Fossils into fuels. A drill bit is edged with diamonds or tungsten carbide to make the cutters extremely hard.
Mud circulates through the bit.
Sometimes, surveys show that a structure is present which may contain oil and gas. Very few exploration wells find oil. Even in areas like the North Sea, where we know a great deal about the geology, only one in every eight wells which are drilled will find oil or gas in quantities worth developing. The next stage is to drill some appraisal wells to find out how much oil and gas are present, and whether it is worth the expense of developing the field. The fluids found in a reservoir are not only made up of crude oil or natural gas, but also contain water and other compounds.