Each hole is unique. The land below a given drill site may be solid bedrock, or it can be mixed sand and rock. Each of these two holes requires different techniques to successfully drill. The solid bedrock hole likely requires a sturdy, diamond tipped blade. It will require constant cooling and may even need to be replaced before the desired depth is reached. The sand and rock hole requires a completely different type of bit. For the sand, a drill bit that looks a bit like a screw may prove to be most effective, since it can scoop sand up from the bottom of the hole and transport it to the surface. When rocks are encountered, another drill bit can be substituted to get through the tough rocky layer.
Deep hole drilling is a technique commonly used in the oil industry. Deep hole drilling companies first send out geologists to scout an area for oil. They may drill a few test wells if the land shows signs that there may be oil below the surface. Most shallow oil deposits have already been drained of all their oil, forcing oil companies to drill deeper. Deep hole drilling is more complicated and requires more expensive equipment to perform properly. There are many added complications as one drill deeper. For example, the deeper a hole is drilled the more pressure the surrounding earth exerts on the drill bit and drill shaft. This added pressure increases the density of the rock, and the friction generated by drilling into it. This means that exotic and expensive drill heads must be used to drill past a certain depth.
Designing a drilling operation takes a lot of careful planning. The geology of the land must be taken into account when designing the drill bit. A geologist can provide insight into the terrain and what one is likely to encounter when drilling. However, there is no way to know exactly what one is going to encounter in a hole until it is drilled. This means that a drilling company must be prepared to adapt to unpredictable and changing circumstances.