Apparatus for controlling a downhole device

Abstract

An apparatus for controlling a downhole device in an oil, gas or water well includes an outer body, defining a central cavity extending along a longitudinal axis of the outer body; a first piston assembly arranged within the central cavity, the first piston assembly moveable along the longitudinal axis to switch the downhole device between different modes, a first seal arranged to seal between the first piston assembly and an inner wall of the central cavity; a first biasing member arranged to bias the first piston assembly in a first direction along the longitudinal axis; a second piston assembly arranged within the central cavity, spaced from the first piston assembly in a second direction along the longitudinal axis, the second direction opposite the first direction, a second seal arranged to seal between the second piston assembly and the inner wall of the central cavity; and a second biasing member arranged to bias the second piston assembly in the first direction. The first seal and the second seal define a sealed hydraulic reservoir therebetween for filling with a hydraulic fluid such that movement of the first piston assembly in the second direction drives movement of the second piston assembly in the second direction.

1 . An apparatus for controlling a downhole device in an oil, gas or water well, the apparatus comprising:
 an outer body, defining a central cavity extending along a longitudinal axis of the outer body;   a first piston assembly arranged within the central cavity, the first piston assembly moveable along the longitudinal axis to switch the downhole device between different modes, a first seal arranged to seal between the first piston assembly and an inner wall of the central cavity;   a first biasing member arranged to bias the first piston assembly in a first direction along the longitudinal axis;   a second piston assembly arranged within the central cavity, spaced from the first piston assembly in a second direction along the longitudinal axis, the second direction opposite the first direction, a second seal arranged to seal between the second piston assembly and the inner wall of the central cavity;   a second biasing member arranged to bias the second piston assembly in the first direction,   wherein the first seal and the second seal define a sealed hydraulic reservoir therebetween for filling with a hydraulic fluid such that movement of the first piston assembly in the second direction drives movement of the second piston assembly in the second direction.   
     
     
         2 . The apparatus of  claim 1 , wherein the central cavity is separated into a primary cavity and a secondary cavity with a flow pathway between the primary cavity and the secondary cavity, the first piston assembly arranged within the primary cavity and the second piston assembly arranged within the secondary cavity. 
     
     
         3 . The apparatus of  claim 2 , further comprising a flow restrictor nozzle arranged within the flow pathway. 
     
     
         4 . The apparatus of  claim 1 , wherein either:
 a) the first piston assembly comprises a control slot and the outer body comprises a pin engaging the control slot; or   b) the outer body comprises a control slot and the first piston assembly comprises a pin engaging the control slot,   wherein the pin is arranged to move along the control slot as the first piston assembly moves with respect to the outer body to thereby switch the downhole device between an at-rest mode, a drilling mode, and a circulation mode.   
     
     
         5 . The apparatus of  claim 4 , wherein the control slot has first loops wherein the pin is moveable between different configurations of the downhole device, and second loops spaced with respect to the first loops, and wherein the pin is moveable in the second loops between different configurations of the downhole device, wherein at least one of the loops has a transition portion for switching the pin between the first loop and the second loops, and wherein the pin is cycleable between the different configurations within each one of the first and second loops without switching between the first and second loops, wherein each of the first loops has a first axial portion at one end, and each of the second loops has a second axial portion at the same end, with a length different from that of the first axial portion, and wherein the control slot has alternating first and second loops spaced circumferentially around the body. 
     
     
         6 . The apparatus of  claim 4 , wherein the control slot has at least one loop having a axial portion, wherein the pin is moveable between different configurations of the downhole device, and at least one elongated axial track arranged in an axial direction of the outer body and having a length in the axial direction longer than the axial portion, and wherein the pin is moveable in the at least one elongated axial track between different configurations of the downhole device, wherein each of the at least one elongated axial track is connected to one of the at least one loop via a deviate branch track, which is configured to track the pin from one of the at least one elongated axial track into one of the at least one loop, and wherein the pin is switchable between each of the at least one elongated track and one of the at least one loop, and wherein the pin is cycleable between the different configurations within each one of the at least one loops without switching from said loop to an adjacent elongated axial track, wherein the control slot has no separate, dedicate return path for returning the pin from the deviate branch track to the elongated axial track. 
     
     
         7 . The apparatus of  claim 1 , wherein the first biasing member is arranged to provide a weaker biasing force than the second biasing member. 
     
     
         8 . The apparatus of  claim 1 , further comprising a valve arranged for filling the sealed hydraulic reservoir with the hydraulic fluid. 
     
     
         9 . A method of controlling a downhole device in an oil, gas or water well, the method comprising the steps of:
 providing an apparatus according to  claim 1 ;   moving the first piston assembly along the longitudinal axis to switch the downhole device between different modes such that the first piston assembly acts on the hydraulic fluid to drive movement of the second piston assembly.