Tips for Sonic Drilling in Environmental, Geotechnical
|The best sonic drillers get a feel when to pull black or push forward when running the drill string. Source: Boart Longyear|
A skilled sonic drilling operator can achieve high production rates and obtain the best quality samples from a wide range of subsurface conditions. The sonic rigs, in concert with trained drillers, can reach greater depths while obtaining near 100 percent in situ core samples.
- Know When to Use Sonic
- Choose the Right Drill Bits and Shoes
- Telescope the Core Barrel
- Don't Just Watch the Gauges
- Pre-Collaring is an Efficient Tactic
- Maintain Your Sonic Rig, Tooling
- Keep Safety Top of Mind
Mostly used for environmental, geotechnical/geo-construction and water drilling — sonic drilling has recently seen growth in exploration drilling. Sonic drilling offers distinct advantages over conventional drilling because the drill string can more easily advance through unconsolidated and difficult overburden formations.
Sonic drilling methods lessen the friction between the ground formation and the drilling equipment. Conventional drilling methods use a combination of torque and thrust to cut into the ground, allowing the drill string to advance the borehole; whereas sonic technology creates a resonant energy that matches the ground conditions. This eases the friction and causes the ground formations to displace, shear or fracture — depending on the type of formation — allowing the drill string to advance.
Future developments in sonic drilling will be focused on a smaller, more mobile, footprint of the rigs that will be able to produce the same high-quality sonic samples as larger rigs. Additionally, extending the life and durability of the sonic tooling will be important.
Boart Longyear has unique insight through their Drilling Services division and development of sonic drill rigs, such as the LS600. Here are a few tips.
Knowing when and where to use sonic drilling over conventional drilling methods is critical to delivering cost-effective results to the customer.
There are three main reasons to choose sonic drilling technology:
- Projects that require a continuous in situ sample to be collected — as opposed to reverse circulation (RC) drilling where chips are collected.
- In situations that require avoiding fluid and air while drilling. No fluid or air is needed in sonic drilling, making it a good method for geotechnical, geo-construction and environmental applications. Environmental projects can realize significant cost savings using the sonic drilling method. These types of projects can require a substantial amount of money and work in order to properly dispose of IDW (investigation-derived waste: drill cuttings). Drilling dry substantially reduces the amount of liquid waste versus rotary (drill mud/water) techniques. Auger drilling contributes about four times the amount of solid IDW versus sonic. On a mining project, specifically a leach pad, adding water or air is a disturbance and could cause erosion which could lead to a failure such as a partial landslide.
- For projects where unconsolidated ground formations are encountered, sonic drilling is a good solution because it can handle pebbles up to boulders while providing borehole integrity through a continuous casing process.
Bits and Shoes
There is a variety of sonic tooling to best suit specific ground conditions and hardness. Ground hardness ranges from unconsolidated all the way up to 10 on the Mohs scale of mineral hardness.
In unconsolidated ground, pay attention to the rock sizes and adjust
the core barrel accordingly. For example, if rock sizes are 3 to 4 inches in diameter, the driller should select a core barrel that is at least 6 inches in diameter. Ensuring an adequate core barrel size allows for the drilling samples to pass through the core barrel for easy collection.
Friction is the enemy. Telescoping the boring reduces friction, allowing the contractor to take the boring deeper. Core barrels should be sized to the casing size.
The best sonic drillers don’t just watch the gauges to know when to pull back or push forward. When you have experienced drillers running the sonic drill string, they can rely on their senses; they can feel, touch and hear how the drill string is progressing. Experienced drillers also rely on their knowledge of the drill site and ground formation. And the best drillers know when to adapt their methods as the hole deepens and encounters new ground formations.
When dealing with a couple
hundred feet of overburden, pre-collaring with sonic drilling is an efficient way of reaching the ore
body. It is a quick and clean method that can also pull better information from the overburden — especially unconsolidated formations.
For greenfield exploration, sonic drilling pre-collaring is preferable because of the unfamiliar location. Unlike brownfield exploration — where the knowledge of the ground comes with previous experience in the area — greenfields need a little more care and information gathering. Pre-collaring in sonic drilling provides an in situ sample of the minerals and can better detect/protect against any water infiltration.
Keeping the sonic rig and tooling in optimal operating condition is essential to the long-term productivity of sonic drilling. Preventive maintenance can identify and fix issues before equipment failure happens — which could lead to costly downtime. Make sure to have your sonic rig serviced on a regular basis.
Safety is the most important aspect to any drill site. Incorporate and promote a safety culture. Encourage drill crews to think before acting — take five minutes before doing anything. This allows the crew to focus on the task at hand, one task at a time.
Boart Longyear gives all employees stop-work authority. An empowered workforce understands safety is everyone’s responsibility and provides transparent accident and incident reporting.
Monika Portman is director of product management for Boart Longyear. Contact her at email@example.com.