Patent Publication Number: US-7913763-B2

Title: Washing a cylindrical cavity

Description:
The present invention relates to a methods and apparatuses for washing generally cylindrical cavities. In particular, the invention relates to washing and/or spraying the walls of pipelines and wells such as mineral wells, geothermal wells, oil wells and natural gas wells. 
     Tools for generating jets of fluid for washing the interior of cylindrical cavities are well known. Such tools are used, for example, for washing the walls of wells, and removing deposits, scale and debris from the walls of the wells. Such tools may also be used to treat rock pores or the interstices in the wall coatings to increase their permeability to improve other chemical and physical characteristics. 
     The composition of the washing fluid used may vary. Water is frequently used, sometimes with additives such as hydrochloric acid (HCl), polymers, abrasive dust, nitrogen (N 2 ), nitrogenous liquids etc. 
     A known washing system involves the use of generally cylindrical tools having one or more punctiform nozzles from which the washing fluid is ejected. The nozzles are mounted on a rotating head, the rotation being driven by the fluid leaving the nozzles. The washing fluid exits the tool in a set of rotating punctiform jets which strike the walls of the well. 
     These tools are costly. The presence of moving parts and a rapidly rotating head leads to reliability problems. The speed of rotation is very difficult to control. In addition, since some of the energy in the washing fluid is used to make the nozzles rotate, there is less energy in the jets striking the wall than would be the case with no rotation. 
     Furthermore, it will be appreciated that, because the jets are constantly moving, each jet plays on a particular part of the wall for a very short time. This substantially diminishes the washing effect because of the intermittent nature of the jet and the inertia of the fluids present in the well. 
     Another known washing system involves the use of tools having an array of stationary punctiform nozzles. Such tools are again usually generally cylindrical in form, and the nozzles are distributed along and around the periphery of the tool. Washing fluid is ejected from the nozzles in an array of stationary punctiform jets. Such tools are cheaper and more reliable than those with rotating nozzles. 
     However, stationary punctiform jets do not achieve a uniform washing action over the area to be washed. The high number of nozzles considerably reduces the exit speed of each jet and consequently the efficiency of the treatment. 
     In accordance with one aspect of the present invention there is provided a tool for washing a wellbore or hollow tubular, the tool having a longitudinal axis and comprising one or more elongate nozzles for ejecting fluid generally radially from the tool, the or each nozzle extending circumferentially around the tool. The nozzle or nozzles preferably collectively extend 360° around the longitudinal axis of the tool so that fluid is ejected in all radial directions. 
     The term “fluid” as used herein is intended to encompass washing fluid, sandblasting fluid, abrasive material etc. that may be useful for washing and/or abrasive cleaning of a wellbore or tubular. The tool may also be useful for cutting tubulars, in which case a suitable material should be selected. 
     Where there is more than one nozzle, the nozzles preferably have complementary circumferential extensions so that they collectively extend a predetermined circumferential distance (usually 360°) around the tool. This may be achieved by locating the nozzles at a variety of axial locations. 
     The nozzles may be provided in a number of different configurations. For example, each nozzle may extend in a plane normal to the longitudinal axis. Alternatively, some or all of the nozzles may include an axial component in their direction of extension. The nozzles may extend in a plane inclined to the longitudinal axis. Some or all of the nozzles may be formed as curved slots. Further configurations may also be envisaged. 
     The nozzles may be arranged so that fluid exits the tool in a purely radial direction with no axial component—i.e. straight out from the tool. Alternatively, the nozzles may be inclined so that fluid exits in a direction inclined axially to the radial direction. The nozzles may be straight, or divergent so that fluid exits the tool at a range of angles relative to purely radial, or convergent. The tool may comprise a body surrounding a central cavity for receiving fluid, the nozzles extending through the body from the central cavity to the exterior of the tool. 
     In one embodiment, a single nozzle extends 360° around the longitudinal axis of the tool. The axial width of this nozzle may be adjustable. 
     In order to provide adjustment of the width of the nozzle, the tool may comprise a generally tubular assembly comprising a larger external diameter portion and a smaller external diameter portion with a shoulder therebetween, at least a part of the smaller diameter portion being externally threaded, and a sleeve, at least partially internally threaded, screwed onto the smaller external diameter portion of the tubular assembly, such that the nozzle is formed between an end of the sleeve and the shoulder, the axial width of the nozzle being determined by the extent to which the sleeve is screwed onto the smaller diameter portion. An annular chamber is preferably formed adjacent to the nozzle, the tool arranged so that the annular chamber is in fluid communication with fluid supplied to the tool. 
     Preferably the sleeve and tubular assembly are lockable together to prevent relative axial movement therebetween. This may be achieved, for example, using grub screws passing through the sleeve. 
     The generally tubular assembly preferably comprises a central cavity, with ports being provided in the smaller diameter portion to provide fluid communication between the central cavity and the annular chamber. The annular chamber may be located between the smaller diameter portion of the tubular assembly and the sleeve, and formed by a reduced external diameter section on the smaller diameter portion and/or an increased internal diameter section on the sleeve. 
     In one embodiment, the tubular assembly comprises an extended member having an increased external diameter portion and a reduced internal diameter portion, and an adjustment sleeve screwed onto the reduced internal diameter portion of the extended member so as to surround a portion thereof, so that the adjustment sleeve and increased diameter portion of the extended member together form the larger external diameter portion of the tubular assembly, the shoulder being formed by an end of the adjustment sleeve. The annular chamber may then be located between the reduced diameter portion of the extended member and the adjustment sleeve, and formed by a reduced external diameter section on the reduced diameter portion of the extended member and/or an increased internal diameter section on the adjustment sleeve. 
     In an alternative embodiment providing an adjustable nozzle, the tool may comprise: a generally tubular assembly comprising a larger external diameter portion and a smaller external diameter portion with a shoulder therebetween; a sleeve located around the smaller external diameter portion of the tubular assembly and axially movable relative to the tubular assembly, such that the nozzle is formed between an end of the sleeve and the shoulder; and a biasing mechanism biasing the sleeve towards the shoulder, so that the nozzle is closed when the fluid pressure in the tool is below a predetermined value. An annular chamber is preferably formed adjacent to the nozzle, the tool arranged so that the annular chamber is in fluid communication with fluid supplied to the tool. The nozzle is preferably openable by fluid pressure overcoming the biasing force and moving the sleeve away from the shoulder. This means that the nozzle can be opened (and kept open) by the washing fluid itself. 
     The tool preferably has a fluid supply end in communication with the central cavity for connecting the tool to a fluid source. The opposite end of the tool to the fluid supply end may be closed. Alternatively, the opposite end may include an axial exit bore in fluid communication with the central cavity for receiving an axial discharge nozzle. 
     In a further alternative, the opposite end may be open to allow the passage of fluid, the tool further comprising a movable sleeve member located in the central cavity which restricts fluid communication between the central cavity and the nozzles and which allows fluid communication between the fluid supply end and the opposite end, said sleeve member being releasably attached to the body and including a seat for receiving a plug, the sleeve member being movable to a position in which it does not restrict fluid communication between the central cavity and the nozzles. The sleeve member is preferably releasably attached to the body by shear screws. 
     The inner end of the or each nozzle may be strengthened with hardened material, to counter erosion otherwise caused by the continuous passage of high pressure washing or abrasive fluid. 
     The invention also provides a method of washing a wellbore, comprising running a tool as described above into the wellbore and ejecting fluid through the nozzles, preferably continuously. 
     In accordance with another aspect of the present invention there is provided a method of washing a wellbore, comprising generating one or more jets of fluid, the or each jet taking the form of a two-dimensional sheet extending at least partially circumferentially relative to the longitudinal axis of the wellbore. The jet(s) may provide 360° coverage of the surface of the wellbore. Another method according to the invention comprises cutting a tubular by generating one or more jets of cutting fluid, the or each jet taking the form of a two-dimensional sheet extending at least partially circumferentially relative to the longitudinal axis of the tubular. Either of these methods may be carried out using a tool as described above. 
    
    
     
       Some preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG. 1  is a longitudinal section view of a washing tool; 
         FIGS. 2 ,  3 ,  4  and  5  illustrate variations to the tool of  FIG. 1 ; 
         FIGS. 6 ,  7  and  8  show, in section, further variations to the tools of  FIGS. 1 to 5 ; 
         FIG. 9  is a partial section view of an alternative washing tool; 
         FIG. 10  shows another alternative washing tool, and 
         FIG. 11  shows a further alternative washing tool. 
     
    
    
       FIG. 1  shows a tool  1  for washing generally cylindrical cavities, such as those found in wellbores. The tool  1  comprises a generally cylindrical body  2  having a central cavity  12 , both having the same central longitudinal axis X. A plurality of elongate, circumferentially extending nozzles  5 ,  6 ,  7  extend radially through the body  2  from the cavity  12  to the exterior of the tool  1 . The nozzles are distributed so that, collectively, they provide 360° coverage around the longitudinal axis X. 
     The tool  1  includes an open fluid supply end  3 , in communication with the cavity  12 , through which washing fluid (typically water or an aqueous solution) is supplied to the tool. The washing fluid exits from the cavity  12  through the nozzles  5 ,  6 ,  7 . Fluid is ejected in all radial directions from the tool and impacts the wall of a cavity or wellbore (not shown) surrounding the tool in a uniform manner. The open fluid supply end  3  has an internal threaded portion to allow mechanical connection of the washing tool to other tools or tubulars and to the fluid supply system. The tool may be connected to coiled tubing, or to other tubing strings. 
     The nozzles may extend directly radially, as shown in  FIG. 6 , or may have an axial component so that they direct fluid with a spray angle α relative to the longitudinal axis X, as shown in  FIG. 7 . This provides a directed washing flow which may be useful, for example, for the removal and subsequent conveyance of deposits. In a further alternative the nozzles may increase in width (in the longitudinal direction of the body) through the width of the body, as shown in  FIG. 8 . 
     Various configurations of nozzle are available. Each nozzle may conveniently be described as a “slot”. In one embodiment, shown in  FIGS. 1 and 2 , the slots extend at right angles to the longitudinal axis X (i.e. purely circumferentially), and are distributed axially along the body  2  in order to give total 360° coverage. The width (in the longitudinal direction of the body) depends on the dimensions of the tool, the available delivery capacity and the particular purpose of the treatment. 
     Alternatively, the slots  5 ,  6 ,  7  may be distributed around the longitudinal axis X but extend over a plane which is inclined in relation to the axis of extension X. In other words, the slots may include an axial component in their direction of extension. 
     In a further alternative, the slots  5 ,  6  and  7  may have spiral or curved shapes, as shown in  FIGS. 3 ,  4  and  5 . It will be appreciated that combinations of flat and curved slots, or slots in different planes, may also be used. 
     Each of the tools shown in  FIGS. 1 ,  2 ,  4  and  5  include four stationary slots, each of which extends circumferentially for at least 90°. It will be appreciated that any arrangement which the necessary circumferential coverage—usually 360°—may be used, including the use of different numbers of slots. 
     In a possible variation, not illustrated, the washing tool of any of  FIGS. 1-6  is formed by two generally tubular bodies, fixed to each other, each of which has nozzles providing partial circumferential coverage around the axis X. The combination of the two tubulars provides complete 360° coverage around the axis X. 
     In many situations the tool will be surrounded in use by well fluids. If the washing fluid is to have any effect on the wall of a well after passing through the well fluids it must exit the tool at very high speed. A constant flow of high speed fluid through the elongate nozzles  5 ,  6 ,  7  may result in erosion, especially at the inner aperture of the nozzle. It is therefore preferred that hardened material  8  is provided to strengthen the nozzle, as shown in  FIGS. 6 ,  7  and  8 . 
     In the example shown in  FIG. 1 , the opposite end of the tool  4 , distal to the fluid supply end  3 , is generally hemispherical in shape. In the preferred embodiment an axial exit bore  41  is provided through the hemispherical end  4 . The exit bore  41  is partially threaded for attachment of a nozzle (not shown), which may be used to remove any debris present in the well. 
       FIG. 9  illustrates an alternative tool  91 , generally similar to that shown in  FIG. 1 , in which the distal end  4  is open and in communication with the cavity  12  of the body  2 . It will be noted that the tool  91  of  FIG. 9  is shown in a reversed orientation compared to the tool  1  of  FIG. 1 , with the fluid supply end  3  at the top of the figure and the distal end  4  at the bottom of the figure. The open distal end  4  is threaded to enable the washing tool  91  to be linked to other tools, either upstream or downstream, such as, for example, vibrating tools to assist with the movement of the tool into the well. 
     A slidable sleeve member  30  is located in the central cavity  12 . The sleeve member  30  is generally cylindrical and includes an axial central bore  31  which allows fluid to pass through the cavity from the fluid supply end  3  to the distal end  4 . The sleeve member  30  is initially located to as to cover the nozzles  5 ,  6 ,  7 , preventing communication between the cavity  12  and the nozzles  5 ,  6 ,  7 . Grooves are provided around the outside of the sleeve member  30  to receive sealing gaskets  34 , and the sleeve member  30  is held against the body  2  by means of shear screws  32  with pre-defined breaking load. In this configuration fluid passes right through the tool from the fluid supply end  3  to the distal end  4 . 
     The axial bore  31  is shaped so that it can act as a seat for a ball  33 . When it is desired to use the tool for washing, a ball is inserted into the string, transported into the tool through the fluid supply end  3 , and comes to rest against the seat formed in the axial bore  31  of the sleeve member  30 . This prevents passage of fluid through the bore  31 . As a result, the fluid pressure within the tool increases, causing the shear screws  32  to fail. The sleeve member  30  then moves through the tool until clear of the nozzles  5 ,  6 ,  7 , which are brought into communication with the cavity  12 . Fluid then exits the nozzles  5 ,  6 ,  7  to wash the surface surrounding the tool. 
       FIG. 10  shows an alternative washing tool  101 , similar to that shown in  FIG. 1 , having a nozzle in the form of single, adjustable, circular slot  50  which extends circumferentially for 360° right around the tool  101 . 
     The tool  101  includes a generally tubular connection element  51  having an open, internally threaded, fluid supply end  52 , through which washing fluid is supplied under pressure. The opposite end  53  of the connection element, distal to the fluid supply end  52 , terminates in a shoulder  57  and is provided with internal threads  108 , to which is secured a head element  54 . 
     The head element  54  is formed by a generally hemispherical end portion  59 , from which extends a narrower hollow stem  55  having a central cavity  102 . A shoulder  58  is formed at the point where the stem  55  extends from the end portion  59 . The stem  55  includes external threads which are screwed into the internal threads  58  of the distal end  53  of the connection element  51 . Once the head element  54  is screwed in place, the circular slot  50  is formed between the shoulders  57 ,  58  on the connection element  51  and head element  54 , respectively. 
     An annular chamber  56 , in communication with the circular slot  50 , is formed between the connection element  51  and the hollow stem  55 . This annular chamber  56  is itself in communication with the cavity  102  of the hollow stem  55  via ports  103 . The central cavity  102  communicates with the open fluid supply end  52  of the connection element  51 . Washing fluid under pressure supplied through the fluid supply end  52  is thus ejected from the circular slot  50 . 
     The width of the circular slot  50  is determined by the extent to which the stem  55  is screwed into the connection element  51 . The narrowest configuration for the slot  50  is achieved when the stem  55  is screwed all the way into the connection element. Wider configurations of the slot  50  are achieved by screwing the stem  55  so that it is not all the way into the distal end  53  of the connection element  51 . Locking grub screws  70  pass through the body of the connection element  51  to lock the stem in the selected position. A seat  104  for the grub screws  70  is set into the stem  55  and provides the limits for the possible widths of the slot  50 . The characteristics of the washing jet can thus be controlled through the width of the nozzle. 
     The circular slot  50  is shown in  FIG. 10  with a convergent profile, resulting in a continuous, focussed jet of washing fluid that extends all the way around the tool. 
     It will be appreciated that the embodiments of  FIGS. 9 and 10  could be combined. The tool of  FIG. 10  is shown with a hemispherical end  59  of the head element  54 , but this could be replaced by an open end similar to the distal end  4  of  FIG. 9 . A constriction element could be shear pinned to the interior of the stem  55 , arranged to cover the ports  103  and act as a seat for a ball inserted into the tool through the fluid supply end  52 . 
     A further alternative washing tool  111  is shown in  FIG. 11 . The washing tool is similar to the tool  101  shown in  FIG. 10 , and again includes a stationary nozzle formed as an adjustable circular slot  60  which extends right around the tool so as to provide radial discharge of washing fluid in all directions. 
     In this embodiment the tool  111  includes an extended generally tubular element  61  having a larger diameter portion  62  and smaller diameter portion  63 . The larger diameter portion  62  has an open, internally threaded fluid supply end for the supply of fluid under pressure. The smaller diameter portion  63  terminates in a distal end  114 . In one embodiment (not shown) the distal end  114  is closed. In another embodiment a threaded exit bore  64  is provided through the distal end  114 , the bore being coaxial with the longitudinal axis X of the tubular element  61 . The bore  64  is intended to house a nozzle (not shown) for removing any debris present within the well. 
     The smaller diameter portion  63  of the hollow element  61  has two externally threaded sections  65 ,  66 . The first externally threaded section  65  is adjacent to the larger diameter portion  62 , and the second  66  is adjacent the distal end  114 . Between these externally threaded sections  65 ,  66  is an intermediate section  115  of smaller external diameter than the externally threaded sections. A plurality of ports  67  are provided which extend generally radially from the interior of the body to the smaller external diameter of the intermediated section  115 . 
     An internally threaded sleeve  77  is screwed onto the first threaded section  65  of the smaller diameter portion  63  of the tubular element  61  so that it abuts or nearly abuts the larger diameter portion  62 . A internally threaded head element  68  is screwed to the second threaded section until it almost abuts the sleeve  77 . The head element terminates in a generally hemispherical end which covers distal end  114  of the tubular element  61 . An axial exit bore  116  may be provided in the hemispherical end to allow fluid to exit through the exit bore  64  in the distal end  114  of the tubular element  61 . Seals  71 ,  72  are provided in circular grooves on the smaller diameter portion to seal to the head element  68  and sleeve  77 , respectively. 
     The threaded sleeve  77  has a non-threaded internal section  116  at the end opposite that abutting the larger diameter portion  62  of the tubular element  61 . The non-threaded internal section  116  sits level with the intermediate section  115  of the tubular element  61 . An annular chamber  69  is defined between the reduced external diameter of the intermediate section and the non-threaded internal section of the sleeve  77 . This chamber is in fluid communication with the interior of the tubular element  61  via the radial ports  67 . 
     As previously mentioned, the head element  68  is screwed onto the second threaded section  66  until it almost abuts the sleeve  77 . The gap between the head element and the sleeve defines the circular slot  60 . The slot  60  is in fluid communication with the annular chamber  69  which, in turn, is in fluid communication with the interior of the tubular element  61 . Fluid under pressure supplied through the open fluid supply end  62  therefore passes through the ports  67  into the annular chamber  69  and is ejected through the slot  60  in all radial directions. 
     The width of the slot  60  is adjustable by rotating the threaded sleeve  77  and/or the head element  68 . This enables control of the characteristics of the washing jet and the treatment. The threaded sleeve  77  and the head element  68 , may be locked in position by grub screws  70 . As with the example shown in  FIG. 10 , the ends of the sleeve  77  and head element  68  may be designed so that the slot  60  has a convergent profile. 
     A further alternative tool  121  is shown in  FIG. 12 . This tool is similar to that shown in  FIG. 10 . In this example, the connection element  51  and head element  54  are not screwed together. Instead, a tension spring  109  (or other suitable biasing mechanism) is used to connect them. The spring  109  is attached at one end to the head member  54  and at the other end to the connection member  51 , in such a way that the head member  54  is biased towards the connection member  51 . A circular slot  100  is formed (in a similar manner to that shown in  FIG. 10 ) between the shoulders  57 ,  58  on the connection element  51  and head element  54 , respectively. When the pressure of fluid supplied to the tool is below a predetermined value, the force provided by the spring  109  closes the slot  100  by pulling the head element  54  and connection element  51  together. In order to begin a washing process, the fluid pressure is increased until it is sufficient to overcome the spring force. The head member  54  is moved longitudinally relative to the connection element  51  and the slot  100  is opened. Fluid can then pass through the ports  103  and out of the slot  100  in a similar manner to that shown in  FIG. 10 . Grub screws  70  pass through the body of the connection element  51 . In this embodiment they are not used to lock the stem in the selected position. Instead, the seat  104  for the grub screws  70  limits the travel of the head member  54 , and provides the limits for the possible widths of the slot  50 . 
     It will be appreciated that variations from the above described embodiments may still fall within the scope of the invention. For example, the tool of  FIG. 11  is described with an annular chamber  69  formed between a reduced external diameter of the tubular element and the sleeve  77 . It would be possible to produce a similar chamber by increasing the internal diameter of a section of the sleeve  77 . 
     Furthermore, the tool has been described as a tool for washing a wellbore. It will be appreciated that there are other purposes for which it could be used. For example, the tool could be used to eject sandblasting fluid or an abrasive material. The tool could then be used for abrasive cleaning and/or tubing cutting. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.