Borehole opener

Abstract

Borehole opener, particularly for enlarging this hole underneath a casing in the field of oil prospecting, comprising a body ( 2 ) of longitudinal axis ( 3 ), a duct ( 4 ) for drilling fluid, formed longitudinally in the body ( 2 ), and at least two hole-opening arms ( 5 ) which have an active part ( 7 ) equipped with cutting means ( 8 ), which are distributed symmetrically in the body ( 2 ) about the longitudinal axis ( 3 ), and which are arranged therein in such a way that they can be moved between a position of rest ( 9 ) in the body ( 2 ) and an active position ( 10 ) partially out of the body ( 2 ); in this hole opener in order to move it from the position of rest ( 9 ) to the active position ( 10 ), each arm ( 5 ) has a face ( 12 ), internal to the body ( 2 ), designed to be subjected directly, in the same way as an active face of a piston, to the pressure of the drilling fluid flowing through the body ( 2 ).

1. A hole opener, particularly for enlarging the borehole underneath a casing, comprising:
 a body of longitudinal axis,  
 a duct for drilling fluid, formed longitudinally in the body,  
 at least two hole-opening arms, each arm having an active part equipped with cutting means distributed symmetrically in the body about the longitudinal axis and arranged in such body in a way that said arms can be moved between a position of rest in the body and an active position partially out of the body, wherein, in order to move said arms from the position of rest into the active position, each arm has a face, internal to the body, designed to be subjected directly to the pressure of the drilling fluid flowing through the body, and wherein, to move the arms from the active position into the position of rest, the hole-opener comprises an elastically effective return for returning the arms to the position of rest.  
 
     
     
       2. The hole opener as defined in  claim 1 , wherein at least one of said arms is mounted in such a way that said at least one arm can slide parallel to itself in the body so as to move from the position of rest into the active position. 
     
     
       3. A hole opener, particularly for enlarging the borehole underneath a casing, comprising:
 a body of longitudinal axis,  
 a duct for drilling fluid, formed longitudinally in the body,  
 at least two hole-opening arms, each arm having an active part equipped with cutting means distributed symmetrically in the body about the longitudinal axis and arranged in such body in a way that said arms can be moved between a position of rest in the body and an active position partially out of the body, wherein, in order to move said arms from the position of rest into the active position, each arm has a face, internal to the body, designed to be subjected directly to the pressure of the drilling fluid flowing through the body, wherein each arm is temporarily kept in a position of rest by at least one pin designed to break when the pressure of the drilling fluid flowing through the duct exceeds a predetermined value.  
 
     
     
       4. A hole opener as defined in  claim 3 , wherein at least one of said arms is mounted in the body by means of an intermediate support which acts as a housing for said at least one arm in the body and which is fixed to said at least one arm. 
     
     
       5. A hole opener as defined in  claim 4 , wherein the aforementioned pin fixes said at least one arm to said intermediate support. 
     
     
       6. A hole opener as claimed in  claim 5 , wherein the intermediate support, the at least one arm, the aforementioned elastically effective return and the pin constitute an assembly designed to be assembled in advance outside the body and then installed in the body. 
     
     
       7. A hole opener as defined in  claim 3 , wherein at least one of said arms is mounted in the body by means of an intermediate support which acts as a housing for said at least one arm in the body and which is fixed to said at least one arm. 
     
     
       8. A hole opener, particularly for enlarging the borehole underneath a casing, comprising:
 a body of longitudinal axis,  
 a duct for drilling fluid, formed longitudinally in the body,  
 at least two hole-opening arms, each arm having an active part equipped with cutting means distributed symmetrically in the body about the longitudinal axis and arranged in such body in a way that said arms can be moved between a position of rest in the body and an active position partially out of the body, wherein, in order to move said arms from the position of rest into the active position, each arm has a face, internal to the body, designed to be subjected directly to the pressure of the drilling fluid flowing through the body, wherein each arm is temporarily kept in a position of rest by at least one pin designed to break when the pressure of the drilling fluid flowing through the duct exceeds a predetermined value wherein the pin comprises a region of calibrated weakness.  
 
     
     
       9. A hole opener, particularly for enlarging the borehole underneath a casing, comprising:
 a body of longitudinal axis,  
 a duct for drilling fluid, formed longitudinally in the body,  
 at least two hole-opening arms, each arm having an active part equipped with cutting means distributed symmetrically in the body about the longitudinal axis and arranged in such body in a way that said arms can be moved between a position of rest in the body and an active position partially out of the body, wherein, in order to move said arms from the position of rest into the active position, each arm has a face, internal to the body, designed to be subjected directly to the pressure of the drilling fluid flowing through the body, wherein on an outer face, between two successive arms, the body has a longitudinal passage for returning drilling fluid, and  
 a boss arranged in this passage so as to define the drilling fluid onto that part of the wall of the borehole on which the arms are acting.  
 
     
     
       10. A hole opener as defined in  claim 3 , wherein the travel of at least one arm between the position of the rest and the active position is limited by stops, and also by the pin so that in the position of rest, said at least one arm is fully retracted into the body and so that in the active position, said at least one arm sweeps through an area, the largest diameter of which area is equal to between 1.05 and 1.3 times the nominal diameter of a drill bit associated with the hole opener for a combined drilling and hole-opening operation.