Wallis Drilling has been operating the Wallis Drilling Aircore system for companies such as BHP, Rio Tinto, Iluka Resources, Tronox, Cristal Resources and Global Oil Shale.
We use a range of Toyota Landcruiser based rigs, Mitsubishi light truck based rigs, MAN light truck based rigs and tracked mounted based rigs to provide a fit for purpose platform to offer Aircore drilling services to our clients.
Aircore is a name our company used to differentiate a dual tube reverse circulation drilling system developed and patented by Wallis Drilling Pty Ltd in 1974 from other dual tube sampling systems used at the time.
Aircore drilling is a system where air is forced down the annulus of two concentric rods then returns up the centre tube carrying sample. This is all carried out without the air leaving the drill string at any stage.
Advantages of Using Aircore Drilling:
- Accurate sampling.
- Uncontaminated samples.
- Rapid penetration in clay materials and sand materials.
- Continuous penetration and sampling in porous and cavity-filled ground.
- Clean walled hole.
- Ability to change drill systems in the same hole with minimum problems.
- Cores and large chips produced.
- Very little additives required
The Wallis Aircore System
During test drilling it was noticed that cores up to 12 inches long were produced in the hard layers. The name “Aircore” was then evolved. Since the “Aircore” system was developed, over four million metres of drilling have been completed in the search for minerals and energy sources. Coal, uranium, oil shale, gold, tin, mineral sands, bauxite and most other sedimentary deposits have been successfully drilled.
Pre-collaring in sediments prior to diamond coring in basement rock, using the same drill rig, is common practice.
“Aircore” drilling is a rapid, accurate sampling system that can speed up drilling rates, thereby lowering field costs. It is a valuable tool in the mineral exploration field, as well as mine grade control. Site investigation drilling and piezometer installation for environmental monitoring is rapid, accurate and safe.
Why Use Aircore?
Sediment Basins and Areas
These areas are normally difficult to drill. Clay bands, running sands, water zones and cavities are just some of the difficulties encountered. Wallis Aircore is specifically designed for fast, accurate sampling in these awkward stratas.
Designed around the Reverse Circulation principle, the sample is returned up the Concentric Inner Tube. There is minimal, if any, contamination. Cuttings, cores, etc. reach the surface almost immediately. Depth calculations within two centimetres are possible. Cores up to 1′ (300mm) long can be cut in competent ground, otherwise chips and cuttings are returned to the surface.
Air is the basic recirculation medium. Cuttings, cores and chips reach the surface clean and without being flooded by muds, foams and other drilling additives. The geologist does not have to grope through gallons of drill mud before he finds any sample. Sample crews can work faster and are unlikely to miss seeing important strata changes.
The system is designed for fast penetration in difficult country. Average metreage expected, including travel between holes, should be 250+ metres per shift. This production rate depends on ground drilled, access and ability of sample crew to keep up with the drill progress.
Clays that normally stop Rotary Air Blast Drilling or conventional Reverse Circulation Drilling, are rapidly drilled using the Aircore system. Because of the feed design and the air flow at the bit face, the clay is removed immediately. Balling of the Clay does not happen. Penetration rates in brick- making clay of one metre per 30 seconds is achieved without great difficulty.
Different clays have different drilling properties. Some slimy clays need a small amount of water injection to stop them sticking to the Inner Sample Tube. Maximum water usage should not be more than 80 gallons (400 litres) per day.
This is a problem for any drill system. Not only do the sands move, they are water- flooded. This can cause difficulties with sample accuracy as well as blocking rods. The Aircore system has proven itself time and again to successfully complete holes to target depth in this type of ground condition.
Cavities And Broken Ground
Unlike most air drilling operations, the Aircore system turns the direction of the compressed air inside the bit face, not outside the drill string, therefore, it does not require a pressure zone in front of the drill bit to recover the sample. Other drilling systems, on encountering broken, fissured or caved ground, lose the air pressure into the surround country. The sample is then lost into the surrounding fissures.
The Aircore system has a slight vacuum at the face of the bit. It lifts the sample into the bit face and the air stream takes it to the surface.
Hole Security For Logging
Internal diameter allows for slimline probes to be lowered down the Centre Tube.
Engineering And Dewatering
The Aircore system provides the easy installation of PVC piezometers for water monitoring and slotted PVC for horizontal drain holes. The PVC is installed down the centre of the rod string prior to withdrawal from the hole. This method ensures accurate placement in unstable ground.