Schlumberger Technology Corporation

Marie-Therese Gounot

Jean-Claude Trouiller

Paul Beguin

Dominique Benimeli

Peter Van Der Wal

Francois Hecquet

Patrick Ehret

Method and apparatus for determining the resistivity of a formation through which a cased well passes

The invention relates to a method of surveying the resistivity of a geological formation through which a borehole provided with metal casing passes, in which method a leakage current is caused to leak into the formation outside the casing, and the leakage current is determined on a casing section at a certain level, the leakage current being indicative of the resistivity of the formation. According to a characteristic of the invention, the resistivity is determined on the basis of the leakage current by applying a factor that depends on the distance z between the level and the surface.

Methods of determining resistivity of a formation through which a cased borehole passes

The invention relates to a logging method and apparatus for determining the electrical resistivity of an earth formation traversed by a borehole. The resistivity is determined using a measuring pad which has a central electrode operable to deliver a measuring current. The measuring current is focused radially by means of two focusing systems: an active focusing system which focuses the measuring current in a first direction; and a passive focusing system which focuses the measuring current in a second direction perpendicular to said first direction.

Method and apparatus for measuring the resistivity of earth formations

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Le Vesinet, France

Marie-Therese Gounot