Benefits and Applications of Sonic Drilling

Overview

This article is intended to describe sonic drilling and its applications across different industries, including infrastructure, mining, environmental and exploration. The article will also address the versatility of sonic drilling and its benefits compared to other standard drilling methods.

1 Introduction

While there are many applications and types of drilling from groundwater wells to pipelines, this article will focus on drilling to characterize the subsurface conditions of a site. Drilling facilitates methods like installing instrumentation, removing soil or rock samples for field or lab identification and testing, or in-situ testing. These methods of subsurface characterization are described in detail in later sections of this article.

Historically, drilling has been used primarily for locating and extracting oil, with the first instance of successful oil retrieval using a drill rig occurring in 1859 by Edwin Drake [1]. Drilling technology in those days was highly primitive, using a combination of steam power and pulleys to advance an iron drill bit. Notably, the use of a casing, which is essentially a pipe driven into the ground to prevent intrusion of water and loose material from outside of the drill hole, was the factor that “proved decisive” in successfully extracting the oil [1]. Casing is still commonly used today in many types of modern drilling.

While drilling today’s capabilities are significantly superior to what has been possible in the past, the basic principles remain the same. Drilling continues to be instrumental in providing site characterization data to engineers for design across multiple industries, including infrastructure, construction and development, mining, and oil and gas. This article explores how sonic drilling is applied to each of these industries and describes the benefits of choosing sonic in these applications over other drilling methods.

2 Sonic Drilling

2.1 History

The concept of sonic drilling was first introduced in the 1950s by Albert Bodine, Jr. [2] and has subsequently been further developed by multiple companies. Due to high-frequency vibrations to cut through rock or soil, there were significant problems with reliability for several years following the technology’s initial releases for commercial use. These reliability issues have been addressed in recent years, and sonic is now a preferred drilling method for its speed and sample quality.

Sonic drilling works by creating a mechanically induced vibration in the drill steel at its resonant frequency [2]. When advancing the drill rods into the subsurface, this high-frequency vibration effectively liquefies the soil or rock and allows for extremely high recovery rates of virtually undisturbed samples [3].

2.2 Site Preparation

2.2.1 Access and Rig Types

Multiple types of drill rigs can support sonic technology, and each drill rig type has different strengths when it comes to accessing a site. Some of the possible rig types are described in the sections below.

2.2.1.1 Truck-Mounted

Truck-mounted sonic rigs are typically used when the ground conditions are competent, such as asphalt or compact gravel. These rigs have quick setup times and can typically arrive at a site and begin work almost immediately. They also can quickly move between site locations that are a significant distance apart, without the need to load and unload the rig onto a trailer between each location. This means that a truck-mounted rig can have significant benefits when drilling multiple shallow holes at large spacings, as long as the ground is competent enough. Since these trucks are heavy and not particularly manoeuvrable, they are not ideal for use on sites with a soft or muddy ground surface, as the rig can easily get stuck.

2.2.1.2 Track-Mounted

Track-mounted rigs are some of the most common sonic rigs. They can be used in virtually any ground surface conditions due to the weight distribution advantages of using tracks over tires. The tracked rigs category consists of rubber or steel tracked rigs, which both have benefits in different applications and site conditions.

Rubber tracks are faster, quieter, more manoeuvrable and do not damage the ground surface when compared to their steel counterpart. Rigs fitted with rubber tracks are highly versatile and can go from a job site with a sensitive ground surface like a paved road to a job site covered in soft soil that would be inaccessible to a truck-mounted rig. The main downsides to rubber tracks include the durability and maintenance and slightly less traction than steel tracks. A broken rubber track would need to be replaced entirely in a scenario where a steel track could be repaired.

Steel tracks are highly durable and can be easily repaired, even in the field, in many cases. Despite these advantages, rubber tracks are more commonly used on sonic rigs for their versatility.

2.2.1.3 Amphibious or Barge-Mounted

It is sometimes necessary to complete a drilling program above water. In these cases, an amphibious or barge-mounted sonic rig is required. Amphibious rigs come in a barge-form fitted with floating tracks, allowing the rig to operate on land or water. One existing application of amphibious rigs is tailings ponds in mining and is discussed in more detail in section 3. Barge-mounted rigs are very common and typically used when drilling in rivers or areas with minimal wave action.

2.2.1.4 Crane or Heli-Access Rigs

There are often sites that traditional rigs cannot access due to extreme topography, a lack of access roads, or dense forest. A portable sonic rig that can be lifted with a helicopter or a crane is required in these situations.

2.2.2 Support Rigs

Sonic drilling requires multiple supplies, both consumable and re-useable, such as a large quantity of water for sampling, drill rods, core boxes and backfill materials. It is often necessary to transport these materials using a support rig, particularly the drill rods, which are heavy and long. Similarly to the drill rigs, multiple support rigs exist and are helpful in different site access scenarios. A list of some examples of the crawler support rigs offered by EPCM is provided below:

• Rod Carriers
• Compressor Carriers
• Utility Carriers
• Fuel & Water Service Carrier
• Personnel Carriers

2.2.3 Setup

The site setup for sonic drilling is relatively quick and straightforward compared to a method like mud rotary. While mud rotary requires a significant amount of preparation time that includes mixing the bentonite mud, sonic drilling can be completed with just water or air supply. Usually, a support rig will back up to the sonic rig so that the drill rods can easily be pulled from the support rig and threaded on to the sonic head.

A primarily level surface is also necessary to drill, which is not specific to sonic but to all drilling types. A rig can adjust to a surface that is not ideal by using jacks but is limited based on how competent the ground is. Using jacks creates more concentrated loads at each jack point, creating differential settlement problems if the soil is soft. It is often more preferable to use a rig mat in this scenario, which distributes the drill rig’s load across a larger footprint and decreases the risk of the drill rig becoming misaligned mid-run.

2.3 Components

Every sonic rig will have similar components that are critical to the functionality of the rig. Some of these components can be swapped out depending on the job requirements and will provide a different result depending on ground conditions and the targeted information. The decision to swap out components is usually made through consultation between the engineer in charge of designing the drilling program and the drilling contractor. Below are brief descriptions of some of the main components and the functionality they provide.

2.3.1 Core and Casing Sizes

Sonic drilling works by using a combination of a core barrel, which is used to capture and extrude the sample, and casing, which is used to ensure the hole stays open while advancing and retreating the core barrel. The most common core diameter for sonic drilling is 4 inches, combined with a 6-inch diameter casing. Other size options are available depending on the purpose of the drilling program, with smaller diameter core being able to reach more significant depths and larger diameters providing more data and instrument installation capacity.

2.3.2 Sampling and Instrumentation

There are multiple options for sampling with a sonic drill rig. Some of these methods include standard sonic sample extrusion, Standard Penetration Testing (SPT), Shelby, Cone Penetration Testing (CPT) and rock coring. Sonic rigs are highly versatile and can be fitted with various other sampling methods that are not listed above.

Along with sampling methods, there is a large variety of instrumentation that can be installed in a sonic drill hole due to its versatility in diameter and depth. Some of these options include piezometers (vibrating wire or standpipe), water pressure head loggers and inclinometers. As mentioned previously, multiple other instruments not listed above can be installed in a sonic borehole due to its versatility.

2.4 Sonic Drilling Operation

After site preparation and setup, the process of operating the sonic rig is relatively straightforward to understand but requires a diligent and experienced operator to complete it efficiently. The process is described below.

The first step is to advance the core barrel to the depth of interest. This usually occurs in 10-foot increments (also known as “runs”) and works by creating a high-frequency vibration that effectively liquefies the soil or rock and allows the core barrel to advance further.

The core bole is then overridden with a casing, ensuring that external factors like sloughing or seepage do not influence the sample. This is one of the essential benefits of sonic drilling, as an effectively undisturbed sample can then be retrieved. Most other drilling methods either do not return a sample or return a highly disturbed sample that does not effectively represent the subsurface conditions.

After the casing reaches the core barrel’s depth, the core barrel is removed from the ground, and the sample is extruded. Samples are usually extruded into a sample bag where the geologist can inspect them, engineer or technician tasked with drilling inspection. In the case of rock coring, the samples are later placed in core boxes where they can be stored with minimal disturbance.

2.5 Material Applications

While sonic drilling is highly effective in most ground conditions, there are some material types that sonic excels in, and some where it is not as cost-effective.

2.5.1 Soil

Soil sites are one of the primary applications of sonic drilling. Sonic sampling in soil provides a continuous sample with close to 100 per cent recovery in all soil types. Some limitations of sonic drilling in soils arise when soils are highly fine-grained. These fine-grained soils can create a large amount of friction on the drill rods when sampling at significant depths. Occasionally, the operator must engage the vibration to reduce the frictional resistance. In rare cases, this can result in a loss of the sample.

2.5.2 Rock

Sonic rigs can be fitting with diamond drilling capabilities, which allows for continuous rock coring of any rock. While sonic rigs can make it through very hard or dense rock, it may not always be the most cost-effective choice.

Many sonic rigs also have directional drilling capabilities, which allows for collecting directional discontinuity information when combined with the inclination and azimuth of the drill hole. This capability has enormous implications for any design that needs to know the orientation of weak rock planes. These applications for directional drilling are discussed in Section 3.

3 Industry Applications

Sonic drilling is one of the most up-and-coming drilling techniques on the market today for its speed and ability to provide a continuous sample in any material. Applications for this drilling method can range from infrastructure to mining exploration and are described using examples of potential real-world projects below.

3.1 Infrastructure

Sonic drilling has many applications in the design of infrastructures like highways, bridges and dams. E.g. for a highway expansion project in a mountainous region, it is essential to understand the rock structure, specifically the presence of weak planes that could potentially release and cause a large-scale failure. Directional sonic drilling facilitates the understanding of these hazards cost-effectively. Using directional drilling data, an engineer can decide whether to create cut slopes, build embankments, armour the slopes or create structural features like bridges. This also applies to large bridge structures and dams, where foundations could be founded directly on rock, supported using piles extending into competent soil and many more options not described in this article. Regardless of the infrastructure project, sonic drilling will provide continuous data and allow the engineer to understand the subsurface conditions quickly and cost-effectively.

3.2 Construction & Development

While governments or municipalities typically fund infrastructure projects, sonic drilling can also be effective in development projects. This drilling could be applied when constructing a high-rise in an area with soft soil overlying dense gravelly soil and bedrock. Where a solid-stem auger rig would likely refuse in the gravelly soil, a sonic rig would provide a continuous sample and allow the engineer to understand where the transition from soil to rock occurs. And this could have massive cost implications for foundation design or the amount of budget allocated to the blasting of rock for underground parking.

3.3 Mining

Whether a mining company wants to create an open-pit mine or an underground mine, sonic drilling can be instrumental in performing a geotechnical investigation. For an open-pit mine, sonic drilling can be completed in the preliminary design phases to determine the most cost-effective design based on the subsurface conditions. Sonic drilling will assist the design engineers in determining the quantity of ore in an area and the distribution waste materials that will need to be excavated. A 3D model of the proposed mine can be built and used to plan budgets and schedule from this data.

3.4 Environmental

Environmental drilling is essential in these times of increasing focus on sustainability. Many mines are required to report their fluid tailings volumes yearly to ensure they are within legal limits. Sonic drilling is a very effective way of determining these fluid volumes due to the possibility of mounting a sonic rig on an amphibious barge. Since the sonic drilling can be completed quickly and provide a continuous sample, it is very cost-effective for mining companies to use this technique. With sonic drilling data, a tailings engineer can optimize the tailings process and accurately report fluid tailings volumes per regulations.

4 Conclusion

It is clear that sonic drilling is a considerable advancement in drilling technology and can be applied to multiple industries, including infrastructure, construction and development, mining and environmental. Sonic drilling has multiple benefits compared to other drilling methods, including speed of testing, the ability for continuous sampling and a near 100 per cent recovery rate. Sonic rigs can also drill through almost any material type, including soil, rock and construction debris, to record-breaking depths. As the technology becomes more commonly accepted as the best on the market, it will only improve speed and reliability.

5 References

[1] L. Maugeri, The age of oil: the mythology, history, and future of the world’s most controversial resource, Greenwood Publishing Group, 2006.

[2] US Department of Energy, “ResonantSonic Drilling: History, Progress and Advances in Environmental Restoration Programs,” in Environmental Remediation ’93, Augusta, Georgia, 1993.

[3] P. A. Lucon, “Resonance: The Science Behind the Art of Sonic Drilling,” Montana State University, Bozeman, Montana, 2013.