Understanding Sonic drilling

What is sonic drilling?

Sonic drilling is a technique that significantly reduces friction on the drill string and drill bit by using energy resonance to affect the soil structure where it contacts the drill string. This combination makes penetrating for a large range of soils much easier. Sonic drilling is most often used when the drilling is difficult and the integrity of the core sample is extremely important.

What makes sonic drilling work?

Sonic drilling uses high-frequency vibration (resonance) to reduce friction and advance the drill string and bit where surrounding particles are either liquified (in loose materials) or fractured (in hard rock). Rotation can also be added when drilling in harder geologic formations. 

The resonate energy is generated inside the sonic head with two counter-rotating weights called eccentrics. One turns clockwise, and one turns counterclockwise, with both weights moving up to 9,000 revolutions per minute.

1. Resonant frequencies of 50 to 150 Hz are audible, and the driller controls the energy generated by the Sonic head’s eccentrics to match the formation being encountered to achieve maximum drilling productivity.
2. This high-frequency, low-amplitude mechanical vibration is combined with rotation and down-pressure.
3. When the resonant Sonic energy coincides with the natural frequency of the drill string, resonance occurs. This causes the maximum amount of energy to be delivered to the face of the drill bit. At the same time, the friction of the soil immediately adjacent to the entire drill string is substantially minimized, resulting in faster penetration rates.
4. Borehole advancement accelerates as a result of shearing and displacement.
5. This high frequency eases retrieval of the drill string, even in quick expanding clays or boulders and difficult conditions.

How does sonic drilling affect the soil?

Sonic vibrations cause liquefaction (or fluidization) of alluvial soils just right at the point of contact where the soil encounters the drill head and entire string. This minimal effect enables excellent and continuous soil sampling through difficult layers such as overburden and other unconsolidated soils.

While harder rock layers may require a strong drill head and rotation along with the sonic vibration, drilling through these layers still allows the sonic energy to greatly reduce the impact of friction.

How do you drill with sonic?

Typical steps for sonic drilling include:

1. Core Barrel Advancement – the core barrel is advanced using sonic frequencies. This step can typically be performed using no fluids, air, or mud. As the sonic energy is increased, resonance occurs with the formation adjacent to the drill string, reducing sidewall friction and increasing the amount of energy placed at the face of the bit.
2. Once the sample is contained in the core barrel, the casing is sonically advanced over the core barrel, protecting the borehole against cave-in in softer formations.
3. The core barrel is then retrieved, producing a relatively undisturbed sample with near 100% core recovery.
4. These steps are repeated to depth, producing a continuous core sample even through unconsolidated formations.

What are the benefits of sonic drilling?

There are many reasons sonic drilling is so successful and effective, but we’ll break them into six key benefits:

1. Fast!
   Because sonic vibrations significantly reduce friction along the drill string, sonic drilling is 3-5 times faster (and sometimes more) compared to conventional drilling (depending on the soil). Drilling rates range up to 260 feet (80 m) or more per day.

2. Clean!
   Due to a fully cased hole, sonic drilling can be done with little or even no liquids required – this is particularly important for drilling in contaminated or environmentally-sensitive areas. Sonic drilling produces up to 80% less waste compared to conventional methods. This saves both money and time for clean-up and disposal of waste.
   
   Note: There are situations when mud or foam might be used, depending on your soil, and sonic drills can do that too.

3. Versatile!
   When you have projects where unconsolidated ground formations are encountered, sonic drilling can easily handle pebbles up to boulders while providing borehole integrity through continuous casing. And, if you do hit hard rock, simply mount an air hammer or tri-cone bit on your sonic drill to do percussive drilling and keep ongoing. You can also capture discrete water samples, inject remediation fluids, and more!

4. Accurate!
   Produce an accurate, continuous relatively undisturbed core sample within 1% deviation – even on an angle – consistently intercepting the target area.

5. Results!
   Sonic drilling can provide continuous, nearly undisturbed core samples. Continuous cores have been obtained at depths as great as 700 feet (215 m). Samples can also be extruded into plastic sleeves, minimizing the loss of volatile organic compounds.

6. Safe!
   The reduction in drilling fluids creates a much safer work area for the crew, reducing slips and falls. Sample sleeves also reduce the risk of operator exposure to in-ground contaminates. Eijkelkamp drills also come with numerous safety features.

When can sonic drilling be used?

Here are a few of the markets where sonic drilling is commonly used. Note that this is not a comprehensive list!

• Environmental Exploration
• Geo-Technical Sampling and Testing
• Construction
• Water Wells Construction
• Lithological Profiling (observation wells)
• Mineral Exploration/Sampling
• Dewatering Wells
• Groundwater Exploration
• Remediation
• Seismic Drilling