Cascade’s Drilling 201 Webinar: Sonic Drilling Methodologies & Best Practices

Posted on Sep 12, 2017 by Cascade

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In our Drilling 201 webinar held in August, we discussed sonic drilling methodologies & best practices. Our goal was to provide a working knowledge of this highly viable drilling methodology to all of those unfamiliar with sonic drilling and it’s typical applications. If you missed the webinar, don’t worry! What follows is a detailed breakdown of all the information we covered. In the meantime, don’t hesitate to sign up for upcoming webinars in the series.

Choosing a Drilling Methodology

When we choose the method of drilling, we’re really weighing the method of penetration, the method of removing cuttings, and the method of stabilizing the boring against the geological constraints of the site and the project’s overall goals. With this is mind, it can be said that sonic drilling is most often used in scenarios when the drilling (whether through particular ground materials, or to a particular depth) is rather difficult and the integrity of the core sample is extremely important.

Method Vs Platform

It’s important to distinguish the drilling method from the rig platform. They are not one in the same. Just because a rig is considered auger or direct push, doesn’t mean it’s always tied to that method. Geoprobe rigs, for example, are capable of accommodating a number of different drilling methods. One of the major benefits of sonic is the fact that we can use it on a variety of rig platforms that it can be done from multiple different rigs or platforms and it can support many different tool types.

How Sonic Drilling Works

Sonic gets its name from the mechanism that drives the drill bit. There are two oscillators in the sonic drill head, that are essentially out of tune, and act as counterweights working against one another. Once you have the two oscillators tuned the way you want, you’re generating resonance down your tool string to your bit, and that’s what drives the drill downward.

Watch the video below for a visual representation of sonic drilling in action:

Method of penetration

Rotation and resonance

Method of removing cuttings

Recovered as core sample or displaced into outside of borehole. We typically slip these into a polyethylene sample, or lexan liner, for storage. These lines are  are also good for samples that might have a longer shelf life.

Method of stabilizing boring

Core and case - we then run the core barrel into the ground, then we run or override the casing over the core barrel before retraction. Sometimes we need to use water to do that if you are working with higher depths. However, it is prefered to do it dry, as it allows us to determine where the groundwater is.

The continuous core is inherent to the sonic drilling method. A continuous core provides a detailed look at the soil at the depths drilled. This results in a better understanding of the subsurface conditions.

Sample delivery system

Once the core sample is retrieved from the subsurface, a polyethylene sleeve (bag) is placed over the core barrel and the sample is extruded out by resonating the drill pipe. Core samples are usually kept  in 3 foot bags so that they’re easily manageable.

Sonic Tooling Sizes

Casing Sizes - 5, 6, 7, 8, 9, 10, 12 inch

Sample Sizes - 3,4,5,6,7,8 inch

Depths are dependent up on casing size and formations.  The typical size is 4x6 - a 4 inch core overridden by a 6 inch casing. Most state regulations require a minimum 6 inch hole for a 2 inch monitoring well. Larger casings are often used in telescope or step down mode to reach greater depths. It’s common to start with a 10 inch casing, move down to 8, and end with 6. Additionally if the smaller casing gets stuck, a larger casing can be used to  get it loose.

Sonic Advantages

Sonic drilling carries with it a very specific set of advantages:

  • Speed

It is a quick way of obtaining samples, especially at shallow depths.

  • Superior information

It provides a lot of really good sample information relative to other drilling methods.

  • Waste minimization

Very little waste is generated with sonic, about a 60-70% reduction compared to hollow stem auger.

  • Safer

It’s generally safer and more stable than comparable drilling methods.

  • Cleaner

It’s a very clean method, especially with dry drilling. On contaminated sites, there’s very little that comes to the surface. Most of the return that does come up is easily contained.

  • No refusal

For the most typical applications, like in unconsolidated formations up 700 feet, sonic has very low to no refusal. Sonic is capable of drilling weathered rock pretty well, but it’s fairly slow through hard rock and may compromise the samples, which is why it’s not always best for drilling bedrock. However, we do have the ability to add on a speed increaser and use rock core tooling, which is pretty common to use within a 6 inch hole for setting instruments or obtaining a bedrock sample.

Value in Total Delivered Cost

One of the main concerns with sonic drilling is the price. Yes, when dealing with upfront costs, sonic is typically a more expensive drilling method. But, when you take into account the overall value produced by the dynamic capabilities of this method, it’s easy to see sonic’s overall value.

  • More/better surface information
  • Schedules maintained much more easily
  • Single mobilization effort
  • Combination packages allow you to use multiple tool types with one rig
  • Waste minimization
  • Better well installations

Typical Sonic Drilling Applications

As we’ve stated before, one of the foremost advantages of the sonic method is the wide variety of applications to which it is well suited. What follows is a brief overview of the typical applications for sonic drilling, and details as to how sonic outweighs conventional drilling methods in that scenario.

Geotechnical Investigation

Sonic drilling provides information to enhance conventional methods, or bridge the gap where conventional methods fail. Poor or no recovery, inability to penetrate, inefficiency, tolerances, and alignment are all issues of conventional drilling that are overcome by sonic.

Typical Projects
  • Dams
  • Tunnels
  • Bridges
  • Landslides
  • Foundations

Sampling

In any geotechnical or environmental investigation, the integrity and quality of core samples is paramount. With sonic, you can stay within less than 2% borehole deviation, oftentimes  we’re closer to 1%. Sampling options include:

  • SPT/spit-spoon sampling
  • undisturbed/shelby tubes
  • Dennison
  • In situ testing
  • Borehole pressure meter
  • Sonic/CPT
  • Diamond coring

Earthen Embankments

Earthen embankments present a number of unique challenges that are successfully mitigated with sonic. For instance, in any Army Corp of Engineering project, where fluid or air-based methods of drilling aren’t allowed, sonic presents a viable method of accomplishing the project within the necessary constraints.

Remediation

As you might expect, sonic drilling presents a number of advantages for environmental remediation projects as well. Both low mobility/compaction grouting and high-mobility for grout curtains are achievable with sonic.

Instrumentation & Monitoring

Sonic is ideal for obtaining accurate subsurface information with minimal impact.  It is often used for the installation of  instruments in a fully cased plumb borehole.  Instruments include:

  • Inclinometers
  • Extensometers
  • VWP’s
  • Freeze pipes
  • Open stand-pipe piezometers

Groundwater Profile

Sonic is perhaps the best drilling method for obtaining a groundwater profile.  A subsurface water pump is lowered into the borehole.  This allows the technician  to draw water to the surface without compromising the integrity of the boring.  

Heat Mitigation for VOC Sampling

When dealing with a particularly difficult drill site, heat will likely become an issue. Friction heats the drill bit as it is driven into the subsurface.   Reducing this heat is important to maintain the integrity of the sample. Here are some of the ways sonic helps mitigate heat:

  • Infrared thermometer determines the temperature on the outside or “skin” of the sample and the temperature of the inside center of the sample
  • Shorten coring run lengths in half
  • SPT sample between sonic core runs below casing
  • Change bits and barrels between core runs
  • Extra time for targeting sampling area

Additional Applications

Additional applications for sonic include::

  • Wireline high speed coring
  • VAS groundwater profiling
  • Dennison & fixed-piston sampler
  • Pressure meter testing
  • Bedrock packer testing
  • DTH hammer drilling

Markets Served

Because of its inherent flexibility and the various advantages that this platform carries with it, there are a number of markets where sonic works well:

Environmental
  • Investigation
  • Remediation
  • Well installation
GeoTechnical
  • Investigation
  • Ground improvements
  • Instrument installation
  • Infrastructure
Mining
  • Exploration
  • Tailings, dumps, leach-pad drilling
Water
  • Hydrogeological evaluations
  • Well & Piezometer installation

Conclusion

In conclusion, sonic drilling is, in it’s most basic sense, a resonating drill string used to overcome friction and drive a bit to a specific depth. To recap, here are the specific benefits of sonic drilling:

  • Faster, cleaner, safer
    • It may cost a little bit more upfront, but the number of benefits of sonic really play out, especially on larger projects
  • High frequency, low amplitude
    • The majority of our rigs are high frequency low, amplitude, although we have some that are vice versa
  • High quality core and water samples
    • Multiple sampling programs with one drill, minimal borehole deviation, with the right rig for the geology
  • Multiple sampling programs with one drill
  • Advance multiple zones by telescoping casings
  • High verticality - minimal borehole deviation
  • Typically the right rig for the the more difficult drilling applications

There you have it. We’ve provide a brief overview of our Drilling 201 Webinar, in which we covered the fundamentals and typical applications sonic drilling. We covered a lot in this post, but the truth is that there’s always more to learn. If you’re interested in learning more about sonic drilling at Cascade, or have a project you need help with, please contact us here.  An expert will be right with you.


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