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BACKGROUND OF THE INVENTION  
       [0001]     The present disclosure relates to the field of borehole drilling for the production of hydrocarbons from subsurface formations. In particular, the present disclosure relates to fishing operations to recover tool strings.  
         [0002]     An example of a fishing operation is the retrieval of a logging tool string that is stuck in a well. Logging tools may become stuck due to encounters with bridges, cave-ins, swelling formations, debris and the like. Often, an overshot device is used to enage the stuck tool string. During fishing operations, it is common practice to circulate mud or other substances down onto the stuck tools to clean the top of the fish that protrudes from the cable head of the tool string, and to determine when the overshot assembly engages the tool string. Typically, when the pump pressure increases, it is assumed that the pressure increase is due to the logging string being swallowed up by the fishing equipment overshot device. Currently, reconnecting the wireline during the fishing operation allows the logging engineer to monitor the down hole tension in order to determine when the drill string is pushing against the tool string and limit the weight that the driller puts down upon the tool string. In this way, the operator can recover the tool in a working condition and continue with the logging operation. It is important that the logging operation continue because the logging operation cost is based largely on the rig operation which is charged on an hourly basis and is generally quite expensive. Recovery of the tool reduces but does not eliminate the possibility that the tool string is dropped when the drill pipe is retrieved to the surface. The problem with the current state of affairs is that the tension increase that is seen by the logging engineer is only an indication that the drill string is pushing on the tool string. The tension increase is not, however, a complete indication that the overshot has actually swallowed the instrument itself or that the tool string is being engaged by the grapple within the overshot device. Instead, the tension increase could be the result of debris or other matter within the borehole itself that is preventing the instrument from being completely grappled by the overshot device.  
         [0003]     If the tool string is not properly engaged by the grapple, the tool string may be dropped while the drill pipe is being retrieved to the surface. Unfortunately, dropping the tool string is a familiar occurrence during fishing operations. The weight of the logging tool string is light by comparison to the drill string, and therefore the driller often does not sense the weight of the logging tool string on his weight indicator because it is so small in comparison to the rest of the equipment. Moreover, once the tool string is engaged, circulation is generally impossible or only possible when a pump out sub is run for the express purpose of providing circulation after the fish is engaged. In many cases it is not recommended to circulate because the possibility exists that the fishing neck of the tool string is not properly engaged and the circulation can push the tool string out of the fishing equipment and be lost once again downhole. There is, therefore, a need in the art for some mechanism to ensure proper engagement with the tool string with the overshot device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, wherein:  
         [0005]      FIG. 1  is an illustration of a downhole operation for hydrocarbon production.  
         [0006]      FIG. 1   a  is an illustration of a tool string that has become stuck or lost downhole.  
         [0007]      FIG. 2  illustrates a tool string.  
         [0008]      FIG. 3  is an exploded diagram of a overshot device.  
         [0009]      FIG. 4  illustrates a tool string with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0010]      FIG. 5  illustrates a tool string with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0011]      FIG. 6  illustrates an overshot device with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0012]      FIG. 7  illustrates an overshot device with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0013]      FIG. 8  illustrates an overshot device with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0014]      FIG. 9  illustrates an overshot device with an embodiment of the sensor according to the teachings of the present disclosure.  
         [0015]      FIG. 10  is a flowchart illustrating the operation of the apparatus according to the teachings of the present disclosure.  
         [0016]      FIG. 11  is a flowchart illustrating the operation of the apparatus according to the teachings of the present disclosure.  
     
    
       [0017]     While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION  
       [0018]     The present disclosure illustrates how shortcomings of the prior art may be overcome by providing an engagement sensor or a mechanical device that can be placed in the cable head of a logging tool string and/or the fishing equipment to allow the logging engineer and/or the pump operator to monitor the fishing operation. The mechanical devices or sensors can be used as an indicator that the overshot device has indeed swallowed the tool string, and/or that the grapple is properly engaging the tool string. The sensor disclosed herein can be positioned and/or designed to allow the engineer or the driller to monitor the fishing grapple, the swallowing of the tool string at one or more points during the swallowing process. In other words, the sensors and mechanical devices disclosed herein can be enhanced further to measure the amount of the tool string that the overshot device may be actually swallowing at one or more points of the swallowing process.  
         [0019]     The sensor disclosed herein can be a mechanical switch in the tool string that may be connected to a resistor or to a variable resistor to indicate the portion of tool string that may be being swallowed by the overshot device. In an alternate embodiment, the sensor could be a Hall effect sensor in the logging tool that indicates the increased presence of metal around the tool string body. In yet another alternate embodiment of the present disclosure, a mechanical setup may be designed such that when the overshot device swallows the tool string to the proper point, a switch or other mechanical device that may be fixed in the fishing equipment opens a circulation port that will cause the mud pumps to pulse or to exhibit some other significant fluctuation in pressure that may be detectable by the operator which will provide a positive indication to the operator that he has properly engaged the tool string. In yet another embodiment, an enhancement can be made to a hydro timer that, after a given time frame, would turn off the pulsing or other significant change mentioned previously, which can be interpreted as a further indication (or lack thereof) that the desired action has transpired.  
         [0020]     If the sensor in the tool string may be connected to a resistor or to a variable resistor, then the conductor within the wireline that the resistor may be in line with can be monitored with a meter on the surface so that the monitoring may be both safe and easy. Such an embodiment would be preferable to monitoring with a computer, either downhole or remotely, such as during the retrieval of a non-detonated perforating device. Such an embodiment would also provide the ability to monitor the operation on the rig floor without reconnecting the wireline. Finally, if a mechanical device is placed in the fishing equipment (such as the overshot device), the mechanical device can be used to fish for the tool string in situations where the wireline has been removed in order to speed the fishing operation, such as in Cased Hole operations.  
         [0021]     Other advantages of the method, system and apparatus disclosed herein include two or more or a combination of the following: (1) an increased level of safety; (2) for situations where the tool may be reconnected electrically, there will be the ability to monitor the downhole tension reading if the tension capability may be included in the logging tool string; (3) sensor data or a positive indication of engagement may be provided in real time; (4) positive indication of engagement of the logging tool string may be transmitted to and/or monitorable on the surface, thereby eliminating guesswork as to whether or not the overshot device may be swallowing the logging tool string rather than simply pushing on the sides or the top of the tools; (5) there may be a decreased possibility of dropping the tool string while retrieving the drill pipe to the surface; (6) no tension increase or decrease may be required to engage the tool string as there may be a positive indication that the overshot device and the tool string are engage—which will decrease the possibility of accidentally breaking the weak point in the string; (7) the decreased tension that may be required to engage the tool string made possible with the system disclosed herein will also reduce the damage to the logging tools that are incurred during the fishing operation, thereby prolonging tool life; (8) apparatus disclosed herein will also allow fishing equipment to be designed for better circulation capabilities, before and after engagement as the pressure increase and circulation loss will no longer be required to confirm that the overshot has properly swallowed the tool string; therefore, the circulation can be used for other purposes such as evacuation from the hole and other applications. The apparatus disclosed herein is in stark contrast to the current state of the art where circulation is limited after the overshot has swallowed the tool unless a pump out sub is incorporated into the fishing equipment. Embodiments disclosed herein obviate the need for the pump out sub.  
         [0022]     An explanation of the problem solved by the apparatus and methods described herein can begin with an illustration of the basic equipment used in downhole operations. As shown in  FIG. 1 , oil well drilling equipment  100  (simplified for ease of understanding) includes a derrick  105 , derrick floor  110 , draw works  115  (schematically represented by the drilling line and the traveling block), hook  120 , swivel  125 , kelly joint  130 , rotary table  135 , drill string  140 , drill collar  145 , and drill bit  155 . Mud is injected into the swivel by a mud supply line (not shown). The mud travels through the kelly joint  130 , drillpipe  140 , and drill collars  145 , and exits through jets or nozzles in the drill bit  155 . The mud then flows up the annulus between the drill string and the wall of the borehole  160 . A mud return line  165  returns mud from the borehole  160  and circulates it to a mud pit (not shown) and back to the mud supply line (not shown). The combination of the drill collar  145 , and drill bit  155  is known as the bottomhole assembly (or “BHA”). In rotary drilling the rotary table  135  may provide rotation to the drill string, or alternatively the drill string may be rotated via a top drive assembly. The term “couple” or “couples” used herein is intended to mean either an indirect or a direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect electrical connection via other devices and connections. Other equipment on the surface  101  may include a real-time processor  185  that can receive and process signals emanating from equipment downhole. Additional equipment, such as the computer  190  can be coupled to the surface real-time processor  185  in order to compute and/or display results of the information gathered downhole.  
         [0023]     It will be understood that the term “oil well drilling equipment” or “oil well drilling system” is not intended to limit the use of the equipment and processes described with those terms to drilling an oil well. The terms also encompass drilling natural gas wells, water wells, geothermal wells, or mineral evaluation wells and/or hydrocarbon wells in general. Further, such wells can be used for production, monitoring, or injection in relation to the recovery of hydrocarbons or other materials from the subsurface.  
         [0024]     Through accident or calamity, a tool string  200  (as well as the wireline) may become stuck or lost downhole.  FIG. 1   a  illustrates a tool string  200  that has been caught on a ledge  192  within a borehole  160 . Other perils for the tool string  200  are things such swelling clay  196  and debris  198 . Finally, high-pressure fluid flows  199  from or into the formation can cause fluid, debris and tool strings  200  to be buffeted within the borehole  160 .  
         [0025]     There are generally four ways that a tool string and/or a wireline can become stuck in a well. First, the tool string may become stuck in a bridge, a cave-in, or swelling formation. Second, the tool string may become stuck at a key seat where the tools, or most likely, the wireline digs into the formation. This latter scenario usually occurs when the well is kicked off or deviates dramatically in a soft formation. A third scenario where a tool string may become stuck is when there is a difference in pressure between the well bore and the formation. The pressure difference occurs when the pressure from the well bore is trying to force the fluid out into the formation, and this may trap either the tools or the wireline by forcing them up against the side usually in a depleted zone that is permeable. A fourth way that the tool string  200  may become stuck is when the downhole tools or an accessory become hung up on a ledge or the bottom of the casing or tubing. Closing the calipers in the tool string may help in this situation, but that technique may not be successful.  
         [0026]     In an open hole, the following conditions can cause the tool or cable to become stuck: debris on the well bottom; mechanical keyseating of the cable at a dogleg in the borehole; split or damaged casing shoe; knotted, birdcaged, or broken cable strands; differential pressure acting on the cable, bridle, tool, or possibly all three, especially across depleted zones; and/or restricted hole size or bridge in the borehole can cause the toolstring to become wedged at the head.  
         [0027]     In a cased hole, the following conditions can cause the tool or cable to become stuck: collapsed or damaged pipe; entry into a reduced pipe size; soft cement; sand flow; excessive logging speeds for hole conditions; tool size exceeding limitations for casing size or conditions; differential pressure sticking opposite perforations or casing; leaks; knotted, birdcaged, or broken cable strands; debris in the well; cable damage by the upthrust of a perforating gun or head resulting from detonation in low hydrostatic pressure; and/or wedging into packers, plugs, and landing nipples.  
         [0028]     The most common problem for fishing in an open hole is when depleted reservoirs “suck” the tools or wireline into the side due to the differential pressure between the borehole and the formation. This can also occur when equipment employs very heavy drilling mud and the borehole is over pressured in comparison to the formation pressure.  
         [0029]     In a cased hole, the most common reason for tools and wirelines becoming stuck is through tubing perforating jobs, where the gun swells or deforms and the gun cannot get back into the bottom of the tubing.  
         [0030]     A typical logging tool string may be illustrated in  FIG. 2 . The tool string  200  can be composed of three main segments. The first segment can be the instrument  206 , which can contain any number of sensors and/or instruments for measuring downhole (or anywhere along the hole). The second segment can be the cable head  204 , which can be positioned between the instrument  206  and the fishing neck  202 . The fishing neck  202  may (or may not if it has been removed) have a cable line  201  that runs from the tool string  200  to the surface  101 . In typical tool strings  200 , there is a tapered shoulder  203  between the fishing neck  202  and the cable head  204 , as illustrated in  FIG. 2 . Although the shoulder  203  is shown as tapered, non-tapered shoulders can be used with the appratus contemplated herein.  
         [0031]     The instrument  206  typically (although not always) has the largest outside diameter (“o.d.”) of any of the segments. The o.d. of the tool string  200  may be the defining factor in selecting the inside diameter (“i.d”) of the overshot device  300 , because in many cases, it can be desirable for at least part of the tool string  200  to fit within the overshot device  300 , and thus the i.d. of the overshot device  300  should be large enough to accommodate the o.d. of the portion of the tool string  200  that is expected to be swallowed by the overshot device  300 . If it is desirable for the overshot device  300  to swallow part of the tool string  200 , then the length of the overshot device  300  should be long enough to accommodate the length of the tool string  200  to be swallowed. The i.d. of the borehole  160  may limit the o.d. of the overshot device  300 , which may limit the part of the tool string  200  that can be swallowed by the overshot device  300  up to the cable head  204  or up to the fishing neck  202 .  
         [0032]     An overshot device can be illustrated in  FIG. 3 . The overshot device  300  can contain one or more parts, as illustrated in  FIG. 3 . In this illustrative example, the overshot device  300  can be composed of a top sub  302 , a bushing  304 , a bowl  306  that has a distal end  305  that can be threadably engaged with the top sub  302 , although other types of engagement is besides threading is possible. Within the postal end  307  of the bowl  306  are placed a packer seat ring  308 , a grapple  310  (used to retain the tool string  200 ), a grapple control  312  (used to activate or deactivate the grapple  310 ), and a guide  314 . In operation, the bottomhole assembly ( FIG. 1 ) can be removed and may be replaced by the overshot device  300 . The overshot device  300  can be oriented so that the guide  314  can be used to guide the fishing neck  202  into the overshot device  300  during the fishing operation. In many cases, the overshot device  300  can be hollow to allow the cable  201  to run contiguously from the tool string  200  to the surface  101 . Moreover, the overshot device  300  has a hollow section at one end (in proximity to the grapple  310 ) to accommodate the tool string  200 .  
         [0033]      FIG. 4  illustrates an embodiment of the present disclosure. This embodiment of the tool string  200  includes a sensor  402 . The sensor  402  can be a mechanical switch that engages an internal shoulder of the overshot device  300  when the tool string  200  can be swallowed to the desired amount. When the sensor  402  is depressed (by the shoulder within the overshot device  300 ), a signal can be passed up through the wire cable  201  to the operator on the surface to inform him that the tool string  200  is properly engaged within the overshot device  300 .  
         [0034]      FIG. 5  illustrates an embodiment of the present disclosure. The embodiment of  FIG. 5  has the sensor  502  on the fishing neck  202 . The sensor  502  in this embodiment can be a Hall effect sensor that indicates the presence of metal around the tool string  200 . The sensor  502  has the advantage of being able to be placed flush with the local surface of the local tool string  200  so that debris (or another part of the overshot device  300 ) do not prematurely trip the sensor  502  as may happen with the sensor  402 . Moreover, the sensor  502 , because it can be flush-mounted, may be placed anywhere along the tool string  200 . For example, the sensor  502   a  can be placed within of the tool string  200 , and would only be triggered (provide a positive indication) if the tool string  200  were swallowed to a particular point by the overshot device  300 . Similarly, multiple sensors  502  could be mounted onto the tool string  200  along the fishing neck  202 , the shoulder  203 , the cable head  204  and the instrument  206  to provide a better indication to the operator of the progress of the fishing operation (as sequential sensors would provide positive indications as the overshot device  300  swallows the tool string  200 . As with the previous embodiment, the sensors  502  can send their positive (or negative) indicator signals through the cable  201  to, for example, the computer  190  for processing and display to the operator.  
         [0035]      FIG. 6  illustrates an embodiment where a valve  602  can be placed on the overshot device  300 . The valve  602  allows the circulation (of mud, etc.) from the overshot device  300  to the downhole environment. Moreover, the valve  602  can be positioned in proximity to the shoulder  604  of the overshot device  300 . When the tool string  200  is brought up into the overshot device  300 , the fishing neck can be pulled through the orifice  606  of the shoulder  604  until the shoulder  203  of the tool string  200  engages the shoulder  604  of the overshot device  300 . A mechanical setup on the overshot device  300  and/or the tool string  200  can be provided to activate when the overshot device  300  swallows the tool string  200  to the proper point (such as when the shoulders  203  and  604  engage). Upon activation, a switch or other mechanical device that can be fixed in the fishing equipment opens a circulation port  602  that will cause the mud pumps (not shown) to pulse or to exhibit some other significant fluctuation in pressure that can be detectable by the operator. Depending upon how the circulation pulse is arranged, the valve  602  may be opened (to relieve the pressure of the circulation pulse that can no longer exit because of the presence of the tool string  200 ), or closed (because the circulation pulse can no longer exit the overshot device  300  via the orifice  606 ). The open or closed position of the valve  602  can be detected and an appropriate signal sent toward the surface  101  for processing and/or display to the operator. The pulse or fluctuation in pressure can provide a positive indication to the operator that he has properly engaged the tool string  200 .  
         [0036]      FIG. 7  illustrates an embodiment of the overshot device  300  that can be fitted with a circulation port  702 . The circulation port  702  can, in one embodiment, be fitted with a membrane. The membrane acts as a safety valve. When the tool string  200  is swallowed by the overshot device  300  (to the point where the shoulders  203  and  604  engage), then the circulation fluid driven through the overshot device  300  can be trapped, with a corresponding pressure increase within the overshot device  300 . The pressure increase may be detectable by instruments within the overshot device  300 . Moreover, the membrane of the circulation port  702  can be constructed and arranged to burst at a predesignated pressure that may also be detected by instruments within the overshot device  300 . Appropriate signals corresponding to the pressure measurements may be sent to the surface  101  for processing and/or display to the operator.  
         [0037]      FIG. 8  illustrates an embodiment where a sensor  802  can be placed onto the engagement side  806  of the shoulder  804 . In this embodiment, the sensor  802  can be engaged when the shoulder  203  of the tool string  200  can be engaged with the engagement side  806  of the shoulder  804 , the sensor  802  is depressed, which can trigger an appropriate signal to the surface  101  for monitoring by the operator. In one embodiment, the sensor  802  can be a mechanical switch. In another embodiment, the sensor  802  can be, for example, a Hall effect sensor, that can be triggered for positive indication only when the proximity of the shoulder  203  of the tool string  200  can be within a preselected tolerance. Other types of sensors  802  can be used with equal effect so long as they provide a positive (or negative) indication of the presence of the tool string  200 .  
         [0038]      FIG. 9  illustrates an embodiment where there are multiple sensors  902  positioned along the overshot device  300 . In this embodiment, as the tool string  200  can be swallowed by the overshot device  300 , the sensors  902  detect the presence of the tool string  200  (by, for example, magnetically, or by the Hall effect, or some similar manner) at various locations during the swallowing procedure. As the tool string  200  can be successively swallowed by the overshot tool  300 , the signals from each individual sensor  902  will sequentially provide a positive indication of the progression of the tool string  200  into the overshot device  300 . The advantage of this embodiment is that the swallowing procedure can be monitored more closely by the operator as the sensors  902  send successive positive signals to the surface  101 . Thus the operator can have a better indication of just how close the shoulder  203  of the tool string  200  can be to mating with the shoulder  604  of the overshot device  300 .  
         [0039]     It should be noted that, while  FIGS. 7, 8  and  9  illustrate single sensor systems, the device disclosed herein may make use of multiple sensors, in any combination. The use of multiple sensors may be desirable in situations where the reliability of one sensor combination is not sufficient, or if lack of power in a particular borehole precludes the use of one of the sensor packages.  
         [0040]      FIG. 10  illustrates the method  1000  of using the apparatus described above. The method begins generally at step  1002 . If the overshot device  300  is not already in place, the bottom hole assembly can be replaced with the overshot device  300  in step  1004 . The overshot device  300  can then be placed downhole, in step  1006 , in proximity to the location of the lost or stuck tool string  200 . Once the overshot device  300  is in position, in step  1008 , the overshot device  300  can begin swallowing the tool string  200 . In step  1010 , the overshot device  300  swallows the tool string  200 . In one embodiment disclosed of step  1010 , herein, the sensor or mechanical device that indicates positive engagement will activate only when the tool string  200  is engaged the overshot device  300  at the final position (i.e., ready to pull up to the surface  101 ). In other embodiments of step  1010 , multiple sensors or mechanical devices on the tool string  200  and/or the overshot device  300  activate at successive (perhaps even or uneven) intervals to indicate the position of the tool string  200  within the overshot device  300  at various points along the swallowing process and the method ends generally at step  1012 . The latter embodiment provides the operator with a better indication of the progress of the method disclosed herein.  
         [0041]      FIG. 11  illustrates an alternate method  1100  of using the apparatus described above. The method begins generally at step  1102 . If the overshot device  300  is not already in place, the bottom hole assembly can be replaced with the overshot device  300  in step  1104 . The overshot device  300  can then be placed downhole, in step  1106 , in proximity to the location of the lost or stuck tool string  200 . Once the overshot device  300  is in position, in step  1108 , the overshot device  300  can begin swallowing the tool string  200 . In step  1110 , a decision is made whether to reconnect the wireline. If the wireline is to be reconnected (e.g., the answer to step  1110  is “yes”), then the tool string  200  can be reconnected to the wireline in step  1112 . In either case, in one embodiment of step  1114 , the sensor or mechanical device that indicates positive engagement will activate only when the tool string  200  is engaged the overshot device  300  at the final position (i.e., ready to pull up to the surface  101 ), an activity which may be monitored by human and/or electromechanical means. In other embodiments of step  1114 , multiple sensors or mechanical devices on the tool string  200  and/or the overshot device  300  activate at successive (perhaps even or uneven) intervals to indicate the position of the tool string  200  within the overshot device  300  at various points along the swallowing process and the method ends generally at step  1116 . The latter embodiment provides the operator with a better indication of the progress of the method disclosed herein.  
         [0042]     The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. The foregoing description is not intended to be exhaustive, or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Summary:
A method and apparatus are provided for enabling reliable retrieval of instrumentation packages from downhole locations. The tool string and/or the overshot device of the drill pipe can be fitted with a variety of mechanical, electrical, and/or magnetic sensors at one or more locations to enable monitoring of the capture process. Such monitoring enables the secure capture of the instrumentation package as well as retrieval of the instrument package to the surface with minimal damage to the instrumentation package, the overshot drill pipe, and any cables involved.