Abstract:
Two well tools ( 100, 200 ) having centrally mounted drive shafts ( 160, 260 ) are provided with a mechanism to remove debris from a coupling between them. Thereafter, the tools can be coupled by inserting a first outer sleeve ( 110 ) on the first tool into and rotationally lock it to a second outer sleeve ( 210 ) on the second tool. The drive shafts ( 160, 260 ) are coupled in a similar manner. The mechanism for removing debris can displace the debris and/or a flushing device ( 170 ) using well fluid to stir up debris. The coupling has space for debris that is not removed, e.g. in the form of a chamber  264 . The female part of the coupling may comprise a spring loaded lid ( 271 ) to reduce pollution by debris when the coupling is not in use.

Description:
BACKGROUND 
     The invention regards a coupling between wellbore tools having central drive shafts. 
     PRIOR AND RELATED ART 
     In recovery of oil and gas, a borehole is drilled through subterranean formations. Parts of the borehole are completed with steel pipes that are cemented to the formation. These steel pipes are known in the industry as ‘casing’ and ‘liners’ depending on diameter and location in the well. In this description and in the enclosed claims both types are collectively denoted ‘casing’. Production pipes can be inserted into the borehole through the casing, and equipment can be run down inside casing or production pipes. In the following, ‘pipes’ comprises casing, liners and production pipes, and are collectively called ‘tubulars’ in the industry. Equipment run into the wellbore is collectively known as ‘wellbore tools’. Hence, in this disclosure ‘wellbore tools’ comprise running tools, plugs, loggers, valves and other equipment with or without a motor. 
     High energy prices make deeper wells commercially viable. Present wells can be several kilometers deep, and may comprise horizontal branches that also can be several thousand meters long. The temperature in a modern well may approach 200° C. Since formation pressure is caused by the weight of rock and water, deeper wells results in correspondingly higher pressures at the bottom of the hole. 
     Previously, drilling mud with high densities was used to control pressure from the formations in practically all boreholes. In many present wells so called underbalanced drilling, where the pressure in the borehole is less than in the ambient formations, is used. Underbalanced drilling increases the amount of available hydro carbons, but also the risk for sudden pressure changes in the borehole due to a high pressure region or a gas reservoir in the formation. 
     The fluid flowing from the subterranean formations is a mixture of gas, oil components, water and solid particles like sand etc. In addition, the fluid can contain material from dressing or milling of pipes, cuttings, and/or other solid particles of various sizes. The solids are in the following collectively called ‘debris’. 
     There is sometimes a need to place a well tool in a wellbore. This may be done by running a running tool (well tractor) coupled to the well tool into the wellbore. When the well tool is placed, the running tool may activate slips on the well tool, be decoupled and return to the surface. When the tool is to be retrieved at a later time, the running tool may be sent back into the wellbore to retrieve it. The running tool may also be used to operate tools in the well, for example to open or close a valve. 
     A first example of a well tool can be a well plug preventing fluid flow in a pipe. Well plugs are used e.g. in the period between casing and production for pressure testing and inspection, or when the fluid flow from a branch or a well no longer contains a sufficient concentration of hydrocarbons. Such plugs are often positioned by a running tool which is returned to the surface when the task is done. If the plug is to be removed at a later time, the running tool is sent back to perform the task. 
     Norwegian patent application NO 2008 1406 (Petro Tolls AS) describes such a well tool that may serve as an example. This plug has a through channel extending along its entire axis of rotation. A ball valve is located in the central channel and can be opened and closed when the driveshaft is rotated within a neutral sector. When the drive shaft is rotated beyond the neutral sector, it rotates a lead screw which moves seals and slips radially. Outside the neutral sector, the ball valve is kept open independent of the direction of rotation. Thereby free passage through the central channel of the plug in the critical phases wherein the seals seal against the pipe wall while the slips do not provide sufficient retaining force. This prevents a plug from being blown with great force through the pipe by a sudden change in pressure. This plug can be set or retrieved by a running tool. 
     From this example, it is clear that the running tool must be capable of providing a relative rotation between the outer housing of the plug and an inner drive shaft in both directions. It is also clear that the central driving shaft of the running tool in some instances should be hollow, so that the running tool does not pull the plug along during a sudden change in pressure as described above. 
     A second example is sleeve valves wherein a relative rotation between two sleeves having a common axis of rotation opens or closes radial side ports. Such valves can be operated by means of a running tool capable of providing a relative rotation between the inner and outer sleeves of the valve in both directions. 
     A third example is modules for well logging which are retained in the well by slips for a shorter or longer period of time. These may also be set or retrieved by a running tool. In some applications, it may be necessary or advantageous to couple such logging tools in series. A running tool may then be sent into the wellbore with another well tool mounted on it, and the mounted well tool can be coupled to a well tool already disposed in the well. In some instances, it may be advantageous to provide more than two concentric sleeves to affect different elements in such a string of tools, or to be able to control one or more tools in the series individually. 
     As well tools for natural reasons tend to be substantially cylindrical, it may be advantageous to provide mechanical operations related to coupling, decoupling, setting, operation and retrieval of them by relative rotation between rotationally symmetric elements. These rotationally symmetric elements can be solid or hollow shafts, sleeves, collets etc. As evident from the third example above, in some applications it may be necessary or advantageous to provide more than two concentric sleeves in a well tool, whether the well tool is a running tool with a motor, or valves and modules without a motor. 
     There is hence a need for a robust coupling between two well tools enabling a simple connection between them, also in a well bore. The coupling has to be secure and reliable, and must be able to provide a relative rotation between two rotationally symmetric elements in both directions. 
     When a well tool has been placed in a wellbore for some time, the coupling of the tool will frequently be covered by collected debris. Such collected debris makes it difficult to connect a running tool or other well tools. 
     It is known to use equipment such as compressors on the surface and long conduits from the surface to wash away debris from a coupling element. This may involve relatively long down times, and may be problematic to perform in e.g. deep wells having long side branches. 
     The objective of the invention is hence to provide a robust coupling between two well tools enabling a relative rotation between an outer sleeve and a driveshaft rotatably mounted in the sleeve. A robust coupling must be able to cope with debris in the well fluids before or around the time of coupling. 
     SUMMARY OF THE INVENTION 
     The invention provides a coupling for wellbore applications between a first tool comprising a first drive shaft rotatably mounted in a first outer sleeve and a second tool comprising a second drive shaft rotatably mounted in a second outer sleeve, distinguished in
         that the outer diameters of the first outer sleeve are less than or equal to corresponding inner diameters of the second outer sleeve and wherein one of the outer sleeves comprises at least one first latching dog fitting into at least one first groove in the second outer sleeve,   that the outer diameters of the first drive shaft are less than or equal to corresponding inner diameters of the second drive shaft, and wherein one of the drive shafts comprises at least one second latching dog fitting into at least one second groove in the other drive shaft, and   that at least one of the tools comprises means for removing debris.       

     When at least one of the tools comprises means for removing debris, most of the debris can be removed from the latching dogs and grooves prior to connecting them. 
     When the first outer sleeve can be inserted into the second outer sleeve, and relative rotation between them prevented by the first latching dog and groove, and the first drive shaft can be inserted into the second drive shaft, and relative rotation between them prevented by the second latching dog and groove, a coupled driveshaft rotatably mounted in a coupled outer sleeve is achieved. The coupled outer sleeve prevents debris from entering the region of latching dogs and grooves. 
     An optional flushing mechanism can use well fluid to stir up debris before coupling. By using well fluid for the flushing, complicated surface operations and transport of flushing fluid from the surface to the well tool is avoided. 
     A lid mechanism over the opening of the second sleeve can limit the amount of debris that can be deposited on the coupling element, and provides a relatively smooth surface without deep grooves or corners that may be difficult to flush clean. 
     There is provided space for remaining debris that is likely to enter the coupling. Thereby, the coupling will work even if it is not completely free of debris. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail in the following with reference to the accompanying drawings, in which like numerals refer to like parts, and in which: 
         FIG. 1  shows a coupling in which two coupled drive shafts are rotatably mounted in a coupled and closed outer housing. 
         FIG. 2  shows a lid that may prevent debris from entering the region of coupling elements according to the invention. 
         FIGS. 3   a - b  show two embodiments of means for mechanical displacement of debris. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a coupling according to the invention. 
     In this embodiment, the first tool is a running tool  100  having a motor  140  and drive shaft  160  rotatably mounted in a housing  110 . The second tool, in the following denoted “the well tool”, is unspecified apart from that it has a central drive shaft  260  rotatably mounted in an outer sleeve or housing  210 . 
     The running tool is collectively referred to by numeral  100 , and parts belonging to this have reference numerals in the range 101-199. 
     The well tool is similarly collectively referred to by numeral  200 , and parts belonging to this, including the female parts of the coupling, have reference numerals in the range 201-299. 
     In the following, ‘backward’ refer to the direction to the left and ‘forward’ to the right in the  FIGS. 1 and 2 . 
     The running tool  100  is substantially rotational symmetric. The main parts are a housing  110 , a motor  140 , a gear assembly  150  and a drive shaft  160 . The drive shaft  160  may be rotated relative to the housing  110 . 
     As noted above, deposited debris can prevent coupling between a running tool and a well tool. The well tool advantageously has a surface making it relatively easy to remove this debris. Furthermore, the drive shaft of the running tool may comprise means for removing debris. Such mechanical means are further described below with reference to  FIGS. 3   a  and  3   b . These may be used alone or in combination with flushing in order to remove the debris from the coupling. 
     In both cases, a male part having a first outer sleeve (housing)  110  and a first drive shaft  160  is inserted into a female part having a second outer sleeve  210  and a second drive shaft  260 . When the outer sleeve (or housing)  110  of the male part is inserted into the outer sleeve  210  of the female part, the outer sleeves may be rotated relative to each other until first latching means on the male part engages corresponding first latching means (latching member) on the female part. These first latching means (latching member), which prevent rotation between the outer sleeves, are in  FIG. 1  illustrated by radially biased latching dogs  121  on the outer surface of the male part capable of snapping into corresponding longitudinal splines or groves on the inner surface of the female part. 
     For flushing, the running tool may further comprise an inlet for well fluid in the outer wall of the running tool, via a pump to a conduit  170  in the head of the drive shaft  160 , and on through one or more outlets in the head of the drive shaft, as illustrated in  FIG. 1 . In order to transport well fluid between the housing  110  and the rotating drive shaft  160 , a conventional swivel joint is used, which by itself is not part of the invention. Inlet(s) and pump are not shown. The well fluid may be discharged with sufficient pressure to stir up the debris, to facilitate its transport backwards and away from the coupling. 
     After mechanical removal and flushing, most of the debris will be removed from the coupling. When connecting, the male part  100  will displace well fluid from the female part  200 . Hence, the coupling needs conduits so that displaced fluids may escape. In  FIGS. 3   a  and  3   b  this is illustrated by depressions in the head of the male part. During connection, residual debris will be let into the coupling. A chamber  264  is provided in the female part to accommodate such residual debris. 
     In the embodiment shown in  FIG. 1 , the male part of the coupling is provided on the running tool, while the female part of the coupling is provided on the well tool, which may be a plug, a valve, a logging tool or some other tool disposed in the well for a period of time. It is possible to provide the female part on a running tool and the male part on a well tool. 
     In both cases, a male part having a first outer sleeve  110  and a first drive shaft  160  is inserted into a female part having a second outer sleeve  210  and a second drive shaft  260 . When the outer sleeve  110  of the male part is inserted into the outer sleeve  210  of the female part, the outer sleeves may be rotated relative to each other until first latching means on the male part engages corresponding first latching means on the female part. These first latching means, which prevent rotation between the outer sleeves, are in  FIG. 1  illustrated by radially biased latching dogs  121  on the outer surface of the male part capable of snapping into corresponding longitudinal splines or groves on the inner surface of the female part. 
     Similar second latching means (latching members), illustrated by latching dogs  131  in  FIG. 1 , can prevent rotation between the drive shafts  160  and  260 . When the driveshaft  160  of the running tool first is inserted into the drive shaft  260  of the female part, the latching dogs  131  are unlikely to enter their respective splines or grooves directly. As described in connection with coupling of the outer sleeves, a relative rotation between the driveshaft  160  of the male part and the drive shaft  260  of the female part bring the second latching means into engagement. In the embodiment of  FIG. 1 , radially preloaded latching dogs  131  on the drive shaft  160  of the male part snap out and into splines on the drive shaft  260  of the female part. 
     It should be understood that one or both of the discussed latching mechanisms can be designed differently from those shown in  FIG. 1 , e.g. in that longitudinally extending shoulders are brought into engagement with each other by other means. 
       FIG. 1  also shows a latch  111  retained at its first proximal end on the outer surface of the male part. It is understood that several similar latches may be disposed around the circumference of the male part. The distal end of the latch  111  has a sliding surface which is inclined axially outward toward the proximal end of the latch, and is preloaded radially outward by one or more springs  112 . When the male part is inserted into the female part, the sliding surface will compress the spring  112 . Once an outer shoulder  113  on the latch  111  passes a corresponding inner shoulder along the inner circumference of the female part, the distal end of the latch is pushed radially outward by the spring  112 . The outer shoulder  113  of the latch will then abut the corresponding inner shoulder in the female part and prevent the male part from being pulled out of the female part. 
     A releasing sleeve  114  can be moved axially relative to the latch  111 , e.g. by means of a linear actuator and a rod. When the sleeve  114  is moved axially toward the distal end of the latch  111 , the latch  111  is forced inward until the shoulder  113  no longer retains it in the female part. The male part can then be pulled out of the female part. 
     At least one latching dog  121  is disposed rotationally locked relative to the outer housing  110  of the running tool, and is forced radially outward by one or more springs  122 . In  FIG. 1 , the latching dog  121  is engaging a corresponding longitudinal spline  221  (see  FIG. 2 ) which is disposed rotation locked relative to the outer housing  210  of the well tool. This prevents relative movement between the outer housing  110  of the running tool and the outer housing  210  of the well tool. Alternatively, the latching dog  121  might have been disposed on an inner surface of the well tool and the spline or groove on an outer surface of the running tool. 
     Similarly, at least one latching dog  131  is disposed rotation locked relative to the drive shaft  160  of the male part, and is forced radially outward by one or more springs  132 . In  FIG. 1 , the latching dog  131  is engaging a corresponding longitudinal spline  231  (see  FIG. 2 ) which is disposed rotationally locked relative to the drive shaft  260  of the well tool. This prevents relative movement between the drive shaft  160  of the running tool and the drive shaft  260  of the well tool. Alternatively, the latching dog  131  might have been disposed on the well tool and the spline or groove on the running tool. 
     The drive shaft  260  of the well tool is rotatably mounted in the outer housing  210  of the well tool by bearings  261  and  263 . These are kept axially apart by a spacer  262 . 
     When the motor  140  of the running tool is activated, torque is transferred through a flexible coupling  141  and a gear assembly  150  to the drive shaft  160  and further to the drive shaft  260  of the well tool. The drive shafts  160 ,  260  will thereby rotate relative to the outer housings  110 ,  210 . This rotational movement can be used to clamp or release the slips of the well tool, open or close a valve in the well tool, et cetera. 
       FIG. 2  shows an alternative embodiment of the female part. Outer sleeve  210  and drive shaft  260  are as in  FIG. 1 . The figure also shows the longitudinal splines  221  and  231  corresponding to the latching dogs  121  and  131  respectively, as previously discussed in connection with  FIG. 1 . 
     The embodiment in  FIG. 2  further comprises a piston  270  axially slidably mounted in an outer piston sleeve  280 . The piston  270  and the outer piston sleeve  280  thereby form a telescopic coupling. A spring  272  preloads piston  270  and outer piston sleeve  280  such that the telescopic coupling is in its maximum extended state when it is not exposed to external forces. A flexible scraper  271  is mounted on the piston  270  and functions as a lid at the outer end of the female part when the coupling is not in use. The preloaded telescopic coupling has no other functions. 
     The flexible scraper  271  can be implemented as a brush having radially extending bristles, as an annular rubber edge, or similar. 
     When most of the debris is removed from the lid by means of mechanical means and flushing, the male part will be inserted into the female part and push the piston  270  against the spring force from the spring  272  (toward the right in  FIG. 2 ). This will displace fluid from the inside of the telescopic coupling to the surroundings or to a flexible bellows (not shown). During this displacement, the flexible scraper  271  will to some extent close toward protrusions and grooves in the interior of the female part. 
     When the male part is pulled out from the female part at a later time, the spring  272  will push back the scraper (toward the left in  FIG. 2 ). During this motion, the scraper  271  will again to some extent close toward protrusions and grooves in the interior of the female part, and push most of the inserted debris out of the female part. When the telescopic coupling again is maximally extended, the flexible scraper again forms a lid at the entrance to the female part. 
       FIG. 3   a  shows a drive shaft having a substantially conical head and a concave depression  161 . When the drive shaft and head is rotated, the concave depression  161  will function as a spoon or spade such that sand and other material is loosened and transported axially backwards away from the coupling. The means for mechanically removing debris are intended to comprise any means and assemblies whereby mechanical means remove debris from the coupling. 
       FIG. 3   b  shows an alternative design of a similar conical head, having a screw  162  on its outer surface. The unwanted debris is here displaced backwards and away from the coupling by the screw  162 . 
     Other conventional mechanical means for removing debris can also be adapted for this purpose. Such means may for example comprise screws having different designs from the one shown in  FIG. 3   b , or other devices functioning as a spade, a drill or a mill. Mechanical removal can be combined with flushing as described above.