A qualitative interpretation of magnetic data can be a very fast and useful approach to making a general evaluation of regional geologic structure, but it does not provide adequate information about the depth of key components of the structural features. In fact, the qualitative approach can lead to a somewhat subconscious, but erroneous, concept that anomaly amplitude rather than anomaly wavelength is a reflection of the magnetic body’s depth. On the other hand, a quantitative magnetic interpretation, especially if integrated with other data (well data, surface and subsurface geology, seismic), can provide significantly more useful information about basement depth and configuration as well as depth and location of intrasedimentary igneous material (dikes, flows, plugs).
The amount of detail, time, and cost of a quantitative magnetic interpretation can vary widely depending on the geologic problem to resolve and the time/cost budget available for the project. Sometimes when there is a large dataset to be interpreted, automated methods of depth estimation and contouring are used by some firms to reduce manpower needs and to increase output. However, automation cannot yet fully substitute for a human’s experience and judgment in evaluating depth estimates and interpreting them in the form of a geologically reasonable contour map.
The primary purpose of this module is to discuss 2D interpretation along magnetic profiles since that is where there the bulk of industry effort is concentrated. However, this module will also touch on some special applications of 3D magnetic interpretation.
Learning Objectives
After completing this module, you will:
- Understand the benefits of making a quantitative magnetic interpretation
- Understand the data required and how to select optimal profiles to analyze
- Understand the fundamentals of different techniques for depth estimation
- Understand how to evaluate depth solutions
- Understand the benefits vs. pitfalls of automated depth solutions
