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BACKGROUND 
       [0001]    This disclosure relates generally to the field of a non-tethered autonomous well intervention tool system for removing scale and similar from a wellbore. The wellbore can be subsea, on an offshore platform or on land. More specifically, the present disclosure relates to a battery operated electrical tool for dissolving mineral build-up in a wellbore, where the tool is stored, deployed from and received in a lubricator and charging system mounted on top of a wellhead (Christmas tree). The wellbore intervention tool system may also perform other wellbore operations, e.g., production logging, setting and retrieval of plugs, and other intervention operations known in the art. The system may operate without the presence of a human operator at the well site, either remotely operated or autonomously at pre-determined times. 
         [0002]    Buildup of scale and paraffin is a frequent problem in producing hydrocarbon wells, where such build up causes drop or total halt of production as well as malfunction of wellbore completion components, for example, downhole safety valves. To remove scale and paraffin deposits, wireline is rigged up on top of the wellbore, followed by an intervention where electrical or mechanical impact based tools are run into the wellbore to hammer loose the scale or cut the paraffin built up. This is a slow process due to the nature of the tools being used, but not least due to the time required to rig up and down the intervention valves, lubricator and so on. In addition, well production is lost due to the required well “shut in” (stopping of fluid production) during rigging operation. The process may also be expensive, where the cost of performing an intervention in a subsea well can amount to tens of millions of United States dollars, plus a significant lost income for the duration of the intervention. 
         [0003]    Due to the foregoing considerations, failures of wellbore components, for example, downhole safety valves, also take place as a result of intentionally infrequent scale removal, causing the production tubing, etc., to become partially or completely non-functional. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1 . illustrates scale in a tube, where it can be understood that this will reduce or totally prevent flow through a tube as well as cause wellbore components to malfunction. 
           [0005]      FIG. 2  illustrates a wellhead with an attached wellhead (“christmas tree”) and a lubricator/valve system installed on top of the christmas tree. Within the lubricator, a wellbore intervention tool system is mounted. Scale build up is indicated within a conduit called production tubing. 
           [0006]      FIG. 2A  shows an enlarged view of an example intervention tool system 
           [0007]      FIG. 3  illustrates that valves in the lower end of the lubricator system have been opened, followed by a wellbore intervention tool moving into the wellbore. 
           [0008]      FIG. 4  illustrates that one or both valves in the lower section of the lubricator system have been closed, so that the well can be flowed at a low rate with the intervention tool being downhole. Scale removal may be started. 
           [0009]      FIG. 5  illustrates that the intervention tool is transported up-hole, either by producing the well or by a built in propulsion drive. 
           [0010]      FIG. 6  illustrates that the intervention tool has latched into the top section of the lubricator/valve system, with both valves closed and well brought back to normal production. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Therefore the present disclosure sets forth a possible solution to removing scale or paraffin in a well where the scale or paraffin removal is performed more frequently than may be performed using conventional wireline conveyed tools. Increased frequency of scale or paraffin deposits may prevent excessive buildup of such scale or paraffin deposits. Scale or paraffin removal at more frequent intervals may be performed by a system mounted on top of the wellhead, where a lubricator, isolated from the wellhead by valves built into the lower section of the intervention system, contains a scale or paraffin removal tool that can be deployed into the wellbore when required. 
         [0012]    The wellbore tool intervention system may include a scale or paraffin removal tool with required ancillary instrumentation attached, such as, for example, a battery package, a wet-mating electrical coupler, a propulsion system, etc. The wellbore tool intervention system may be deployed into the wellbore from a storage place within the lubricator and may be returned to the lubricator by causing fluid to flow from the formations external to the well thence into the well. In some embodiments, the wellbore intervention tool system may contain a propulsion system built in that returns the wellbore tool system to the lubricator when required. 
         [0013]    Electrical, hydraulic or pneumatic operated impact (e.g. hammer, so called “broach” and similar) based scale removal tools can be coupled to the wellbore intervention tool system. A wellbore intervention tool system according to the present disclosure allows more frequent wellbore scale or paraffin removal operations than would be ordinarily performed using interventions from a vessel, workover rig or a drilling rig. More frequent deposit removal may result in the scale or paraffin deposits being of less extent than would occur with less frequent intervention; such more frequent deposit removal ensures improved production of hydrocarbons from the well. 
         [0014]    To perform a wellbore intervention, pressure equalizing between the wellbore and the lubricator may be performed, followed by opening of valves between the lubricator and the wellhead. This will enable the wellbore intervention tool system to drop, or drive down, into the wellbore where it reaches a restriction caused by scale or paraffin. Then the removal of such restriction will be commenced, until the restriction has been removed or until an internal power source (e.g., batteries) is exhausted. When the foregoing takes place, the wellbore intervention tool system may be transported up to the lubricator again by a built in “swab cup” that uses fluid flow from the wellbore to lift the wellbore intervention tool system. When reaching the wellhead, the wellbore intervention tool system will be further pushed up into the lubricator and latch onto a holding device and/or an electrical coupler enabling battery recharging. 
         [0015]    After the wellbore intervention tool system has been returned to the lubricator, the valves between the lubricator and the wellhead can be closed and pressure tested, so that the well can commence fluid production again. 
         [0016]    When scale or paraffin removal is required again, the above sequence may be repeated. 
         [0017]    For those skilled in the art of wellbore interventions, it will be understood that the method described herein may also be used for other type interventions, e.g., memory type production logging, and other intervention operations. 
         [0018]      FIG. 1 . illustrates scale  14  in a tube  12 . The tube  12  may be, for example, a wellbore production tubing or “velocity string.” It will be appreciated that the scale  14  will reduce or totally prevent flow through the tube  14 . The scale  14  may also cause wellbore components to malfunction. Such scale needs to be removed, where various methods can be used, as for example mechanically breaking the scale, pulsed electrical energy pulverizing the scale, release of scale-dissolving chemicals, or abrasive means such as milling. 
         [0019]      FIG. 2  illustrates a wellhead  20 , for example a sea bottom wellhead with an attached christmas tree (e.g., valves  30  and  32 ). A lubricator system  22  may be affixed to the upper end of the wellhead. The lubricator system  22  may include isolation valves  22 A such as gate valves to selectively pressure isolate the lubricator system  22  from the wellhead  20 . The isolation valves  22 A may be operated by respective actuators  22 B. The actuators  22 B may be electrically, pneumatically or hydraulically operated, for example. The lubricator system  22  may include pressure equalization valves  28  that connect the interior of the lubricator system to below each of the isolation valves  22 A. The pressure equalization valves  28  may also be actuated electrically, hydraulically or pneumatically. The isolation valves  22 A and the pressure equalization valves  28  may be operated by a controller  29 . The controller  29  may be operated using, for example, telemetry from the water surface or electrical connection using a remotely operated vehicle (ROV). The lubricator system  22  may also include a pressure relief valve  24  to enable release of pressure from the interior of the lubricator system after the well intervention tool system  10  is retrieved into the lubricator system  22 . The pressure relief valve  24  may also be electrically, hydraulically or pneumatically operated and may be controlled by the controller  29 . 
         [0020]    The upper end of the lubricator system  22  may include a sealing cover  22 D that is retained in place on the upper end of the lubricator system  22  and is pressure sealed. The sealing cover  22 D may include an automatically operable latch  22 E to retain the wellbore intervention tool system  10  when it is retrieved into the lubricator system  22 . The latch  22 E may include electrical connections (not shown separately) for providing electrical power to the wellbore intervention tool system  10 , e.g., to recharge batteries therein (see  FIG. 2A ). 
         [0021]    The sealing cover  22 D may have a profile for a retrieval and running tool, a receptacle  22 F for an electrical cable from an external power source as well as various sensors for monitoring pressure, etc. It may also contain a telemetry system for transmitting and receiving commands and data from a surface vessel or the like. The sealing cap  22 D may also be removed, so that a wellbore intervention pressure control system (with riser, etc.) can be landed on top of the lubricator system  22 , followed by the possibility of deploying and setting plugs and other equipment in the wellbore. Setting a plug within a tubing hanger or further down into the wellbore tubing  14  may enable a safe removal of the complete lubricator system  22  if such is required. 
         [0022]    The isolation valves  22 A valve system on the lower end of the lubricator system  22  may be used for pressure testing of the lubricator system  22  and enable the well to operate normally without subjecting the lubricator system  22  to wellbore production fluids and pressure when the wellbore intervention tool system  10  is not in use. 
         [0023]      FIG. 2A  shows the wellbore intervention tool system  10  in more detail. The wellbore intervention tool system  10 , hereinafter “tool” for convenience, may include a self-contained power supply  10 E such as batteries within a pressure sealed housing  11 . A control and power module  10 F disposed in the housing  11  may be used to operate a wellbore intervention device  10 A. In the present embodiment, the wellbore intervention device may be a scale removal device disposed proximate the bottom of the housing  11 . The scale removal device may be any type known in the art, including a chemical storage and release mechanism, motor-rotated blades or abrasive mills, electric shock (sparker) discharge devices, acoustic devices, heater(s) to remove paraffin deposits, or any other such device for removal of deposits in the tubing ( 12  in  FIG. 1 ). The tool  10  may include combinations of any or all of the foregoing as well. The tool  10  may include a propulsion device  10 G, such as a fluid operated jet or a propeller to cause the tool  10  to move within the tube  14  during operations if gravity is insufficient to move the tool  10  downwardly to the depth of any obstruction, and to return the tool  10  to the lubricator system ( 22  in  FIG. 2 ) if fluid flow from the well is insufficient to lift the tool  10 . The housing  11  may include annular seals  10 D such as swab cups to enable free movement of the tool  10  downwardly, but may seal to engage the interior of the tubing ( 14  in  FIG. 1 ) to enable fluid flow into the well to lift the tool into the lubricator system ( 22  in  FIG. 2 ). The upper end of the housing  11  may include a mating latch  10 B to engage the latch ( 22 E in  FIG. 2 ) in the lubricator system sealing cover ( 22 D in  FIG. 2 ). The housing  11  may include centralizers  10 C to enable relatively free movement of the tool  10  in the tubing ( 14  in  FIG. 2 ) and to keep the tool  10  centered in the tubing for proper operation of the scale removal device. 
         [0024]    Scale or paraffin build up may be indicated within the production tubing ( 14  in  FIG. 2 ), for example, by a decrease in fluid production from the well. Thus it may be necessary to deploy the tool  10 . The tool  10  may be installed into the lubricator system ( 22  in  FIG. 2 ) prior to installing the lubricator system ( 22  in  FIG. 2 ) onto the wellhead ( 20  in  FIG. 2 ) or the tool  10  may be installed into the lubricator system ( 22  in  FIG. 2 ) by unlatching and removing the sealing cover ( 22 D in  FIG. 2 ). Retrieval of the tool  10  may be performed by unlatching and retrieving the entire lubricator system with the tool  10  inside the lubricator system, or by unlatching the sealing cover ( 22 D in  FIG. 2 ) and retrieving the tool  10 . It is also possible to perform tool replacement using an ROV in marine operations where the wellhead is on the water bottom. 
         [0025]    In other embodiments, the wellbore intervention device  10 A may be any other type of wellbore tool, including, without limitation, a production logging instrument, a plug or packer setting tool or a video camera. 
         [0026]      FIG. 2  shows the tool  10  engaged with the latch  22 E and the isolation valves  22 A and pressure equalization valves  28  closed so that the well can operate normally. When it is determined that deployment of the tool is necessary,  FIG. 3  illustrates that the pressure equalization valves  28  may be opened to equalize pressure in the well with the pressure in the lubricator system  22 . The isolation valves  22 A may then be opened and the latch  22 E may be released to enable the tool  10  to move downwardly through the well tubing  14 . Movement of the tool  10  into the wellbore may be by gravity or by a propulsion device ( 10 G in  FIG. 2A ) in the tool  10 . It is also here illustrated that the tool performs scale or paraffin removal. 
         [0027]      FIG. 4  illustrates that one or both of the isolation valves 28  has been closed, so that well can be flowed at low rate with the tool  10  being in the wellbore. Scale or other deposit removal may then be started by operating the deposit removal device  10 A. When the tool  10  reaches the area of restriction caused by scale or paraffin, the tool  10  performs the removal of this restriction as explained above. As the deposits are removed and the flow restriction is alleviated, the tool  10  will by move further down into the wellbore by gravity (or by use of the propulsion device  10 G in  FIG. 2A , e.g., for highly inclined or horizontal wells) The tool  10  control and power module ( 10 F in  FIG. 2A ) may include an internal mechanism that detects length of free fall, e.g., integrating accelerometers or an integrating velocity meter and/or area with no unwanted restriction. The power and control module may be programmed to enable the tool  10  to stop itself, e.g., by energizing its swab cups ( 10 D in  FIG. 2A ), a mechanical breaking mechanism or the propulsion device ( 10 G in  FIG. 2A . 
         [0028]    A device preventing the tool  10  from going further into the wellbore than a selected depth may also be installed in the wellbore, for example, a narrow internal diameter packer or similar restriction. Such a device can be set up to trigger the power and control module ( 10 F in  FIG. 2A ) to cause the tool  10  to return the lubricator/system  22 . An example of such device may be a contact switch, shown at  13  in  FIG. 2A  which would not be triggered by scale or other deposits, but would be triggered by contact with a packer or similar internal diameter restriction. 
         [0029]      FIG. 5  illustrates that the tool  10  is transported up-hole, either by producing the well at low flow rate or by the propulsion device ( 10 G in  FIG. 2A ). The isolation valves  28  are opened to enable the tool  10  to enter the lubricator system  22 . 
         [0030]      FIG. 6  illustrates that the tool  10  has latched into the lubricator system  22  on the latch  22 E in the sealing cover  22 D. At such time the isolation valves  28  may be closed and the well brought back to normal production. The tool  10  is now coupled to the electrical coupler (part of latch  22 E) in the sealing cover  22 D so that the batteries ( 10 E in  FIG. 2A ) can be charged. In some embodiments it may be possible to retrieve logged data and transmit new commands to the tool  10  through the electrical connector  22 F. 
         [0031]    After the isolation valves  28  are closed, pressure inside the lubricator system  22  may be released using the pressure relief valve  24 . Such may be performed prior to any required removal of the sealing cap  22 D or the lubricator system  22  from the wellhead  20 . 
         [0032]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Summary:
An autonomously operated well intervention tool system includes a lubricator sealingly affixable to an upper end of a well. The lubricator has a latch at an upper end thereof. A well intervention tool system is releasably matable with the latch. The well intervention tool system comprises a wellbore intervention device at a longitudinal end thereof. The lubricator has at least one isolation valve to close fluid communication between the well and the lubricator.