Method and a tool for electrically investigating a wall of a borehole in a geologic formation
AssigneeSchlumberger Technology Corporation
InventorsAndrew Hayman, Philip Cheung
Life of this patent
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Abstract
A method for electrically investigating a wall of a borehole in a geologic formation including injecting a current into the formation at a first position along the wall and returning the current at a second position along the wall, the formation current having a frequency below about 100 kHz, measuring a voltage in the formation between a third position and a fourth position along the wall, the third and fourth positions being located between the first and second positions, and determining an amplitude of a component of the voltage in phase with the current.
Claims11
A method for micro electrically investigating a wall of a borehole filled with a non conductive fluid in a geologic formation, the method comprising:
- injecting a current into the formation at a first position along the wall and returning the current at a second position along the wall, the formation current having a frequency below about 100 kHz;
- measuring a voltage in the formation between a third position and a fourth position along the wall, the third and fourth positions being located between the first and second positions;
- wherein the method further comprises:
- calculating a formation current by subtracting a leakage current from the current;
- and
- determining an amplitude of a component of the voltage in phase with the formation current.
A well-logging tool for making micro electrical measurements in a borehole filled with a non conductive fluid comprising:
- a pad adapted to be placed into contact with a wall of the borehole;
- a source electrode located on the pad, the source electrode adapted to inject an electrical current into a formation;
- a return electrode located on the pad, the return electrode adapted to receive the electrical current injected by the source electrode;
- an ammeter operatively connected to a circuit including the source and return electrodes;
- at least one pair of voltage electrodes located on the pad between the source and the return electrodes;
- wherein the tool further comprises:
- a phase sensitive detector operatively coupled to the voltage electrodes and adapted to measure an amplitude of a component of a voltage across the voltage electrodes in phase with the electrical current.
Dependencies are inferred from the claim text.