As we all know, the purpose of core drilling is to get a good core sample from the ground that will be used by geologists to determine where mineral deposits lie and in what quantity. We use drilling equipment to do this and each component of the equipment has a specific purpose that we will review, starting with the drill string.
At one end of the drill string we find the core bit, a ring-shaped bit that is impregnated with diamonds or tungsten carbide to make it easier to cut the rock. The core bit cuts the core sample out of the rock by rotating at a high speed and with a certain amount of pressure being forced on the ground. This core bit is attached to a reaming shell which reams the hole to the desired diameter size. The reaming shell may also be impregnated with diamonds or tungsten carbide. The reaming shell also helps to stabilize the core bit.
The reaming shell is attached to the core barrel, the part of the equipment that will collect the core sample. A wireline core barrel includes three components: an inner tube assembly, and outer tube assembly and the overshot. The inner tube assembly includes the head assembly and the inner tube, the piece that will actually hold the core sample during the drilling process. The inner tube does not rotate.
The core barrel is connected to the drill rig by drill rods. The further into the bore hole we drill, the more drill rods that are needed. Drill rods transfer the torque, feed, force and rotation speed required to drill into the rock, from the drill rig to the drill bit. The more drill rods that are attached, the greater the chance of the bore hole deviating.
Casing is used to hold back overburden, and prevent it from entering the borehole. This is common when you are drilling in fractured, unconsolidated ground.
A drill’s pressure pump is used to pump drilling fluids in to the drill string. The fluids will flush the rock cuttings and carry them to the surface and will cool the bit at the same time.
The list of components above includes what you would find in any core driller’s tool box. Each is a vital component in the drilling cycle. The ‘cycle’ consists of:
- Advancing the core bit into the rock and filling the core barrel
- Retrieving the core tube and filing the core
- Cleaning, inspecting and lubricating the inner barrel then adding a drill rod
And the cycle continues.
We will be looking at this drilling “cycle” in more detail in upcoming blogs. If you have questions regarding the mechanics of this equipment, you can always contact our technical support team for answers, advice or guidance.