Circulating Sub with Activation Mechanism and a Method Thereof

Abstract

The present invention relates to an activation method, an activation mechanism and a downhole tool comprising the activation mechanism. The activation mechanism com-prises a pressure switch for turning power to the electrical components, a control unit connected to a pressure sensor for sensing the internal pressure of the drilling fluid located in a first fluid conduit. The control unit controls an actuator unit connected to a moveable valve element. The actuator unit moves the valve element from a closed position when activated. A seat for the valve element is arranged relative to a second fluid conduit so that the valve element closes the second conduit when it is placed in its seat. This provides a very fast and accurate activation method that involves the use of balls or RFID tags. Furthermore, the downhole tool can be activated even if no actual flow is passing through the tool.

1 . An activation mechanism for activating a circulating sub in a drill string, comprising:
 at least one sensor configured to sense at least a pressure of a drilling fluid located in a first fluid conduit in the circulating sub when installed,   a control unit connected to the sensor and configured to monitor the sensed signal of the at least one sensor, wherein the control unit is configured to electronically activate the movement of at least one moveable valve element in one direction based on the sensed signal,   wherein the at least one valve element is configured to be arranged relative to at least a second fluid conduit in the circulating sub when installed, the at least one valve element is configured to move between an open position and a closed position,   wherein the second fluid conduit is in fluid communication with the first fluid conduit, and the at least one valve element comprises at least one valve end configured to close the second fluid conduit in the closed position and to open the second fluid conduit in the open position, wherein   the control unit is electrically connected to at least one actuator unit arranged relative to the at least one valve element, the at least one actuator unit is configured to perform a reciprocating movement of the at least one valve element an endless number of times between the open position and the closed position, wherein the control unit is further configured to electronically activate the movement of the at least one moveable valve element in an opposite direction an endless number of times.   
     
     
         2 . An activation mechanism according to  claim 1 , wherein the control unit is configured to apply at least a first time window to the sensed signal and to determine whether the sensed signal remains stable relative to at least a first threshold value within the at least first time window or not, where the at least one valve element is activated if a stable pressure level is detected. 
     
     
         3 . An activation mechanism according to  claim 1 , wherein the actuator unit comprises at least one solenoid element for inductively moving at least one push rod mechanically connected to the at least one valve element. 
     
     
         4 . An activation mechanism according to  claim 1 , wherein the at least one valve element is a poppet valve arranged inside a chamber of the activation mechanism, wherein the poppet valve is configured to move relative to the chamber when activated. 
     
     
         5 . An activation mechanism according to  claim 4 , wherein at least one sealing element is arranged in an outer surface of the poppet valve, the outer surface is facing an inner surface of the chamber, wherein the at least one sealing element remains in contact with the inner surface during movement of the poppet valve. 
     
     
         6 . An activation mechanism according to  claim 4 , wherein a valve housing is arranged inside the chamber, wherein the poppet valve extend at least partly into the valve housing via an opening in one end of the valve housing. 
     
     
         7 . An activation mechanism according to  claim 1 , wherein the control unit is further connected to activation circuit, e.g. a pressure switch, which is configured to activate the control unit at a predetermined pressure level. 
     
     
         8 . An activation mechanism according to  claim 1 , wherein the activation mechanism is configured to be implemented in a cavity located in an outer side surface of a housing of the circulating sub. 
     
     
         9 . An activation mechanism according to  claim 1 , wherein the at least one sensor comprises a first sensor configured to sense a first pressure of the drilling fluid in the first fluid conduit and a second sensor configured to sense a second pressure of the drilling fluid in a returning drilling fluid when installed, wherein the control unit is configured to determine a differential pressure using the first and second pressures. 
     
     
         10 . A circulating sub for positioning in a borehole, comprising:
 a housing having an outer side surface facing an inner wall of the borehole, where the housing is configured to be placed inside the borehole,   a first fluid conduit connected to a first opening in one end of the circulating sub and a second opening in the other end of the circulating sub for leading a drilling fluid through the circulating sub,   at least a second fluid conduit in fluid communication with the first fluid conduit via at least one inner opening, and connected to at least one outer opening located in the outer side surface of the housing,   wherein   at least one cavity is provided in the outer side surface of the housing, in which at least one activation mechanism according to  claim 1  is arranged.   
     
     
         11 . A circulating sub according to  claim 9 , wherein a removable cover is arranged at an opening of the at least one cavity for closing off the at least one cavity, wherein an optional seal is provided between said cover and the housing. 
     
     
         12 . A circulating sub according to  claim 10 , wherein at least one of the inner and outer openings of the second fluid conduit comprises a nozzle configured to regulate the speed of the drilling fluid entering or exciting the second conduit. 
     
     
         13 . A method for activating a circulating sub using an activation mechanism according to  claim 1 , where the method comprises the steps of:
 positioning the circulating sub at a predetermined depth of a borehole,   increasing a pressure of a drilling fluid located in the first fluid conduit of the circulating sub,   monitoring the pressure of the drilling fluid inside the first fluid conduit using at least one pressure sensor,   activating the circulating sub when a certain event is detected using a control unit, wherein   the step of activating the circulating sub comprises moving a valve element arranged in a chamber of the activation mechanism from a closed position to an open position so that at least a second fluid conduit is open for leading at least a part of the drilling fluid through the second fluid conduit.   
     
     
         14 . A method for activating a circulating sub according to  claim 13 , wherein the sensed pressure is monitored within at least one time window, and the circulating sub is activated by the control unit if it is determined that the sensed pressure has remained stable relative to at least one threshold value within the at least one time window. 
     
     
         15 . A method for activating a circulating sub according to  claim 13 , wherein an action circuit activates the control unit when the sensed pressure of the drilling fluid exceeds a predetermined pressure level.