Patent Abstract:
An apparatus that is usable with a subterranean well includes a liner and a wiper. The liner is to be cemented inside the well bore, and the wiper, in a first mode, is connected to the liner when the liner is run downhole. In a second mode, the wiper is released to respond to a cement flow.

Full Description:
Pursuant to 35 U.S.C. § 119, this application claims the benefit of U.S. Provisional Application Serial No. 60/262,746, entitled “SYSTEM FOR CEMENTING A LINER OF A SUBTERRANEAN WELL,” filed on Jan. 19, 2001. 
    
    
     BACKGROUND 
     The invention generally relates to a system for cementing a liner of a subterranean well. 
     Liners are commonly used in subterranean wells. As the name implies, a liner lines a section of a well bore. Such liners typically “hang” from a parent casing and may be cemented in place to the casing to provide structural support to the well bore. 
     In a typical liner cementing application, the liner is first hung on the parent casing, and the cementing tool is thereafter lowered to the liner. Cement is then pumped through the cementing tool to the area between the liner and the well bore. To force the cement down into the particular space being cemented, a displacement fluid, such as water (for example), may be used. In this manner, at the surface of the well, a device called a dart may be placed between the displacement fluid and the cement to form a barrier to prevent mixing of the cement and the displacement fluid. The dart follows the displacement fluid/cement interface downhole as more displacement fluid is introduced from the surface of the well to push the cement into the region to be cemented. 
     When the dart approaches the bottom of the cementing tool, the dart may engage a wiper that is part of and located at the bottom of the cementing tool. The dart seals a central passageway of the wiper through which the cement passes and dislodges the wiper from the cementing tool, thereby forming a barrier that wipes cement from the interior surface of the liner. 
     Unfortunately, the conventional wiper for use in liner applications typically is located at the bottom of the cementing tool and thus, is contacted by surfaces of varying diameters as the cementing tool is lowered downhole. As a result, depending on the geometry of the well bore and well bore completion, the wiper may be broken off or damaged as the cementing tool is being run downhole. 
     Conventional wiper darts are also not adapted to efficiently seal on a wide range of tubing diameters. For instance, conventional wiper darts may not be adequate to efficiently seal on larger diameter tubing (such as 4″) as well as smaller diameter tubing (such as 1.75″). Many completions currently include such a range of tubing diameters. 
     In addition, conventional systems often leave plug-mounting hardware in place that reduces the liner drift diameter and may prevent the performance of subsequent operations, such as cement evaluation. Retrieval of such plug mounting hardware is often required prior to the performance of the subsequent operations. 
     Moreover, in some instances as shown in the case of FIG. 1, the typical liner cementing application would provide undesirable consequences. FIG. 1 shows a casing  6  of a multilateral well. The casing  6  may include a junction  5 , a part of the casing  6  in which a main vertical well bore  7   a  transitions into lateral well bores, such as lateral well bores  7   b  and  7   c  that are depicted in FIG.  1 . Before the lateral well bores  7   b  and  7   c  are drilled, the main well bore  7   a  is drilled, and the junction  5  is cemented in place. To accomplish this, a cementing tool (not shown) may be lowered downhole to deliver cement into the region of the well bore  7   a  that surrounds the junction  5 . 
     After the junction  5  is cemented in place, the lateral well bores  7   b  and  7   c  are drilled. After each lateral well bore  7   b ,  7   c  is drilled, a liner  8  is hung from one of the legs of the junction  5  by a liner hanger  3 . After the liner  8  is hung, the liner  8  is then cemented in place. 
     To cement the liner in place, a cementing tool is typically deployed to the liner  8 , and cement is pumped into the area between the liner  8  and the well bore. As the cement fills up such area, the cement displaces a fluid which must find a return path uphole of the liner hanger  3 . To enable such return path, an operator either runs the liner cementing operation with the packer  2  unset, or installs a through port collar on the liner top. In either case, the return path enables displaced fluid, cement, or other debris to pass into the interior of the junction  5 , which is undesirable for a variety of reasons. One of these reasons is that it may be necessary to mill out such displaced fluid, cement, or other debris from the junction after the end of the cementing operation, which milling operation may harm the structural integrity of the junction. 
     Thus, there is a continuing need for an arrangement and/or technique that addresses one or more of the problems that are stated above. 
     SUMMARY 
     In an embodiment of the invention, an apparatus that is usable with a subterranean well includes a liner and a wiper. The liner is to be cemented inside the well bore, and the wiper, in a first mode, is connected to the liner when the liner is run downhole. In a second mode, the wiper is released from its connection to the liner to respond to a cement flow. 
     Advantages and other features of the invention will become apparent from the following drawings, specification and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a junction of a multilateral well of the prior art. 
     FIGS. 2 and 10 are schematic diagrams of systems to cement a liner of a multilateral well according to different embodiments of the invention. 
     FIG. 3 is a flow diagram depicting a technique to cement the liner using the system of FIG. 2 according to an embodiment of the invention. 
     FIGS. 4,  5 ,  6 ,  7  and  8  are illustrations depicting operation of a wiper dart and wiper assembly of the system of FIG. 2 according to an embodiment of the invention. 
     FIG. 9 is a schematic diagram of the wiper dart according to an embodiment of the invention. 
     FIG. 11 is a schematic diagram of a junction of a multilateral well, including a liner that is cemented according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 2, an embodiment  10  of a system for use in a subterranean well includes a liner top or liner string  18  that is run downhole to both hang a liner  11  in a lateral well bore  16  and aid in cementing the liner  11  in place, as described below. In this manner, the liner top  18  includes both a hanger  20  (dogs or slips, for example) that secures the liner top  18  to a casing  12  and a packer  15  that seals the liner top  18  to the casing  12 . During a cementing operation to cement the liner  11  in place, the seal that is provided by the packer  15  prevents cement from the cementing operation (described below) from contaminating a region  13  of the parent casing  12  above the packer  15 . In this manner and as shown in FIG. 11, near the lateral well bore  16 , the casing  12  may include a junction  401 , for example, that forms the transition between the lateral well bore  16  and a main well bore  402 . As an example, the region  13  to be isolated from the cement may include the interior of this junction, as the junction may include interior profiles that are used to guide tools that are lowered downhole after the liner  11  has been cemented in place. 
     Before the lateral well bore  16  is drilled to accept the liner top  18 , the parent casing  12  is cemented in place. After the lateral bore  16  is drilled to accept the liner top  18 , the liner top  18  is run downhole and cemented using a cementing tool  22  and features of the liner top  18 , described below. 
     More specifically, referring also to FIG. 3, in some embodiments of the invention, a technique  70  may be used to install the liner top  18  downhole. As noted above, the first part of this technique includes running (block  72 ) the liner top  18  downhole, hanging the liner top  18  (block  74 ) to the parent casing  12  and setting (block  76 ) the packer  15 . This part of the technique may be performed in numerous different ways. For instance, blocks  74  and  76  may be performed concurrently if the same downhole tool performs both functions. However, unlike conventional techniques and conventional liner tops  18 , the liner top  18  includes a wiper assembly  50  that, in a first mode of operation, is located inside the liner top  18  and thus, is run downhole with the liner top  18 . The use of the wiper assembly  50  is described further below. 
     After the packer  15  is set and the liner top  18  is hung from the casing  12 , a cementing tool  22  is run (block  78 ) downhole and received into the central passageway  41  of the liner top  18  to engage the string  18 . At this point, the well is circulated and conditioned (block  403 ). The cementing tool  22  is used to introduce (block  79 ) a predetermined volume of cement into a well bore region  36  that exists between the liner top  18  and the wall of the lateral well bore  16 . In this manner, the cement is communicated downhole from the surface of the well through the central passageway of a drill string that, in turn, communicates the cement to a central passageway  32  of the cementing tool  22 . After the predetermined volume of cement is introduced into the drill string, a wiper dart  200  (see FIG.  9 ), further described below, is introduced (block  82 ) into the central passageway of the drill string. Once the cementing operation is complete, the cementing tool  22  is moved to the reverse position and the excess cement is circulated out (block  404 ). 
     Referring to FIG. 2, the wiper dart  200  forms a barrier between the incoming cement and a displacement fluid (water, for example) that is introduced above the wiper dart  200  in the drill string. In this manner, three different fluids may exist in the drill string/cementing tool  22  during the initial stages of the cementing operation: a lower fluid (mud, for example) that is located in the region  36  to be cemented and in the lower end of the drill string/cementing tool  22 ; the cement that is located above the lower fluid in the drill string/cementing tool  22 ; and the displacement fluid that is located above the cement. As more displacement fluid is introduced, the displacement fluid/cement interface (and the wiper dart  200  at this interface) and the cement/lower fluid interface move downhole. 
     To circulate the lower fluid out of the region  36  to permit the cement to enter the region  36 , a return path to the surface is created. This return path includes the region  36 , radial ports  24  (of the liner top  18 ) that are in communication with the region  36 , ports  28  formed on the cementing tool  22 , and an annular region  40  in the interior of the cementing tool  22 . In one embodiment, the central well bore  32  forms the inner boundary of the annular region  40 . In some embodiments of the invention, the annular region  40  of the cementing tool  22  may be in communication with a central passageway of the parent casing  12  above the isolated region  13 . 
     To establish communication between the region  36  outside of the liner top  18  and the region  40  inside the cementing tool  22 , the liner top  18  includes radial ports  24  that are initially covered by an inner sleeve  26 . As the cementing tool  22  is run in, a profile  21  on the cementing tool  22  engages the inner sleeve  26  causing it to slide downwardly thereby uncovering the radial ports  24  and allowing fluid communication between the radial ports  24  and the tool ports  28 . The tool ports  28 , in turn, provide fluid communication to the annular region  40 . In one embodiment, the profile  21  remains latched to the open inner sleeve  26 . In another embodiment, the profile  21  and the inner sleeve  26  are designed so that the profile  21  detaches from the inner sleeve  26  after the inner sleeve  26  opens. In either case, once the cementing operation is completed and the cementing tool  22  is picked up, the profile  21  can be adapted to once again selectively engage the inner sleeve  26  causing it to slide upwardly thereby covering the radial ports  24 . Seals  30  on the cementing tool  22  and inner sleeve  26  provide a sealing communication for the return fluid as it flows from the well bore region  36  to the tool annular region  40 . 
     The liner top  18  further includes a polished bore receptacle  42  that has a central passageway that is coaxial with the central passageway  32  (of the cementing tool  22 ). The polished bore  42  extends to the liner  11 . 
     As more displacement fluid is introduced at the surface, the displacement fluid forces the cement to flow through a check valve  34  (located at the bottom of the liner  11 ) into the region  36  and thus, displaces lower fluid from the region  36  by forcing the lower fluid to return via the annular region  40  of the cementing tool  22 . The wiper dart  200  (and the displacement fluid/cement interface) eventually enters the central passageway  32  of the cementing tool  22 . 
     As described below, the wiper dart  200  is constructed to engage a wiper assembly  50  that is mounted inside the liner top  18 . More specifically, the wiper assembly  50  includes a central passageway  51  that is coaxial with the central passageways of the cementing tool and seal bore  42  and permits the cement to flow through the wiper assembly  50 . When the wiper dart  200  reaches the wiper assembly  50 , the wiper dart  200  plugs the central passageway  51  and disengages (as described in more detail below) the wiper assembly  50  from the liner top  18  to place the wiper assembly  50  in a second mode of operation. Thus, from this point on, the combination of the wiper dart  200  and wiper assembly  50  form the barrier between the displacement fluid and the cement. 
     As depicted in FIG. 2, the wiper assembly  50  includes fins  116  that swab the interior surface of the liner  11  to clean cement from the interior surface as the disengaged wiper assembly  50  travels down through the liner  11 . Eventually the wiper assembly  50  reaches its bottom point of travel as the wiper assembly  50  reaches a landing collar  400  and stops. The landing collar  400  is attached to the liner  11  and may include an anti-rotation mechanism (such as tabs or grooves) that cooperates with a similar mechanism on the wiper assembly  50  to prevent the relative rotation of the two when the wiper assembly  50  is landed on the landing collar  400 . At this point, the desired volume of cement has been pushed into the annular region  36 , and this event may be detected at the surface of the well due to a significant increase in the pressure of the displacement fluid, as flow of the fluid is halted. 
     FIG. 11 schematically shows the cementing tool  22  described herein cementing a liner and liner top  18  in a leg of multilateral junction  401 . The junction  401 , proximate the main well bore  402 , includes a profile  408  that mates with the latching element  407  of a deflector  410 . The deflector  410  and junction  401  may further include an orienting mechanism to correctly orient the deflecting surface  411  of the deflector  410  towards the relevant liner top  18  and lateral well bore  16 . The deflector  410  and junction  401  may also include a locking mechanism that prevents the longitudinal movement of the deflector  410  within the junction  401 . The cementing tool  22  is run in hole and is guided by the deflecting surface  411  towards the liner top  18 , as previously discussed. 
     The cementing tool  22  includes a tool head  405 . In one embodiment (shown in the Figures), the tool head  405  sits on the upper surface of the deflector  410 . In another embodiment (not shown), the tool head  405  is located a distance above the deflector  410  and is supported in that position by the work string that suspends it and by a shoulder on the cementing tool exterior that sits on the liner assembly, such as on the liner packer or hanger. In yet another embodiment (not shown), the tool head  405  includes locking keys that engage another profile located on the junction  401  or on the casing above the junction  401 . In any of these embodiment, the tool head  405  includes at least one sealing element  406  that is activated to provide a seal between the tool head  405  and the junction  401  or casing. 
     Fluid from the well bore annular region  36  being returned within the annular region  40  of the cementing tool  22  flows within the annular region  40  until it reaches the tool head  405 . At the tool head  405 , the fluid is diverted through bypass ports  412  to the exterior of the cementing tool  22 . The bypass ports  412  are located above the sealing elements  406 ; therefore, the fluid flowing therethrough does not and may not pass into the interior region  13  of the junction  401 . 
     The interior region  13  is thus located between the sealing elements  406 , which seal the tool head  405  to the junction  401  or casing, and the packers  15 , which seal the liner top  18  to the junction  401 . And, since the cementing tool  22  ensures that the return fluid is located internally of the cementing tool  22  (within the annular region  40 ) as it passes through the interior region  13 , the cementing tool  22  and the system described herein ensure that the fluid displaced from the well bore annular region  36  does not invade the interior region  13 . The interior region  13  is therefore isolated from the cementing operation. As previously discussed, it is preferable to maintain the interior region  13  of the junction  5  free of such fluids, cement, and other debris. 
     Referring to FIG. 9, in some embodiments of the invention, the wiper dart  200  includes a bullnose section  202  that has a streamlined profile suitable for stabbing the wiper assembly  50 , as described below. The wiper dart  200  also includes a tail section  204  that includes wiper fins  206 . The fins  206  may have various sizes to form seals and/or barriers in the various inner diameters that are encountered by the wiper dart  200  in its downward travel. 
     FIGS. 4,  5 ,  6 ,  7  and  8  depict, in more detail, the engagement of the wiper dart  200  with the wiper assembly  50  and the resulting disengagement of the wiper assembly  50  from the liner top  18 . In these figures, only the bullnose section  202  of the wiper dart  200  is depicted for purposes of clarifying the discussion. It is noted, however, that in operation the wiper dart  200  includes the tail section  204 . 
     Referring to FIG. 4, when the wiper dart  200  approaches the wiper assembly  50 , the bullnose section  202  of the dart  200  enters an opening  109  of a knockout ring  102 , a ring that is coaxial with the central passageway  51  and is sized to allow all but a trailing upset ring  218  of the bullnose section  202  to pass through. The knockout ring  102  is held in place by shear pins  108 , each of which radially extends away from the ring  102  into an end  104  of a different collet finger  105 . In this manner, the collet fingers  105  are part of a collet sleeve  112  that is coaxial with the central passageway  51 . The collet fingers  105  extend from an annular base  113  of the collet sleeve  112  to their respective ends  104 . Due to the resiliency of the collet fingers  105 , the fingers  105  have a tendency to inwardly collapse in a direction toward the axis of the collet sleeve  112 . However, the knockout ring  102  forces the ends  104  of the collet fingers  105  into an annular groove  106  that has a beveled cross section. When the collet fingers  105  are forced into the groove  106 , the position of the collet sleeve  112  is locked into place. 
     As depicted in FIG. 4, the annular base  113  of the collet sleeve  112  holds the upper end of a generally cylindrical mandrel  114  that extends downhole from the annular base  113 . The mandrel  114  is coaxial with the central passageway  51 . As an example, an interior surface (of the annular base  113 ) that contacts the upper exterior surface of the mandrel  114  may include teeth that mate with respective grooves of the mandrel  114  to secure the mandrel  114  to the collet sleeve  112 . The mandrel  114  provides support for a resilient wiper  115  that circumscribes the mandrel  114  below the annular base  113  of the collet sleeve  112 . The wiper  115  includes fins  116  that circumscribe the axis of the mandrel  114  and serve to both form a barrier between the cement and the displacement fluid and wipe cement from the interior of the liner  11 . 
     Referring to FIG. 5, as noted above, the opening  109  of the knockout ring  102  is not sized to permit the upset ring  218  to pass through. As a result, the knockout ring  102  catches the wiper dart  200 . In this position of the wiper dart  200 , leaf springs  216  of the bullnose section  202  extend outwardly into an annular notch  120  that is formed in the mandrel  114 . The notch  120  includes an upper shoulder  122  that is perpendicular to the axis of the central passageway  51 , an orientation that prevents the leaf springs  216  from leaving the notch  120  should pressure downhole tend to force the wiper dart  200  uphole. Thus, the notch  120  and leaf springs  122  provide a ratchet mechanism to prevent the wiper dart  200  from moving back uphole. A lower shoulder  123  of the notch  120  is beveled to not impose a restriction to downward travel of the wiper dart  200  with respect to the mandrel  114 , as described below. 
     Referring to FIG. 6, when sufficient pressure is applied to the displacement fluid at the surface of the well, this pressure produces a force (due to the engagement of the wiper dart  200  with the knockout ring  109 ) on the wiper dart  200  to cause the shear pins  108  to shear. As noted above, the leaf springs  122  do not restrict downward travel of the wiper dart  200 . Therefore, the wiper dart  200  and the engaged knockout ring  109  travel in a downward direction until the knockout ring  109  rests on the annular base  113  (of the collet sleeve  112 ), as the opening in the annular base  113  is sized to prevent the knockout ring  109  from passing through. 
     Referring to FIG. 7, the removal of the knockout ring  109  between the ends  104  of the collet fingers  105  permits the ends  104  to collapse toward the axis of the collet sleeve  112 , thereby allowing the ends  104  to slip out of the groove  106 . As a result, the collet sleeve  112 , knockout ring  109 , mandrel  114 , wiper  115  and wiper dart  200  move as one assembly down the sealbore  42 , leaving the sealbore  42  free from any obstructions due to the wiper assembly  50 , as depicted in FIG.  8 . Leaving the sealbore  42  and the liner unobstructed is important for the performance of subsequent operations, such as evaluation of the cementing job. With the sealbore  42  and liner unobstructed, such subsequent operations may be performed without having to retrieve any hardware left behind during the cementing operation. 
     The positions of the radial ports  24  generally define the height of the concrete within the region  36 . It is desirable for the height of this cement to reach the bottom level of the cement that surrounds the parent casing  12 . However, it may be difficult to raise the heights of the ports  24  due to the geometries involved, and as a result a gap may exist between the top of the cement that surrounds the liner top  18  and the bottom of the cement that surrounds the casing  12 . An alternative liner top  318  that is depicted in FIG. 10 may be used to raise the height of the cement in the region  36  to decrease the span of the gap or eliminate the gap altogether. 
     The liner top  318  has a similar design to the liner top  18  except for the following features. In particular, unlike the liner top  18 , the liner top  318  includes an extension sleeve  302  that circumscribes the outer housing of the liner top  318  to force the cement upward above the ports  24  to at least partially fill the otherwise present gap. The sleeve  302  has a cup-like design in that the bottom of the sleeve  302  is attached to the outer housing of the liner top  18  just below the ports  24 . The sleeve  302  extends in an upward and in a slightly radially outward direction to extend above the ports  24 . The top of the sleeve  302  is not attached to the outer housing of the liner top  18 . Therefore, due to this design, a circulation flow is established as depicted by the exemplary circulation path  307 . In this flow, the cement flows in an upward direction between the exterior surface of the extension sleeve  302  and the lateral well bore  16 . Once the cement reaches the top of the extension sleeve  302  (which is near or above the lower end of the casing  12 ), the cement flows in a downward direction between the interior surface of the extension sleeve  302  and the exterior surface of the outer housing until the cement reaches the radial ports  24  in the liner top  18 . Other embodiments of the extension sleeve  302  are possible. 
     In the preceding description, directional terms, such as “upper,” “lower,” “vertical,” “horizontal,” etc., may have been used for reasons of convenience to describe the liner top and its associated components. However, such orientations are not needed to practice the invention, and thus, other orientations are possible in other embodiments of the invention. 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.

Technology Classification (CPC): 4