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Gravity, Magnetic and Electromagnetic Exploration Methods

Competency Statement:

Recognize uses and limitations of gravity, magnetics and electromagnetic (EM) methods of exploration. List survey design criteria for each technique. Estimate the thickness of the sedimentary section of a basin using different data types.

Learning Objective:

  • Describe the basic principles and tools used in gravity, magnetic and electromagnetic techniques.
  • Identify main exploration application for gravity, magnetics and electro-magnetic surveys.
  • Outline design considerations of gravity, magnetic and electromagnetic surveys.
  • Apply basic interpretation techniques to determine depth to basement.

Assignment Instruction:

Potential Fields (Gravity, Magnetism and Electromagnetic) data are very often neglected as an exploration tool.

In the early history (1900 to 1960) of the petroleum industry, these methods played a significant role in the discoveries of most of the reserves already consumed worldwide.  These discoveries included almost 100% of the onshore fields in Texas, California, Russia, Iraq, Iran, Saudi Arabia and Venezuela, which are still under exploitation today.

Since the 90's, an integrated interpretation (using gravity, magnetism, seismic, well and outcrop data) is the common standard in many major O&G companies.

Electromagnetic methods were the preferred tool of choice used by the Russians in the exploration and discovery of its vast reserves until the 70`s, using either magneto-telluric or conventional arrays.  Also, in the present, electrical methods are used to detect aquifers which are of interest for water formation disposal and /or CO2 sequestration.

In this Assignment, you will play the role of a Geophysical advisor to diverse E&P teams within your company.  Your duties will include:

  • Defining the feasibility of gravity and/or magnetic surveys (establishing if a given geological configuration is detectable using gravity and/or magnetic measurements)
  • Defining parameters for gravity data acquisition and processing
  • Interpreting gravity and/or magnetic data in order to detect and characterize causative bodies (basement and/or within the sedimentary section), and for establish next steps in exploration
  • Interpreting Magneto-Telluric data to interpret basement structural features
  • Defining the feasibility of electrical surveys (establishing if a given geological configuration is detectable using conventional electrical methods)
  • Defining parameters for acquisition and processing of electrical data
  • Interpreting electrical data in order to recommend future activities in either water formation disposal and /or CO2 sequestration, produced at fields presently under exploitation