Abstract:
A method and device for controlling the disconnection of a wireline ( 4 ), of the kind used in wireline operations in a wellbore, from a wireline tool ( 8 ), the wireline ( 4 ) being provided with a conductor ( 6 ) arranged to communicate signals, the signals being monitored at the wire-line tool ( 8 ) by means of a lower monitoring and control circuit ( 24 ), and the lower monitoring and control circuit ( 24 ) activating, by disappearance of signals from the surface, a disconnect device ( 12 ) after a predetermined time, the disconnect device ( 12 ) being arranged to disconnect the wireline ( 4 ) from the wireline tool ( 8 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method for controlling the disconnection of a wireline. More particularly it concerns a method for initiating the disconnection of a wireline from a wireline tool after the wireline tool has become stuck and the wireline has possibly been damaged. The invention also includes a device for practicing the method. 
   2. Discussion of the Prior Art 
   In wireline operations in a wellbore it may happen that the wireline tool becomes stuck. Then, when the wireline tool is to be freed, or otherwise in unfavourable conditions and in incorrect manoeuvring, it may happen that one or more of the conductors of the wireline are damaged and that the unit in the wellbore will thereby be without contact with an operator on the surface. 
   In order to access the tool assembly with a so-called fishing tool, the wireline portion present in the wellbore must first be removed. 
   According to the prior art, a wireline, which is to be used in wireline operations, is provided with a weakened portion near its point of attachment in the wireline tool. The weakening is normally provided by removal of a portion of the strands of the wireline. The purpose of the weakening is that a possible wireline rupture is to be directed to this weakened portion, so that after rupturing, essentially the entire wireline can be pulled up to the surface. The wireline tool may then be retrieved by means of a so-called fishing tool. 
   It is evident that the method mentioned reduces the carrying capacity of the wireline to a substantial degree, and may therefore cause unnecessary rupturing of the wireline and a considerable reduction in the permitted total weight of the tool that may be used. 
   The invention has as its object to remedy the drawbacks of the prior art. 
   The object is realized according to the invention through the features specified in the description below and in the following Claims. 
   Prior art wireline tools are often provided with electric equipment, which is arranged to communicate with instruments on the surface during the wireline operations. Thus, it is common for the wireline to be provided with a bundle of electrical conductors, referred to below as a conductor, arranged to transfer electrical signals and possibly also electrical power for the operation of equipment in the wireline tool. 
   SUMMARY OF THE INVENTION 
   According to the invention the signal flow in the conductor of the wireline at the wireline tool is monitored by means of a lower control apparatus in a manner known per se. Should the signal flow from the surface cease, this indicates that the wireline is damaged, possibly ruptured. After a predetermined time, the lower control apparatus initiates a disconnection of the wireline from the wireline tool by means of a disconnect device arranged in connection with the wireline tool. 
   In a preferred embodiment the conductor also extends through a monitoring and control apparatus on the surface, referred to below as the upper control apparatus, in which the signal flow through the conductor is monitored essentially without affecting the signal flow. The upper control apparatus is preferably provided with a display window, in which the state of the disconnect device is shown, and in which a warning of a begun disconnecting operation is given at the same time as an acoustic alarm is emitted by, for example, a bell. 
   The upper control apparatus is also provided with an override function, which is arranged to initiate disconnection of the wireline from the wireline tool, or to interrupt an erroneously initiated disconnection. Before the upper control apparatus can take over the control of the lower control apparatus, the conductor must be connected, by means of manual reconnection, to the control circuit of the upper control apparatus. 
   The wireline being automatically disconnected from the wireline tool on a possible wireline rupture, the wireline portion present in the wellbore can relatively easily be retrieved from the wellbore, so that access to the wireline tool with a fishing tool is facilitated. 
   The disconnect device may be of an embodiment of electro-mechanical or electro-chemical activation, for example. 
   The device is also suitable for disconnecting the wireline from the wireline tool if the wireline tool is stuck and it is not desirable to risk breaking the wireline in an attempt to free the wireline tool. 
   In what follows, a non-limiting example of a preferred embodiment will be described, which is visualized in the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGS. 
       FIG. 1  shows schematically the components incorporated in a disconnection control; 
       FIG. 2  shows on a larger scale the wireline attachment area in the wireline tool; 
       FIG. 3  shows on an even larger scale the disconnect device in a locking position; 
       FIG. 4  shows the disconnect device as the first part of the release has been carried out; and 
       FIG. 5  shows the disconnect device as the wireline has been released and the wireline attachment is on its way out of the wireline tool. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the drawings the reference numeral  1  identifies a disconnection control comprising a lower control apparatus  2 , which is arranged to monitor the signal flow in the conductor  6  of a wireline  4  between a wireline tool  8  and a computer  10  on the surface. 
   The lower control apparatus  2  is connected to and controls a disconnect device  12 . The disconnect device  12  forms a load-carrying connection between the wireline tool  8  and the wireline  4  through a wireline attachment  14 . The wireline attachment  14  is arranged to transmit a load corresponding to the breaking load of the wireline  4  to the disconnect device  12 , and is disposed in a first bore  13  of the wireline tool  8 , see  FIG. 3 . The first bore  13  ends in a second bore  15  of the wireline tool  8 , in which the disconnect device  12  is placed. 
   An upper control apparatus  16  is arranged on the surface and connected to the conductor  6  in such a way that the signal flow in the conductor  6  can be monitored in a manner known per se by means of an upper monitoring and control circuit  18  without disturbing the signal flow. The upper control apparatus is provided with a display window  20 , which is arranged to show the state of the disconnect control  1 , and a bell  22 , which is arranged to give a signal when the disconnecting operation is initiated. 
   The upper control apparatus  16  is also arranged, after the conductor  6  has been reconnected in the upper control apparatus  16 , to override the lower control apparatus  2  to initiate disconnection, or if the conductor  6  is intact, to interrupt an erroneously initiated disconnecting operation. 
   The lower control apparatus  2 , which is placed in the wireline tool  8  at the disconnect device  12 , includes a lower monitoring and control circuit  24  which is arranged to monitor the signal flow in the conductor  6  without disturbing the signal flow. The lower control apparatus  2  and the disconnect device  12  are supplied with energy from a battery  26 . The disconnect device  12  is connected to the lower control apparatus  2  by wires  28 . 
   The disconnect device  12  includes a releaser housing  32 , which is fixed to the wireline tool  8  and can be released by means of locking bodies  34  connected to the mounting sleeve  36  of the wireline attachment  14 . The releaser housing  32  is provided with a through central bore  38 , which is arranged to form a passage for the conductor  6  of the wireline  4 . In a diametrically widened portion  40  of the bore  38 , the portion  40  extending from the lower end portion  42  of the releaser housing  32  inwards to a shoulder  44 , a release spring  46  is disposed. 
   The release spring  46  is mounted between a spring retainer  48 , which is connected to the lower end portion  42  by means of threads  50 , and a release piston  52 . The release spring  46  is kept in a tensioned position by means of a number of electrically conductive and isolated load carrying strands  54  extending between the spring retainer  48  and the release piston  52 . The spring retainer  48  is arranged to tighten the releaser housing  32 , by means of the threads  51 , against a shoulder  53  between the bores  13  and  15  of the wireline tool  8 . 
   The strands  54 , which are preferably provided with weakened portions, are connected to the lower monitoring and control circuit  24  by means of the wires  28 . 
   The release piston  52  is provided with a through central bore  56  for the passing of the conduit  6  and is movably arranged within the bore  38 . 
   At its end portion facing the releaser housing  32 , the mounting sleeve  36  is provided with an internal bore  57 , complementarily fitting externally round the projecting locking neck  58  of the releaser housing  32 . The locking neck  58  is provided with at least two through radial bores  60  evenly spaced round the locking neck  58 , corresponding with suitable bores  62  of the mounting sleeve  36 . 
   Each of the corresponding bores  60 ,  62  is provided with a respective locking body  34  in the form of a ball. The diameter of the locking bodies  34  is adapted in such a way that the centre of the locking bodies  34  is positioned within the diameter of the bore  57 . The locking bodies  34  are retained in their locking position, in which the mounting sleeve  36  cannot be moved out of the locking neck  58 , by a bead  63  on the piston-rod-like portion  64  of the release piston  52 . The release piston  52  is prevented from being displaced from its locking position by a relatively weak support spring  66 , which is pre-tensioned between the shoulder  44  and the release piston  52 . 
   A clamp  68  gripping round the wireline and complementarily fitting into the bore  57  of the mounting sleeve  36  forms the wireline attachment  14 . 
   When the lower monitoring and control circuit  14  does not pick up any signals through the conductor  6  from the computer  10 , voltage is coupled, after a predetermined time has passed, from the battery  26  through the wires  28  to the strands  54 . The strands  54  are heated, due to their electrical resistance, until they lose their strength, possibly melt, so that the release spring  64  can overcome the force of the support spring  66 , whereby the release piston  52  is moved axially within the releaser housing  32  into its releasing position, see  FIG. 4 . 
   When the release piston  52  is in this releasing position, the bores  60  no longer correspond with the bead  63  on the piston-rod-like portion  64 , whereby the locking bodies  34  can be moved radially inwards out of their locking engagement within the bores  62 . Thereby, the mounting sleeve can be moved out of the locking neck  58 , whereby the wireline  4  is released from the wireline tool  8 , see  FIG. 5 . The wireline with the wireline mounting  14  can then be pulled up to the surface.