Underreamer Apparatus and Method

Abstract

A wellbore underreamer has a tubular body, a central body cavity, and pivotally mounted blades in slots on the periphery of the tubular body. A translatable piston in the central body cavity is urged away from cam surfaces on the blades by a biasing spring. The piston has an orifice restricted fluid passage and translates in response to fluid pressure determined by the selected piston orifice and biasing spring. Fluid circulates through the piston fluid passage and fluid passages in the underreamer while piston movement is restrained by the spring. At a predetermined fluid pressure, the piston moves to engage the blade cam surfaces to pivotally extend the blades outward from the blade slots. The blades are held in the slots by a spring biased ball until they are extended by the piston.

I claim: 
     
         1 . An underreamer apparatus comprising:
 (a) a longitudinally extending tubular body, said tubular body having a top end, a bottom end, a central cavity, and at least one elongated blade retaining slot;   (b) a blade pivotally mounted within said elongated blade slot;   (c) a piston positioned within said central cavity of said tubular body;   (d) a spring creating a biasing force urging said piston away from said blade toward said top end of said tubular body; and   (d) whereby movement of said piston against said biasing force of said spring to engage said blade will thereby pivot said blade radially outward from said blade slot and said tubular body.   
     
     
         2 . The underreamer apparatus recited in  claim 2 , further comprising:
 (a) a plurality of longitudinally extending fluid passageways in said tubular body;   (b) fluid ports in said piston in fluid communication said fluid passageways in said tubular body and said central cavity of said tubular body;   (c) a central fluid passage in said piston in fluid communication with said central cavity of said tubular body; and   (d) at least one fluid port in communication with at least one of said longitudinally extending fluid passageways in said body whereby fluid may exit said tubular body.   
     
     
         3 . The underreamer apparatus recited in  claim 2  wherein at least one of said longitudinally extending fluid passageways in said tubular body directs fluid to said blade and said elongated blade slot. 
     
     
         4 . The underreamer apparatus recited in  claim 3  further comprising a flow control orifice positioned in said central fluid passage of said piston. 
     
     
         5 . The underreamer recited in  claim 4  wherein:
 (a) fluid may be circulated through said piston fluid passage and said plurality of fluid passageways while movement of said piston in said central cavity is restrained by said spring; 
 (b) wherein said piston may be translated against said spring in response to fluid pressure determined by a selected said flow control orifice and a selected said spring; and 
 (c) wherein fluid is provided to said central cavity of said tubular body and said piston by an attached pipestring having a central fluid bore in fluid communication with said central cavity of said tubular body. 
 
     
     
         6 . The underreamer apparatus recited in  claim 5  comprising:
 (a) a spring biased ball and ball detent combination holding said blade in said blade slot; 
 (b) at least one magnet contained within said elongated blade slot; and 
 (c) a cam surface on said pivotally mounted blade for engagement with said piston. 
 
     
     
         7 . A wellbore underreamer comprising:
 (a) a tubular body having a central body cavity and a plurality of blade slots;   (b) a pivotally mounted blade in each said blade slot, each said blade having a cam surface and a cutting surface;   (c) a translatable piston in said central body cavity, said piston having a fluid passage restricted by an orifice; and   (d) a biasing spring urging said piston away from said cam surfaces on said blades.   
     
     
         8 . The underreamer recited in  claim 7  further comprising a plurality of fluid passageways in said tubular body around said central body cavity. 
     
     
         9 . The underreamer recited in  claim 8  wherein fluid circulates through said piston fluid passage and said plurality of fluid passageways while movement of said piston is restrained by said biasing spring. 
     
     
         10 . The underreamer recited in  claim 9  wherein said piston translates in response to fluid pressure determined by a selected size of said orifice and a selected said biasing spring. 
     
     
         11 . The underreamer recited in  claim 10  wherein said piston moves to engage said cam surface on said blades thereby pivotally extending said blades and said blade cutting surface outward from said blade slots. 
     
     
         12 . The underreamer recited in  claim 11  wherein said blades are held in said blade slots by a spring biased ball and ball detent combination. 
     
     
         13 . The underreamer recited in  claim 12  wherein at least one fluid passageway of said plurality of fluid passageways directs fluid through one of said blade slots. 
     
     
         14 . The underreamer recited in  claim 13  wherein said tubular body of said underreamer is attached to a mud motor mounted on a drillstring. 
     
     
         15 . The underreamer recited in  claim 13  wherein said tubular body of said underreamer is attached to a pipestring having a central fluid bore whereby said central fluid bore of said pipe string is in fluid communication with said central body cavity of said tubular body. 
     
     
         16 . A wellbore underreamer comprising:
 (a) a tubular body having a central body cavity and a plurality of blade slots;   (b) a pivotally mounted blade in each said blade slot, each said blade having a cam surface and a cutting surface;   (c) a translatable piston in said central body cavity, said piston having a fluid passage restricted by an orifice;   (d) a biasing spring urging said piston away from said cam surfaces on said blades; and   (e) a plurality of fluid passageways extending through said tubular body around said central body cavity.   
     
     
         17 . The underreamer recited in  claim 16  wherein:
 (a) fluid circulates through said piston fluid passage and said plurality of fluid passageways while movement of said piston is restrained by said biasing spring; 
 (b) said piston translates in response to fluid pressure determined by a selected said orifice and a selected said spring; and 
 (c) wherein said piston moves to engage said cam surface on said blades thereby pivotally extending said blades and said blade cutting surface outward from said blade slots. 
 
     
     
         18 . The underreamer recited in  claim 17  wherein said tubular body of said underreamer is attached to a pipestring having a central fluid bore whereby said central fluid bore of said pipestring is in fluid communication with said central body cavity of said tubular body. 
     
     
         19 . The underreamer recited in  claim 18  wherein at least one fluid passageway of said plurality of fluid passageways directs fluid through one of said blade slots. 
     
     
         20 . The underreamer recited in  claim 19  wherein said blades are held in said blade slots by a spring biased ball and ball detent combination.