Drill string

Abstract

A drill string for use in the directional drilling of wellbores is described. A downhole reamer apparatus (202) is mounted in a drill string incorporating a drilling motor (300), stabiliser (302) and drill bit (304) operable either by rotation of the drill string or activation of the drilling motor (300). The drill string is located in wellbore (306) at the end of drill pipe (310). If the operator wishes to drill upwardly, the reamer elements are locked in the retracted condition. This results in the reamer apparatus being under gauge which results in build angle (308) pointing the drill bit upwardly.

1 . A drill string comprising:
 a drill bit;   a drilling motor, wherein the drill bit is configured to be rotated either by rotation of the drill string or by operation of the drilling motor; and   a downhole reamer apparatus comprising:
 a mandrel arranged to be disposed in the drill string; 
 an outer housing disposed on the mandrel, wherein the mandrel is rotatable relative to the outer housing; and 
 at least one reaming element moveable between an inwardly retracted condition and an outwardly deployed condition in response to rotation of the mandrel in a first direction relative to the outer housing; 
   wherein operation of the drilling motor to rotate the drill bit causes a reaction torque in the drill string in a second direction, opposite to the first direction, to cause the mandrel to rotate in the second direction relative to the outer housing to move said at least one reaming element to the inwardly retracted condition.   
     
     
         2 . A drill string apparatus according to  claim 1 , wherein the downhole reamer apparatus further comprises:
 at least one first recess formed in the mandrel, wherein said at least one reaming element sits in said at least one first recess in the inwardly retracted condition; and   at least one inclined surface disposed adjacent said at least one first recess, such that when said mandrel is rotated relative to said outer housing in said first direction, said at least one inclined surface urges said at least one reaming element into the outwardly deployed condition.   
     
     
         3 . A drill string apparatus according to  claim 2 , wherein the downhole reamer apparatus further comprises at least one aperture formed in said outer housing through which said at least one reaming element projects in the outwardly deployed condition. 
     
     
         4 . A drill string apparatus according to  claim 2 , wherein said at least one reaming element is retained in the apparatus by a pair of wings configured to engage an inner surface of said outer housing. 
     
     
         5 . A drill string apparatus according to  claim 1 , further comprising at least one retention spring arranged to retain said at least one reaming element in said at least one first recess. 
     
     
         6 . A drill string apparatus according to  claim 1 , wherein said mandrel further comprises at least one second recess in which at least one lug mounted to said outer housing is received, said at least one second recess being sized to limit the angle of rotation possible between the mandrel and the outer housing by engagement of said at least one lug with the sides of said second recess. 
     
     
         7 . A drill string apparatus according to  claim 6 , further comprising a torsional spring arranged to bias the mandrel to the position relative to the outer housing in which said at least one reaming element is in the inwardly retracted condition. 
     
     
         8 . A drill string apparatus according to  claim 1 , further comprising a plurality of reaming elements disposed around the mandrel. 
     
     
         9 . A drill string apparatus according to  claim 1 , wherein the weight of the drill string urges the mandrel to rotate in the second direction relative to the outer housing to move said at least one reaming element to the inwardly retracted condition. 
     
     
         10 . A downhole reamer apparatus comprising:
 a mandrel arranged to be disposed in a drill string;   an outer housing disposed on the mandrel, wherein the mandrel is rotatable relative to the outer housing; and   at least one reaming element moveable between an inwardly retracted condition and an outwardly deployed condition in response to rotation of the mandrel in a first direction relative to the outer housing;   wherein said outer housing is moveable along a longitudinal axis of said mandrel to enable locking means to be engaged to prevent rotation of the mandrel relative to the outer housing.   
     
     
         11 . An apparatus according to  claim 10 , wherein said locking means comprises at least one first male spline or first female spline disposed on an end of said outer housing; and
 at least one corresponding second female spline or second male spline fixed relative to the mandrel;   wherein movement of said outer housing along the longitudinal axis of the mandrel enables said at least one first male spline or first female spline to engage the corresponding said at least one second female spline or second male spline to prevent rotation of the mandrel relative to the outer housing and set a first outward extend to which said at least one reaming element is deployed.   
     
     
         12 . An apparatus according to  claim 11 , further comprising at least one third female spline disposed on one of an end of said outer housing or fixed relative to the mandrel, wherein said at least one third female spline has a depth different to the depth of said at least one second female spline to prevent rotation of the outer housing on the mandrel when engaged with said at least one first or second male spline and set a second outward extent to which said at least one reaming element is deployed. 
     
     
         13 . An apparatus according to  claim 11 , further comprising biasing means to urge the outer housing into a longitudinal position on the mandrel in which none of said first, second or third male or female splines are engaged to enable free rotation of said outer housing on said mandrel. 
     
     
         14 . An apparatus according to  claim 10 , wherein said outer housing is moveable along the longitudinal axis of said mandrel in response to an increase in fluid pressure in a longitudinal bore of said mandrel. 
     
     
         15 . An apparatus according to  claim 14 , further comprising at least one expansion chamber in fluid communication with said longitudinal bore, wherein an increase in fluid pressure in said expansion chamber causes said outer housing to move along the longitudinal axis of the mandrel. 
     
     
         16 . An apparatus according to  claim 15 , further comprising first valve means configured to prevent longitudinal movement of said outer housing on the mandrel until a predetermined fluid pressure is reached in said expansion chamber. 
     
     
         17 . An apparatus according to  claim 15 , further comprising a hydraulic locking and return means defining a chamber of fixed volume, said chamber further comprising:
 a first chamber in which said biasing means is disposed;   a second chamber separated from said first chamber by said first valve means, wherein a floating piston is disposed in said second chamber such that when said first valve means opens when fluid pressure in the expansion chamber reaches said predetermined pressure, hydraulic fluid disposed in said first chamber vents through said first valve means into said second chamber to move said floating piston relative to said mandrel.   
     
     
         18 . An apparatus according to  claim 17 , further comprising second valve means disposed between said first and second chambers, said second valve means configured to enable hydraulic fluid to return from said second chamber into said first chamber in response to pressure in the expansion chamber decreasing below said predetermined pressure. 
     
     
         19 . An apparatus according to  claim 14 , further comprising at least one annular port formed in said mandrel to enable fluid to vent from the longitudinal bore into the mandrel when a corresponding port disposed on said outer housing is aligned with said at least one annular port. 
     
     
         20 . A drill string comprising:
 a drill bit;   a drilling motor, wherein the drill bit is configured to be rotated either by rotation of the drill string or by operation of the drilling motor; and   a downhole reamer apparatus according to  claim 10 .