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BACKGROUND 
       [0001]    In a variety of well related operations, tools are used to carry out desired tasks at downhole locations. For example, different types of tools are used to drill wellbores, to deploy tubing and other equipment downhole, to perform testing operations, and to conduct servicing operations. During these operations, a tool occasionally becomes stuck in the wellbore or disconnected from its conveyance. If the tool is stuck in the wellbore, the tool can be cut free to enable retrieval of the conveyance and other downhole equipment. 
         [0002]    To retrieve the tool left downhole, a fishing operation is conducted in which a fishing tool is deployed downhole from a surface rig. The fishing tool comprises a latching or attachment end designed to engage the tool, i.e. fish, to be retrieved. However, attachment of the fish can occur deep within the wellbore which makes it difficult to determine whether the fishing tool has contacted and adequately engaged the fish. Many hours of rig time can be wasted in withdrawing the fishing tool to discover the fishing expedition was not successful. 
       SUMMARY 
       [0003]    In general, the present invention provides a system and method to verify attachment of a fishing tool with a fish. The fishing tool comprises a latching mechanism to latch onto the fish to be retrieved and a detection device to verify connection of the latching mechanism. The detection device provides a signal uphole to verify attachment of the fish. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0005]      FIG. 1  is a front elevation view of a fishing tool system being deployed into a wellbore, according to an embodiment of the present invention; 
           [0006]      FIG. 2  is a front elevation view similar to that of  FIG. 1  but showing the fishing tool engaged with a fish, according to an embodiment of the present invention; 
           [0007]      FIG. 3  is a front elevation view similar to that of  FIG. 1  and also showing a communication system for communicating signals uphole, according to an embodiment of the present invention; and 
           [0008]      FIG. 4  is a front elevation view showing an alternate communication system, according to an alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0010]    The present invention relates to a system and methodology for performing a fishing operation. The system and methodology are used to provide an indicator as to when a well tool, i.e. fish, is engaged with the fishing tool. The indicator may be in the form of a signal provided uphole when the fishing tool is engaged with the fish. The signal also can be continually provided uphole while the fish is pulled from the well to inform an operator that the fish remains attached to the fishing tool. The ability to provide this indication to an operator helps avoid withdrawal of the fishing tool without the fish being attached, thus preventing wasted rig time. 
         [0011]    In one embodiment, a fishing tool is deployed downhole into a wellbore via a conveyance, such as a coiled tubing fishing tool conveyance. However, other types of conveyances, including drill string, wireline and other conveyance mechanisms, can be used. The fishing tool usually is deployed downhole through a tubing, such as a casing or a production tubing positioned within the casing. The fishing tool comprises a latching mechanism for engaging and gripping the fish and a cooperating detection device that is able to provide, e.g. transmit, a signal uphole indicating the latching mechanism has engaged or latched onto the fish. A signal can be sent uphole to an operator to indicate full engagement of the fishing tool with the fish, and this signal also can be provided during withdrawal of the fish to indicate continued attachment of the fish to the fishing tool. Depending on the type of detection device used, the signal can be an individual signal, a constant signal, or an intermittent signal. 
         [0012]    Referring generally to in  FIG. 1 , one example of a well system  20  is illustrated according to an embodiment of the present invention. In this example, well system  20  comprises a fishing tool  22  that is being delivered downhole into a well via a conveyance  24 , such as a coiled tubing conveyance or other suitable conveyance. The fishing tool  22  is moved downhole towards a well tool  26 , i.e. fish, which is to be retrieved. 
         [0013]    The fishing tool  22  is moved downwardly along a wellbore  28  and often down through a tubing  30 , such as a well casing. In other applications, tubing  30  may comprise production tubing or other tubing positioned in wellbore  28 , often within a surrounding casing. Fishing tool  22  is appropriately sized for movement through the tubing as necessary for a given application. As illustrated in  FIG. 1 , wellbore  28  extends down from surface equipment  32  positioned at a surface location  34 . Surface equipment  32  may comprise a rig for deploying fishing tool  22  and conveyance  24 . 
         [0014]    In the embodiment illustrated, fishing tool  22  comprises a latching mechanism  36  designed for attachment with fish  26  when moved into engagement with fish  26 , as illustrated in  FIG. 2 . The design of latching mechanism  36  can vary according to the application and according to the type of well tool/fish to be retrieved within wellbore  28 . For example, latching mechanism  36  can be designed to engage the fish  26  internally or externally. Additionally, latching mechanism  36  may have various configurations and components that allow fishing tool  22  to be latched onto specific types of well tools. 
         [0015]    Fishing tool  22  further comprises a detection device  38  positioned to detect when fishing tool  22  has latched onto fish  26  and to provide an appropriate signal uphole indicating the attachment. By way of example, detection device  38  may comprise a switch  40 , such as a contact switch, appropriately positioned so that it is automatically switched upon full engagement of fishing tool  22  with fish  26 . The detection device  38  is then able to output a signal uphole indicating fishing tool  22  has been latched onto fish  26 . By way of example, the detection device  38  may be a powered device able to output the signal, or the detection device  38  can simply be used to complete a circuit that extends uphole to the surface location  34 . 
         [0016]    In the embodiment illustrated in  FIG. 3 , for example, fishing tool  22  is a “smart” tool coupled with a surface display system  42  via a communication line  44 . Surface display system  42  may be part of an overall control system utilized in conducting the fishing operation. According to one example, communication line  44  is a hardwired line designed to carry signals from detection device  38  to display system  42 . For example, communication line  44  may comprise an electrical line for carrying an electrical signal uphole from detection device  38 . Alternatively, communication line  44  may comprise an optical fiber or optical communication line able to carry optical signals uphole from detection device  38 . The hardwired communication line  44  can be routed along conveyance  24 . If conveyance  24  comprises a coiled tubing conveyance, the communication line  44  can be secured along the coiled tubing or routed within a wall of the coiled tubing. In other applications, communication line  44  may comprise a wireless communication line. 
         [0017]    Regardless of the specific type of communication line  44 , detection device  38  may be a constant signal device able to output or convey a constant signal to display system  42  while fishing tool  22  is attached to fish  26 . By way of example, detection device  38  may comprise contact switch  40  that is switched upon full engagement of the fishing tool  22  with the fish  26  to enable transmission of a constant signal during the attachment. Thus, an operator is provided with an indication that the fish  26  remains attached during the entire retrieval process as the fish is withdrawn from wellbore  28 . 
         [0018]    In alternate embodiments, the detection device  38  may be of a design that enables output of the signal only upon initial engagement of fishing tool  22  with fish  26 . Other designs enable the detection device  38  to provide periodic or intermittent signals uphole indicating retention of the fish  26 . This latter approach can be useful when the fishing tool  22  is not a smart tool and does not have an electrical line or fiber-optic cable extending to the surface. 
         [0019]    As illustrated in  FIG. 4 , for example, detection device  38  may comprise a pressure device able to output an individual or multiple pressure pulses that do not require a hardwired communication line extending between the fishing tool  22  and the surface. The pressure pulses are delivered uphole along an interior of conveyance  24 , as indicated by arrows  46 , or along an annulus surrounding conveyance  24 , as indicated by arrows  48 . By way of example, this embodiment of detection device  38  may comprise a valve  50  that actuates to provide a pressure response upon engagement of the fishing tool  22  with the fish  26 . The valve  50  may be a pressure inducing or pressure indicating valve actuated mechanically upon engagement of the fishing tool  22  with the fish  26 , or the valve  50  can be actuated by another source of energy. For example, valve  50  can comprise a solenoid actuated valve or otherwise actuated valve that is activated upon attachment of the fish  26 . 
         [0020]    The system and methodology can be used to provide an operator with better information during a fishing operation. Knowledge of the status of the well tool fished from a downhole location enables more consistent and efficient fishing operations. It should be noted that the specific size, configuration and components of the fishing tool  22  can vary according to the environment and according to the type of tool that is to be fished from the wellbore. Furthermore, the configuration of the detection device also can vary according to the desired signal output, available communication lines, environment, and other factors that affect the overall operation. 
         [0021]    Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.

Summary:
A technique provides a system and method to verify attachment of a fishing tool with a downhole well tool. The fishing tool comprises a latching mechanism that latches onto the well tool to be retrieved. The fishing tool also comprises a detection device to verify connection of the latching mechanism. The detection device provides a signal uphole to verify attachment to the well tool.