Geophysical Investigations

• Geophysical Investigation - involves simple methods of study made on the subsurface to ascertain subsurface detail.
• Gravimetric Method - the primary goal is to study detailed gravity data to provide a better understanding of the subsurface.
• Radiometric Method - A geophysical method for estimating potassium, uranium, and thorium concentrations by calculating the gamma-rays that the elements’ radioactive isotopes emit during radioactive decay.
• Seismic method - is based on the principle that subsurface rock formations bear different elastic properties.
• Electromagnetic methods - electrical conductivity, magmatic permeability and dielectric constant of subsurface bodies are the relevant properties.
• Electrical Resistivity Methods - Type of geophysical method that helps with subsurface imaging. These methods rely of differences in electric potential to identify subsurface material.
• GEOPHYSICAL METHODS

  • Gravimetric Method
  • Radiometric Method
  • Electrical Resistivity Method
  • Electromagnetic Method
  • Seismic Method
• Surface geophysical methods - involve techniques that are conducted from the Earth's surface to investigate subsurface characteristics and structures.
• Electrical Resistivity Tomography (ERT) - measures the electrical resistivity of subsurface materials by injecting electrical current into the ground through surface electrodes and measuring the resulting potential differences.
• Seismic refraction - involves sending seismic waves into the ground from the surface and measuring their travel times and velocities.
• Electromagnetic (EM) Methods - measure variations in electromagnetic fields induced by surface or airborne transmitters and received by ground-based sensors.
• Magnetic surveying - measures variations in the Earth's magnetic field caused by subsurface geological features, mineral deposits, or anthropogenic objects.
• Subsurface geophysical methods - involve techniques that are applied beneath the Earth's surface to investigate properties, structures, and features of the subsurface.
• Seismic methods - involve generating and analyzing seismic waves that travel through the subsurface.
• Ground Penetrating Radar (GPR) - uses radar pulses to image the subsurface and is particularly effective for shallow-depth investigations.
• Magnetic methods - measure variations in the Earth's magnetic field caused by subsurface materials with different magnetic properties.
• Gravity methods - measure variations in the Earth's gravitational field caused by differences in subsurface density.
• "Nuclear logs" and "Non-nuclear logs" refer to two categories of well logging techniques used in the oil and gas industry and other subsurface investigations.
• Nuclear Logs (Gamma Ray Logs)

  • Density Logging - Utilizes gamma source to measure the bulk density of the formation. Density logs are useful for determining porosity and lithology
• Nuclear Logs (Gamma Ray Logs)

  • Spectral Gamma Ray Logs - Provides detailed information about the distribution of radioactive elements in the formation, aiding in lithology identification and stratigraphic correlation.
• Nuclear Logs (Neutron Logs)

  • Neutron Porosity Logs - Measures the response of formation materials to neutron radiation.
• Nuclear Logs (Neutron Logs)

  • Pulsed-Neutron-Lifetime (PNL) Logs - Measures the decay rate of thermal neutrons in subsurface formations to determine the hydrogen content and, consequently, the porosity and saturation of the rock.
• NON-NUCLEAR LOGS

  • Resistivity Logs - Measure the electrical resistance of formations to identify fluid content and type (e.g., hydrocarbons vs. water).
• NON-NUCLEAR LOGS

  • Acoustic/Sonic Logs - Use sound waves to measure the speed of sound through rock formations, providing information about porosity and mechanical properties.
• NON-NUCLEAR LOGS

  • Electromagnetic Logs - Utilize electromagnetic fields to assess theconductivity and resistivity of subsurface materials.
• NON-NUCLEAR LOGS

  • Electromagnetic Logs - Utilize electromagnetic fields to assess the conductivity and resistivity of subsurface materials.
• NON-NUCLEAR LOGS

  • Induction Logs - Measure the conductivity of formations, often used in conductive environments where resistivity logs may be less effective.
• Nuclear Magnetic Resonance (NMR) Logs - Use magnetic fields and radiowaves to provide detailed information about porosity and fluid types without radioactive sources.
• Surface and subsurface methods refer to two broad categories of geophysical techniques used to investigate the Earth's properties and structures, each with its advantages and applications.