Borehole logging is extremely important in the mining, engineering and environmental industry for doing a detailed study of the geological formations occurring beneath the earth’s surface. With the advancement of technology the way the logging is conducted has changed. The equipment has become more mechanised, the software has enabled digital logging.
This new technology can aid the measurement process of different types of logs:
1. Electrical logs – Electrical logs mainly include resistivity log and borehole imaging. The subsurface ability to hinder flow of electric current is measured under resistivity logging. It helps identify the presence of hydrocarbons since the parts of the subsurface with salty water are a good conductor of electricity while the hydrocarbons are bad conductors. Under borehole imaging uses centimetre-scale images of the borehole. It reveals detailed data on reservoir performance, fractures, breakouts, sedimentological features.
2. Porosity logs – Porosity logs measure the percentage of pores in the rock. It includes density logging, neutron porosity and sonic logging. Density probe is used to measure the bulk density of underground formations following radioactive bombarding. Similarly, neutron porosity is measured by bombarding formations with high energy epithermal neutrons. The sonic log uses the time taken for sound waves to travel to measure lithology and rock texture.
3. Lithology logs – Gamma ray logging and spontaneous potential logging are lithological logs. The gamma ray helps identify the presence of radioactive material in the different types of rock formation. The SP method measures the difference in the electrochemical potential between the borehole and surface.
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