Expandable Bi-Center Drill Bit

Abstract

A downhole tool for enlarging a borehole, the tool including a body having a central axis, an uphole end, a downhole end, a bore extending from the uphole end, and an aperture extending radially from the bore to a radially outer surface of the body. Additionally, the tool includes a mandrel disposed in the bore, the mandrel having a first end, a second end, a radially outer surface, and a radially inner surface. The mandrel outer surface includes an inclined surface. Further, the tool includes a first blade disposed in the aperture. The first blade has a radially retracted position and a radially extended position configured to engage with a borehole sidewall to enlarge the borehole. The mandrel is configured to translate axially relative to the body to slide the inclined surface along the first blade to transition the first blade between the radially refracted and extended positions.

What is claimed is: 
     
         1 . A drill bit for drilling a borehole in a subterranean formation, the drill bit comprising:
 a bit body having a central axis, an uphole end configured to be coupled to a drill string, and a downhole end including a cutting structure configured to engage the formation, wherein the bit body includes a bore extending axially from the uphole end and an aperture extending radially from the bore to a radially outer surface of the bit body;   a mandrel movably disposed in the bore, wherein the mandrel has a first end, a second end, a radially outer surface extending axially from the first end to the second end, and a radially inner surface extending axially from the first end to the second end, wherein the outer surface of the mandrel includes an inclined surface oriented at an acute angle relative to the central axis; and   a first blade moveably disposed in the aperture and axially positioned between the cutting structure and the uphole end, wherein the first blade has a radially retracted position and a radially extended position configured to engage a sidewall of the borehole to enlarge the borehole;   wherein the mandrel is configured to translate axially relative to the bit body to slide the inclined surface of the mandrel along the first blade to transition the first blade between the radially retracted position and the radially extended position.   
     
     
         2 . The drill bit of  claim 1 , further comprising a biasing member engaging the mandrel and configured to bias the mandrel axially toward the downhole end. 
     
     
         3 . The drill bit of  claim 2 , wherein the biasing member is coiled spring axially compressed between the first end of the mandrel and an inner shoulder of a connection sub coupled to the uphole end of the bit body. 
     
     
         4 . The drill bit of  claim 2 , wherein the first end of the mandrel comprises a first end face and the second end of the mandrel comprises a second end face, wherein the first end face has a first surface area and the second end face has a second surface area that is greater than the first surface area. 
     
     
         5 . The drill bit of  claim 1 , wherein the inner surface of the mandrel defines a central throughbore configured to flow drilling fluids therethrough. 
     
     
         6 . The drill bit of  claim 1 , wherein the first blade has a radially inner end comprising a recess including an inclined surface oriented at an acute angle β relative to the central axis and configured to slidingly engage the inclined surface of the mandrel. 
     
     
         7 . The drill bit of  claim 1 , wherein the inclined surface on the mandrel is an annular frustoconical surface. 
     
     
         8 . The drill bit of  claim 1 , wherein the axial translation of the mandrel toward the uphole end of the bit body is configured to transition the first blade to the radially extended position and axial translation of the mandrel away from the uphole end of the bit body is configured to transition the first blade to the radially retracted position. 
     
     
         9 . The drill bit of  claim 1 , wherein the first blade includes a plurality of cutter elements configured to engage the sidewall of the borehole to enlarge the borehole. 
     
     
         10 . The drill bit of  claim 1 , further comprising a fixed second blade extending radially outward from the radially outer surface of the bit body and configured to engage the sidewall of the borehole to enlarge the borehole, wherein the first blade extends radially outward beyond the second blade when the first blade is in the radially extended position. 
     
     
         11 . A downhole tool for enlarging a borehole extending through a subterranean formation, the downhole tool having a central axis and comprising:
 a body having a central axis, an uphole end configured to be coupled to a drill string, a downhole end, a bore extending axially from the uphole end, and an aperture extending radially from the bore to a radially outer surface of the body;   a mandrel movably disposed in the bore, wherein the mandrel has a first end, a second end, a radially outer surface extending axially from the first end to the second end, and a radially inner surface extending axially from the first end to the second end, wherein the outer surface of the mandrel includes an inclined surface oriented at an acute angle relative to the central axis; and   a first blade movably disposed in the aperture, wherein the first blade has a radially refracted position and a radially extended position configured to engage with a sidewall of the borehole to enlarge the borehole;   wherein the mandrel is configured to translate axially relative to the body to slide the inclined surface of the mandrel along the first blade to transition the first blade between the radially retracted position and the radially extended position.   
     
     
         12 . The downhole tool of  claim 11 , further comprising a biasing member engaging the mandrel and configured to bias the mandrel axially toward the downhole end. 
     
     
         13 . The downhole tool of  claim 12 , wherein the biasing member is coiled spring axially compressed between the first end of the mandrel and an inner shoulder of a connection sub coupled of the uphole end of the body. 
     
     
         14 . The downhole tool of  claim 11 , wherein the first end of the mandrel comprises a first end face and the second end of the mandrel comprises a second end face, wherein the first end face has a first surface area and the second end face has a second surface area that is greater than the first surface area. 
     
     
         15 . The downhole tool of  claim 11 , wherein the inner surface of the mandrel defines a central throughbore configured to flow drilling fluids therethrough. 
     
     
         16 . The downhole tool of  claim 11 , wherein the first blade has a radially inner end comprising a recess including an inclined surface oriented at an acute angle relative to the central axis and configured to slidingly engage the inclined surface of the mandrel. 
     
     
         17 . The downhole tool of  claim 11 , wherein the inclined surface on the mandrel is an annular frustoconical surface. 
     
     
         18 . The downhole tool of  claim 11 , wherein axial translation of the mandrel toward the uphole end of body is configured to transition the first blade to the radially extended position and axial translation of the mandrel away from the uphole end of the body is configured to transition the first blade to the radially refracted position. 
     
     
         19 . The downhole tool of  claim 11 , wherein the first blade includes a plurality of cutter elements configured to engage the sidewall of the borehole to enlarge the borehole. 
     
     
         20 . The downhole tool of  claim 11 , further comprising a fixed second blade extending radially outward from the radially outer surface of the bit body and configured to engage the sidewall of the borehole to enlarge the borehole, wherein the first blade extends radially outward beyond the second blade when the first blade is in the radially extended position. 
     
     
         21 . A method for enlarging a borehole extending through a subterranean formation, the method comprising:
 (a) rotating a downhole tool about a central axis, the downhole tool including a central bore and a blade;   (b) flowing drilling fluid through the bore of the downhole tool, wherein the drilling fluid has a pressure in the bore;   (c) increasing the pressure of the drilling fluid in the bore;   (d) moving a mandrel axially within the bore in a first direction in response to the increase in pressure in (c);   (e) slidingly engaging the blade with an inclined surface on the mandrel during (d); and   (f) moving the blade radially outward in response to the sliding engagement in (e).   
     
     
         22 . The method of  claim 21 , further comprising:
 (g) axially biasing the mandrel in a second direction opposite the first direction with a biasing force; and   (h) overcoming the biasing force with a force applied to the mandrel by the drilling fluid during (c).   
     
     
         23 . The method of  claim 21 , wherein the inclined surface on the mandrel is a frustoconical surface and the blade includes a frustoconical surface;
 wherein (e) comprises slidingly engaging the frustoconical surface of the mandrel with the frustoconical surface of the blade.   
     
     
         24 . The method of  21 , further comprising:
 (g) decreasing the pressure of the drilling fluid in the bore after (f);   (h) moving the mandrel axially within the central flow passage in a second direction opposite the first direction in response to (g); and   (i) moving the blade radially inward in response to (h).