Milling and Collecting Debris in Depleted or Sub-Hydrostatic Wells

Abstract

An approach to milling obstructions in sub-hydrostatic wells uses a bottom hole assembly. The bottom hole assembly includes a tool to collect debris downhole and then mechanically, rather than hydraulically, transport the debris to the surface after milling.

What is claimed is: 
     
         1 . A bottom hole assembly for milling obstructions in sub-hydrostatic wells, the bottom hole assembly comprising:
 a milling tool comprising a primary bit and a side window or a reverse circulation port;   a junk basket tool rotatably attached to the milling tool; and   a downhole high-pressure coiled tubing motor or electric motor coupled to the milling tool and operable to rotate a bit of the milling tool.   
     
     
         2 . The bottom hole assembly of  claim 1 , wherein the junk basket tool is an inline Venturi junk basket tool. 
     
     
         3 . The bottom hole assembly of  claim 1 , wherein the junk basket tool is an annular Venturi junk basket tool. 
     
     
         4 . The bottom hole assembly of  claim 3 , wherein the annular Venturi junk basket tool comprises a flow shroud extending along the downhole high-pressure coiled tubing motor to define an annulus between the motor and the flow shroud. 
     
     
         5 . The bottom hole assembly of  claim 4 , wherein the milling tool further comprises a secondary drill bit extendable through the primary drill bit and activatable separately from the primary drill bit. 
     
     
         6 . The bottom hole assembly of  claim 5 , further comprising an umbrella-type extension coupled to the secondary drill bit, the umbrella-type extension moveable between an undeployed position within the secondary drill bit and a deployed position extending radially outward from the secondary drill bit. 
     
     
         7 . The bottom hole assembly of  claim 6 , further comprising a fill indicator comprising a poppet valve. 
     
     
         8 . The bottom hole assembly of  claim 7 , wherein the poppet valve is disposed inside the Venturi junk basket tool at an uphole end of the Venturi junk basket tool. 
     
     
         9 . The bottom hole assembly of  claim 4 , further comprising a nitrogen gas pump coupled to the coiled tubing and downhole control valves operable to separate an interior of the coiled tubing from the annulus between the motor and the flow shroud. 
     
     
         10 . The bottom hole assembly of  claim 1 , wherein the milling tool further comprises a secondary drill bit extendable through the primary drill bit and activatable separately from the primary drill bit. 
     
     
         11 . The bottom hole assembly of  claim 10 , further comprising an umbrella-type extension coupled to the secondary drill bit, the umbrella-type extension moveable between an undeployed position within the secondary drill bit and a deployed position extending radially outward from the secondary drill bit. 
     
     
         12 . The bottom hole assembly of  claim 1 , further comprising a fill indicator comprising a poppet valve. 
     
     
         13 . The bottom hole assembly of  claim 12 , wherein the poppet valve is disposed inside the Venturi junk basket tool at an uphole end of the Venturi junk basket tool. 
     
     
         14 . A method for milling obstructions in a wellbore, the method comprising:
 assembling a bottom hole assembly comprising:
 a milling tool comprising a primary bit and a side window or a reverse circulation port; 
 a Venturi junk basket tool rotatably attached to the milling tool; and 
 a downhole high-pressure coiled tubing motor or electric motor coupled to the milling tool and operable to rotate a bit of the milling tool; 
   running the bottom hole assembly downhole in the wellbore to an obstruction in the wellbore; and   operating the milling tool to remove the obstruction while also operating the Venturi junk basket tool to collect debris generated by operation of the milling tool.   
     
     
         15 . The method of  claim 14 , wherein the Venturi junk basket tool is an inline Venturi junk basket tool. 
     
     
         16 . The method of  claim 14 , wherein the Venturi junk basket tool is an annular Venturi junk basket tool. 
     
     
         17 . The method of  claim 16 , wherein the annular Venturi junk basket tool comprises a flow shroud extending along the downhole high-pressure coiled tubing motor to define an annulus between the motor and the flow shroud. 
     
     
         18 . The method of  claim 14 , further comprising operating a secondary drill bit extendable through the primary drill bit and activatable separately from the primary drill bit. 
     
     
         19 . The method of  claim 18 , further comprising positioning an umbrella-type extension coupled to the secondary drill bit downhole of the obstruction and moving the umbrella-type extension between an undeployed position within the secondary drill bit and a deployed position extending radially outward from the secondary drill bit. 
     
     
         20 . The method of  claim 14 , wherein the bottom hole assembly further comprises a fill indicator comprising a poppet valve disposed inside the Venturi junk basket tool at an uphole end of the Venturi junk basket tool.