Conventional Core Drilling
Drillpower QLD and SJ Drilling have the capability to carry out diamond core drilling in various diameters - to depths up to 400m.
NLMC = 51.94mm diameter core, resulting in a 75.69mm diameter hole.
HMLC = 63.5mm diameter core, resulting in a 99.21mm diameter hole.
4C = 101.6mm diameter core, resulting in 139.7mm diameter hole.
Core drilling provides a continuous intact core sample from the borehole. Coring is the most expensive drilling option but provides the most detailed information on the rock material and allows sampling and laboratory testing of the samples.
As the drill bit advances, a cylindrical core of rock progressively fills a triple tube core barrel (double tube barrels are also used by some companies) immediately above the core bit. Core samples are periodically recovered, (we use 3.0m long core barrels,) at the end of the core "run" the complete barrel and the drill rods are pulled from the hole, the end of the barrel is disassembled by removing the core bit and catcher, the the stainless steel splits are then pumped out of the inner barrel by using high pressure water. The splits are then opened to reveal the core in virtually undisturbed condition.
Rotation speeds during diamond core drilling can vary up to 1500 rpm depending on the material being drilled and core size and drill bit being used. Penetration rates are slower than other methods generally due to the hardness and at times the weakness of the rock, plus the time taken to retrieve the core barrel when drilling at deeper depths. An alternative to conventional core drilling is wireline core drilling this can speed the drilling progress up especially when drilling deeper holes.
Wireline Core Drilling
Drillpower QLD and SJ Drilling also have the capability to carry out wireline core drilling.
NQ3 = 45m diameter coare, resulting in a 75.7mm diameter hole.
HQ3 = 63.5mm diameter core, resulting in a 96mm diameter hole.
PQ3 = 83mm diameter core, resulting in a 122.3mm diameter hole.
Wireline core drilling is the same principle as conventional core drilling whereby a solid core of rock is collected within the core barrel, the difference is how the core barrel is retrieved from the borehole. When the core barrel is full or the run is finished instead of the complete drill string - rods and core barrel being pulled from the hole, the core rods and outer core barrel remain in the hole and only the inner core barrel is retrieved by lowering a cable with an overshot down the core rods. The overshot attaches to the top of the inner tube/barrel of the core barrel and then the assembly is winched to the surface. The inner barrel is disassembled and the core pumped from the inner barrel as is done in conventional core drilling.
Wireline core drilling requires a completely different set of gear - bits, rods and associated tooling to that used for conventional core drilling which is not generally carried with the rigs at all times - please let your contact know if you require wireline core drilling prior to mobilisation to site.