Patent Publication Number: US-9422775-B2

Title: Downhole casing system

Description:
This application is the U.S. national phase of International Application No. PCT/EP2012/057793 filed 27 Apr. 2012 which designated the U.S. and claims priority to EP Patent Application No. 11164295.5 filed 29 Apr. 2011, the entire contents of each of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a casing module for being part of a downhole casing system, comprising a base pipe extending in a longitudinal direction and having a circumference, a functional assembly mounted over the base pipe to define a casing module flow path between the functional assembly and the base pipe, and a main flow path arranged substantially in a centre of the base pipe and extending in a longitudinal direction of the casing system. The present invention furthermore relates to a downhole casing system for performing operations in a wellbore containing well fluid. 
     BACKGROUND ART 
     In the design of a completion for an oil well, multiple screen modules are usually connected to cover the length of a producing zone. Typically, each screen module comprises individual inflow control means arranged in a base pipe of the screen module, directly under a filtering element. The inflow control means are often comprised by valves or throttles and a sliding sleeve to block and open the inflow control means, respectively. Such screen modules are often sealed off at opposite ends so that fluid, entering the filtering element of one screen module, cannot flow to the subsequent screen module. This configuration of screen modules requires the use of a large number of inflow control means and sliding sleeves in a completion. Using many sliding sleeves in a completion renders the construction, the maintenance and the ongoing operation and control of the completion more expensive. Another inexpedient issue of prior art screen modules is the position of the inflow control means. Inflow control means arranged in the base pipe of at screen module will often reduce the flow area or drift diameter of the screen module, thereby reducing flow and the size of tool that can be used in the well. Further, the flow between the filtering element and the base pipe of a screen module may be of great importance. The production along a single screen module or string of screen often varies considerably with high and low producing areas. It is desirable to provide a flow path between the filtering element and the base pipe, which is as unrestricted and continuous as possible. Multiple separated narrow flow paths along a screen module often result in some flow paths being overloaded, and some having excess capacity. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved downhole casing system wherein fluid flow along the outside of the casing is optimised to increase production or the yield of intervention procedures. Further, it is an object to provide a casing system wherein the inflow control is improved and the number of inflow control sections to be operated is reduced. 
     The above objects, together with numerous other objects, advantages, and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a casing module for being part of a downhole casing system, comprising a base pipe extending in a longitudinal direction and having a circumference, a functional assembly mounted over the base pipe to define a casing module flow path between the functional assembly and the base pipe, and a main flow path arranged substantially in a centre of the base pipe and extending in a longitudinal direction of the casing system, wherein at least a part of the casing module flow path is an annular flow path extending both in the longitudinal direction of the base pipe and continuously around the entire circumference of the base pipe, and the base pipe has end sections at which a plurality of supporting structures protrude from an outer surface to provide support for the functional assembly, the supporting structures defining a plurality of casing module flow paths extending in the longitudinal direction. 
     In an embodiment, the functional assembly may comprise a filtering element, such as a screen, mounted over the base pipe to provide a screen casing module for preventing scales in the well fluid from entering the casing module flow path. 
     Further, the functional assembly may comprise a perforated outer pipe element mounted over the base pipe to provide an injection casing module for injecting fluid into an annulus surrounding the downhole casing system. 
     Also, the functional assembly may comprise end rings mounted over the end sections of the base pipe. 
     The present invention may also relate to a downhole casing system for performing operations in a wellbore containing well fluid, the downhole casing system comprising at least one casing module as described above, and at least one inflow control module extending in a longitudinal direction and adapted to be connected with the casing module, the inflow control module comprising at least one control module flow path in fluid communication with the casing module flow path, a main flow path fluidly connected with the main flow path of the base pipe, and a plurality of connecting passages fluidly connecting the control module flow path with the main flow path extending through the inflow control module and the casing module. 
     Said downhole casing system may further comprise at least one coupling module extending in a longitudinal direction and adapted to be connected to the casing module and/or another module such as an inflow control module, the coupling module comprising at least one coupling flow path in fluid communication with the casing module flow path and/or the control module flow path, and a main flow path fluidly connected with the main flow path of the base pipe and/or the main flow path of the inflow control module. 
     Also, the present invention relates to a downhole casing system for performing operations in a wellbore containing well fluid, the downhole casing system comprising: at least one casing module comprising; a base pipe extending in a longitudinal direction and having a circumference, a functional assembly mounted over the base pipe to define a casing module flow path between the functional assembly and the base pipe, and a main flow path arranged substantially in a centre of the base pipe and extending in a longitudinal direction of the casing system, wherein at least a part of the casing module flow path is an annular flow path extending both in the longitudinal direction of the base pipe and continuously around the entire circumference of the base pipe. 
     By an annular flow path extending continuously around the entire circumference of the base pipe is meant a casing module flow path extending in a continuous manner 360 degrees around on an outside of the base pipe. A fluid flow along an outer surface of the base pipe is better distributed to optimise the flow of e.g. oil into the main flow path. A continuous flow path around a periphery of the base pipe prevents a restricted or overloaded flow path on one side of the base pipe, e.g. due to blocking scales or high flow volume on the other side, from reducing the overall flow properties of the casing module. 
     In one embodiment, the functional assembly may comprise a filtering element, such as a screen, mounted over the base pipe to provide a screen casing module for preventing scales in the well fluid from entering the casing module flow path. 
     In another embodiment, the functional assembly may comprise a perforated outer pipe element mounted over the base pipe to provide an injection casing module for injecting fluid into an annulus surrounding the downhole casing system. 
     The functional assembly may further comprise a filtering element mounted over the base pipe and a perforated outer pipe element mounted over the filtering element. 
     Also, a downhole casing system according to the invention may comprise: at least one inflow control module extending in a longitudinal direction and adapted to be connected with the casing module, the inflow control module comprising: at least one control module flow path in fluid communication with the casing module flow path, a main flow path fluidly connected with the main flow path of the base pipe, and a plurality of connecting passages fluidly connecting the control module flow path with the main flow path extending through the inflow control module and the casing module. 
     A plurality of connecting passages may also be provided in the base pipe of the casing module for fluidly connecting the casing module flow path and the main flow path of the base pipe. Thus, the plurality of connecting passages provided in the base pipe may be an alternative or a supplement to the inflow control module. 
     A downhole casing system according to the invention may further comprise: at least one coupling module extending in a longitudinal direction and adapted to be connected to the casing module and/or another module such as an inflow control module, the coupling module comprising: at least one coupling flow path in fluid communication with the casing module flow path and/or the control module flow path, and a main flow path fluidly connected with the main flow path of the base pipe and/or the main flow path of the inflow control module. 
     Further, internal threaded connections may be provided at the opposite ends of the coupling module. 
     In one embodiment, the base pipe may have end sections at which a plurality of supporting structures protrude from an outer surface to provide support for the functional assembly, the supporting structures defining a plurality of casing module flow paths extending in the longitudinal direction. 
     Hereby, the functional assembly mounted over the base pipe may better withstand the considerable force and tear induced by an iron rough neck when the casing modules, coupling modules and/or inflow control modules are assembled on the drilling rig. 
     External threaded connections may be provided at the opposite ends of the base pipe. 
     Also, an external threaded connection may be provided at one end of the base pipe and an internal threaded connection may be provided at an opposite end of the base pipe. 
     In another embodiment, the functional assembly may comprise end rings mounted over the end sections of the base pipe. 
     The end rings may be manufactured from a material providing increased strength and tear resistance to the functional assembly at the end sections 
     Hereby, the casing modules may better withstand the considerable force and tear induced by an iron rough neck when the casing modules, coupling modules and/or inflow control modules are assembled on the drilling rig. 
     In another embodiment, the inflow control module may comprise a sliding sleeve arranged along a surface of the main flow path to control the flow through the connecting passages. 
     In yet another embodiment, the inflow control module may have end sections at which a plurality of longitudinal grooves may be arranged for providing part of the control module flow path, the inflow control module further comprising end rings mounted over the longitudinal grooves. 
     External threaded connections may be provided at opposite the ends of the inflow control module. 
     An external threaded connection may further be provided at one end of the inflow control module and an internal threaded connection may be provided at an opposite end of the inflow control module. 
     A downhole casing system according to the invention, wherein the inflow control module may comprise a plurality of longitudinal extending bores fluidly connecting the longitudinal grooves with the connecting passages. 
     In one embodiment, each of the connecting passages may comprise a circumferential groove connected to at least one of the longitudinally extending bores. 
     In another embodiment, the circumferential groove of one connecting passage may intersect the circumferential groove of another connecting passage. 
     Hereby, fluid may bypass a plug or a blocked valve arranged in the connecting passage and flow towards a subsequent connecting passage. 
     In yet another embodiment, one or more connecting passages may be provided in the casing module or in the coupling module for fluidly connecting the main flow path extending through the casing system with the casing module flow path and the coupling flow path, respectively. 
     Finally, valves, throttles and/or inflow control devices may be arranged in the connecting passages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which 
         FIGS. 1 a  and 1 b    show a downhole casing system comprising a casing module, 
         FIG. 2 a    shows a cross-section of an inflow control module, 
         FIG. 2 b    shows a principle drawing of the connecting passages in an inflow control module, 
         FIGS. 3 a  and 3 b    show a coupling module, 
         FIG. 4 a    shows a casing module comprising a filtering element, 
         FIG. 4 b    shows a casing module comprising a perforated tubing element, 
         FIG. 4 c    shows a casing module comprising both a filtering element and a perforated tubing element, 
         FIG. 4 d    shows a casing module comprising a filter element and connecting passages, and 
         FIG. 5  shows a downhole casing system comprising different casing system modules connected to each other. 
     
    
    
     All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a downhole casing system  1  for being lowered into a wellbore. When arranged in a wellbore, an annulus is defined between the casing system and the sides of the wellbore. The casing system comprises a casing module  2  adapted to be connected to other casing system modules described further in the following. The casing module  2  comprises a base pipe  21  extending in a longitudinal direction and having a circumference  211  as shown in  FIG. 1 b   . The base pipe  21  has a hollow bore defining a main flow path  24  extending through the casing module  2 . The main flow path  24  is shown substantially in a centre of the base pipe  21 , but may in an alternative design be arranged off centre. Around the base pipe, a functional assembly  22  is mounted, thereby defining a casing module flow path  23  extending between the functional assembly  22  and the base pipe  21  in the longitudinal direction of the casing module. The functional assembly  22  is mounted at a distance from an outer surface  27  of the base pipe  21  to provide a casing module flow path  23  extending continuously around the entire circumference  211  of the base pipe. Thus, the casing module flow path  23  is an annular flow path extending both in the longitudinal direction of the base pipe and around the entire circumference  211  of the base pipe. By parts of the functional assembly not being supported around the circumference  211  of the base pipe, fluid may flow unhindered 360 degrees around the base pipe. A single uninterrupted flow path around the base pipe provides optimal flow conditions between the base pipe and the functional assembly by allowing distribution of fluids around the whole circumference  211  of base pipe. If an increased amount of fluid flows to or from a specific area of the casing module, the entire continuous encircling flow path can be used to direct the flow to or from that area. A fluid flow along an outer surface of the base pipe is better distributed to optimise the flow of e.g. oil into the main flow path. A continuous flow path around a periphery of the base pipe prevents a restricted or overloaded flow path on one side of the base pipe, e.g. due to blocking scales or high flow volume on the other side, from reducing the overall flow properties of the casing module. 
     The functional assembly  22  may be constructed as one element as shown in  FIG. 1 a    or by combining several elements connected with each other as shown in  FIGS. 4 a   - 4   c.    
     The casing module  2  has end sections  25 , defined as sections adjacent each end of the casing module. In each end section  25  a plurality of supporting structures  26  protrude from the outer surface  27  of the base pipe  21  to provide a support for the functional assembly  22 . The functional assembly is thereby connected to the base pipe  21  via the supporting structures  26  and thus span an area of the base pipe located between the end sections  25 . In the end sections, the supporting structures  26  divide the encircling casing module flow path  23  into a plurality of separate casing module flow paths each extending over a limited part of the circumference  211  of the base pipe  21  as shown in  FIG. 1 b   . The plurality of separate casing module flow paths are defined by the supporting structures  26  and extend from the encircling casing module flow path towards the ends of the base pipe. The supporting structures  26  strengthen the casing module in the end sections so that when the casing module is connected with another casing module, e.g. by means of an iron rough neck on a drilling rig, the base pipe  21  of the casing module do not collapse. 
     Adjacent the ends, the separate casing module flow paths  23  are open and adapted to be connected to flow paths of abutting modules as described in the following. Further, the base pipe of the casing module comprises external threaded connections  28  at opposite ends for connecting the casing module  2  to other modules, as will also be described further below. It is obvious to the person skilled in the art that the threaded connections may be designed in a number of different ways, e.g. as internal threaded connections or as a combination. 
       FIGS. 4 a -4 c    show different designs of a casing module  2  comprising different types of functional assemblies  22 . In  FIG. 4 a   , the functional assembly  22  comprises a filtering element  221  mounted over the base pipe  21  to provide a screen for the casing module  2 . The filtering element  221  is mounted on a number of circular struts  224  arranged at a distance apart along the longitudinal direction of the casing module  2 . The struts  224  encircle the base pipe  21  and provide structural integrity to the filtering element  221 . The filter itself may be of various types such as, but not limited to, perforated tubing, a net of mesh arranged over the struts  224 , a filtering element  221  wound around the struts  224  and possible additional supporting members, etc. The functional assembly  22  further comprises end rings  223  arranged in opposite ends of the filtering element  221  and mounted over the supporting structures  26  protruding at the end sections  25  of the base pipe  21 . The filtering element  221  is connected to the end rings, e.g. by welding, to provide structural support to the filtering element. In one design of the functional assembly the end rings may be manufactured from a material adapted to withstand considerable force and tear induced by e.g. an iron rough neck when the casing modules are assembled on a drilling rig. 
     In  FIG. 4 b   , the functional assembly  22  comprises a perforated outer pipe element  222  as an alternative to the filtering element  221 . The perforated outer pipe element  222  is mounted over the base pipe  21  to provide an injection casing module for injecting fluid into the annulus surrounding the downhole casing system  1 . The perforated outer pipe element  222  is connected to the base pipe  21  via a set of end rings  223  mounted at opposite ends of the perforated outer pipe element and arranged over the supporting structures  26  of the base pipe  21 . 
     In  FIG. 4 c   , the functional assembly comprises both a filtering element  221  and a perforated pipe element  222 . The combination of a filtering element  221  and a perforated pipe element  222  may be used as a two step filter having varying filtering properties, as a combined screen and injection module, etc. 
       FIG. 2 a    shows a cross-section of an inflow control module  3  taken along a line corresponding to the dotted line shown in  FIG. 2 b   . The inflow control module extends in a longitudinal direction and is adapted to be connected with the casing module  2 , either directly or via a connecting module as described below. The inflow control module  3  comprises a pipe element  41  having a hollow bore defining a main flow path  34  extending in a longitudinal direction from one end of the pipe element  41  to the other. In opposite ends of the pipe element  41  external threaded connections  43  are provided, for connecting the inflow control module  3  to other casing system modules  2 ,  3 ,  5 . 
     When the inflow control module  3  is connected with a casing module  2 , the main flow path  34  is fluidly connected with the main flow path  24  in the base pipe  21 . 
     The pipe element has an outer surface  42  and an inner surface  36  encircling the main flow path  34 . Adjacent the ends of the pipe element  41 , end sections  37  of the inflow control module  3  are defined. In the end sections  37 , the pipe element  41  comprises a plurality of longitudinal grooves  38  provided in the outer surface  42 . The plurality of longitudinal grooves  38  provides part of a control module flow path  31  extending from one end of the control module to the other. The control module flow path  31  extends through the longitudinal grooves  38  in the end sections and through a middle portion of the pipe element  41  via a number of longitudinal extending bores  40  fluidly connecting the longitudinal grooves  38 . In the longitudinal extending bores  40 , a plurality of connecting passages  32  are provided to fluidly connect the control module flow path  31  with the main flow path  34 . The connecting passages  32  may be open holes or provided with valves, e.g. pressure or fluid controlled valves, throttles or other inflow control devices. The inflow control device may be adapted to control the flow rate through the connecting passages and may be controllable e.g. from the surface of the well or by a tool operating downhole. The inflow control devices may be controlled by applying different pressure levels, specific fluids or other types of signals or commands. 
     As shown in  FIG. 2 b   , two longitudinal extending bores  40  are provided between the longitudinal grooves  38  and the connecting passages  32 . The longitudinal extending bores  40  are in fluid communication with the connecting passages  32  via a circumferential grove  321  provided in each of the connecting passages  32 . By arranging the circumferential grooves  321  in a continuous pattern wherein a circumferential groove of one connecting passage intersects with the circumferential groove  321  of a subsequent connecting passage, the connecting passages become fluidly connected, thereby providing fluid communication between the longitudinal grooves  38 . Hereby, fluid may bypass a blocked or overloaded connecting passage  32  and flow towards a subsequent connecting passage and/or inflow control module. 
     The inflow control module  3  further comprises a sliding sleeve  35  arranged in a recess  351  in the main flow path  34 , for controlling the flow through the connecting passages. By arranging the sliding sleeve  35  in a recess  351  the sleeve does not reduce the maximum inner diameter of the hollow bore which could e.g. compromise the flow through the main flow path or hinder a tool from moving through the casing system. The sliding sleeve  35  is slidable between an open position, wherein the connecting passages are in fluid communication with the main flow path  34 , and a closed position, wherein the fluid connection is cut off. The sliding sleeve is a conventional sliding sleeve and may be operated by any means known to the person skilled in the art. The inflow control module  3  further comprises end rings  39  mounted over the longitudinal grooves to seal of the control module flow path  31  from the annulus. 
       FIG. 3 . a  shows a coupling module  5  for interconnecting the casing modules  2  described above and for connecting inflow control modules  3  to the casing modules  2 . The coupling module  5  extends in a longitudinal direction and comprises a pipe element  52  having an outer surface  53  and an inner surface  55  encircling a main flow path  54 . In the outer surface  53 , a number of coupling flow paths  51  are provided extending from one end of the pipe element to the other. The coupling flow paths  51  are covered by a cover element  56  encircling the pipe element. When the coupling element is connected to a casing module  2  or an inflow control module  3 , the coupling flow paths  51  are in fluid communication with the casing flow paths  23  or the control module flow paths  31 , respectively, and the main flow path  54  is fluidly connected to the main flow path of the casing module or the inflow control module, respectively. The coupling module  5  comprises internal threaded connections  57  in opposite ends of the pipe element. 
     As an alternative or a supplement to the inflow control module  3 , a plurality of connecting passages  32  and a sliding sleeve  35  may be arranged in the base pipe of the casing module or in the pipe element of the coupling module. These connecting passages may provide fluid communication between the casing module flow path and the main flow path of the base pipe and between the coupling flow path and the main flow path of the coupling module. 
     In use, the modules of the downhole casing system  1  are assembled at the surface and continuously lowered into the wellbore. The modules may be assembled using regular tools available, such as an iron rough neck. According to the requested functionality of the casing system, the appropriate number and types of modules are assembled. Each of the casing module, the inflow control module and the coupling module is self-contained modules that are pre-assembled before the modules are assembled into the downhole casing system  1  and lowered into the well. Assembling two separate modules may thus be performed in one operation, not requiring assembly of multiple parts at the rig site. Consequently, the time required for the assembly of separate modules is reduced and the casing system may be lowered into the wellbore at a faster rate. 
     As shown in  FIG. 5 , the casing modules are attached to the coupling modules by connecting the external threaded connections  28  of the casing modules to the internal threaded connections  57  of the coupling modules. In a similar manner, the inflow control module  3  is attached to the coupling modules  5  by the external threaded connections  43  of the inflow control module  3  being connected to the internal threaded connections  57  of the coupling modules. 
     The downhole casing system  1  may comprise a string consisting of multiple casing modules interconnected by coupling modules  5  and coupled to a single inflow control module  3 . Hereby, the number of inflow control modules  3  and sliding sleeves  35  are reduced. When the casing modules  2 , the coupling modules  5  and the inflow control modules  3  are connected, the main flow paths  24 ,  34 ,  54  are in fluid communication, whereby hydro carbons or other well fluids may flow from the formation through the casing system towards the surface or injection fluids may be injected into the formation through the casing system. At the same time, the casing module flow path  23 , the coupling flow path  51  and the control module flow path  31  are fluidly connected along the periphery of the casing system. Hereby, fluid may flow along multiple consecutive casing system modules  2 ,  3 ,  5  either from or into the formation. 
     As showed in the design, the downhole casing system comprises coupling modules for connecting other modules of the system. As should be obvious to the person skilled, the coupling modules may be omitted if the other casing system modules are provided with an internal threaded connection in one end and an external threaded connection in an opposite end. By utilising a system of alternating internal threaded female connections and external threaded male connections, the coupling modules become superfluous. A downhole system may thus be devised with no coupling modules, without departing from the subject matter of the invention. 
     By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively. 
     By a casing is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production. 
     Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.