Patent ID: 7064551

Claim:
Process for determining the resistivity (Rt) of a geological formation ( 9 ) surrounding a well ( 10 ) equipped with a casing ( 11 ) consisting of several casing segments ( 11 . i , 11 . s ) following each other, in which two successive casing segments ( 11 . i , 11 . s ) have an overlapping part ( 1 ), the cement ( 3 ) located between the casing ( 11 ) and the formation ( 9 ) and in the overlapping part ( 1 ) between two adjacent casing segments ( 11 . i , 11 . s ), in which a current is injected into the casing ( 11 ) to cause a leakage current (Ifor) into an area ( 8 ) of the formation ( 9 ) for which measurements are required, offset from the overlapping part ( 1 ), the leakage current (Ifor) in the measurement area ( 8 ) is determined and is used to deduce the measured resistivity (Rm) of the formation in the measurement area ( 8 ), wherein a current is injected into the casing ( 11 ) to cause a current leakage (Icem) in the cement ( 3 ) of the overlapping part ( 1 ), the leakage current (Icem) in the cement ( 3 ) in the overlapping part ( 1 ) is determined, and is used to deduce the measured resistivity (Rcem) of the cement ( 3 ), and the measured resistivity (Rm) of the formation is corrected using a factor to take account of the measured resistivity (Rcem) of the cement ( 3 ) to obtain the resistivity (Rt) of the formation ( 9 ).