Abstract:
A connector latch includes a housing body having an internal cavity, a grippable member slidably coupled to the housing body, and a hydraulic mechanism on the housing body for delaying sliding of the housing body relative to the grippable member when an external force is applied to the housing body.

Description:
BACKGROUND OF INVENTION 
     The invention relates to methods and apparatus for making electrical connections in remote locations, e.g., inside an oil well. More specifically, the invention relates to a mechanical latch for connecting two mating parts of an electrical connector. 
     When a well is drilled, it is common to survey, or “log,” certain sections of the well. Well logging involves obtaining and recording data related to one or more characteristics of the formations penetrated by the well. Many types of logs, e.g. mechanical, acoustic, electric, and radioactivity, can be made using appropriate logging tools. In wireline logging, the logging tools are deployed into the well by means of an armored electrical cable, or wireline, wound on the drum of a winch. The logging tools make measurements at selected depths of the well and send signals to a logging unit at the earth&#39;s surface through the cable. With the aid of gravity, the logging tools can be lowered into vertical wells by simply unwinding the cable from the winch drum. In horizontal or highly-deviated wells, however, gravity is frequently insufficient to move the logging tools to the depths to be logged. In these situations, it is sometimes necessary to push the logging tools along the well with drill pipe, coiled tubing or the like. 
     Wireline logging with drill pipe is complicated by the presence of the cable. It is cumbersome and dangerous to string the cable through all of the drill pipe before lowering the logging tool into the well. Some deployment systems have therefore been developed, such as one offered under the trade name Tough Logging Conditions System (TLCS) by Schlumberger Technology Corporation, Houston, Tex., which allow an electrical connection to be made between the logging tool and the cable after the logging tool has been lowered to the desired depth in the well. In these deployment systems, the logging tool is deployed with standard drill pipe. Then, the cable is run through the drill pipe and connected to the logging tool. After logging, the cable is detached from the logging tool and removed before the logging tool is retrieved. 
     In the TLCS and other deployment systems, the cable is remotely connected to the logging tool using a downhole connector. One mating part of the connector is mounted inside a docking head, which is attached to the logging tool. The logging tool is then lowered into the well on drill pipe. The other mating part of the connector is mounted in a pump-down head, which is attached to the end of the cable. The pump-down head is forced down the drill pipe with a flow of fluid, such as drilling mud, that circulates out of holes at the bottom of the drill pipe and into the well. An electrical connection is established when the mating parts come in contact. This connection is typically referred to as a “wet connection” because it is made in the flow of fluid, which is often conductive and challenges the reliability of the electrical connection. A mechanical latch joins the mating parts together and maintains the integrity of the joint during the logging operation. In most systems, the latching is established using the kinetic energy of the pump-down head that is pushed down by the circulating fluid. At the completion of the logging operation, the pump-down connector head is unlatched from the docking head, allowing the cable to be pulled out of the drill pipe. The pump-down head is usually unlatched from the docking head by pulling on the cable with a predetermined amount of tension. 
     In deeper wells, it becomes more difficult to meet all functional requirements for the mechanical latch. In particular, existing wet connector latch mechanisms do not meet two conflicting requirements for the strength of the mechanical latch. On one hand, the tensile force available for unlatching at the pump-down head diminishes quickly with depth and well curvature due to friction between the cable and the drill pipe and the weight of the cable itself. Thus, a weak latch that can be easily released is required under these conditions. On the other hand, pushing the pipe down into a deep and/or highly-deviated well is often characterized by stick and slip motion of the drill pipe. This uneven motion creates very short-lived, but high-amplitude, forces on the mechanical latch because the pipe motion and cable motion do not correspond. In order to avoid accidental unlatching due to these forces, the latch has to be strong. 
     Mechanical latches for downhole wet connectors have been disclosed and are commercially available. U.S. Pat. No. 5,967,816 issued to Sampa et al. discloses a latch mechanism which includes a three-finger latch collet and a latch ring. The latch collet is attached to the docking head, while the latch ring is part of the pump-down head. During latching, the latch ring forces the fingers open and passes through the collet. The fingers then close behind the ring, preventing the pump-down head from separating from the docking head. The unlatching is conducted by applying tension to the logging cable. When this force is strong enough to exceed the yield strength of the ring material at the points of contact, the fingers break loose, destroying a portion of the ring. The mechanism has the advantages of simplicity and reliability and has been very successful commercially. In addition, its release forces are highly predictable. Different levels of force can be achieved by varying the strength of the latch ring. However, the number of latch/unlatch cycles is limited because the ring suffers substantial damage every time it is unlatched. Further, the unlatching force is constant and cannot be adjusted once the latch is downhole. Hence this mechanism reaches the limit of its usefulness at a certain well depth. 
     U.S. Pat. No. 4,799,546 issued to Hensley et al. and U.S. Pat. No. 4,700,778 issued to Smith et al. disclose latch mechanisms based on J-shaped slots, or J-slots. These latch mechanisms typically include protrusions on one mating part of the connector and J-slots cut in the other mating part of the connector. One mating part of the connector is attached to the pump-down head, while the other mating part is mounted in the docking head. During latching, the protrusions engage the J-slots and then slide along them, forcing the pump-down head to rotate a predetermined amount. At the end of the travel, a spring pushes back the mating part containing the protrusions. The shape of the J-slots prevent the protrusions from traveling back along the same path. Instead, the protrusions are forced towards a different section of the J-slot, thus locking the two mating parts of the connector together. The protrusions can be separated from the J-slots by either tensioning and slackening of the cable or by pushing the pump-down head down. This forces the protrusions to travel along a third section of the J-slot, which frees the protrusions from the J-slots and allows the pump-down head to be separated from the docking head. The advantage of the J-slot system is that it allows multiple latch/unlatch cycles. Another advantage is that no elements of the system are destroyed, and there is no risk of leaving debris in the well. The system is relatively complex, however, and there is a higher risk of accidentally unlatching due to an unintended pull on the cable caused, for example, by stick-slip motion of the drill pipe. 
     U.S. Pat. No. 5,058,683 issued to Godfrey et al. discloses a J-slot latch mechanism that has reduced risk of accidental unlatching. In this mechanism, the shape of the J-slot is modified such that multiple tensioning and slackening cycles on the cable are required before the latch is released. This mechanism, however, does not completely eliminate the occurrence of an accidental unlatch. The Godfrey et al. patent also discloses an electrically activated wet connector latch which uses electromagnetic devices to create the force holding the two mating parts of the wet connector together. This connector has many potential advantages, the most important of which is that the latch can be controlled remotely. However, this latch mechanism has not received wide commercial acceptance due to its complexity, difficulties with downhole power supplies, and safety concerns, especially when the tool string contains perforating guns. 
     U.S. Pat. No. 5,158,142 issued to Miszewski et al. discloses an apparatus for releasing a pipe string from an object stuck downhole. This apparatus uses a hydraulic time-delay mechanism that selectively releases only when a predetermined tension is applied to the pipe string for a predetermined amount of time. This mechanism does not release under accidental high tensile loads, such as those that may result from shooting perforating guns. However, the mechanism releases when a much smaller tensile force is applied for much longer periods of time. This mechanism is not suitable for wet connectors because it cannot latch, it only releases. Hence, it can only be used once, and the mechanical connection has to be established in some other way. 
     Therefore, what is needed is a latch mechanism for electrical connectors which can be easily released, does not accidentally unlatch, and has multiple latch/unlatch cycles. 
     SUMMARY OF INVENTION 
     In one aspect, the invention relates to a connector latch which comprises a housing body having an internal cavity, a grippable member slidably coupled to the housing body, and a hydraulic mechanism on the housing body for delaying sliding of the housing body relative to the grippable member when an external force is applied to the housing body. 
     In another aspect, the invention relates to a connector latch which comprises a housing body having an internal cavity, a grippable member slidably coupled to the housing body, a gripping member for selectively engaging the grippable member, and a hydraulic mechanism on the housing body for delaying sliding of the housing body relative to the grippable member when an external force is applied to the housing body. 
     In another aspect, the invention relates to a connector latch which comprises a housing body having an internal cavity, a grippable member slidably coupled to the housing body, a sealed chamber defined within the internal cavity, the sealed chamber having a volume which varies with relative movement between the housing body and the grippable member, and a flow restriction for controllably releasing fluid from the sealed chamber to the internal cavity as the volume of the sealed chamber decreases. 
     In another aspect, the invention relates to a mechanical latch for connecting two mating parts of an electrical connector which comprises a housing body having an internal cavity, a grippable member slidably coupled to the housing body and attached to one of the mating parts, a gripping member adapted to selectively engage the grippable member and attached to the other mating part, and a hydraulic mechanism on the housing body for delaying movement of the housing body relative to the grippable member when an external force is applied to the housing body. 
     In another aspect, the invention relates to a method for connecting and selectively disconnecting a gripping member. The method comprises lowering a tool comprising a grippable member to the gripping member, bringing the grippable member in contact with the gripping member, pushing the gripping member against the grippable member until the gripping member engages the grippable member, and applying a tension to the tool for a duration determined by a hydraulic time-delay mechanism in the tool, and moving the tool relative to the gripping member to release the grippable member. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIGS. 1A-1D show a cross-section of a wet connector latch according to one embodiment of the invention. 
     FIG. 2 is a three-dimensional view of the latch collet shown in FIG.  1 D. 
     FIG. 3A shows the wet connector latch prior to latching. 
     FIG. 3B shows the beginning phase of the wet connector latching process. 
     FIG. 3C shows the wet connector latch in the latched position. 
     FIG. 3D shows the beginning phase of the wet connector unlatching process. 
     FIG. 3E shows the wet connector latch in an unlatched position. 
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention provide a wet connector latch for mechanically joining two mating parts. In general, the invention includes a latch collet, an inner and outer body, a pre-load spring, and a hydraulic time-delay system. The latch collet is attached to one of the mating parts, while all other elements of the wet connector latch are attached to the other mating part. The latch collet and the inner body engage to provide a mechanical latch between the two mating parts. The time-delay system comprises a fluid-filled chamber and means for controllably releasing fluid from the chamber. To separate the mating parts, a force is applied to the outer body. If the force is larger than the force necessary to compress the spring, the outer body starts to slide relative to the inner latch body. This movement reduces the volume of the chamber and causes the pressure of the fluid inside the chamber to increase. The pressurized fluid is slowly squeezed out through components of the time-delay system. The time-delay system ensures that the latch does not release unless a force with a predetermined magnitude is applied for a predetermined amount of time. As the outer body travels a predetermined distance with respect to the inner body, it engages the latch collet and forces the latch collet to release the inner body. At this point, the mechanical coupling between the two mating parts is released. 
     Various embodiments of the invention will now be described with reference to the accompanying drawings. FIG. 1A shows a partial cross-sectional view of a wet connector latch, generally indicated by reference numeral  2 , according to one embodiment of the invention. FIG. 1B is a continuation of the drawing of FIG. 1A, FIG. 1C is a continuation of the drawing of FIG. 1B, and FIG. 1D is a continuation of the drawing of FIG.  1 C. The wet connector latch  2  comprises a pump-down head  4  and a latch collet ( 6  in FIG.  1 D). The pump-down head  4  includes an outer latch body  8  and an inner latch body ( 10  in FIG.  1 B). The outer latch body  8  and the inner latch body ( 10  in FIG. 1B) enclose the elements of a time-delay system, generally indicated by reference numeral  11  in FIG.  1 B. 
     Referring to FIG. 1A, the outer latch body  8  includes an upper head  12 , a pressure chamber body  14 , and an outer housing weldment ( 16  in FIG.  1 B). The upper head  12  includes a feedthrough  18 . The upper head  12  is attached to the upper end of the pressure chamber body  14 . A bulkhead connector  20  is mounted at the upper end of the pressure chamber body  14 . The bulkhead connector  20  and the feedthrough  18  allow electrical connection between the wires (not shown) inside the pump-down head  4  and an external cable (not shown). As shown in FIG. 1B, the lower end of the pressure chamber body  14  is connected to the outer housing weldment  16  by a threaded ring  22 . Static seal  24  prevents fluid from entering this joint. 
     Still referring to FIG. 1B, the inner latch body  10  includes a piston  26 , a mud/oil crossover  28 , a wire mandrel  30 , a female connector housing ( 32  in FIG.  1 D), a latch ring ( 34  in FIG.  1 D), a clamp ( 36  in FIG.  1 D), and a protective sleeve ( 38  in FIG.  1 D). The piston  26  is located within the pressure chamber body  14  and is movable relative to the pressure chamber body  14 . A chamber  42  is defined between the piston  26  and the pressure chamber body  14 . The piston  26  carries a hydraulic restriction  44 , such as an orifice, a check valve  46 , and a dynamic seal  48 . A seal cartridge  50  is mounted at the lower end of the pressure chamber body  14 . The seal cartridge  50  holds dynamic seals  52 . The dynamic seals  48 ,  52  isolate the chamber  42  from the rest of the internal volume of the pump-down head  4 . The chamber  42  is filled with a substantially incompressible fluid, typically oil. The pressure chamber body  14  preferably includes a port  37  through which fluid can be supplied to the chamber  42 . The port  37  is sealed with a plug  39  when not in use. 
     The piston  26  has a bore  40  through which fluid can be communicated to a space  43  above the chamber  42 . Fluid in the space  43  can flow into the chamber  42  through the check valve  46 . A pre-load spring  54  is located inside the chamber  42 . When the spring  54  is compressed, fluid is squeezed out of the chamber  42  through the hydraulic restriction  44 . The fluid-filled, sealed chamber  42  and the hydraulic restriction  44  form part of the time-delay system  11 . Another element of the time-delay system  11  is a flooding valve  45  located in the mud/oil crossover  28 . The purpose of the flooding valve  45  will be explained later. The pre-load on the spring  54  can be adjusted by a nut  56  threaded to the lower end of the piston  26 . The pre-load spring  54  exerts a force on a surface  58  of the nut  56 , bringing the surface  58  against a surface  60  of the pressure chamber body  14 . The force of the spring  54  is sufficient to prevent relative movement between the inner latch body  10  and the outer latch body  8  during latching. A threaded ring  62  connects the lower end of the piston  26  to the mud/oil crossover  28 . The mud/oil crossover  28  is welded to the wire mandrel  30 . 
     Referring to FIG. 1D, the wire mandrel  30  is connected to the female connector housing  32  by shear blocks  64 . The female connector housing  32  carries female contacts  66 . The female contacts  66  are connected to wires (not shown) that run along the pump-down head ( 4  in FIG.  1 A). An insulating shuttle  68  is disposed in a cavity  62  in the female connector housing  32 . The insulating shuttle  68  prevents any electrical communication between the female contacts  66 . The shuttle  68  is biased downwardly by a spring  70 , which causes an internal grip  69  of the shuttle  68  to engage a dynamic seal  72 . The dynamic seal  72  and seals ( 74 ,  76  in FIG. 1B) isolate the internal volume of the pump-down head  4  from external fluid during latching and unlatching. 
     The protective sleeve  38  is mounted on the female connector housing  32 . Attached to the upper end of the protective sleeve  38  is the clamp  36 , which holds the latch ring  34 . The latch ring  34 , clamp  36 , and protective sleeve  38  are the parts of the pump-down head  4  that are engaged by the latch collet  6  when the wet connector latch  2  is in the latched position. The latch collet  6  includes a base  78  with openings ( 80  in FIG.  2 ). The openings ( 80  in FIG. 2) are for circulating fluid flow out of the latch collet  6 . Flexible latch fingers  82  (also shown in FIG. 2) are joined together at the base  78 . The latch fingers  82  are shaped so as to form a latching surface  84 , an unlatching surface  86 , and a holding surface  88 . During latching, the slanted surface  90  of the protective sleeve  38  slides against the latching surface  84  and pushes the latch fingers  82  outward. This allows the pump-down head  4  to slide inside the latch collet  6  until the fingers  82  snap on the latch ring  34 . In this position, the holding surface  88  is in contact with the recess  89  provided by the latch ring  34 . 
     The latch ring  34  is preferably made from a material that forms a low friction pair with the material the latch fingers  82  are made from. During unlatching, there is sliding between the latch ring  34  and the latch fingers  82 , which will generally result in a certain amount of wear on the latch ring  34  and latch fingers  82 . The material of the latch ring  34  is preferably a softer material than the material used in the latch fingers  82 . In this way, the wear occurs primarily on the surface of the latch ring  34 , which extends the life of the latch collet  6 . In this configuration, the latch ring  34  is essentially the sacrificial part and is replaced after a predetermined number of latch/unlatch cycles. The protective sleeve  38  and clamp  36  can be dismounted from the female connector housing  32  to facilitate easy replacement of the latch ring  34 . 
     Referring to FIG. 1C, the pump-down head  4  includes a pressure compensating system, generally indicated by reference numeral  92 . In the illustrated embodiment, the pressure compensating system  92  includes a piston  94 , seal  96 , spring  98 , and pressure relief valve  100 . The piston  94  can move inside the wire mandrel  30 . The piston  94  separates the internal fluids of the pump-down head  4  from the external fluid which enters through opening ( 102  in FIG. 1B) of the mud/oil crossover ( 28  in FIG.  1 B). The pressure compensating system  92  keeps the pressure of all fluid-filled internal volumes of the pump-down head  4  higher than ambient pressure. Similar pressure compensating systems are widely used in all fluid-filled downhole devices. 
     The pressure compensating system  92  also supplies extra fluid required for unlatching. During unlatching, the inner latch body  10  is pulled out of the outer latch body  8 , thus increasing the internal volume of the pump-down head  4 . Because the amount of fluid in the pump-down head  4  cannot change, a redistribution of the fluid inside the pump-down head  4  must occur. During unlatching, oil flows from the pressure compensating system  26  through the mud/oil crossover ( 28  in FIG. 1B) and the piston bore ( 40  in FIG. 1B) to the chamber ( 42  in FIG.  1 B). If the pump-down head  4  inadvertently loses much of its internal fluid during unlatching, a hydraulic lock-up may occur which may make it impossible to unlatch. To prevent this situation, the flooding valve ( 45  in FIG. 1B) allows external fluid to flow into the pump-down head  4  if the external pressure becomes higher than the internal pressure. 
     FIG. 3A shows a logging system  106  incorporating the wet connector latch ( 2  in FIGS.  1 A- 1 D). It should be noted that several details of the logging system  106 , such as the logging unit and logging tools, are omitted for clarity of the illustration. The wet connector latch  2  is shown in the unlatched position, with the pump-down head  4  attached to a cable  108  that runs to the surface, and shows the latch collet  6  coupled to a docking head  110 . It should be noted that for the sake of simplicity, some of the elements of the pump-down head  4  shown in FIGS. 1A-1D are omitted in this drawing. Also, the outer latch body  8  and the inner latch body  10  are shown as single solid pieces. 
     The female contacts  66  are connected to insulated electrical conductors in the cable  108  by wires (not shown) that run inside the pump-down head  4 . The latch collet  6  is attached to the upper body  112  of the docking head  110 . The docking head  110  includes a male wet connector contact assembly  114 , which consists of alternating electrically conductive rings or contacts  116  and insulating rings  118 . The conductive rings  116  are attached to wires  120  that run inside a passage  122  in the docking head body  112  and are connected to downhole logging tools (not shown). The docking head body  112  also has passages  124  for fluid flow. The docking head body  112  is rigidly attached to a drill pipe  126 . The drill pipe  126  is generally located downhole in a well (not shown) during operation. The pump-down head  4  is pushed down the drill pipe  126  by a flow of fluid, as indicated by the arrows. 
     FIG. 3B shows the beginning phase of the latching process in which the internal grip  69  (also shown in FIG. 1D) of the insulating shuttle  68  has just engaged the tip  128  of the male contact wet connector assembly  114 . At this time, the pump-down head  4  is still moving downward, pushed by the mud flow pumped down the drill pipe  126 . The slanted surface  90  of the inner latch body  10  slides against the latch surface  84  of the latch collet  6  and pushes the flexible fingers  82  outward. This allows the pump-down head  4  to slide into the latch collet  6 . It should be noted that there is no relative motion between the inner latch body  10  and the outer latch body  8  at this time. Also, it should be noted that surface  130  of the inner latch body  10  and surface  132  of the docking head body  112  are still far apart and that the downward motion of the pump-down head  4  continues. 
     As the pump-down head  4  continues to move downward, the male contact assembly  114  penetrates the pump-down head  4 , pushing the insulating shuttle  68  inward. This in turn compresses the spring  70 . The extra volume of fluid that is displaced by the movement of the insulating shuttle  68  is taken up by the pressure compensating system ( 92  in FIG.  1 C). The downward motion of the pump-down head  4  stops when surface  130  of the inner latch body  10  contacts surface  132  of the docking head body  112 . This position of the pump-down head  4  is shown in FIG.  3 C. At the time this happens, the latch fingers  82  latch onto the latch ring ( 34  in FIG.  1 D), and the holding surface  88  of the latch fingers  82  comes into contact with recess  89  in the inner latch body  10 , preventing the separation of the surfaces  130 ,  132 . In this way, relative motion between the female contacts  66  and male contacts  116  is prevented. In this position, latching of the pump-down head  4  and the docking head  110  is complete. The pump-down head  4  and docking head  110  remain in this position during the entire logging operation. It should be noted that flow of fluid can continue throughout the entire logging operation as needed. Thus, the invention does not interfere with the effective control of the well. 
     FIG. 3D shows the beginning phase of the unlatching process. This process starts by applying an upward pull on the cable  108 , indicated by the upward-pointing arrow  109 . This force is transmitted from the cable  108  to the outer latch body  8 . Since the inner latch body  10  is still held in place by the latch fingers  82 , the external force applied to the outer latch body  8  will tend to cause the outer latch body  8  to start sliding with respect to the inner latch body  10  in the upward direction. This, however, can happen only if the external force is strong enough to overcome the initial pre-load of spring  54 . Thus, the initial pre-load on spring  54  determines the minimum unlatch force. 
     Further, the relative motion between the inner latch body  10  and outer latch body  8  causes the volume of the chamber  42  to decrease. Because the chamber  42  is filled with substantially incompressible fluid, when the volume of the chamber  42  decreases, the fluid flows out of the chamber  42 . Fluid can flow out of the chamber  42  only through the hydraulic restriction  44 , however. In FIG. 3D, the flow through the hydraulic restriction  44  is indicated by the arrow  111 . The hydraulic restriction  44  allows fluid to escape only at a relatively slow rate, thus creating a positive pressure differential between the chamber  42  and the rest of the pump-down head  4  internal volume. This pressure differential counteracts the tendency of the inner latch body  10  and outer latch body  8  to slide with respect to each other. If the force applied to the outer latch body  8  is high, but of short duration, the fluid will not have enough time to escape from the chamber  42 . This causes a very high pressure differential. In this case, the external force is almost entirely balanced by the pressure increase in chamber  42 . On the other hand, if the external force is applied for an extended period of time, the fluid will have sufficient time to escape from the chamber  42 , and the pressure differential caused by the hydraulic restriction  44  will be much lower. 
     The force required to move the outer latch body  8  with respect to the inner latch body  10  determines the strength of the mechanical latch. From the above discussion, it is clear that this strength will be variable and will depend on the characteristics of the force applied through the cable  108  and on the flow restriction provided by the hydraulic restriction  44 . By appropriately designing the hydraulic restriction  44 , it is possible to obtain a variety of latch strength levels that are suited for any specific downhole conditions. 
     Referring to FIG. 3D, as the outer latch body  8  slides with respect to the inner latch body  10 , surface  134  of the outer latch body  8  engages the unlatching surface  86  of the latch fingers  82 . This causes the latch fingers  82  to spread out. As the latch fingers  82  move in the outward direction, the holding surface  88  of the latch fingers  82  starts to disengage from the recess  89  of the inner latch body  8 . When the fingers  82  move far enough, they no longer hold the inner latch body  8  in place, and the coupling between the pump-down head  4 and the docking head  110  is released. Because there is still a tension  109  on the cable  108 , the pump-down head  4  is moved out of the latch collet  6 . 
     It should be noted that as the pump-down head  4  and the docking head  110  are pulled apart, the male contact assembly  114  is pulled out of the pump-down head  4 . At the same time, spring  70  pushes the insulating shuttle  68  downward, back to its original position in the pump-down head  4 . After the pump-down head  4  is released by the latch collet  6 , there is no force counteracting the elastic energy built up in spring  54 . The spring  54  is now free to expand, and in doing so, pulls the inner latch body  10  back into the outer latch body  8 . This action tends to enlarge the chamber  42 . Fluid flows into the chamber  42  through the check valve  46 . By the time the pump-down head  4  is pulled out of the latch collet  6 , the outer latch body  8  has already moved to its original location. At this time, the latching/unlatching cycle is completed, and the pump-down head  4  and docking head  110  are back in the position shown in FIG. 3A, ready for another latching if necessary. 
     Now consider how the invention will react to transient forces that may result from the stick-slip motion of the drill pipe  126 . In this case, a very strong tensile force will be applied to the outer latch body  8 . This tensile force is created because the motion of the drill pipe  126  does not correspond to the motion of the cable  108 . As explained earlier, this force will cause a pressure increase in chamber  42 . In response to the pressure increase, fluid will start flowing out of the chamber  42 , and the outer latch body  8  will start moving with respect to the inner latch body  10 . So far, these events are similar to those of the unlatching process. The main difference is that the force caused by stick-slip motion of the drill pipe  126  is of very short duration. Since the unlatching takes a relatively long time, this force will typically be relieved before the unlatching can be completed. Once the external force is gone, there is nothing to balance the compression of spring  54 , and the spring  54  will quickly bring the outer latch body  8  back to the position indicated in FIG.  3 C. Thus, the system quickly resets once the external force is removed. Consequently, the invention can withstand an unlimited number of transient tension events without unlatching. 
     The invention may provide several general advantages. As discussed above, the wet connector latch of the present invention allows a joint to be formed mechanically between two mating parts of a tool string. This joint can be selectively uncoupled when necessary. The wet connector latch is particularly suited for mechanically joining two parts of a downhole wet connector used for drill-pipe conveyed logging. An important characteristic of the wet connector latch is that it releases only when a predetermined force is applied to it for a predetermined amount of time. Another important characteristic of the wet connector latch is that it can be operated multiple times. 
     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.