History of the Development of Sonic Drilling Technology
Much of the credit for the successful introduction of this technology to the drilling industry is due to the on-going efforts of Ray Roussy, P.Eng., who is currently the President of the Sonic Drill Corporation and of Sonic Drilling Ltd. The Sonic Drill Corporation (www.sonic-drill.com) is based in Bellingham, Washington, USA and Sonic Drilling Ltd. (www.sonic-drilling.com) is based in Surrey, British Columbia, Canada.
Original experiments aimed at using vibrations to drill holes in the earth started in the late 1940’s. The initial goal was to speed up oil well drilling operations and most of the research was financed by the petroleum industry. The best funded and documented of these efforts was the work of an American firm called Drilling Research Incorporated (DRI), which was in operation from 1948 to 1959. They developed a magnetostrictive-rotary-vibratory drilling system. This method was not successful but it demonstrated that vibrations could speed up rotary drilling rates substantially. At that time the Russians were also working on a ‘vibro-drilling’ system, which was reported to have drilling rates of 3 to 20 times those of conventional rotary drilling.
Mr. Roussy and his associates then decided to try to see if the smaller vibrator could be used for drilling purposes. A basic drill rig was designed and constructed in a hurry as a major oil company wanted to see if this vibratory machine could be used as a seismic drill. They had an urgent requirement to place blasting charges in approximately 150 feet of wet clay and sand beneath frozen lakes in the Arctic. The machine proved successful in this application and a few rigs were then built to work in this field for a few years. Major oil and gas discoveries were made in the Mackenzie Delta at that time, but this activity came to an end in 1977 as a result of a 10-year moratorium imposed on oil and gas development in the Arctic.
The early rotary-vibratory drills, or ‘sonic drills’ as they were called, were not configured specifically as drill heads. They were basically oscillators that were modified for drilling. The machines were very unreliable and prone to frequent breakdowns. These earlier sonic drills were using currently available ‘standard’ drill tooling which was not designed to take the high frequency vibratory loads imposed by the sonic drill. The result was frequent breakage of drill tools. Nonetheless, the rotary-vibratory technique demonstrated that it had great potential in the drilling industry.
It was discovered during early experimentation that, in addition to being capable of drilling holes fast, the machine had an outstanding ability to take truly representative continuous cores of almost any overburden material. It was also able to core through boulders and into bedrock. In fact, it has shown in later years that it is capable of drilling through almost any material, including solid steel plate, ships propellers and almost any item that could be found in a landfill site.
Method of Operation of the Sonic Drill
A sonic drill is more precisely identified as a rotary-vibratory drill. It is capable of high drilling speeds as well as accomplishing tasks, such as continuous coring that cannot be carried out by any other equipment.
At first glance, a sonic drill rig looks very much like a conventional air or mud rotary drill rig. The biggest difference is in the drill head, which is slightly larger than a standard rotary head. The head contains the mechanism necessary for rotary motion, as well as an oscillator, which causes a high frequency force to be superimposed on the drill string. The drill bit is physically vibrating up and down in addition to being pushed down and rotated. These three combined forces allow drilling to proceed rapidly through most geological formations including most types of rock.
In overburden, the vibratory action causes the surrounding soil particles to fluidize, thereby allowing effortless penetration. In rock, the drill bit causes fractures at the rock face, creating rock dust and small rock particles, which facilitates advancement of the drill bit. In many instances the drilling and coring of rock and earth can be accomplished without the use of any drilling fluid whatsoever. This is an important requirement for environmental drilling projects. Compressed air, drill mud, or plain water can be utilized to remove the cuttings and speed up the operation further, depending on the application that the machine is used for.
The oscillator is driven by a hydraulic motor and uses out of balance weights to generate high sinusoidal forces that are transmitted to the drill bit. An air spring is also incorporated in order to confine the alternating forces to the drill string. The frequency can be varied to suit operating conditions and is generally between 50 and 120 hertz (cycles per second). As a comparison, ordinary household current in many countries alternates at 60 hertz. This frequency range falls within the lower range of sound vibrations that the human ear is capable of hearing. Thus the term ‘sonic drill’ has been applied to this class of rotary-vibratory drilling machine.
While the principle behind the sonic drill appears complicated, the machine is actually very simple to operate. The driller only adds vibratory energy to the normal rotary motion. He simply chooses a frequency that gives him the best drilling rate or best core recovery, as the case may be.