Patent Publication Number: US-11639641-B2

Title: Degradable in-line buoyant system for running casing in a wellbore

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/949,246 filed on Dec. 17, 2019, the entirety of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to downhole equipment for hydrocarbon wells. More particularly, the present disclosure pertains to a method and apparatus for floating casing to depth in a wellbore. 
     BACKGROUND 
     Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore is drilled, a casing is then lowered and set in place. 
     In many wells, it can be difficult to run the casing to great depths because friction between the casing and the wellbore during run-in often results in a substantial amount of drag. This is particularly true in horizontal and/or deviated wells, where, in some cases, the drag on the casing can exceed the available weight of the casing in the vertical section of the wellbore that would otherwise tend to progress the casing further along. If there is insufficient weight in the vertical portion of the wellbore, it can be difficult or impossible to overcome the drag in the wellbore, thus limiting the depth to which the casing can be run or preventing completion of a horizontal or deviated well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention are described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. Various embodiments of the current invention are shown and described in the accompanying drawings of which: 
         FIG.  1    schematically illustrates a casing string assembly, including a degradable plug assembly, being run into a non-vertical wellbore, according to an embodiment. 
         FIGS.  2 A and  2 B  are cross-sectional views of a tool with a degradable plug assembly when in a closed state and an open state, respectively, according to an embodiment. 
         FIGS.  3 A and  3 B  are cross-sectional views of a tool with a degradable plug assembly when in a closed state and an open state, respectively, according to an embodiment. 
         FIGS.  4 A,  4 B,  4 C,  4 D and  4 E  are cross-sectional views of a degradable plug assembly, according to an embodiment. 
         FIG.  5    is a cross-sectional view of a degradable plug assembly, according to an embodiment. 
     
    
    
     The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of what is claimed in the present disclosure. 
     Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numbers are used to identify like elements illustrated in one or more of the figures, wherein showings therein are for purposes of illustrating embodiments of the present disclosure and not for purposes of limiting the same. 
     DETAILED DESCRIPTION 
     Various examples and embodiments of the present disclosure will now be described. The following description provides specific details for a thorough understanding and enabling description of these examples. One of ordinary skill in the relevant art will understand, however, that one or more embodiments described herein may be practiced without many of these details. Likewise, one skilled in the relevant art will also understand that one or more embodiments of the present disclosure can include other features and/or functions not described in detail herein. Additionally, some well-known structures or functions may not be shown or described in detail below, so as to avoid unnecessarily obscuring the relevant description. 
     Certain terms are used throughout the following description to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. Any reference to up or down in the description is made for purposes of clarity, with “up”, “upper”, “upwardly”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. 
     Systems and techniques for lowering a casing or a liner (either referred to herein as casing) to a desired depth or location in a borehole that penetrates a hydrocarbon reservoir are well known. However, because friction between the casing and the borehole can create drag, running the casing to great depths or over extended horizontal distances can be challenging. In boreholes that are non-vertical, such as horizontal or deviated wellbores, the drag can present a large obstacle to completing the well. Various techniques have been developed to overcome this drag so that greater vertical well depths and greater non-vertical well lengths can be achieved. For instance, techniques to lighten or “float” the casing have been used to extend the depth or length of or to complete the well. For example, techniques are known in which the ends of a casing string portion are plugged and are filled with a low density, miscible fluid to provide a buoyant force. However, after the plugged portion is placed in the wellbore, the plug must be drilled out, and the low density miscible fluid is forced out into the wellbore. 
     According to other known techniques for floating casing, a rupture disc assembly is provided where, after the casing is installed in the wellbore, the rupture disc can be ruptured by engagement with an impact surface of a tube. However, engagement with the impact surface shatters the disc, resulting in shattered disc fragments that remain in the wellbore. These fragments can damage the casing string or tools lowered within the string as fluid circulates within the wellbore. Moreover, the inside diameter of the casing may be restricted following the rupture of the disc, which can later prevent or impede conveyance of downhole tools within the restricted region of the casing string so that further operations, such as cementing, cannot be readily performed using conventional techniques. 
     Embodiments disclosed herein are directed to devices and methods to float a casing string in a wellbore in order to extend the depth or non-vertical distance and that, when employed, do not introduce damaging debris or unduly restrict the inside diameter of the casing. 
     Referring now to  FIG.  1   , a casing string assembly  100  that is being deployed in a wellbore  110  is schematically shown. The wellbore  110  has been drilled through an earth surface  112  and penetrates a region of interest  113  (e.g., a hydrocarbon reservoir). As shown, the wellbore  110  includes a non-vertical or deviated section  114 . Within the section  114 , the casing string assembly  100  includes a tool  116  with a degradable plug assembly  124  to assist with running the casing string assembly  100  to the desired location or depth in the wellbore  100 . As will be described in further detail below, during run-in of the casing string  100 , the tool  116  is in a closed state in which fluid communication between upper and lower sections of the tool  116  is blocked. Once the string  100  is landed at a final desired location in the wellbore  110 , the tool  116  is transitioned to an open state in which fluid communication between the upper and lower sections is allowed. 
     The casing string assembly  100  also includes a fluid blocking device  132  located in a lower portion of the casing string  100 , such as at or near the terminal end of the string  100 . In embodiments, the blocking device  132  can be located one or more thousands of feet from the tool  116 . The blocking device  132  prevents drilling fluids or other wellbore fluids from entering the casing string assembly  100  as it is being run into the wellbore  100 . As such, when the tool  116  is added to the string  100  and is in its closed state, the blocking device  132  and tool  116  operate in conjunction to form a buoyant chamber  130  in the lower portion of the casing string assembly  100  in which a light fluid (e.g., air, gas or other lightweight fluid) is trapped, as will be further described below. In embodiments, the blocking device  132  can be a temporary plug that is removed after the casing  100  is positioned at the desired final location. Or, the device  132  can be a one-way float valve that prevents fluid from entering the casing string  100 , but allows fluid to be pumped through the string  100  during circulation and/or cementing after the tool  116  has been converted to its open state. 
       FIGS.  2 A and  2 B  show cross-sectional views of an embodiment of the tool  116  that, in  FIG.  1   , is positioned in the non-vertical portion  114  of the wellbore  110 . In this embodiment, tool  116  includes a cylindrical housing  118  defining an internal fluid passageway  119  that extends between first and second ends  120 ,  122 . Ends  120  and  122  are configured so that the tool  116  can be connected within the casing string assembly  100 , such as by a threaded connection. For ease of reference, end  120  will be referred to as the “upper” end and end  122  will be referred to as the “lower” end. In this context, when the tool  116  is assembled within the casing string  100  and run into the wellbore  110 , the upper end  120  is the end closer to the surface  112  and the lower end  122  is the end closer to the terminal end of the wellbore  110 . 
     Tool  116  can be converted between an initial closed state (shown in  FIG.  2 A ) and a final open state (shown in  FIG.  2 B ). In the closed state, a degradable plug assembly  124  temporarily provides for fluid isolation between an upper section  126  and a lower section  128  of the internal passageway of the tool  116 . In the embodiment shown, the degradable plug assembly  124  includes a degradable plug portion  202  and an upper cover  204 . The degradable plug portion  202  can be a composite of sand with a degradable material, such as sugar and/or salt, but can be made of other degradable materials that degrade, deteriorate and/or dissolve upon exposure to a fluid (e.g., water, well fluid, or other substance present in the wellbore). In embodiments, plug portion  202  can be made of a compressed degradable material (e.g., salt) that is formed in a shape that substantially fills the inner passageway  119 . In other embodiments, plug portion  202  can be non-compressed degradable material that is contained within a container that includes the upper cover  204  and a lower cover. In embodiments, the upper cover  204  and/or lower cover (if used) can be discs made of a material that can be ruptured, bent or easily moved within the axial passageway of the tool  116 , such as a metal or a ceramic. Or, the upper cover  204  can be made of a ceramic or a metal material and the lower cover can be made of a compressed degradable material, as examples. 
     Returning to the embodiment shown in  FIGS.  2 A and  2 B , upper cover  204  is movable within the axial inner passageway  119 . In the embodiment shown, fluid pressure applied from the surface  112  holds the upper cover  204  against the degradable plug portion  202  and an end portion  206  of a spring-loaded slidable sleeve  208 . In the closed state of the tool  116 , the fluid pressure is sufficiently high to press the upper cover  204  against the plug portion  202  and the end portion  206  so that the spring  210  is in a biased state. To place the tool  116  in an open state, fluid pressure is decreased sufficiently to allow the spring  210  to release and move the slidable sleeve  208  upwards in the axial passageway  119 , thus pushing the cover  204  in the upwards direction. Movement of the cover  204  results in rupture of the cover  204 . For example, the cover  204  can be moved so that it impacts a structure that ruptures the cover. Alternatively, upward movement of the cover  204  can create a pocket beneath the cover  204  into which fluid can enter. Fluid pressure in the pocket then increases until the cover  204  bursts. 
     Regardless of how the cover  204  is ruptured, fluid is introduced to the degradable plug portion  202 . In embodiments, the fluid washes away the material of the plug portion  202  so that it exits the end of the string  100  into the wellbore  110 . In other embodiments, the fluid degrades or dissolves the material of the plug portion  202 , thereby opening the axial passageway  119  to fluid flow or the introduction of equipment or tools. 
     In embodiments, once the upper cover  204  has ruptured, the movable sleeve  208  continues to move the upper cover  204  so that the fragmented portions of the cover  204  are contained within compartments  212  along the sidewall of the axial passageway  119 . Containment of the portions of the upper cover  204  within compartments  212  helps ensure that the axial passageway  119  is not obstructed and that sharp fragments of the cover  204  do not interfere with or damage equipment or tools that later may be directed through the axial passageway  119 . 
     Another embodiment of the tool  116  is shown in cross-section in  FIGS.  3 A  (closed state) and  3 B (open state). This embodiment employs an expanding seat configuration. In  FIG.  3 A , a seat  302  is in the unexpanded state, preventing the degradable plug portion  304  from passing through the axial passageway  119 . In  FIG.  3 B , the pressure is increased in the upper portion of the passageway  119  so that the eat  302  expands. The debris from the degradable plug portion  304  can then exit the end of the string  100 , thereby opening the axial passageway  119 . 
     Another embodiment of the tool  116  is shown in cross-section in  FIGS.  4 A- 4 E . In this configuration, a plug  402  is made of a compressed degradable material and is shaped to fit within the axial passageway  119 . The plug  402  includes a funnel-shaped recess  404  in which fluid can be introduced. The plug  402  with funnel  404  are configured so that, over time, the fluid in the passageway  119  erodes the degradable material until the passageway  119  is opened, as shown in the series of  FIGS.  4 A  (closed)- 4 E (open). 
     Another embodiment of a degradable plug assembly  502  that can be used in the tool  116  is shown in cross-section in  FIG.  5   . In this embodiment, degradable material  503  (in a non-compressed form) is contained in the axial passageway  119  between an upper cover  504  and a lower cover  506 . When the tool  116  is in the closed state, fluid pressure applied from the surface  112  holds the upper cover  504  against the degradable material  503 . When the pressure is decreased, the upper cover  504  can rise, creating a pocket thereunder in which fluid is introduced. The upper cover  504  then bursts. The lower cover  506  is made of a thin material, which may be a thin metal that is readily burst or which may be a compressed degradable material that eventually degrades or dissolves. In either case, the lower cover  506  falls through the passageway and exits the string  100  along with any debris from the degradable plug portion  503 . The axial passageway  119  is then open to fluid flow and/or the introduction of other equipment or tools that are run through the string  119 . 
     In an embodiment, the upper cover  504  can be a non-fragmenting rupture disc so that, when ruptured, the cover  504  does not shatter into fragments that later can restrict the inside diameter of the tool  116  or present sharp edges or shards that can damage equipment or tools that later are run through the casing string  100 . In other embodiments, the upper cover  504  be a movable barrier that can be contained within protective regions within the casing string so as not to impede the passageway  119  (as shown, for example, in the embodiment of  FIG.  2 B ) when other tools or equipment are run through the string  100 , such as during a cementing operation. 
     According to an embodiment, the tool  116  is connected within the casing string  100  so as to maximize vertical weight on the casing string  100 , while minimizing horizontal weight. To that end, in an embodiment, the plug assembly  124  traps air and/or other low weight fluid in the lower tool portion  128  (and lower portion of the casing string  100 ) and isolates the lower portion  128  from heavier fluid in the upper portion  126  of the tool  116  (and the upper portion of the casing string  100  and wellbore  110 ). In operation, when the tool  116  is in the closed state, the plug assembly  124  isolates the upper portion  126  of the fluid passageway (which is filled with a heavier fluid) from the buoyant chamber  130  in the passageway that extends between the plug assembly  124  and the fluid blocking device  132  (which contains a lighter weight fluid). As an example, heavier fluid in the upper portion  126  can be drilling mud, and the lighter weight fluid in the buoyant chamber  132  can be air, nitrogen, carbon dioxide, oil and/or other lightweight or miscible fluid. As will be appreciated by persons skilled in the art, this configuration reduces weight of the casing string  100  and consequently the drag and frictional force acting on the casing string  100  in accordance with Archimedes&#39; Principle. 
     In an embodiment, the casing string  100  is run into the wellbore  110  for a desired initial distance using a conventional technique. The fluid blocking device  132  at the end of the string  100  prevents fluids in the wellbore  110  from entering the casing  100 . Once the desired initial distance is reached, the tool  116  is added to the casing string  100 , e.g., by threadedly coupling the ends  120  and  122  of the tool  116  to casing string  100  subs. When the tool  116  is added to the string  100 , the plug assembly  124  is in the closed state in which it blocks the internal passageway of the tool  116  and, thus, fluidly isolates the upper section  126  from the lower section  128 . In the closed state, air, gas and/or other light weight fluid are trapped in the buoyant chamber  130 . Heavier fluid, such as drilling mud, is then provided above the isolation barrier  124  to continue the run-in of string  100  in the wellbore  110 . 
     The distance that the casing string  100  is run before adding the tool  116  depends on the configuration of the particular wellbore  110 . In general, the tool  116  is added at a location within the casing string  100  to create buoyancy so that the casing string  100  can be run in non-vertical or deviated sections of the wellbore  110  without generating a drag force that is great enough to prevent the string  100  from reaching its final desired location. To that end, the tool  116  is positioned at a location within the casing string  100  to assist in overcoming the drag forces on the casing string  100 , thereby allowing the casing string to be positioned at greater depths or extended to greater non-vertical distances. 
     Once the casing string  100  has been run and landed at the final desired location in the wellbore  110 , the plug assembly  124  is transitioned to the open state in which fluid communication is provided between the upper section  126  of the passageway and the buoyant chamber  130 . Different techniques and structures for transitioning the plug assembly  124  to the open state have been discussed above. 
     For the purposes of promoting an understanding of the principles of the invention, reference has been made to the embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments unless stated otherwise. The terminology used herein is for the purpose of describing the particular embodiments and is not intended to be limiting of exemplary embodiments of the invention. 
     The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Numerous modifications and adaptations will be readily apparent to those of ordinary skill in this art without departing from the scope of the invention as defined by the following claims. Therefore, the scope of the invention is not confined by the detailed description of the invention but is defined by the following claims.