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This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 60/117,877, entitled “SECURING A WELL CASING TO A WELLBORE,” filed Jan. 29, 1999. 
    
    
     BACKGROUND 
     The invention relates to securing a well casing to a well bore. 
     As shown in FIG. 1, a subterranean well might have a lateral wellbore that is lined by a casing  12 . Besides supporting the lateral wellbore, the monobore casing  12  serves as a conduit to carry well fluids out of the lateral wellbore. The lateral wellbore extends through several regions called production zones where a producing formation has been pierced by explosive charges to form fractures  14  in the formation. Near the fractures  14 , the monobore casing  12  has perforations  16  which allow well fluid from the formation to flow into a central passageway of the casing  12 . The casing  12  is typically secured to the well bore by cement. 
     SUMMARY 
     In one embodiment, the invention features a well casing for receiving well fluid from a producing formation. The well casing has a first tubular section that has a tortuous outer surface for directing the flow of a bonding agent around the exterior of the first tubular section. The first tubular section has a central passageway. The well casing also has a second tubular section that is coaxial with and is connected to the first tubular section. The second tubular section has at least one opening for directing well fluid into a central passageway of the second tubular section. 
     In other embodiment, the invention features a well casing for receiving well fluid from a producing formation. The well casing has a tubular section that has a central passageway for receiving well fluid and a port for directing a bonding agent from the central passageway to a region outside of the tubular section. The casing has a wiper that is slidably mounted on an outer surface of the tubular section and is configured to apply pressure to the bonding agent. 
     In another embodiment, the invention features a method for use in a well. The method includes using a central passageway of a tubing to receive well fluid from a producing formation and using a tortuous outer surface of the tubing for directing the flow of a bonding agent around an exterior region of the tubing. 
     In yet another embodiment, the invention features a method for use in a well. The method includes using a central passageway of a tubing to receive well fluid from a producing formation and using a wiper on the outer surface of the tubing to direct flow of a bonding agent around an exterior region of the tubing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a lateral well bore of the prior art. 
     FIG. 2 is a schematic diagram of a well casing according to one embodiment of the invention. 
     FIG. 3 is a schematic diagram of an insulation zone of the well bore of FIG.  2 . 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG.  3 . 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG.  3 . 
     FIG. 6 is a schematic view illustrating the injection of cement within the well bore. 
     FIG. 7 is a schematic diagram of an alternative embodiment of the isolation section of the invention. 
     FIGS. 8 and 9 are schematic diagrams of well casings according to other embodiments of the invention. 
     FIGS. 10 and 11 are schematic diagrams of portions of tubing. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 2, cement is selectively placed around a well casing  21  to secure the casing  21  to a lateral well bore  20 . To accomplish this, at selected isolation zones  24  of the well bore  20 , a wet cement mixture is injected into the annular space between the casing  21  and the well bore  20 . Due to gravitational forces, the cement mixture tends to settle before hardening which results in a nonhomogeneous, mixture. However, to combat this, the casing  21  has auger-shaped isolation sections  30  which are placed in the isolation zones  24  to create turbulence in the flow of wet cement around the well casing  21 . As a result, water in the wet cement mixture is more evenly distributed, and debri in the well bore  20  is not concentrated in the cement at the bottom of the well bore  20 . 
     The casing  21  is used to support the lateral well bore  20  and carry well fluids away from a producing formation through which the well bore  20  extends. The casing  21  extends through production zones  22  (regions of the well bore capable of furnishing well fluid) and the isolation zones  24  (regions of the well bore  20  in which the casing  21  is cemented to the well bore  20 ). To capture the well fluid from the production zones  22 , the casing  21  has open, screen sections  32  which allow the well fluid to radially enter a central passageway of the casing  20 . The region between each screen section  32  and the well bore  20  is packed with a bed  31  of sized gravel, or sand, which filters debri from the well fluid entering the casing  21 . The isolation zones  24  are located between the production zones  22 , and annular packers  26  separate the two zones  22  and  24 . 
     Among the advantages of the invention may be one or more of the following may be more uniformly distributed; water in wet cement may be more evenly distributed; and debri in a lateral well bore is not concentrated in the cement at the bottom of the well bore. 
     As shown in FIG. 3, each isolation section  30  of the casing  21  has outer fins  39  which extend in a helical pattern around the exterior of the casing  21 , with the orientation of the fins  39  determining the direction of flow of wet cement along the section  30 . The section  30  has a group of radial openings  34  which divert wet cement from the center passageway of the casing  21  into the annular region between the exterior of the section  30  and the well bore  20 . Due to the orientation of the fins  39 , the cement flows away from the openings  34  (and away one of the packers  26 ), through the isolation zone  24  and toward the packer  26  farthest from the openings  34  (i.e., to the end of the isolation zone  24 ). 
     To facilitate the flow of the cement around the exterior of the section  30 , the section  30  may be slowly rotated in a direction to force the wet cement along the isolation zone  24 . At the surface of the well, the casing  21  is rotated. However, due to the construction of the casing  21 , each screen section  32  (portions of which extend through the packers  26 ) remain stationary even if the isolation section  30  is being rotated. To accomplish this, the casing  20  has an inner metal tubing  54  (see FIG. 4) which receives the torsional forces (at the surface of the well)to rotate the section  30 . Each section  30  has an outer sleeve  50  that circumscribes the tubing  54  and is attatched to the tubing  54  via shear members  52  that radially extend at selected points between the tubing  54  and the outer sleeve  50 . The fins  39  are attatched to the exterior of the sleeve  50 . Thus, when the tubing  54  rotates, the fins  39  rotate. 
     Referring to FIG. 5, unlike the outer sleeve  50  of the isolation section  32 , an outer sleeve  51  of the screen section  30  is not attached to the tubing  54 . As a result, torsional forces are not exerted on the packers  26  when the tubing  54  is rotated. A tubular sleeve  56  having a low coefficient of friction covers the exterior of the tubing  54 , and the sleeve  51  surrounds the sleeve  56 . Annular swivels  53  are located between the rotating sleeves  50  and the stationary outer sleeves  51 . 
     As described below, the wet cement is injected into the isolation zones  24 , one at a time. As a result, the cement in some of the zones  24  hardens before the cement in other zones  24 . To prevent this hardened cement from preventing rotation of the tubing  54 , the spacers  52  (FIG. 4) of each isolation section  30  are designed to shear when the torsional forces exerted by the tubing  54  on the sleeve  50  exceed a predetermined level. 
     As shown in FIG. 6, the wet cement is furnished to each isolation zone  24  through a cementing tool  60 . The tool  60  has a tubing  61  that receives the wet cement from the surface of the well. The tubing  61  has radial openings  62  that allow the cement to pour into the casing  21 . Two annular packers  64  located on opposite ends of the openings  62  seal off the annular region between the exterior of the tubing  61  and the interior of the casing  21 . The resultant annulus between the packers  64  directs the wet cement through the radial openings  34  in the casing  21 . 
     Referring to FIG. 7, in an alternative isolation section  70 , the fin  31  may be replaced by opposing helical fins  72  and  74  which are located near opposite ends of the isolation section  70  and compact the wet cement in the region between the fins  72  and  74 . Among other advantages, the compaction of the cement removes air pockets to provide a better adhesive bond. 
     Referring to FIG. 8, instead of having fins extending from the exterior of the casing, an alternative isolation casing section  80  has an exposed channel  82  formed in the outer surface of the casing  21 . The channel  82  extends around the casing  21  in a helical pattern and directs the flow of wet cement similar to the fins  31 . 
     As shown in FIG. 9, conical wipers  84  and  86  may also be used to distribute the concrete within the isolation zone  24 . The wipers  84  and  86  are coaxial with and circumscribe the casing  80 . Furthermore, both wipers  84  and  86  are concave with respect to each other and to radial openings  82  in the casing  80 . The radial openings  82  are used to inject the wet cement into the isolation zone  24 . One wiper  84  is abutted against one of the packers  26  and remains stationary as the cement flows into the isolation zone  24 . The other wiper  86  is in frictional contact with the exterior of the casing  80 . As the wet cement flows into the annular region surrounding the casing  80 , the cement is confined between the two wipers  84  and  86 . After the cement fills the void between the two wipers  84  and  86 , the pressure exerted by the incoming cement pushes the wiper  86  away from the openings  82 . The newly created void is then filled with the incoming wet cement, and the above-described process continues until the wiper  86  rests against the packer  26  and the annulus is filled with cement. 
     As shown in FIG. 10, in some embodiments, at least a portion of the tubing may be formed out of one or more joined modular sections  173 . Adjoining sections  173  may be connected by a variety of different couplers, like the one shown in FIG.  11 . At the union of adjoining sections  173 , an annular gasket  176  placed at the end of the sections  173  seals tubings  40  of both sections  173  together. To secure the adjoining tubings  40  together, a threaded collar  178  mounted near the end of one tubing  40  is adapted to mate with threads formed near the end of the adjoining tubing  40 . The threaded collar  178  is slidably coupled to the tubing  40  and adapted to protect and radially support the gasket  176  once the adjoining tubings  40  are secured together. 
     After the tubing  40  of adjoining sections  173  are attached to one another, the communication infrastructures of the adjoining sections  173  are coupled together (e.g., via connectors  175  and  177 ). Once the connections between the tubings  40  and communication infrastructures of adjoining sections  173  are made, a slidably mounted, protective sleeve  174  (located on the outside of the casing  21 ) is slid over the connections and secured to the encapsulant  33 . 
     The modular sections  173  may be connected in many different arrangements and may be used to perform many different functions. For example, the modular sections  173  may be connected together to form a section of a production string. The sections  173  may be detachably connected together (as described above), or alternatively, the sections  173  may be permanently connected (welded, for example) together. The sections  173  may or may not perform the same functions. For example, some of the sections  173  may be used to monitor production, and some of the sections  173  may be used to control production. The sections  173  may be located in a production zone or at the edge of a production zone, as examples. In some embodiments, a particular section  173  may be left free-standing at the end of the tubing, i.e., one end of the section  173  may be coupled to the remaining part of the tubing, and the other end of the section  173  may form the end of the tubing. As another example, the section(s)  173  may be used for purposes of completing a well. Other arrangements and other ways of using the sections  173  are possible. 
     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.

Summary:
A well casing for receiving well fluid from a producing formation includes a first tubular section that has a tortuous outer surface for directing the flow of a bonding agent around the exterior of the first tubular section. The first tubular section has a central passageway. The well casing also has a second tubular section that is coaxial with and is connected to the first tubular section. The second tubular section has at least one opening for directing well fluid into a central passageway of the second tubular section.