Patent Publication Number: US-11661816-B2

Title: Method and apparatus for cementing a casing in a wellbore

Description:
FIELD 
     The disclosure relates generally to completion of wellbores, for example, for hydrocarbon production and more particularly to cementing of casings in wellbores. 
     BACKGROUND 
     When drilling a wellbore through subsurface formations to produce hydrocarbons, it is common practice to protect the wellbore with one or more casings. The first casing installed in a wellbore is called a conductor casing (or conductor pipe). The conductor casing typically prevents drilling fluids from circulating outside the wellbore and causing surface erosion. The conductor casing is usually no more than 20 to 50 feet long. The next casing installed after a conductor casing is a surface casing, which typically prevents hydrocarbons from encroaching into fresh water zones. Surface casing may also be used to anchor blowout preventers. Surface casing may extend several thousand feet into the subsurface. In some wells, intermediate casing may be installed in the wellbore after the surface casing. Intermediate casing may be used to protect against weak or abnormally pressured formations. The final casing installed in the wellbore is a production casing. Each of these casings extends from the surface to a depth in the wellbore and protects a certain section of the wellbore. Each casing is typically made of casing sections or joints that are screwed together to form a desired length of casing. Typically, the screwing together of the casing joints occurs as the casing is lowered into the wellbore. The first joint of a casing run into the well typically has a guide shoe, which is a short heavy cylindrical section filled with concrete and rounded at the bottom. The guide shoe prevents the casing from hitting rock ledges or washouts in the wellbore as the casing is lowered. The casing joints may also carry centralizers that assist in centering the casing in the wellbore. 
     Casings are typically bonded to the wellbore and other casings by cement. The process for cementing a casing in a wellbore typically includes pumping cement slurry down the interior of the casing and allowing the cement slurry to flow out of the bottom of the casing, around the guide shoe, and into an annulus outside of and surrounding the casing. The wellbore is then shut in to allow the cement slurry in the annulus to set or harden. Some wells require complete cementing of the casing, where the cement in the annulus extends from the bottom of the casing to the surface. In these cement jobs, cement slurry is pumped through the casing and into the annulus outside of the casing until cement return from the annulus is observed at the surface, indicating that the annulus has been filled with cement. However, there are instances where cement return is initially observed at the surface, followed by a drop in the column of cement in the annulus. This may occur if the bottom of the casing is set above a lost circulation zone (i.e., a formation zone that steals fluids from the wellbore) so that the cement slurry that should fill the annulus is sucked into the formation, which leaves the area above the lost circulation zone unprotected. In cases where the top of the cement is below the surface, a “top job” (i.e., filling the annulus with cement from the surface opening of the annulus) may be performed to bring the top of the cement to the surface. However, the top job will only be successful if the loss of cement from the annulus can be controlled. 
     SUMMARY 
     A method of cementing a casing in a wellbore extending from an Earth&#39;s surface into a subsurface includes providing a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower tube part. The method includes positioning the tube in an annulus formed between the casing and a wall of the wellbore from a surface opening of the annulus. The method includes urging the tube in a direction down the annulus and along the casing until the tube lands on a collar radially projecting from an outer surface of the casing into the annulus. The act of urging the tube in a direction down the annulus and along the casing may include loading an initial amount of a cement slurry into the upper tube part, wherein the tube moves down the annulus and along the casing under a weight of the cement slurry. The method may include loading an additional amount of the cement slurry into the annulus and on top of the initial amount of cement slurry until a top of the cement slurry is at a predetermined height within the annulus. Alternatively, the method may include loading an additional amount of the cement slurry into the annulus and on top of the initial amount of cement slurry until a top of the cement slurry is at or proximate the surface opening of the annulus. The method may include hardening the cement slurry to form a column of cement in a portion of the annulus above the upper tube part with the column of cement forming a seal between the wall of the wellbore and the outer surface of the casing. The method may include lowering the casing into the wellbore to form the annulus prior to positioning the tube in the annulus. The act of lowering the casing into the wellbore may include lowering the casing into a conductor section of the wellbore. The method may include installing a cement basket on the outer surface of the casing prior to lowering the casing into the wellbore. The cement basket may provide the collar on which the tube is landed. 
     A system for protecting a wellbore includes a casing disposed in the wellbore and separated from a wall of the wellbore by an annulus, a collar surrounding the casing and radially projecting from an outer surface of the casing into the annulus, and a cementing tool to be landed on the collar. The cementing tool includes a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower part. The upper tube part and the lower tube part may be joined at the waist. The tube may have an asymmetric bi-frustoconical shape. The upper tube part may be sized to engage the casing and the wall of the wellbore when the cementing tool is landed on the collar. The inner diameter of the tube at the waist may be smaller than an outer diameter of the collar such that the lower tube part hangs off the collar when the cementing tool is landed on the collar. The system may include a cement basket retained on the casing with the cement basket providing the collar surrounding the casing. The casing may be disposed in a conductor section of the wellbore. The tube may be made of a metal or an alloy or an elastomeric material. 
     An apparatus to be landed on a collar surrounding a casing includes a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower tube part. The tube engages an outer surface of the casing at the waist when landed on the collar. The tube may have an asymmetric bi-frustoconical shape. 
     The foregoing general description and the following detailed description are exemplary of the invention and are intended to provide an overview or framework for understanding the nature of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of the specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The following is a description of the figures in the accompanying drawings. In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not necessarily intended to convey any information regarding the actual shape of the particular elements and have been solely selected for ease of recognition in the drawing. 
         FIG.  1    is a vertical cross-sectional view of a cementing tool according to one illustrative implementation. 
         FIG.  2    is a perspective view of the cementing tool. 
         FIG.  3    is a schematic diagram showing the cementing tool surrounding a casing. 
         FIG.  4    is a schematic diagram showing a casing disposed in a wellbore and a cement basket retained on the casing. 
         FIG.  5    is a schematic diagram showing the cementing tool positioned in an annulus formed between the casing and the wellbore. 
         FIG.  6    is a schematic diagram showing the cementing tool filled with a cement slurry that pushes the cementing tool in a downward direction towards the cement basket. 
         FIG.  7    is a schematic diagram showing the cementing tool after landing on the cement basket with cement slurry partially filling the annulus above the cementing tool. 
         FIG.  8    is a schematic diagram showing a column of cement in a portion of the annulus above the cementing tool. 
     
    
    
     DETAILED DESCRIPTION 
     In this detailed description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments and implementations. However, one skilled in the relevant art will recognize that embodiments and implementations may be practiced without one or more of these specific details, or with other methods, components, materials, and so forth. In other instances, well known features or processes associated with cementing jobs have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments and implementations. For the sake of continuity, and in the interest of conciseness, same or similar reference characters may be used for same or similar objects in multiple figures. 
       FIGS.  1  and  2    are different views of an exemplary cementing tool  100  that may be used to perform a cementing top job. Cementing tool  100  includes a tube  104  to be disposed around a casing in a wellbore. Tube  104  may be made of a metal, an alloy, or an elastomeric material such as nitrile rubber or carboxylated nitrile rubber. Tube  104  has a top end  108 , a bottom end  112 , and a bore  116  extending between the top and bottom ends  108 ,  112 . Tube  104  has a waist  120  (narrow part) at a location intermediate between top and bottom ends  108 ,  112 . The diameter of bore  116  is smallest at waist  120  compared to at top and bottom ends  108 ,  112 . The diameter of bore  116  at waist  120  may be approximately the same as or slightly larger than the outer diameter of the casing to be cemented in the wellbore with cementing tool  100 . Tube  104  has an upper tube part  124  above waist  120  and lower tube part  128  below waist  120 . Upper tube part  124  includes an upper portion  116   a  of bore  116 , and lower tube part  128  includes a lower portion  116   b  of bore  116 . Upper tube part  124  has an inverted frustoconical shape with a wide diameter at top end  108  and a narrow diameter at waist  120 . The diameter of upper tube part  124  may increase linearly or nonlinearly from waist  120  to top end  108 . Lower tube part  128  has a frustoconical shape with a narrow diameter at waist  120  and a wide diameter at bottom end  112 . The diameter of lower tube part  128  may increase linearly or nonlinearly from waist  120  to bottom end  112 . In this example, tube  104  may be described as having a bi-frustoconical shape. 
     The outer diameter of upper tube part  124  at top end  108  may be approximately the same as or slightly larger than the diameter of the section of the wellbore in which the casing is to be cemented. In general, a radial width w of upper tube part  124  may be selected such that when cementing tool  100  is disposed in an annulus between a casing and a wall of a wellbore (in  FIGS.  5 - 8   ), upper tube part  124  engages the casing at waist  120  and the wellbore at top end  108  (the radial width w is half of the outer diameter of upper tube part  124  at top end  108  less the inner diameter of upper tube part  124  at waist  120 ). The outer diameter of upper tube part  124  at top end  108  may be larger than the outer diameter of lower tube part  128  at bottom end  112  such that the inverted frustoconical shape formed by upper tube part  124  is larger than the frustoconical shape formed by lower tube part  128  (i.e., tube  104  has an asymmetric bi-frustoconical shape). 
     For illustrative purposes,  FIG.  3    shows cementing tool  100  relative to an example casing  132 . Tube  104  of cementing tool  100  has been slipped over casing  132  and surrounds casing  132 . A collar  136  disposed around casing  132  acts as a stop and support for tube  104 . A collar is a restraining or connecting band, ring, or pipe. Collar  136  may be provided by any suitable structure installed on casing  132 . In the illustrated example, the outer diameter of collar  136  is larger than the outer diameter of casing  132  such that collar  136  projects radially from an outer surface of casing  132 . In the landed position of cementing tool  100  on collar  136 , lower tube part  128  engages and hangs off collar  136 . In the landed position, upper tube part  124  opens upwardly and provides a receptacle to hold cement slurry. When cementing tool  100  is disposed in an annulus between a casing and a wellbore, a column of cement in the annulus can be formed on upper tube part  124 . In this case, upper tube part  124  preferably has sufficient rigidity to maintain its shape while supporting the column of cement. The thickness of tube  104  is chosen depending on the selected depth of at which tube  104  will be set in an annulus such that upper tube part  124  is able to carry a column of cement above. 
       FIG.  4    shows a wellbore  200  drilled below an Earth&#39;s surface  204 . Wellbore  200  penetrates subsurface formation(s)  208 . In one example, wellbore  200  may also penetrate a lost circulation zone  212  in the subsurface. A casing  216  has been lowered into wellbore  200 , and an annulus  220  is formed between the wall of wellbore  200  and outer surface of casing  216 . In one example, casing  216  is a conductor casing, and the portion of wellbore  200  in which casing  216  is disposed is the conductor section of the wellbore (i.e., the first drilled section of the wellbore). In one example a cement basket  224  may be installed on casing  216  prior to lowering casing  216  into wellbore  200 . For illustrative purposes, cement basket  224  includes thin petals  228  arranged in an overlapping pattern to form a basket  232 . Overlapping petals  228  are disposed within a reinforcing structure formed by flexible ribs  236  that are attached to spaced apart collars  240 ,  244 . Cement basket  224  is retained on casing  216  by fixed collars  248 ,  252  on casing  216 . Overlapping petals  228  spread to expand flexible ribs  236  of cement basket  224  into annulus  220  and against the wall of wellbore  200 . In this case, cement basket  224  may act as a centralizer for casing  216 . Cement basket  224  also provides collar  240  on which cementing tool ( 100  in  FIGS.  1  and  2   ) may be landed. In the illustrated example, collar  240  of cement basket  224  sits on fixed collar  248  on casing  216 . In the illustrated example, cement basket  224  is set above lost circulation zone  212 . 
     A method of cementing a casing to a wall of a wellbore may generally include pumping cement slurry through the casing into the wellbore, where the cement slurry should then rise up an annulus between the casing and the wellbore wall. If cement loss to a lost circulation zone is observed, the next action may be a cementing top job.  FIGS.  5 - 8    illustrate a top job using cementing tool  100 . In  FIG.  5   , cementing tool  100  is slipped over casing  216  at surface  204  and positioned proximate a surface opening of annulus  220  (the surface opening of annulus  220  is the end of annulus  220  at surface  204 ). In this position, cementing tool  100 , engages an outer surface of casing  216  and the wall of wellbore  200  by friction. Cementing tool  100  is also free to move down annulus  220  and along casing  216  under the influence of a downward force that overcomes the friction. In  FIG.  6   , cement slurry  256  is loaded into upper tube part  124  of cementing tool  100  to apply the downward force to cementing tool  100 . Cement slurry  256  can be loaded by pouring or pumping the cement slurry into upper tube part  124  (or the space between upper tube part  124  and casing  216 ). The weight of cement slurry  256  in upper tube part  124  will push cementing tool  100  down and along casing  216  until cementing tool  100  (lower tube part  128 ) lands on upper collar  240  of cement basket  224  as shown in  FIG.  7    (it should be noted that cementing tool  100  may land on a collar provided by structures other than a cement basket). Any suitable cement composition may be used to prepare the cement slurry. 
     After upper tube part  124  is filled with cement slurry, additional cement slurry  256  can be loaded into the portion of annulus  220  above upper tube part  124 , as shown in  FIG.  7   . This additional loading of cement slurry  256  can occur as cementing tool  100  moves down casing  216  towards cement basket  224 . This additional loading of cement slurry  256  can also occur after cementing tool  100  has landed on collar  240 . Additional loading of cement slurry  256  can continue until a top of the cement slurry is at a desired height in annulus  220 . In one example, this desired height is at surface  204 . After annulus  220  has been filled with cement slurry to the desired height, the cement slurry can be allowed to harden.  FIG.  8    shows a column of cement  260  (hardened cement) formed in a portion of annulus  220  extending from cementing tool  100  to surface  204 . Cement  260  forms a seal between casing  216  and wellbore  200 . Cementing tool  100  remains in place in annulus  220  after the cementing job has been completed and isolates the portion of annulus  220  above cementing tool  100  from the remainder of wellbore  200  (and from the lost circulation zone  212 ). 
     Although specific embodiments, implementations, and examples have been described for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein can be applied to other cementing scenarios besides the exemplary casing to wellbore cementing generally described above.