Exploration Drilling

There are two ways to do core drilling: conventional and wireline. The main difference is how you recover the core sample once the inner tube is full. In conventional drilling, the entire drill string needs to be pulled out of the bore hole for each drilling cycle. This means that all the drill rods must be removed from the hole and the threads must be taken apart and rejoined for each core sample.

In wireline core drilling, a piece of equipment called an overshot is sent down the hole to release and retrieve the inner tube. The overshot and inner tube are then brought up to the surface using a wireline hoist, allowing the rods and core bit to remain in the hole. A new inner tube is then lowered down and locked into place. The wireline method is more common these days as it is more efficient and safe.

Three major operations make up the core drilling cycle: the actual drilling into the ground (or the advancement of the bit), retrieving the core sample from the core barrel using one of the 2 methods listed above, and replacing the equipment with a clean, lubricated inner tube assembly which will allow you to resume the drilling cycle. These 3 actions make up a drilling cycle. After each drilling cycle, the bore hole is made deeper by the length of the core barrel.

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