Down the hole (DTH) drilling is a widely used drilling technique with the following characteristics:
Working Principle
In DTH drilling, high pressure air enters the DTH hammer from the rig's intake valve and passes through the drill pipe. The air is then channeled in two directions by the air distribution valve. One path directs air to the bottom of the hole, where it expels rock fragments through the drill bit's exhaust holes, keeping the drill path clear. The second air stream powers the piston inside the hammer, causing it to strike the drill bit in a rapid, repetitive motion. This powerful impact mechanism enables efficient rock penetration. As the drill string rotates, the combined action of the hammer's impact and the drill string's rotation crushes the rock effectively. The driving medium, usually compressed air, also serves as the flushing medium, which is pressed down through the drill pipes, DTH hammer and the drill bit, and then forced back out of the borehole along with the cuttings through the annular gap between the drill pipe and the borehole.
Application Scenarios
Mining: It is used for drilling blast holes, buffer holes and perimeter holes in surface and underground mining. It can also drill holes for cables, ventilation or other“communication” needs between different areas or levels in the mine.
Quarrying: Commonly used for drilling blast holes in limestone and aggregate quarries to obtain the required stone materials.
Construction: In civil engineering, it is used for blasting rock in road and railway projects and the construction of plants. It is also used for foundation drilling to reinforce or stabilize rock and soil, including soil nails, earth/rock anchors, umbrella drilling, sinkhole repair, and compact grouting.
Well Drilling: Applied in water well drilling and geothermal well drilling. It can drill wells with a depth of over 600m and a hole size of 115-400mm.
Applicable Industries
Mining Industry: Essential for both surface and underground mining operations, including coal, metal and non metal mines, improving mining efficiency and ore recovery rates.
Quarrying Industry: Widely used in limestone, granite, and other stone quarries to produce construction aggregates and dimension stones.
Construction Industry: Plays a crucial role in infrastructure construction projects such as roads, railways, bridges, and buildings, providing support for foundation construction and rock excavation.
Oil and Gas Industry: Used in the early stage of oil and gas well drilling to drill through the hard rock layer above the reservoir, improving the speed and efficiency of well construction.
Geothermal Energy Industry: Applied in geothermal well drilling to extract geothermal energy, enabling the development and utilization of geothermal resources.
Advantages
High Drilling Efficiency: The piston of the DTH hammer directly impacts the drill bit at the bottom of the hole, generating a high frequency hammering action that can penetrate tough materials like granite and basalt much faster than traditional drilling methods. The rate of penetration of DTH is 2- 5 times greater than the rotary drilling technique.
Good Hole Quality: The DTH hammer's piston impacts the drill bit directly at the bottom of the hole, providing increased control and stability, which minimizes the chances of the drill bit deviating from its path, resulting in a consistently straight hole. This is critical for applications such as water wells, geothermal installations, and foundation drilling.
Energy Saving and Environmental Protection: DTH hammers work directly at the bottom of the hole, where energy is concentrated and directly transferred to the drill bit, reducing the amount of power required from the compressor and extending its service life. It also produces less noise and vibration compared to other drilling methods, and uses low amounts of drilling mud and additives, reducing the amount of drilling fluid that needs to be recycled and disposed of.
Versatile and Adaptable: DTH hammers can perform effectively across a wide range of formations, including soft, medium, and hard rock, as well as in fractured or unconsolidated ground. This adaptability reduces the need for multiple types of drilling equipment on a single project.
Less Wear and Tear: Since the cutting force is mainly supplied by the hammer's impact, the drill bit encounters less deflection and wear during the drilling operation, reducing the frequency of bit replacement and maintenance costs.