We will describe sonic drilling as an advanced form of drilling. This method employs the use of resonant energy created inside a high-frequency sonic head which will help in advancing the casing or core barrel into subsurface formations.
During a drilling process, the resonant energy will be transmitted down the drill string at different sonic frequencies. By virtue of rotating simultaneously, the drill string will distribute the energy simultaneously, significantly impacting the bit face.
Inside the sonic head, there are two counter-rotating weights and they help in generating resonant energy. What keeps the resonant energy from being transmitted to the drill rig and direct the energy instead of the drill string is the pneumatic isolation system.
The resonant energy being produced by the sonic head’s oscillator is under the control of the driller. This should help in matching the formation it encounters paving the way for maximum drilling productivity.
If the sonic resonant energy is in line with the intended drill string frequency, resonance occurs. This will produce a tremendous amount of energy being delivered to the face.
Alongside this, the soil friction immediately adjacent to the drill string is dramatically minimized, leading to faster rates of penetration.
The Procedure of Sonic Drilling
There are a number of ways you can drill with a sonic method (although this will have to depend upon project objectives and site-specific conditions), but the most utilized involves the advancing of a core barrel.
This is often overridden by a much bigger diameter drill string, encasing the borehole and in the process prevents the occurrence of collapse.
Step 1: Advancement of Core Barrel
With the help of the sonic frequencies, core barrel can be advanced. This phase can be carried out even in the absence of air, fluids or mud.
Step 2: Casing Override
After installing the core barrel in place, the casing will be sonically advanced. This measure should help in protecting the integrity of the borehole in the loose unconsolidated ground.
Step 3: Core Retrieval
It is during this stage that the core barrel will be retrieved, and in the process of doing so produces a relatively undisturbed sample. It is nearing the borderline of complete core recovery.
STEP 4 – Repeat Core Advancement
From steps 1 to 3, they are being repeated to depth. This will help in producing a continuous core sample via unconsolidated formations with 1% deviation or even less.
There are numerous advantages with a sonic rig, one of which is that it can fluidize the soil. A fluidized soil will allow for controlled flow of water, pushing the material out its way. This method’s sonic advantage is its ability to case the borehole after advancing the sample tooling to the up and coming sample interval.
In case that the cored sample is not required, the core barrel will further advance, keeping a clean hole. This happening, it will minimize the risk of the tooling from getting lodged below the ground surface.
If this should occur when the override casing is becoming tight, sonic will be made capable of drilling a much bigger override casing to limit the skin friction on the downhole tooling without having to remove the already installed steel drill.
This makes it possible for sonic drilling to optimize its depth capability, which ranges from 250 to 500, and it would highly depend upon the situation.