Patent ID: 7259564

Claim:
Method for determining the position, in a formation ( 1 ) containing at least one electrolytic liquid, of an interface ( 6 ) in relation to a bore hole ( 2 ), comprising the following steps: a o ) stimulating, from the bore hole ( 2 ) at a first depth, the interface ( 6 ), at a first instant (t 1 ), with a first excitation signal ( 20 ) corresponding to a first type of energy in such a way tat said first excitation signal ( 20 ) is converted at the level of the interface ( 6 ) into a first response signal ( 23 ) corresponding to a second type of energy, one of the energies being a mechanical type of energy and the other an electromagnetic type of energy, b o ) detecting the first response signal ( 23 ) at a second instant (t 2 ) by means of a first detection device ( 9 ) placed in the bore hole ( 2 ) and, if the first response signal ( 23 ) is greater than or equal to a first threshold, calculating the distance (d 1 ) between the interface ( 6 ) and the first detection device ( 9 ) from the time separating the first instant (t 1 ) and the second instant (t 2 ) and knowing the propagation velocity (Vp) of sound in the formation ( 1 ), c o ) at least in the case where the first response signal ( 23 ) is less than the first detection threshold, detecting the first excitation signal ( 20 ) after a reflection against the interface ( 6 ) at a third instant (t 3 ) by means of a second detection device ( 10 ) placed in the bore hole ( 2 ) and calculating the distance (d 2 ) between the interface ( 6 ) and the second detection device ( 10 ) from the time separating the first instant (t 1 ) and the third instant (t 3 ) and knowing the propagation velocity (V), in the formation ( 1 ), of the first excitation signal ( 20 ).