WELLOG                                        ELECTROMAGNETISM

 

 

APPLICATIONS:

Electromagnetism is used to measure Conductivity and Resistivity. The principals of electromagnetic induction are applied in Airborne, surface and borehole logging systems.

Electromagnetic methods include a number of surface geophysical applications. Surface geophysical applications include Frequency Domain systems and Time Domain Systems.

 

FREQUENCY DOMAIN:

Frequency Domain systems use continuous wave, usually sine wave transmitters. The receiver usually is designed to measure in-phase (I) and quadrature (Q) portions of the signal.

 

TIME DOMAIN:

Time Domain systems usually transmit an electromagnetic pulse. The pulse enters the surrounding ground and creates eddy currents in conductors.

The Eddy currents in the conductors generate a secondary magnetic field that is measured by receiver electronics.

WELLOG has webpages that are directed toward specific applications related to electromagnetic methods.

An overview of electromagnetic theory follows:

 

ELECTROMAGNETIC INDUCTION: (Faraday’s Law)

When electron current flows in a conductor, a magnetic field is created.

The current in amperes multiplied by the number of turns defines the magnetomotive force (Ampere-Turns).

 

 

Magnetic field FLUX intensity is directly related to Ampere-Turns x Area:

 

 

Relationship of Flux Intensity and Flux Density:

 

 

CONDUCTIVITY:

A changing magnetic field created by a sinusoidal alternating current will induce a current in a conductor.

The induced current will flow in a direction opposite to the current that is causing the magnetic field.

This opposing “SECONDARY” magnetic field and current is directly related to “CONDUCTIVITY”.

 

A Receiver coil measures the secondary magnetic field.

 

Induction logging tools are used to measure conductivity and its reciprocal, Resistivity.

 

Revised 11-07-2018 © WELLOG ALL RIGHTS RESERVED