Calibration of xx, yy and zz induction tool measurements

Abstract

Measurements made with a multicomponent logging system oriented in a horizontal position above the surface of the earth must satisfy certain relationships. These relationships are used to establish calibration errors in the system.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention is related generally to the field of transverse electromagnetic induction measurements wherein the multicomponent measurements are made with antennas that may be transversely inclined to one another. The method is applicable for both well logging operations and for airborne electromagnetic measurements. [0003] 2. Description of the Related Art [0004] Electromagnetic induction resistivity well logging instruments are well known in the art. Electromagnetic induction resistivity well logging instruments are used to determine the electrical conductivity, and its converse, resistivity, of earth formations penetrated by a borehole. Formation conductivity has been determined based on results of measuring the magnetic field of eddy currents that the instrument induces in the formation adjoining the borehole. The electrical conductivity is used for, among other reasons, inferring the fluid content of the earth ...

AI Technical Summary

Benefits of technology

[0016] Another embodiment of the invention is a system for making multicomponent induction measurements. The system includes one or more transmitters and one or more receivers for making multicomponent measurements at one or more frequencies at one or more rotational angles. The system also includes a processor which determines from multicomponent measurements made at a substantially horizontal configuration of the system an indication of a calibration error in at least one of the multicomponent measurements. The system may include three orthogonal transmitters that may not be co-located on a logging tool. In another embodiment of the invention, the transmitters and receivers may be conveyed on a fixed wing aircraft or a helicopter. The multicomponent measurements may be selected from xx, xy, yy, and zz measurements. The processor may be at a downhole location, a surface location, or a remote location.

[0017] Another embo

Problems solved by technology

Conventional induction logging devices, which tend to be sensitive only to the horizontal conductivity of the formations, do not provide a measure of vertical conductivity or of anisotropy.

One difficulty in interpreting the data acquired by a transversal induction logging tool is associated with vulnerability of its response to borehole conditions.

There are a few hardware margins and software limitations that impact a conventional transversal induction logging tool performance and result in errors appearing in the acquired data.

The general hardware problem is typically associated with an unavoidable electrical field that is irradiated by the tool induction transmitter simultaneously with the desirable magnetic field, and it happens in agreement with Maxwell's equations for the time varying field.

The transmitter electrical field interacts with remaining modules of the induction logging tool and with the formation; however, this interaction does not produce any useful information.

Indeed, due to the always-existing possibility for this field to be coupled directly into the receiver part of the sensor section through parasitic displacement currents, it introduces the noise.

When this coupling occurs, the electrical field develops undesirable electrical potentials at the input of the receiver signal conditioning, primarily across the induction coil receiver, and this voltage becomes an additive noise component to the signal of interest introducing a systematic error to the measurements.

Hardware solutions of the type discussed by Fanini et al. are not practical for airborne systems where the transmitter and receiver are spatially separated.

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