Baker Hughes Corporation

Western Atlas International, Inc.

Antonio Fabris

Leonty Abraham Tabarovsky

Rashid W Khokhar

Alberto G Mezzatesta

Otto N Fanini

Gregory Boris Itskovich

Zeljko Jericevic

An azimuthal resistivity logging tool includes one or more pads for making azimuthal resistivity measurements of earth formation. Current from the pads, guard electrodes and a measure electrode are measured while monitoring the voltage difference between pairs of monitor electrodes. The pads and an adjacent portion of the tool body form a guard electrode. In addition, microelectrodes are provided on the pads for obtaining high resolution resistivity measurements.

Method and apparatus for azimuthal resistivity measurements in a borehole

A mud resistivity measuring device for use in a borehole includes a pair of current electrodes disposed between a pair of guard electrodes. The measure electrodes are carried on a recessed portion of a logging tool so that the measure current flows substantially along the borehole axis and is relatively insensitive to the formation resistivity. A pair of measure electrodes on the logging tool determines a voltage difference caused by the current flow in the borehole.

Apparatus and method for measuring mud resistivity using a defocused electrode system

A method for correcting data measured by a well logging instrument for effects of cable yo-yo. The data are first preprocessed to reduce magnitude of spatial frequency components in the data occurring within a bandwidth of axial acceleration of the logging instrument which corresponds to the cable. Then eigenvalue, of a matrix are shifted, over depth intervals where the smallest absolute value one of the eigenvalues changes sign, by an amount such that the smallest absolute value eigenvalue does not change sign. The matrix forms part of a system of linear equations by which the measurements made by the instrument are converted to values of a property of interest of earth formations. Artifacts which may remain in the data after the step of preprocessing are substantially removed by the eigenvalue shifting. In one embodiment, the step of preprocessing includes low pass filtering using a cutoff at the axial resolution limit of a sensor on the instrument. In another embodiment, preprocessing includes phase shifting the response of one sensor to another sensor on the instrument within the spatial frequency bandwidth of the cable yo-yo. Still another embodiment of preprocessing include phase synthesis of the response of one sensor to that of another sensor within the spatial frequency bandwidth of the cable yo-yo.

Method for correcting well log data for effects of changes in instrument

A differential array instrument for determining selected parameters of an earth formation surrounding a borehole, including an instrument mandrel carrying a single source electrode for injecting an electrical current of a predetermined value into the formation surrounding the borehole, and an array of a plurality of measurement electrodes uniformly and vertically spaced from said source electrode along the instrument mandrel. A predetermined group of the uniformly and vertically spaced electrodes are adapted to derive first and second difference potentials between the predetermined group of electrodes, wherein successive ones of a plurality of the predetermined group of selected measuring electrodes uniformly and vertically spaced at increasing distances from the source electrode axially of the borehole are adapted to derive a plurality of the first and second difference potentials between the predetermined group of electrodes. The first and second difference potentials are derived in response to current from the source electrode travelling generally vertically in an orientation generally parallel to the axis of the borehole in the formation to successive ones of the predetermined groups of selected measuring electrodes and which plurality of first and second difference potentials may be correlated to a plurality of values representative of the selected formation parameters. The plurality of values representative of the selected formation parameters may provide a profile of the selected parameters over an increasing radial distance from the borehole.

Method and apparatus for determining the resistivity and conductivity of

An apparatus for determining radial distribution of resistivity of earth formations surrounding a wellbore. The apparatus includes a sonde mandrel having an insulating exterior surface and electrodes disposed on the insulating surface at spaced apart locations. The electrodes are connected to circuits for measuring a focused current resistivity within a predetermined longitudinal span. The electrodes are also connected to circuits for measuring electrical impedance between pairs of electrodes spaced apart at a plurality of different longitudinal spacings. The preferred embodiment includes a voltage measuring circuit interconnected between a pair of electrodes which is positioned between a closest spaced pair of electrodes connected to the impedance measuring circuits, so that a vertical resolution of the impedance measurements can be limited to approximately the axial spacing of the pair of electrodes connected to the voltage measuring circuit. A method according to the invention for determining the distribution of resistivity of earth formations surrounding a wellbore includes the steps of measuring a focused current resistivity of the earth formations to determine a composite resistivity of an uninvaded zone, an invaded zone and a flushed zone. Impedance is measured between pairs of electrodes, each pair having a different longitudinal spacing, and resistivity of the flushed zone and the invaded zone are determined from the measurements of impedance. The resistivity of the uninvaded zone can then be determined from the measurement of focused current resistivity.

Radial sounding electrical well logging instrument

An apparatus for measuring resistivity of an earth formation. The apparatus includes at least one source of measuring current. The source includes a delta-sigma modulator and a serial bit source coupled to the modulator. The serial bit source represents the magnitude of the measuring current at spaced apart time intervals. The apparatus includes a sensor responsive to formation current resulting from interaction of the measure current with the earth formation. The sensor is coupled to a sigma-delta modulator. The modulator is coupled to a digital mixer and a digital filter. The output of the digital filter corresponds to the magnitude of the measure current detected by the sensor sampled at spaced apart time intervals. In a preferred embodiment, the apparatus includes a plurality of current sources each having a different frequency. The sigma-delta modulator is coupled to a plurality of mixers each for demodulating one of the different source frequencies.

Growing community of inventors

Houston, TX, United States of America

Antonio Fabris