Boreholes or wells are one of the most expensive investments made by oil and gas companies. Petrophysics, in the oil and gas business, is the study of the physical properties of rocks, and it attempts to measure the mineralogy and amount of open pore space available to store hydrocarbons. Well logs, which are paper or digital plots of depth versus various petrophysical measurements taken from a borehole, are often the only record of the rocks and fluids encountered in drilling a well.