Characterizing Subsurface Environments Using Borehole Magnetic Gradiometry

Area of Science:

• Geophysics
• Computational electromagnetics

Background:

• Magnetic anomaly inversion relies on forward modeling to estimate subsurface magnetization.
• Accurate modeling of magnetic field components is crucial for geophysical interpretation.

Purpose of the Study:

• To develop and validate a numerical method for calculating magnetic potential, anomaly, and gradient components of cylindrical prisms.
• To quantify magnetic gradient components for cylindrical bodies, enabling new interpretation applications.
• To propose a conceptual design for a borehole instrument measuring magnetic gradient effects.

Main Methods:

• Numerical least-squares Gauss-Legendre quadrature (GLQ) integration was employed.
• The method was used to evaluate magnetic potential, anomaly, and gradient components of a cylindrical prism.
• Computational performance was compared to existing methods for full cylinder analysis.

Main Results:

• The study quantifies magnetic gradient components for cylindrical bodies for the first time.
• The GLQ integration method demonstrates comparable or improved computational accuracy and speed.
• A conceptual design for a borehole magnetic gradient instrument is presented.

Conclusions:

• The developed GLQ method offers an accurate and efficient approach for modeling magnetic effects of cylindrical sources.
• The proposed borehole instrument can determine azimuthal directions of magnetic sources, improving borehole geophysics.
• This work advances the interpretation of cylindrical geological structures and borehole magnetic data.