Abstract:
A self contained logging tool comprising electronic apparatus for logging a well is disclosed. This tool includes a normally open fluid flow valve structure being activated to operation by differential movement of drill pipe in which the logging tool resides. The valve structure operates to gradually close and thereby restrict the flow of fluid through the valve, which in turn restricts the flow of fluid within the drill pipe. This flow restriction results in increasing the back pressure within drill pipe to provide an indication at the surface that the logging tool is struck.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to down hole tension/compression devices and more particularly to devices for use with battery powered self contained logging tools employed in oil well drilling operations. 
     A problem which arises in such operations is that when a logging tool is deployed on the end of drill pipe or coiled tubing. If the logging tool becomes stuck in the borehole there is no indication at the surface that this has occurred in contrast to a logging tool connected by cable to the surface where the movement or non-movement of the cable will indicate movement or non-movement of the logging tool. 
     In the event that a self-contained logging tool becomes stuck movement of the drill pipe can result in damage to the tool. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a down hole tension/compression device which provides an early warning of when a tool is shuck to enable drill pipe motion to be halted, thereby preventing damage to the tool. 
     The present invention therefore provides a self contained logging tool comprising apparatus for logging a well, said tool including normally open fluid flow valve means, said valve means being operable when the drill pipe moves with respect to the logging tool to close and to restrict flow of fluid through said valve to thereby restrict the flow of fluid within said drill pipe, thereby creating back pressure within said drill pipe to provide an indication at the surface that the logging tool is stuck. 
     The present invention also provides a valve for use in a logging tool, said valve comprising an inlet and an outlet for fluid flow, said outlet comprising first and second overlapping slot means, said first overlapping slot means being operable as movement increases to move relative to said second overlapping slot means to progressively restrict the flow of fluid through said valve. 
     The present invention also provides a down hole device including a valve means as described above and further including poppet valve means operative to be actuated at an excessive pressure to provide a bypass flow route for said fluid. The present invention further comprises a method of operating a logging tool comprising the steps of connecting said logging tool to the end of a drill pipe, lowering said logging tool, on the end of said drill pipe, into a drill hole; and pumping mud down said drill pipe, said mud flowing through said logging tool via valve means situated within said logging tool; 
     said method comprising the further steps of detecting when said logging tool becomes stuck in the drill hole by detecting restriction of mud flow in the drill pipe caused by operation of said valve means, and on detection of such restriction halting movement of said drill pipe in said drill hole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings in which: 
     FIG. 1 shows diagrammatically an oil or gas drill pipe system including a self contained logging tool incorporating a down hole tension/compression device according to the present invention; 
     FIG. 2 shows a battery powered self contained logging tool according to the present invention; 
     FIG. 3 shows a mud pressure operated down hole tension and compression tool in accordance with the present invention in a neutral, non-operative condition; 
     FIG. 4 shows the tool of FIG. 3 in a tension condition illustrating the further operation of the valve means; 
     FIG. 5 shows the tool of FIG. 3 in a compression condition illustrating the further operation of the valve means; 
     FIG. 6 shows the tool of FIG. 3 in a further condition illustrating release of the poppet valve; 
     FIG. 7 shows an alternative embodiment of the down hole compression and tension tool; 
     FIG. 8 shows the tool of FIG. 7 in a tension condition; 
     FIG. 9 shows ˜e tool of FIG. 7 in a compression condition, 
     FIG. 10 shows the tool of FIG. 7 illustrating the safety valve release; and 
     FIG. 11 shows the tool of FIG. 7 in its several states; 
     a) steady 
     b) compression 
     c) tension and 
     d) safety valve blown 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to FIG. 1, a drill hole  10  which may, for example, be an exploratory drilling for an oil or gas field is schematically shown. A drilling rig or head  12  is shown which is provided with pump means  14  which pumps mud down the drill pipe in known manner. 
     The pump means  14  will be provided with pressure measurement means  16  for measuring the pressure of the mud mixture in the drill pipe  11 . The pressure measurement means is provided with control means  18  for controlling the pump  14  to regulate the pressure of the mudflow. 
     A battery powered self contained logging tool  20  is shown at an exemplary position in the drill pipe  11 . In known manner this tool  20  is used for logging the properties of the well. The operation of the logging tool in logging these properties will not be described further in this application. 
     A problem with such self-contained logging tools is that they are not connected in any manner to the surface. The movement of the tool within the drill hole is executed solely by moving the drill pipe upwards or downwards. 
     However because the logging tool is self-contained its movement along the drill hole cannot be monitored by movement of an attached cable. Thus if the tool becomes stuck in the drill hole this will not be immediately detected. 
     Continued motion of the drill pipe to force the tool past an obstruction can result in damage to the tool. The present invention provides a means for avoiding such damage by providing an indication at the surface if the tool becomes lodged in the hole. 
     With reference now to FIG. 2, the tool  20  comprises a first logging section  22  and a second valve section  24 . As stated the logging section  22  is not part of the present invention and may comprise conventional logging electronic circuitry. The valve section  24  comprises a generally cylindrical elongate tubular assembly which is rigidly attached to the logging portion  22  to comprise the logging tool string. The assembly  24  includes slotted outlet holes  2422 ,  244  for the flow of mud, the purpose of which will be explained with reference to FIGS. 3 to  6  which describe the valve section  24  in greater detail. The portion  25  is connected directly to the C.T. (coiled tubing) or drill pipe. 
     With reference now to FIG. 3, the valve section  24  comprises a mud pressure operated down hole tension and compression tool which is actuated by mud pressure. The normal mudtlow is indicated by arrows  2400  and  2402 , the path of which is via internal slotted holes  2404  in a hollow piston member  2406 . 
     The piston member  2406 , attached to portion  25 , is constrained to move within an external tube member  2408  by springs  2410 ,  2412  acting against collars  2414 ,  2416  which are in turn restricted in final movement by internal flanges  2418 ,  2420  attached to tube member  2408 . 
     At the right-hand end of hollow piston member  2406  a poppet valve  2422  is mounted. This valve is provided with shear pin means  2424 . For example, the poppet valve may be designed to open at a pressure of 500 psi and the shear pins may be rated at 1500 psi. The poppet valve/shear pin assembly provides a final safety flow path as described hereinafter. 
     With reference to FIG. 4 the tension/compression tool device is shown in tension with restricted mudflow through the centre slotted holes  242 . This restricted flow is caused by movement of collar  2414  when the tool  20  becomes stuck either completely or partially in the drill pipe. This causes spring  2412  to be compressed and piston  2406  to move to the left in FIG.  4 . This causes the slots  2404  and  242  to be only partially aligned and thereby restricts the flow of mud through the centre slots  242 . 
     This restriction will cause an increase in pressure of mud within the drill pipe, which increase is detectable at the surface and thereby indicates that the logging tool has become completely or partially stuck. 
     FIG. 5 shows the tension and compression tool device in compression with restricted mud flow through centre slots, illustrating that compression of spring  2410  against collar  2414  will also cause the centre slot  242  to become restricted and thereby create a build up of mud pressure which will be detectable at the surface, thereby indicating that the logging tool has become partially or completely stuck. 
     With reference now again to FIGS. 4 and 5, in the event that the tool becomes completely stuck and the pressure build up continues, the poppet valve  2422  will open allowing mud to flow through the hollow piston  2406 , through the poppet valve  2422  and out through outer vents  244 . 
     Should the poppet valve  2422  fail then this valve is provided with shear pins  2424  which will release the valve from its mounting, as shown in FIG. 6 so that the mud can flow through the hollow cylindrical piston. Otherwise, mud flows through both inner and outer vents without restriction. 
     The present invention therefore provides a method of detecting, when a self contained logging tool becomes lodged in a drill hole, as defined, and therefore, by constricting the mud flow and causing a detectable change in the mud pressure to occur, allowing action to be taken to prevent damage to the logging tool. With reference now to FIGS. 4 and 5, the slotted holes  2404 ,  242  are shown with dimensions that ensure that they completely overlap in the unoperated condition and just completely close when the springs are completely compressed. 
     However, by designing the springs to be more elongate or, alternatively, the slots to be shorter in length, the valve may be completely closed well in advance of the springs being completely compressed. This enables detection of the lodging of the tool in the drill hole before the springs are completely compressed, thereby enabling the withdrawal or insertion of the drill pipe to be stopped in advance of final compression of the springs, thereby providing an elastic stop for the logging tool, thereby further preventing damage to the tool. 
     With reference now to FIG. 7, in a second embodiment the valve section  24  also comprises a generally cylindrical elongate tubular assembly which is rigidly attached to the logging portion  22  to comprise the logging tool string. The assembly  24  includes an outlet path via holes  241 ,  243  for the flow of mud, the purpose of which will be explained with reference to FIGS. 8 to  11  which describe the valve section  24  in greater detail. 
     The valve section  24  comprises a mud pressure operated down hole tension and compression tool. The normal mudflow is indicated by arrows  2401  and  2403 , the path of which is via internal holes  241  in a hollow piston member  2405 . 
     The piston member  2405  also incorporates sliding pistons  2417 ,  2419  constrained to move within an external tube member  2411  by mud pressure acting in chambers  2413 ,  2415  which acts against pistons  2417 ,  2419  which are in turn restricted in final movement by internal flanges  2421 ,  2423  attached to tube member  2411 . When the device is in its rest position the pistons  2417  and  2419  are at the outer ends of the chamber and the holes  241 ,  243  align, allowing mud to flow into the drill hole. 
     At the left-hand end of hollow piston members  2405  a hollow poppet valve  2425  is mounted. This valve is provided with shear pin means  2427 . For example, the poppet valve may be designed to open at a pressure of 500 psi and the shear pins may be rated at 1500 psi. The poppet valve/shear pin assembly provides a final safety flow path as described hereinafter. In further reference to FIG. 7, shear pin(s)  2427  fixing the annular piston to the outer tube are located adjacent the drill pipe cross over end (up hole) of the tool. These shear pin(s)  2427  implement a 1500 psi overpressure dump valve. On the down hole side is the 500 psi pressure relief valve implemented with the hollow poppet valve  2425 . The compression piston bearing  2417  and the tension piston bearing  2419  are located on either side of bearing supported internal flanges (vents)  2423 . An optional restrictor  2431  to provide a detent is down hole in the tool adjacent the flow cut-off vents  243 ,  2403 . 
     A further bearing  2433 , with internal vents is provided to support piston member  2405 . 
     With reference to FIG. 8, the tension/compression tool device is shown in tension with mud flow restricted by the misalignment of holes  241 ,  243  and piston member  2405  displaced from its rest position. This restricted flow is caused by movement of the hollow piston means  2405  when the tool  20  becomes stuck either completely or partially in the drill hole. The force applied to the logging tool is now controlled by the force on the left-hand piston  2417  applied by the mud pressure in the chamber  2415 , which, in turn, is limited by the pressure required to operate the poppet valve  2425 . When the flow control valve cuts off flow to the borehole, the spring operated relief valve limits the pressure increase to 500 psi. 
     The restriction will cause an increase in pressure of the mud within the drill pipe, which increase is detectable at the surface and thereby indicates that the logging tool has become completely or partially stuck. The tensional load on the tool equals about 1000 lbs. With the flow cut off vents closed, a pressure increase of 500 psi is recorded at the surface over the full 2 foot stroke. This two foot stroke is marked by the “X” dimension lines shown in FIG.  7 . 
     FIG. 9 shows the tension and compression tool device in compression, illustrating the misalignment of holes  241 ,  243  which will also cause the flow to become restricted and thereby create a build-up of mud pressure which will be detectable at the surface, thereby indicating that the logging tool has become partially or completely stuck. The force on the logging tool is now controlled by the pressure in chamber  2413  acting on the right-hand piston  2419 . 
     With reference now to FIG. 10, in the event that the tool becomes completely stuck and the pressure build-up continues, the shear pin  2427  will break allowing piston  2426  in the poppet valve assembly to shift, permitting mud to flow to the drill hole through the vents  2429 , without restriction. 
     An internal constriction  2431  is also provided so that a modest pressure (say 100 psi) is developed in the chamber so that this needs to be overcome before any displacement at all can take place. If the pressure relief valve blocks, mud pressure increases to 1500 psi, at which point the shear pin on the annular piston breaks allowing the piston to slide forward to uncover the vents letting mud escape into the well. 
     With reference to FIG. 11, for ease of understanding the tension/compression tool of the embodiment of FIG. 7 is shown in all four conditions. In the condition shown in FIG. 11A the tension/compression tool is in the steady state condition. In FIG. 11B the tool is in its compression condition. 
     In FIG. 11C the tool is in its tension condition and in FIG. 11D the tool is shown with the safety piston  2426  blown. 
     The present invention therefore provides a method of detecting when a self contained logging tool becomes lodged in a drill hole, as defined, and therefore, by constricting the mud flow, causing a detectable change in the mud pressure to occur, allowing action to be taken to prevent damage to the logging tool.