In our previous article, we briefly introduced some drill rods and various other tools. Today, we focus on the most crucial drilling tools in water well drilling: the DTH hammer and drill bits.

DTH hammer

The DTH hammer, a fundamental piece of equipment required for drilling operations, is generally categorised into pneumatic and hydraulic types.

In water well drilling, DTH hammer are generally employed in conjunction with air compressors. Utilising compressed air as the power medium, they harness its energy to generate continuous impact. Compressed air also serves concurrently as a hole-cleaning medium. Typically, the DTH hammer connects directly to a carbide-tipped bit to fracture rock through impact, employing low-speed rotation without core extraction for full-face drilling.

Classified by operating air pressure (international standards define below 0.8MPa as low pressure, 0.8–1.4MPa as medium pressure, and above 1.4MPa as high pressure). Given that water well boreholes are typically deep—ranging from several hundred metres to over a kilometre—high-pressure downhole hammers are predominantly employed, paired with air compressors operating at 10bar or higher.

Each brand employs proprietary designs, with common examples including Sandvik’s Mission and SD series; Atlas Copco’s Copco, DHD, QL, and CIR series (acquired from Ingersoll Rand); and the American Numa and BR series. The DHD series is prevalent among high-pressure models, and our company frequently supplies this range. Different DTH hammer series correspond to specific TDD designs.

Drill Bit

Soft Soil Layers

In many regions, water wells are typically situated in remote areas where the surface layer predominantly consists of soft soil. Such soil conditions preclude the use of down-the-hole hammers and down-the-hole bits. Excessively soft soil compacts the strata, thereby increasing the risk of drill string damage. Additionally, large-diameter drill bits are typically selected for initial hole-making to create clearance for subsequent drilling. Large tricone bits are costly, whereas scraper bits cost merely a fraction of the price. Paired with mud pipes (i.e., auger pipes), they are highly suitable for drilling through the initial metres of soft soil.

Hard Rock Formations

For such strata, either tricone bits or down-the-hole hammers with down-the-hole bits may be employed. This depends on your chosen drilling method. When using a mud pump + drill rig, tricone bits are appropriate. If employing an air compressor with the drill rig, opt for a down-the-hole hammer with down-the-hole bits. However, the latter has limited depth capabilities. Drilling beyond 400 metres becomes challenging, and the air compressor equipment is prohibitively expensive. When tailoring solutions for clients, we typically offer both water-drilling and air-drilling options. This allows clients to meet diverse end-user requirements and extends the achievable drilling depth range.

Sandy Soil/Gravel/Cobbly Subsoil

Sandy soil and gravel are loose, causing drilled holes to collapse easily. Consequently, handling such formations is complex and costly. Solutions involve protective tools like PVC pipes or metal casings to prevent collapse, alongside specialised eccentric or concentric drill bits designed for loose strata that can sink with casing. Eccentric and concentric drill bits are primarily categorised as follows: