TonaTec Management has over 125 combined years of core drilling experience in every application and condition. Core drilling services are the backbone of our operations and most other services and specialty are offered in conjunction with core drilling.
The core barrel assembly consists of an inner and outer barrel, bit, reaming shell, latch and rotating head assembly, overshot, wire line cable and an adapter sub to match the threads on the drilling rod (pipe). Core Drilling utilizes a hollow centered coring bit, much like a donut. The bit kerf (or the donut) has cutters, usually very small diamonds, which are set on the surface or embedded in the matrix of the bit kerf. As the bit is forced against the bottom of the hole and rotated, the diamonds on the bit kerf cut through the rock. This creates a round ring, or channel, around the rock to be sampled called the “core.” As the core bit drills ahead, the retrievable inner barrel slides over core (undisturbed rock) which is still attached to the bottom of the drill hole. After the inner barrel is full or blocks off when broken pieces or swelling core becomes lodged inside the inner barrel and will not allow additional core to enter, it is brought to the surface typically by an overshot via wire-line cable which is lowered or pumped into the hole and latched onto the top of the inner barrel for retrieval of the core sample.
The most commonly used inner barrel is 10 feet long so this cycle would be repeated every 10 feet unless the core sample is badly broken and will not slide the entire length inside the inner barrel. Shorter core barrel assemblies are commonly used in broken or fractured rock which blocks or jams going into the inner barrel more frequently. Longer barrel assemblies of 20 feet or more can be used in competent rock or in ultra deep-hole situations where the inner barrel retrieval times are excessively long.