Method of compensating laterlog measurements for perturbation of survey voltage by cable armor voltage
AssigneeHalliburton Energy Services, Inc.
InventorsRobert A. Moore, Horacio A. Zea
Life of this patent
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Abstract
A method and apparatus are disclosed for correcting erroneous downhole resistivity measurements. In particular, capacitive coupling downhole leads to erroneous resistivity readings. The invention compensates for such coupling by measuring a survey voltage between the resistivity tool voltage and a reference voltage on the wireline cable. A correction voltage is measured between a point on the armor around the wireline cable and the reference voltage. The characteristics of a transmission wireline used at a specific site are measured and are combined with the measured downhole correction voltage and survey voltage to determine more accurately formation resistivity.
Claims12
A resistivity tool configured for use in a borehole, and configured for attachment to a wireline conductor with armor, comprising:
- a current source;
- a laterolog array connected to said current source;
- a return electrode connected to said laterolog array;
- a first measurement amplifier connected to said laterolog array and configured to measure a voltage between said laterolog array and a reference voltage;
- and
- a second measurement amplifier configured for connection to said armor, said second measurement amplifier configured to measure a voltage between said armor and said reference voltage.
A resistivity logging system comprising:
- a current source suitable for insertion in a wellbore;
- a return electrode configured for connection to said current source;
- a reference electrode configured for connection to said current source and suitable for placement at a location outside said wellbore;
- a first comparator suitable for connection to said current source, said first comparator suitable to generate a survey voltage dependent upon a potential drop between said current source and a reference voltage;
- a second comparator suitable to generate a correction voltage to measure a potential drop between said reference voltage and a first voltage;
- a processor to compute resistivity based on said survey voltage and said correction voltage.
A method of operating a resistivity tool comprising:
- (a) electrically connecting a laterolog array of said resistivity tool and a reference electrode of said resistivity tool such that the voltage at said laterolog array equals zero, said resistivity tool further comprising a wireline connection between said laterolog array and said reference electrode, said wireline having armor along at least a portion of its length, a first comparator attached to said laterolog array and a first point located along said wireline, said first comparator providing a first output, a second comparator attached proximate to said first point and to a second point located along said armor, and said second comparator providing a second output;
- (b) applying a voltage to said second point;
- (c) monitoring said first output of said first comparator and said second output of said second comparator.
Dependencies are inferred from the claim text.