What is well logging?
Drilling an oil well is an expensive endeavor and can cost millions of dollars in the process. Therefore, it is critical to gather and record as much information as possible throughout the drilling process in order to make educated business decisions regarding the well. Well logging is a means by which oil and gas companies gather detailed information about the layers of rock they drill through. They can then analyze this data to make the judgment with greater certainty of whether or not hydrocarbons are present. If the data looks promising, the company can continue on and complete the well. However, if the well is not promising, the process can be halted and the well abandoned before incurring the additional cost of completing the well.
The above well logging animation video will help give you a more thorough understanding of the logging process.