 A- 9 B) and thus the disablement of the ratchet mechanism  450 . Once the ratchet mechanism  450  is disabled, the resulting upward movement of the first member  111  a relative to the second member  111   b  results in the position shown in FIGS. 4 and 6, wherein the first member  111   a  no longer prohibits the inward motion of the keys  114   a  (the protruding portion  111   c  of the first member  111   a  is no longer wedged against the keys  114   a ). Continued upward movement eventually results in the first member  111   a  picking up on the second member  111   b  (at shoulder  115  of the first member  111   a ) and the second member  111   b  being pulled upwardly together with the first member  111   a.    
         [0050]    Continued upward movement causes the keys  114   a  to be released from (forced out of) the landing profile  102   b . This release is facilitated by the angled portions  300  of the keys  114   a  and the landing profile  102   b  that interact with each other and due to the fact that the keys  114   a  are no longer locked in place by the first member  114   a  and are now free to retract radially inward. After the keys  114   a  are released from the annular recess  102   a,  the cementing tool  110  can be removed from the casing assembly  200  upon completion of the cementing operation, as further described below.  
         [0051]    In the FIG. 7 embodiment, the cementing tool  110  may further include a barrier  126  disposed about a periphery of at least one bypass device  120  to prevent cement  124  from back filling into the internal volume  100   a  of the junction  100 . In one embodiment, the barrier  126  includes a deformable rubber retainer. The barrier  126  may include an opening therein for receiving a bypass device  120 . When the cementing tool  110  is inserted into the casing assembly  200 , the barrier  126  may deform into a retracted position to fit down the primary borehole of the casing assembly  200  and then may expand in the casing junction assembly  100  between a bypass device  120  and the inside of the lateral branches  100   b  of the casing junction assembly  100 . The barrier  126  may also be configured, such as with sloped edges capable of scaling the wall of the junction, to retract as the tool is moved up the casing junction assembly  100  and primary bore of the casing assembly  200  for removal after the cementing operation. Alternatively, the barrier  126  may be designed to break away from the portion of the tool  110  removed from the wellbore  128  and remain downhole after the cementing operation. In such case, the barrier  126  will have to be milled or drilled out before resuming drilling operations. In other embodiments, the barrier may include any device or material capable of preventing the back flow of cement into the junction  100  without departing from the spirit of the invention. In one embodiment, the barrier  126  prevents cement back flow without forming a pressure seal to allow for pressure equalization across the walls of the junction  100  during the cementing operation.  
         [0052]    Alternatively, in the FIG. 3 embodiment, the cement is prevented from back filling into the internal volume  100   a  of the casing junction assembly  100  (at  127 ) by the drilling fluid trapped in the internal volume  100   a  of the casing junction  100 . In this embodiment, drilling fluid in the internal volume  100   a  of the casing junction  100  prior to cementing is trapped in the internal volume  100   a  between the seals  116  of the cementing tool  110  and cement exiting the guide shoe  108  and flowing up the annulus between the casing assembly  200  and the wellbore  128 .  
         [0053]    To perform a cementing operation with the example tools shown, the cementing tool  110  is attached to the end of the work string  112 , which is then lowered into a casing assembly  200  in the wellbore  128 . In the embodiment including the bypass device  120 , the orienting profile  301  of the coupling section  102  acts to orient the cementing tool  110  so that each bypass device  120  lands in an inlet  109   a  of the fluid channel  109  of the guide shoe  108 . The at least one bypass device  120  at the lower end of the cementing tool  110  lands in the corresponding inlet  109   a  of the fluid channel  109  of the guide shoe  108 . The bypass device  120  and the inlet  109   a  in the guide shoe  108  may be configured with sloped mating surfaces to guide the bypass device  120  into position in the guide shoe  108 . Downward axial force on the cementing tool  110  may further force the mating surfaces of the bypass device  120  and guide shoe  108  together which may help them form a fluid seal.  
         [0054]    As the bypass device  120  lands in the guide shoe  108 , the anchoring mechanism  114  enters the landing profile  102   b  above the casing junction assembly  100 . The keys  114   a  are biased to extend radially outwardly when brought into substantial axial alignment with the landing profile  102   b  to engage in the landing profile  102   b . This anchors the cementing tool  110  in place. As a result, an increased downward axial force on the cementing tool  110  shears the shear pin ( 111   e  in FIGS. 4 and 6) between the first member  111   a  and the second member  111   b  of the body  111 . The first member  111   a  then slides axially downwardly with respect to the second member  111   b  and anchoring mechanism  114  to lock the keys  114   a  into the landing profile  102   b  in the casing assembly  200 . The first member  111   a  comes to rest against shoulder  111   d  of the second member  111   b  of the body  111  and further downward movement of the cementing tool  110  ceases. As the first member  111   a  concludes its sliding motion, the ratchet mechanism  450  engages (the teeth  452 ,  458  mate) thereby securing the first member  111   a  to the second member  111   b.    
         [0055]    At the surface, proper landing and locking of the cementing tool  110  into the casing assembly  200  may be determined based on the “hung weight” at the top of the work string  112  at the surface. Thus, the cementing tool  110 , advantageously, can provide positive feedback on the positioning of the cementing tool  110  in the casing assembly  200  based on hung weight reductions corresponding to the landing of the anchoring mechanism  114 , the shearing of the shear pin  111   e , and the locking of the tool  110  into the casing assembly  200 .  
         [0056]    In another embodiment, instead of or in addition to the anchoring mechanism  114 , the casing junction  100  includes a shoulder (not shown) in its interior. The cementing tool  110  sits on the shoulder, which shoulder absorbs all or a portion of the weight.  
         [0057]    Once the cementing tool  110  is locked into place, the sealing element  116  is hydraulically set. Prior to pumping cement, the cementing tool  110  and work string  112  will be surrounded by drilling fluid or the like. Thus, prior to pumping cement down the work string  112 , the internal volume  100   a  of the casing junction  100  will be filled with drilling fluid.  
         [0058]    Cement is then pumped down the work string  112  to the cementing tool  110 . A fluid separator, such as a rubber plug ( 129  in FIG. 7), may precede the flow of cement in the work string  112  to separate the cement from drilling fluid in the work string  112  and the cementing tool  110  prior to the pumping of cement. Cement is then pumped on top of the plug  129  to displace drilling fluid down the work string  112  and out of the cementing tool  110 . The plug  129  eventually comes to rest proximal the flow control device  118  in the body  111  of the cementing tool  110 .  
         [0059]    In the embodiment of FIG. 3, the rubber plug (not shown), if used, may seat above the check valve  119  at the internal lip shown at  130 . The plug may include a membrane that ruptures due to continued pumping of the cement on top of the plug once it seats to cause a membrane in the plug to rupture, opening a passage in the plug that permits the flow of cement through the cementing tool  110  and into the guide shoe  108 .  
         [0060]    In the embodiment of FIG. 7, rubber plug  129  seats in the sleeve  121  below the orifice(s)  121   a  such that the flow of cement behind the plug is permitted to exit the sleeve  121  of the tool and flow through the at least one bypass device  120  to the guide shoe  108 .  
         [0061]    In the embodiments including the bypass device  120 , the connection between the at least one bypass device  120  and guide shoe  108  and fluid trapped in the internal volume  100   a  of the casing junction  100  may prevent the cement from back flowing into the internal volume  100   a  of the multilateral casing junction assembly  100 . However, as noted above the barrier  126  in FIG. 7 may be provided on the tool  110  to extend between the bypass device  120  and the corresponding branch  100   b  of the casing junction assembly  100  to prevent the back flow of cement  124  into the internal volume  100   a  of the junction assembly  100 , while permitting pressure equalization across the walls of the junction assembly  100 .  
         [0062]    At the surface, once the predetermined amount of cement has been pumped down the work string  112 , displacement fluid is pumped down the work string  112  to force the last of the cement down the work string  112  and out of the cementing tool  110 . A second fluid separator, or rubber plug  131  (in FIG. 7), may be placed in the work string  112  to separate the cement from the displacement fluid as the displacement fluid is pumped down the work string  112 .  
         [0063]    As illustrated in FIG. 7, the pumping of displacement fluid continues until the second rubber plug  131  displaces the last of the cement through the body of the cementing tool  110 . The second rubber plug  131  comes to rest against the first plug  129  seated in the cementing tool  110  and prevents further flow of displacement fluid through the cementing tool  110 .  
         [0064]    In the embodiment of FIG. 3, the second plug  131  may seat in the first plug (described above) to block the fluid passage in the first plug. In the embodiment of FIG. 7, the second plug  131  seats on the first plug  129 , as shown, and blocks the orifice(s)  121   a  in the sliding sleeve  121 . The seating of the second plug  131  in the cementing tool  110  is indicated at the surface by a pressure increase, at which time pumping of displacement fluid ceases.  
         [0065]    In the embodiment including the bypass device  120 , the cement pumped through the cementing tool  110  passes through the at least one bypass device  120 , into the fluid channel  109 , and out of the fluid channel  109  through outlet  109   b.  Once out of the outlet  109   b,  the cement is forced upward to the annular area between the casing junction assembly  100  and the wellbore to cement the casing assembly  200  in place. The displacement fluid pumped on top of the second plug  131  ensures that the necessary volume of cement is forced into such annular area. As the displacement fluid is pumped, the cement is forced upwardly in the annular area. The cement will typically surround at least the entire casing junction assembly  100 , but may also surround a substantial portion of the remainder of the casing assembly  200 .  
         [0066]    In the embodiment not including the bypass device  120 , cement flows through the bottom (outlets) of the cementing tool  110  and through the outlets of the casing junction assembly  100 . The cement is then forced upward to the annular area between the casing assembly  200 /casing junction assembly  100  and the wellbore to form the cement layer  124 .  
         [0067]    Once the cement pumping phase is complete, the cementing tool  110  (in part or in whole) will remain in place until the cement  124  in the wellbore has hardened. The work string  112  may be detached from the cementing tool  110  and returned to the surface during this time. Once the cement has cured, the anchoring mechanism  114 , being isolated from the cement operation, may be unlocked and disengaged from the casing so that the cementing tool  110  can be retrieved from the wellbore  128 .  
         [0068]    Depending on the type of anchoring mechanism used, retrieval of the cementing tool  110  from the wellbore may require a retrieving tool to unlock the anchoring mechanism  114  from the landing profile  102   b  of the casing assembly  200 . However, in the embodiments shown in FIGS. 3 and 7, the cementing tools are configured such the work string  112  attached to the first member  111   a  of the cementing tool  110  may be used to provide a sufficient upward axial force to pull the first member  111   a  into its upward position to disengage the ratchet mechanism  450  (by shearing the shear pins  460 ) and unlock the anchoring mechanism  114  from the landing profile  102   b . Once unlocked, an additional upward force can be applied to the tool  110  to force the anchoring keys  114   a  to retract as they are forced up the landing profile  102   b . In an alternative embodiment, the anchoring keys  114   a  may be, at this point, biased radially inward, in which case the keys  114   a  will automatically disengage once unlocked from the landing profile  102   b . Other devices and techniques for locking and retrieving downhole tools may be used in other embodiments.  
         [0069]    In one embodiment, once the cementing tool  110  is unlocked from the casing assembly  200 , the only connection retaining the cementing tool  110  in the wellbore  128  is the column of hardened cement  124  in the at least one bypass device  120  leading into the guide shoe  108 . The connection between the cementing tool  110  and the guide shoe  108  may be severed simply by applying a rotational torque and/or an upward axial force to the cementing tool  110  to break the cement column between the at least one bypass device  120  and the guide shoe  108 . In this manner, the cementing tool  110  in its entirety is retrieved, including the bypass device  120  as a whole. In such case, no clean up or drill-out in the internal volume  100   a  of the junction  100  is typically required. This, advantageously, allows normal drilling operations to be resumed quickly and safely down the selected lateral branch  100   b  of the junction assembly  100  without harm to the mechanical integrity of the junction assembly  100 .  
         [0070]    In other embodiments, once the cementing tool  110  is unlocked from the casing assembly  200 , a simple upward force on the cementing tool  110  is not sufficient to break the connection between the cementing tool  110  and the cement  124 . In some applications, this connection may be broken by providing at least one bypass device  120  of the cementing tool  110  that is frangible such that in response to a sufficient upward force, the connection between the at least one bypass device  120  and the second member  111   b  of the body  111  is broken. This results in the at least one bypass device  120  being left in the casing junction  100  and the body  111  and other portions of the cementing tool  110  being released from the wellbore  128  and pulled to the surface.  
         [0071]    Alternatively, the cementing tool  110  may be designed to have one or more selected weak points, such that a sufficient upward force or torque on the tool will result in the breaking off of a portion of the tool  100  below the weak point. For example, the at least one bypass device  120  may be bypass tubes configured to have a weak point, such as a narrowed section or neck ( 140  in FIG. 8), configured to break in response to a sufficient upward or twisting force applied to the cementing tool  110 . Thus, if cement is allowed to backfill to a limited degree into the casing assembly  200  around the end of the bypass device  120 , as shown in FIG. 3, rotation of or an upward force on the cementing tool  110  may result in the shearing of the at least one bypass device  120  at or above the portion of the bypass device  120  embedded in the cement  124 .  
         [0072]    Alternatively, the lower part of the body  111  may include a subsection designed to break off, such as at  133  in FIG. 3 where the at least one bypass device  120  inserts into the body. The location of the weak point or breakaway point may be located at various points along each bypass device  120 . However, in some embodiments, a substantial portion of the cementing tool  110  is retrievable from the wellbore  128  so that milling or drill out operations originate in the branches  100   b  of the junction  100  rather than above the junction divider  106  to minimize the likelihood of damage to the junction  100  during milling.  
         [0073]    If a portion of the at least one bypass device  120  is left in place in the cement  124 , then that portion, along with the cement  124  and a portion of the guide shoe  108  below the internal volume  110   a  of the junction  100  will need to be milled before the lateral wells can be drilled. Therefore, the at least one bypass device  120  and the guide shoe  108  may be formed of a material that is easily milled, such as a plastic, rubber, thin-walled aluminum, or other frangible or drillable material, so that milling can be easily done without producing large resultant forces on the milling tool that could cause the mill to forcibly knock against and damage the divider  106  and branches  100   a  of the casing junction  100 .  
         [0074]    FIGS.  10 A- 10 J are schematic diagrams of a different embodiment of a cementing tool  500  adapted to be installed in the casing assembly  200 . A longitudinal sectional view of the cementing tool  500  is shown in FIGS.  11 A- 11 D. FIGS.  12 A- 12 D are a side view of the cementing tool corresponding to the view of FIGS.  11 A- 11 D. Reference is made to FIGS.  10 A- 10 J,  11 A- 11 D, and  12 A- 12 D in the following description. The cementing tool  500  includes locking keys  502  for engagement in landing profiles  102   b  of the casing assembly. Upper ends of the locking keys  502  are engaged by leaf springs  506  (FIG. 11B) to an upper housing  504  of the cementing tool  500 , while the lower ends of the locking keys  502  are engaged by leaf springs  506  to another body portion  520 .  
         [0075]    The cementing tool  500  also includes a retrieving mandrel  508  that has a retrieving profile  510  to which a retrieving tool can be engaged to lift the cementing tool  500  for retrieval from the well. The cementing tool  500  also includes a control mandrel  512 . A lower end of the control mandrel  512  is attached to a sleeve  514  by a shearing mechanism  516  (see FIG. 11A). In one embodiment, the shearing mechanism  516  includes one or more shear screws.  
         [0076]    The lower end of the retrieving mandrel  508  is attached to an anchoring mandrel  509 , which has enlarged portions  518   a  and  518   b  that protrude outwardly from an outer surface of the anchoring mandrel  509 . The outer portions of the enlarged portions  518   a  and  518   b  are adapted to engaged corresponding portions of the locking keys  502  when the anchoring mandrel  509  is pushed downwardly (as shown in FIG. 10B). In the position shown in FIG. 10A, which is the landing position, the enlarged portions  518   a  and  518   b  are disengaged from the locking keys  502 .  
         [0077]    The anchoring mandrel  509  also extends a substantial length of the cementing tool  500 . As shown in FIG. 11C, the outer surface of the anchoring mandrel  509  has a pair of grooves  562  and  556  that are adapted to be engaged by stop rings  560  and  558 , respectively, when the anchoring mandrel  509  moves downwardly by a predetermined distance. Also, the stop rings  560  and  558  are engaged to unsetting members  572  and  574 , respectively, to enable the unsetting of the sealing elements  532  and  534 .  
         [0078]    The sleeve  514  defines an inner bore  522  in the cementing tool  500  through which fluid can pass. Examples of such fluid include cement slurry as well as displacement fluid to push the cement slurry during cementing operations. The lower end of the sleeve  514  is attached to a valve member  524  (FIGS. 10A and 11D). The sleeve  514  is movable longitudinally (with movement of the control mandrel  512 ) in the cementing tool  500  to move the valve member  524  up and down to open or close radial ports  526 . In the position of FIG. 10A and 11D, the radial ports  526  are open to enable fluid flow between the inner bore  522  and an annular passageway  549  that leads to a chamber  550  in the cementing tool. Fluid in the chamber  550  flows out of the cementing tool  500  through one or more outlet ports  551  into the casing assembly  200 .  
         [0079]    The cementing tool  500  includes two sealing elements  532  and  534  (as compared to the one sealing element in the embodiments of FIGS. 3 and 7). The sealing elements  532  and  534  are expandable to engage an inner wall of the casing assembly  200 . The sealing elements  532  and  534  are set by a downward force applied by respective setting pistons  528  and  530 , which are moveable downwardly by an increased pressure communicated down the work string and through the inner bore  522  of the cementing tool  500 . Chambers  536  and  538  are provided above respective setting pistons  528  and  530  that cooperate with reference chambers  540  and  542  (which can be filled with air, for example) to create a differential pressure for moving the setting pistons  528  and  530  downwardly. The setting pistons  528  and  530  are initially attached to the body of the cementing tool  500  by shearing mechanisms  580  (FIG. 11B) and  582  (FIG. 11C), respectively.  
         [0080]    Pressure in the bore  522  of the cementing tool  500  is communicated through radial ports  544  of the sleeve  514  and the anchoring mandrel  509  to the chamber  536  when the sleeve  514  and anchoring mandrel  509  are lowered into axial alignment with an inlet of the chamber  536  (as shown in FIG. 10B). Similarly, radial ports  546  formed in the sleeve  514  and the anchoring mandrel  509  communicate fluid pressure from the inner bore  522  of the cementing tool  500  into the chamber  538  when the ports  546  are axially aligned with inlets of the chamber  538 . In addition, the chamber  538  has an outlet  548 . A nozzle (not shown) is provided at the outlet  548  that provides pressure buildup in the chamber  538  in response to pressure flow through the nozzle.  
         [0081]    An outer sleeve  590  is formed around an outer portion of the cementing tool  500  below the sealing element  534 . The outer sleeve  590  is formed of a stretchable material, such as rubber or other stretchable material, to facilitate the retrieval of the cementing tool  500  after the cement layer around the cementing tool  500  hardens.  
         [0082]    In operation, the cementing tool  500  is attached to a work string, with the cementing tool  500  lowered to a position such that the locking keys  502  are aligned with the landing profiles  102   b  of the casing assembly  200 , as shown in FIG. 10A. Next, as shown in FIG. 10B, the cementing tool  500  is actuated to its anchoring position, where the control mandrel  512  is moved downwardly a predetermined distance to push the sleeve  514  and the anchoring mandrel  509  downwardly by the same distance. This causes the enlarged portions  518   a  and  518   b  of the anchoring mandrel  509  to engage the locking keys  502  so that the locking keys are locked against the landing profiles  102   b  of the casing assembly  200 . Also, downward movement of the sleeve  514  and the anchoring mandrel  509  causes the radial ports  544  and  546  to be aligned with inlets of the chambers  536  and  538 , respectively. The downward movement of the sleeve  514  also causes the valve member  524  to move downwardly, closing the ports  526  to prevent communication of fluid between the inner bore  522  and the annular region  549 .  
         [0083]    The downward movement of the anchoring mandrel  59  is stopped when a stop ring  558  (biased radially inwardly) engages a groove  556  in the outer surface of the anchoring mandrel  509  (FIG. 11C), and when a stop ring  560  engages a groove  562  in the outer surface of the anchoring mandrel  509 . Note that the distance between the initial positions of the groove  556  and stop ring  558  and between the initial positions of the groove  562  and stop ring  560  are the same.  
         [0084]    Next, fluid is pumped down the work string and into the inner bore  522  of the cementing tool  500  to communicate fluid to chambers  536  and  538 . This causes pressure to build up in the chambers  536  and  538 , which in turn causes creation of a differential pressure between the chambers  536  and  540  and between chambers  538  and  542 , which shears the shearing mechanisms  580  and  582  and pushes respective setting pistons  528  and  530  downwardly to set the sealing elements  532  and  534 , respectively.  
         [0085]    Setting of the sealing elements  532  and  534  are shown in FIG. 10C. Once the sealing elements  532  and  534  are set against the inner wall of the casing assembly  200 , the annular region above the sealing element  532  is isolated from the annular region below the lower sealing element  534 .  
         [0086]    After being set, the sealing elements are tested to ensure that there are no leaks. By using two sealing elements  532 ,  534 , fluid under pressure communicated through the workstring and into the inner bore of the cementing tool  500  is communicated to an annular space outside the cementing tool  500  between the sealing elements  532 ,  534  (now set as shown in FIG. 10C). The fluid under pressure is communicated through the ports  546 , into the chamber  538 , and out of the chamber  538  into the annular space between the sealing elements  532 ,  534 . Any leaks around the sealing elements  532 ,  534  can be detected at the well surface.  
         [0087]    Next, as shown in FIG. 10D, the cementing tool  500  is actuated to its cementing position. This is performed by pulling the control mandrel  512  upwardly. Note that the control mandrel  512  can be moved upwardly without causing a corresponding movement of the anchoring mandrel  509 . However, since the control mandrel  512  is connected to the sleeve  514 , upward movement of the control mandrel  512  causes a corresponding movement of the sleeve  514  by the same distance. The upward movement of the sleeve  514  causes the valve member  524  to move to its open position so that radial ports  526  are allowed to communicate fluid between the inner bore  522  of the cementing tool  500  and the annular region  549 . Thus, cement slurry pumped down the work string and into the inner bore  522  is communicated through the radial ports  526  to the annular region  549  and chamber  550 , which in turn is communicated out of the port  551  of the cementing tool  500  into the lateral legs of the casing junction assembly  100 .  
         [0088]    As shown in FIG. 10E, in accordance with one embodiment, a plug  554  (in the form of a dart) is provided ahead of cement slurry  556 . The dart  554  has an inner bore  558  through which fluid can communicate. Initially, a rupture disk  560  is provided in the bore  558  of the dart  554 . Once the dart  554  lands in a profile provided by the valve member  524 , the pressure generated by the cement slurry  556  causes the rupture disk  560  to rupture, thereby allowing the cement slurry to flow through the dart  554  and out through radial ports  526 . As shown in FIG. 10F, a second plug  562  is run behind the predetermined volume of the cement slurry, with displacement fluid provided behind the second dart  562 . Once the second dart  562  lands on the first dart  554 , further movement of the cement slurry is stopped. Although not shown, the cement actually flows to the annular space outside the junction assembly to cement the casing assembly to the wellbore.  
         [0089]    The valve member  524  is then moved upwardly to close the radial ports  526 , as shown in FIG. 10G. This is performed by lifting the control mandrel  512  a predetermined distance. By applying a sufficiently large upward force, the shear screws  516  (FIG. 11A) are sheared to allow the control mandrel  512  to be disconnected from the cementing tool  500 , as shown in FIG. 10H. Next, a retrieving tool is lowered into the wellbore, with a retrieving element  570  provided at the lower end of the retrieving tool, as shown in FIG.  10 I. The retrieving element  570  engages the retrieving profile  510  of the retrieving mandrel  508 .  
         [0090]    Once the cement has cured after a predetermined time period, a block  592  of cement hardens around the outer surface of a lower portion of the cementing tool  500  below the sealing element  534 . The retrieving tool is then lifted to unset the sealing elements  532  and  534 . As the retrieving tool is lifted, the retrieving mandrel  508  and anchoring mandrel  509  are moved upwardly so that the anchoring mandrel  509  is disengaged from the locking keys  502 . Also note that the stop rings  558  and  560  (FIG. 11C) are engaged in corresponding grooves  556  and  562  of the anchoring mandrel  509  at this time. As a result, upward movement of the anchoring mandrel  509  causes a corresponding upward movement of unsetting members  572  and  574 . The unsetting members  572  and  574  have respective shoulders  566  and  570  (FIG. 11C) that are configured to engage protruding portions  564  and  568 , respectively, of setting pistons  528  and  530 . Thus, upward movement of the unsetting members  572  and  574  causes a corresponding upward movement of the setting pistons  528  and  530 . This allows the sealing elements  532  and  534  to unset.  
         [0091]    After disengagement of the locking keys  502  and unsetting of the sealing elements  532  and  534 , further upward movement causes the cementing tool  500  to be filled. This unlocks the locking keys  502 . The outer sleeve  590  is stretched to detach or unbond the sleeve  590  from the cement block  592 . This enables easier lifting of the cementing tool  500  out of the cement block  582 . The stretching of the sleeve  590  is illustrated in FIGS.  13 A- 13 B.  
         [0092]    Some embodiments of the invention may provide one or more of the following advantages over the prior art. A retrievable cementing tool, in some embodiments, can be used to selectively cement around objects or volumes in a casing assembly to avoid the accumulation of cement around the object or in the volume during cementing operations. A casing assembly including a casing junction assembly can be cemented in a wellbore such that clean up at the junction assembly is minimized. A cementing tool is configured to match closely with the internal geometry of a casing junction assembly, which includes one or more bypass devices to convey cement through the internal volume of the junction assembly, thereby preventing cement from filling the junction assembly during the cementing process. Some embodiments of the invention may also be used to reduce the number of downhole trips required for clean up of the junction after cementing operations and to preserve the integrity of the casing junction assembly.  
         [0093]    Advantageously, some embodiments of the invention also include an anchoring mechanism, which can be mechanically set and/or released from the surface. This allows for anchoring the cementing tool in the casing during cementing operations and then releasing it from the casing after cementing operations are completed without the need for a subsequent milling operation. Further, because the volume around the anchoring mechanism and body of the cementing tool are protected from cement invasion, the operation of the anchoring mechanism is not altered by the cementing operation and the cementing tool, in whole or in part, can be retrieved from the wellbore. It should be understood that the advantages noted above are merely examples of possible advantages associated with one or more embodiments, and are not intended as limitations on the invention.  
         [0094]    While the invention has been described with respect to exemplary embodiments, those skilled in the art will appreciate that numerous modifications and variations can be made therefrom without departing from the spirit of the invention.