Method and device for determining the nature of a formation at the head of drilling tool

Abstract

The invention concerns a method for determining the nature of a formation ( 11 ) at the bottom ( 8 ) of a drilling well ( 4 ), the well ( 4 ) being equipped with a drill string ( 2 ) fitted with a drilling tool ( 14 ) and filled with a drilling fluid ( 18 ) circulating within the well ( 4 ) from inside to outside said drill string ( 2 ). According to the invention, the method includes the following steps: differential measurement, between the outside and the inside of the drill string ( 2 ) in the vicinity of the drilling tool ( 14 ), of at least one physicochemical property of the drilling fluid ( 18 ); using the differential measurement to determine the nature of the formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 14 ). The invention also concerns a device ( 9 ) suitable for implementing such method.

1 . Method for determining the nature of a formation ( 11 ) at the bottom ( 8 ) of a drilling well ( 4 ), the well ( 4 ) being equipped with a drill string ( 2 ) fitted with a drilling tool ( 14 ) and filled with a drilling fluid ( 18 ) circulating within the well ( 4 ) from inside to outside said drill string ( 2 ), characterised in that it comprises the following steps: 
 differential measurement between the outside and the inside of the drill string ( 2 ), in the vicinity of the drilling tool ( 14 ), of at least one physicochemical property of the drilling fluid ( 18 );    using the differential measurement to determine the nature of the formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 4 ).    
     
     
         2 . Method according to  claim 1 , characterised in that the determination of the nature of the formation ( 11 ) at the bottom ( 8 ) of drilling well ( 4 ) consists of a qualitative determination of at least one physicochemical property of the formation ( 11 ) at the bottom ( 8 ) of drilling well ( 4 ).  
     
     
         3 . Method according to  claim 1  or  claim 2 , characterised in that the determination of the nature of formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 4 ) consists of a quantitative determination of at least one physicochemical property of the formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 4 ).  
     
     
         4 . Method according to  claim 1 , characterised in that the determination of the nature of formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 4 )is made by comparison with pre-set values.  
     
     
         5 . Method according to any of the preceding claims, characterised in that it comprises a data transmission step, from the bottom ( 8 ) of the drilling well ( 4 ) towards a ground surface level ( 6 ).  
     
     
         6 . Method according to any of the preceding claims, characterised in that measurement is made of at least one of the physicochemical properties of drilling fluid ( 18 ) chosen from among the group made up of electrical impedance, pH, nuclear density and electric voltage.  
     
     
         7 . Method according to any of the preceding claims, characterised in that it is implemented continuously during a drilling operation.  
     
     
         8 . Device ( 9 ) for determining the nature of a formation ( 11 ) at the bottom ( 8 ) of a drilling well ( 4 ), the well ( 4 ) being equipped with a drill string ( 2 ) fitted with a drilling tool and filled with a drilling fluid ( 18 ) circulating within the well ( 4 ) from inside to outside said drill string ( 2 ), the said device comprising primary ( 26 ) measuring means and secondary measuring means ( 28 ) mounted on the drill string ( 2 ) in the vicinity of the drilling tool ( 14 ), characterised in that the primary measuring means ( 26 ) and the secondary measuring means are suitable for measuring at least one physicochemical property of the drilling fluid ( 18 ) respectively located inside and outside said drill string ( 2 ), so as to obtain a differential measurement of each measured physicochemical property, at least one measured physicochemical property enabling determination of the nature of formation ( 11 ) at the bottom ( 8 ) of the drilling well ( 4 ).  
     
     
         9 . Device ( 9 ) according to  claim 8 , characterised in that the device ( 9 ) also comprises tertiary measuring means ( 30 ) mounted on the drill string ( 2 ) in the vicinity of the drilling tool ( 14 ) and suitable for measuring at least one physicochemical property of a formation ( 33 ) located at the level of the tertiary measuring means ( 30 ).  
     
     
         10 . Device ( 9 ) according to  claim 8  or  claim 9 , characterised in that the device ( 9 ) comprises a data transmitter ( 10 ) assembled on the drill string ( 2 ) in the vicinity of the measuring means ( 26 ,  28 ,  30 ), and a data receiver ( 16 ) positioned outside the drilling well ( 4 ).  
     
     
         11 . Device ( 9 ) according to any of  claims 8  to  10 , characterised in that the primary ( 26 ) and secondary ( 28 ) measuring means are able to measure at least one of the physicochemical properties of the drilling fluid ( 18 ) chosen from the group comprising impedance, pH, nuclear density and electric voltage.