Logging – studying lithosphere by creating special wells for sounding and performing the required measurements. In Russian this word relates to French carotter, which means core sampling in geology. Schlumberger brothers (Conrad and Marcel) first introduced this term in geophysics as the name for electric exploration method invented by them. This method partially replaced very expensive core sampling.

Today a great variety of logging methods exists. The most important ones are acoustic, electric and radioactive logging. Combination of data obtained through all of these methods allows for lithological sectional layering, indentifying oil and gas reservoirs, defining the saturation factor and controlling the development of oil and gas fields.