Under-reamer tool

Abstract

The invention provides an under-reamer tool and method for creating a large diameter volume within a well bore. The under-reamer tool includes a mandrel for connection to a drill pipe and for supporting a torque arm assembly and hole initiator assembly. The hole initiator assembly, upon activation, creates a nominally larger diameter volume that triggers activation of the torque arm assembly thereby allowing the torque arm assembly to extend to cut away a cutting face thereby creating a significantly larger diameter volume within the wellbore as the under-reamer is rotated within the wellbore. Reverse circulation of a circulation medium in combination with the geometry of the cutting face provides effective removal of the cuttings from the cutting face.

What is claimed is:  
     
         1 . An under-reamer tool for creating a large diameter cavity within a well bore comprising: 
 a mandrel for operative connection to a drill pipe, the mandrel operatively supporting a torque arm assembly and hole initiator assembly, the hole initiator assembly, upon activation, for creating a nominally larger diameter cavity thereby triggering activation of the torque arm assembly.    
     
     
         2 . An under-reamer tool as in  claim 1  wherein the mandrel and hole initiator assembly are hollow enabling reverse circulation of the well bore after activation of the hole initiator assembly.  
     
     
         3 . An under-reamer tool as in  claim 1  wherein the torque arm assembly includes a cutter arm carrier in sliding engagement with the mandrel.  
     
     
         4 . An under reamer tool as in  claim 1  wherein the torque arm assembly includes at least one cutter arm and at least one torque arm, wherein each cutter arm is pivotally connected to the cutter arm carrier and to a torque arm and wherein each torque arm is pivotally connected to the mandrel.  
     
     
         5 . An under-reamer tool as in  claim 1  wherein the torque arm assembly includes an activator spring operatively connected to the mandrel for biasing the at least one cutter arm and the at least one torque arm to an extended position.  
     
     
         6 . An under-reamer tool as in claim wherein the torque arm assembly includes a torque arm carrier for pivotal connection to each torque arm.  
     
     
         7 . An under-reamer tool as in clam  6  wherein the torque arm carrier is slidingly engaged with the mandrel.  
     
     
         8 . An under-reamer tool as in  claim 1  wherein the hole initiator system includes at least one initiator finger operable between a retracted and an extended position wherein the at least one initiator finger has dimensions such that in the extended position, the at least one initiator finger is in cutting contact with the borehole or the casing of a borehole.  
     
     
         9 . An under-reamer tool as in  claim 8  wherein the at least one initiator finger has a first end extending into the mandrel for enabling actuation of the hole initiator system in response to an initiator tool contacting the first end.  
     
     
         10 . An under-reamer as in  claim 1  further comprising a drill bit in operative connection with the mandrel for crushing oversized debris cuttings that are milled from a formation during an under-reaming operation.  
     
     
         11 . An under-reamer tool as in  claim 3  wherein the torque arm carrier includes at least one flushing port behind the torque arm.  
     
     
         12 . An under-reamer tool as in  claim 6  wherein the cutter arm carrier includes at least one flushing port behind the cutter arm  
     
     
         13 . An under-reamer tool for creating a large diameter cavity within a well bore comprising: 
 a mandrel for operative connection to a drill pipe, the mandrel operatively supporting a torque arm assembly and a hole initiator assembly, the hole initiator assembly, upon activation, for creating a nominally larger diameter cavity thereby triggering activation of the torque arm assembly, wherein the torque arm assembly includes a cutter arm carrier, a torque arm, a torque arm carrier and an activator spring, the cutter arm carrier in sliding engagement with the mandrel, the torque arm pivotally connected to the cutter arm carrier and to a cutter arm, the torque arm pivotally connected to the mandrel and the activator spring operatively connected to the mandrel for biasing the at least one cutter arm and the at least one torque arm to an extended position.    
     
     
         14 . An under-reamer tool as in  claim 13  wherein the hole initiator system includes at least one initiator finger operable between a retracted and an extended position wherein the at least one initiator finger has dimensions such that in the extended position, the at least one initiator finger is cutting contact with the borehole or the casing of a borehole.  
     
     
         15 . An under-reamer tool as in  claim 14  wherein the at least one initiator finger has a first end extending into the mandrel for enabling actuation of the hole initiator system in response to an initiator tool contacting the first end.  
     
     
         16 . A method of under-reaming a well bore comprising the steps of: 
 advancing an under-reamer tool on a drill string as in  claim 1  to a location in a well bore;    activating the at least one initiating fingers;    advancing the under-reamer tool to create a nominally larger diameter cavity and trigger the torque arm assembly to create a large diameter cavity.    
     
     
         17 . A method as in  claim 16  further comprising withdrawing the drill pipe to retract and extract the under-reamer.  
     
     
         18 . A method as in  claim 16  wherein the well bore is reverse circulated during advancement of the under-reamer tool while creating a large diameter cavity.  
     
     
         19 . A method as in  claim 16  wherein the cutter arms are interconnected to ensure simultaneous extension and retraction.  
     
     
         20 . A method as in  claim 16  wherein the cutter arms are allowed to cut a tapered hole that ensures that the cuttings are preferentially travel to the bottom of the well bore to be further evacuated by reverse circulation.  
     
     
         21 . A method as in  claim 16  wherein the cutter arms are allowed to cuta tapered hole that ensures that the cuttings are preferentially travel to the bottom of the well bore and any oversized cutting debris to be reduced in size by a typical tri-cone bit to better enable all the cutting debris to be crushed to a size that can be the further evacuated by reverse circulation.  
     
     
         22 . An under-reamer tool as in  claim 1  wherein the under-reamer tool includes a drill pipe connector connected to the main mandrel with non-torque transmitting shear pins.  
     
     
         23 . An under-reamer tool as in  claim 1  wherein the under-reamer tool includes a drill pipe connector slidingly connected to the main mandrel, the drill pipe connector having a bumper spring between the drill pipe connector and the torque arm carrier for enabling controlled torque relief for the cutter arm assembly.