Boart Longyear’s New Overshot Resolving Pointy Issues

In all this time, this system (seen in photo on the right) has had the same basic issues:

Spearhead Handling: in up-hole applications underground, a driller is required to manually push the head assembly into the hole by the spearhead. Since it has a pointed end and pivots by design, it can be difficult to handle this operation comfortably.

Inner Tube Handling: When hoisting the inner tube assembly, elastic action of the wireline cable or accidental impact during handling can un-load cable tension and overcome spring loads which allows the hooked lifting dogs to accidentally release the spearhead. The surface ‘Ezy-Lock’ overshot includes a twist-sleeve that locks onto the spearhead even without cable tension, whereas competing overshots require cable tension to maintain a lock.

Lifting Dog and Spearhead Wear: To balance strength and wear resistance, lifting dogs and spear points are heat treated to a medium hardness. However, it’s difficult to visually evaluate or functionally test the degree of wear, especially in underground applications. 

Boart Longyear currently provides a secondary safety pin that clips through the overshot, passing just under the spearhead tip. This adds an extra layer of protection in case the lifting dogs are excessively worn or deformed. However, spearheads are loaded cyclically and often loaded ‘off-pivot’, which deforms the components over time, to the point of disassembly. While the more recent MKII version of the spearhead assembly is much more robust, in the case of spearhead failure, the head assembly will release from the overshot regardless of lifting dog or safety pin use or condition.

This patent-pending overshot leverages our previous experience with Roller Latch head assemblies to create a more reliable and longer lasting system that eliminates spearheads and lifting dogs entirely. The spearhead assembly is replaced by a one-piece socket receptacle (spearhead adapter) that accepts the overshot itself, which has rollers that latch into an internal groove in the spearhead adapter.

Swapping the pointed, jointed spearhead for a simple cylindrical socket makes for much easier handling of head assemblies in up-holes. Surface Quick Descent Roller Latch head assemblies don’t even require the spearhead adapter since the internal groove geometry was pre-built into their design.

The increased toughness and hardness of the bearing quality latch rollers have a proven history of outlasting traditional pivoting latches for wear life. The new overshot will also feature the same Nitreg-ONC surface treatment as Roller Latch head assemblies that drastically improves corrosion resistance (Nitreg is a trademark of Nitrex Inc.).

Safety pin integration in the new underground Quick Pump-In overshot now pulls double duty of both locking the overshot from accidentally releasing while hoisting, as well as holding the head assembly and overshot together in case of component failure due to excessive wear. Also, the socket and rollers are not affected by side loading and ‘off-pivot’ loading during tube handling outside the hole, eliminating gradual deformation or disassembly. The new surface overshot will also include a one-hand twist-lock sleeve to maintain a locked position while hoisting outside the hole, even with a loss of wireline cable tension.

It’s also easy to use.  Instead of pushing the backs of the lifting dogs together, the driller pushes the two halves of the assembly together, retracting the rollers and releasing the head assembly. This operation takes about the same amount of force as the current overshot, so drillers won’t miss a beat.

Additional benefits have been included[CA1]  apart from the elimination of the spearhead and lifting dogs. While the current design uses a solid pivot pin that is peened into place (making it difficult to re-build), the Roller Latch Overshot has no pins whatsoever. Everything is held in place by simple threaded connections for easy maintenance.

First, in the event of a stuck tube, the driller needs to disengage and retrieve wireline cable in order to pull rods. Today, that is done by overloading and breaking a shear pin placed just underneath the cable swivel. In theory this pin breaks at under half the wireline cable’s max load capacity, but in practice its strength is highly variable because shear pins are inherently weak and ductile. Many operators remove the shear pin, which removes release capability and may result in excessive wireline cable replacement.

The Roller Latch Overshot features a brand new pump-in cable release system, originally conceptualized and prototyped by one of our expert underground drillers in Canada. A slotted sleeve and pumping seal assembly is placed over the wireline and pumped up to the overshot. The sleeve engages a quick-release mechanism and releases the wireline. This system has proven to be much more reliable, and may be the feature drillers are most thrilled to have going forward.  Reports of fewer broken wirelines have been received from several sites testing the pump-in cable release system.

Second, while Q/P Roller Latch head assemblies with built-in brake features have had great success in stopping runaway tubes and creating a safer drilling environment underground, they are perhaps “too” successful. Currently, when retrieving the head assembly from an inclined hole, pressure has to be applied to disengage the brake. Getting this pressure and procedure exactly right can be difficult, especially with hydrostatic pressure at depth.

To combat this and make Q/P Roller Latch easier to use while maintaining its safety features, a ‘brake release spring’ was created. This spring assembles quickly inside of the spearhead adapter on the head assembly. While tripping on its own, the head assembly brake works normally, but when the overshot latches into it this spring is compressed, disengaging the brake. This feature has also been received very positively by drillers in the field.

A surface-style overshot is also in development in B/N/H sizes. In addition to many of the features outlined in this article, the aim is to add more innovations, including:

• An improved lock sleeve to disable accidental head assembly release and stop drillers from accidentally sending the overshot down the hole while locked.

• A built-in 360° pivot and shorter overall length for increased ease of handling.

Excitement is high as testing continues. Drillers are noting the various positive developments: it’s easier to use, saves on wireline, and makes working with Q/P Roller Latch head assemblies much easier in difficult conditions. We’re looking forward to further field success as testing begins on the surface design.

For more information and downloads, visit: 
Roller Latch Quick Pump-In Overshot - Boart Longyear

This article was originally published in Coring Magazine, Issue 13, 2020.

In 2004, Chris started as a driller’s assistant with Drillcorp at Sunrise Dam, drilling initial diamond coring holes at Tropicana mine when it was still an exploration site, before moving onto deep directional drilling programs at Leonora and Forrestania. In 2006, Chris joined Boart Longyear (BLY) initially as a driller, before moving into a supervisory role at BHP Billiton’s Leinster and Mt Keith operations. This was when Chris developed a thorough appreciation of industry safety, and he’s grateful for the front row seat during a notable period of change in safety systems and workplace cultural maturity. In 2014, the Great Financial Crisis adversely impacted Australia’s mining and exploration with widespread reduction across all surface drilling. Chris was redirected to BLY’s Waterwell division across multiple Pilbara sites. Chris eventually returned to the Goldfields to assume a regional supervisor role before being rewarded with his current role as operations manager for BLY’s underground division, APAC.

Chris Hopkins: My father worked within Chevron’s lubrications business, collecting many small-scale models of heavy mining equipment. As a kid, I was fascinated by his ‘toys’ – sparking my interest and a subsequent stream of questions to my patient, receptive Dad who has since retired. I greatly admire my Dad for his genuine want to be of value to his community and local church. At age 24, I became a father for the first time while working in the liquor industry and wanted to veer to an industry where hard work, commitment and dedication were appreciated. I was also itching for adventure and a change in scenery, having been inside a lively wine store for too long. The prospect of working in the great outdoors at remote locations, being physical, and solving mechanical issues really appealed, so I made the switch.

CH: My professional role models and mentors include the esteemed and respected likes of Dale Barron, Des Forde, Gregor Stephenson, the late John Emerson, and Murray Hillier. Their collective drilling knowledge, willingness to engage and educate, while offering support has had the most profound effect on my career.

CH: I can’t recall a specific moment or project, as I’ve enjoyed many adventures during my career. Drilling challenges me on so many levels – from working and living away in remote locations and interesting environments, to geological undertakings through difficult formations, and the eventual satisfaction of completing a deep directional drilling program. In true A-type style, I beam with unwavering pride when my rig, fleet and team present well and drill effectively.

CH: 1. Good work habits and a positive mental attitude: the underground space is a very physical and challenging workplace, but it’s also a great place to work – I love it! Every task has an exacting set of measures which must be followed, as short cuts are not tolerated. Determination and attention to detail is necessary given the restricted work areas, equipment limitations and specific underground drilling requirements that can vary from +90 to -90 degrees. Excellent communication is paramount as daily interaction with mining teams is necessary to deliver quality samples within specific time frames. It is quite common for a mining team to immediately assume an area once drilling is complete.

2. Safety culture maturity: we must respect and understand our working environment, and maturity toward safety is a prerequisite to the underground mining sphere, given the inherent risk in what we do. I cannot and will not tolerate immaturity or lack of focus as either will result in someone being hurt and equipment being damaged.

3. People: are the most important and defining facet to success – in any industry. People who genuinely care and take pride in their work and accomplishments are who you want on your team. I’ve been fortunate to have worked with talented and capable people, and I’m most proud of my current team – they are enthusiastic, professional, highly motivated and experienced. We’ve developed an amazing and supportive working culture as a result.

CH: My somewhat cheeky response is whatever drilling type I’m currently focused on and involved in. Seriously, every discipline – underground or surface drilling has its own challenges including ground conditions, technical drilling requirements to achieve targets, underground grade control programs requiring multiple rig locations and set-ups per shift, to large diameter holes requiring large tooling to complete. The challenge of individual hole completion is what deems the drilling industry such an exciting business to work in. Up-hole drilling is a constant challenge, as underground geology departments strive to keep costs down. Sometimes the only way or location to achieve target is to drill ‘up’. Boart Longyear’s Roller Latch system allows crews to successfully and safely do so while following best drilling practices.

CH: Underground mining and drilling teams work closely, attending the same pre-start meetings and engaging more frequently than would occur at surface. When underground, everyone is under the supervision of the shift boss and underground mine manager, with increased engagement with the mining safety team. My drilling team has forged greater cohesion between the two groups, implementing exemplary practice and innovation that has been adopted by all, and I couldn’t be prouder.

CH: There are two reasons – risk and cost. Drilling is dangerous especially when poorly managed, so it makes sense to hire a professional contractor to complete the work. Contractors must be accountable and continually improve to secure future work. A lot of effort goes into delivering safe, seemingly hassle-free (for the client) drilling. Then there is cost. Most mining companies are incapable of cost-effective and productive in-house drilling. Contractors remain focused on achieving safe and productive outcomes for their ongoing financial survival and reputation.

CH: Delays associated with mine blasting and other mining activities significantly reduce the amount of time drilling crews must complete work, while eliciting an added expense to the client. BLY’s Drill Control Interface (DCi) system enables continuous drilling, even while the rig is unattended. Semi-autonomous capability within the underground drilling space is subject to an anticipated transformation, and it’s an exciting time. Many mines have, and continue to install underground Wi-Fi communication systems for enhanced communication between the drill crew and surface-based support crew.

CH: The underground space is in need of innovation, and Boart Longyear’s dynamic approach has meant that I’ve been involved in the development and release of some of the industry’s leading improvements including Roller Latch, diamond coring bits – designed and tested in the field by our drillers, and safety improvements to both drilling equipment and in the field training systems. Our fleet features machines that enhance the driller interface with improved safety and increased performance thanks to BLY’s ability to design and manufacture reliable rigs and drilling equipment, backed by adept and supportive maintenance teams, and an extensive global supply chain. I’m particularly excited about current innovations and advancements we expect to release within the next year. I can’t elaborate just yet, so watch this space.

CH: Most Australian underground drilling is N-size as it yields clients respectable sized core samples for the cost. For drilling contractors, N-size improves productivity with wireline systems, reduces manual handling when compared to conventional systems, and improves hole completion in poor formations. Boart Longyear’s Roller Latch system also provides much safer operations when drilling up holes, veering away from conventional processes.

CH: The potential to intercept an underground water source when drilling underground is both great, and undesirable. Thorough planning, detailed risk assessment and experience round out the high-pressure prevention trifecta, coupled with having the necessary tooling at the ready – should it be required.

CH: Drilling fluids are critical to hole completion in broken, unstable or pressurized formations – supporting all aspects of hole conditioning from reducing torque, assisting in the removal of cuttings, increasing hydrostatic pressure, stopping hydro sensitive formations from reacting, and some products hold together loose formations. Cost is critical and all staff – not just drilling crews must be educated as to correct usage to ensure zero to minimal wastage as this can greatly affect cost per meter. Reliable terminal equipment is key to ensure the most time down the hole. I’ve encountered many holes where formation stability is greatly reduced due to tripping of rods or introducing unnecessary pressures onto the formation, leading to extensive hole cleaning which then increases the likelihood of an unsuccessful hole completion.

CH: Boart Longyear makes use of wedging in both surface and underground operations. Wedging needn’t be a safety concern if effective planning and good communication are upheld. Importantly, we work closely with our clients to ensure this is the best option for them, as the cost to drill a new hole within the underground space can be cheaper than attempting directional drilling.

CH: Cementing works best when it is kept simple, checking everything twice. Like the carpentry adage, ‘measure twice; cut once.’ Training is key – as it is with all aspects of drilling. Be mindful of setting and correctly calculating grout volume. Other points to note: is the cement type correct or best suited to the formation? Is the product within its best before date, and has it been stored correctly? Are the slurry volume calculations correct? Is the potential for contamination being limited while mixing and displacing slurry? Be sure to extract a slurry sample to reference. Importantly, if you’re using an additive, be sure to follow the manufacturer guidelines as more is not always better. Lastly, don’t feel pressured when attempting as this is when most mistakes do occur. In Australia, we use VAN RUTH® cementing plugs as they’re a proven product that work well.

CH: Lack of preparation. A driller’s day starts with the all-important pre-start meeting, where supervisors outline and ensure that their teams understand what is expected to occur during that shift. Appropriate and reliable equipment is made available for the crew to safely complete every task and activity. Rushing to complete a job, particularly due to failure to plan, or lack of preparation is a recipe for disaster – namely injury.

CH: I’ve been fortunate to have been involved in many deep directional drilling programs throughout Western Australia, however, it’s important to note that this drilling method varies from production-based drilling within the underground space. The focus is on hole completion and hitting the desired target. It’s complex, extremely technical, and requires intensive supervision, as every decision affects how the hole is drilled from start to finish. I enjoy drilling at depth – the planning, preparation, and necessary attention to detail (correct choice and use of equipment, barrel configurations and monitoring the hole’s deviation) to achieve target. It’s a proud moment to be part of a team that successfully reaches end of hole, delivering a sample of an ore body to a client from over 2000-meters depth.

CH: Directional drilling using down hole motors is an effective method to hit multiple targets from a ‘parent’ hole. The method is best applied to deeper targets and areas where the cost to drill through waste rock exceeds the cost to complete the directional requirements to reach the targeted zone.

CH: The survey industry and its products are rapidly advancing in capability and reliability, with fantastic products available. Most importantly, the system must meet client requirements and be easy to operate, with flexibility for drilling teams to utilize tools to maintain effectiveness. I’m a firm advocate of the Azimuth Aligner® as it reduces rig set up time and relieves pressure on mine survey teams.

CH: Mining is critical to Australia’s economy, and every operation has been closely monitored to eliminate or minimize risk. Australia truly is the ‘lucky country’ for a few reasons – our geographic isolation and relatively small population combined with our swift acting government’s measures (international and state border lockdowns and mandatory 14-day self-isolation), has so far protected us as a nation. Over 25 million people live in Australia, yet our death rate from the pandemic is deemed low – just over 100 people. We must never be complacent and we’re mindful of the much talked about second and third phases, hence Australia’s strict border controls.

CH: Exciting technologies are being harnessed and adapted within diamond drilling. Many contractors are relentless in their pursuit to remove manual handling for a twofold result – eliminate and minimize injuries, while encouraging the broader community to consider the profession. Drilling cannot occur without people and the industry benefits when dedicated, focused and diligent people continually strive to improve perception and conditions. People are the future of drilling, so we must ensure that our industry evolves with safety, education, innovative systems and solutions at its forefront, as evidenced by key groups such as Australian Drilling Industry Association (ADIA) – endeavoring to improve standards and protocol for collective success – now and in the future. I’m currently involved at a research and development level, applying expert advice and feedback to hone various soon-to-be-released Boart Longyear equipment and tools that will greatly improve safety and productivity, while questioning how we approach drilling. It’s an incredibly exciting time to be in the industry and I personally cannot wait to see it come to fruition. Watch this space!

What many people may not know is that the drillers and engineers of Boart Longyear have been involved in some exciting historical drilling projects in a variety of other applications, too. Drilling equipment for moon exploration is one such example (read Drilling Beyond Earth); but closer to home, the company has assisted with projects to explore and define foundation and structural integrity below the earth or even under bodies of water.

In the late 1920s, members of the Longyear team were contracted to test drill the route of a proposed vehicular tunnel under the East River to connect Manhattan to Brooklyn in New York, USA. The tunnel was intended to reduce transportation congestion due to the slow and unreliable ferry service that existed at the time. The Longyear company provided preliminary boring samples used to determine what was beneath the surface of the river. Characterizing the samples’ type of rock and its hardness allowed geologists and engineers to determine what equipment should be used for tunneling, how long it should take, and at what cost. Although the initial tunnel project didn’t receive support and funding, it laid the groundwork for a later project—the Brooklyn-Battery Tunnel—which was started in 1940 and opened in May of 1950.

A similar challenge of traversing a wide body of water required assistance from the Longyear team in 1929. Joseph B. Strauss, a visionary engineer, was tasked with his team to design the proposed Golden Gate Bridge in San Francisco, California, USA. As chief engineer, Strauss requested the services of Longyear to investigate the rock formations beneath the San Francisco Bay where the bridge would be constructed. Longyear started boring in the Bay in November 1929 along the sites of the proposed piers and anchorages. [i]

Due to the turbulent waters of the channel, the drillers had to be creative as to how they would retrieve the core samples beneath the tumultuous surface. Strauss was big on safety, requiring bridge workers use safety lines, work over safety nets, and even wear some of the first hard hats. The Longyear crew constructed a platform over the water supported by a boom—an A-frame—and guy-wires anchored to the shore. The platform allowed the team to suspend their drilling equipment securely on top and safely above the bay. Despite the problems of deep water, ocean traffic, storms, and tidal movement, the team was able to finish the work on schedule with complete core sample recovery.

The geological samples and subsequent data supplied to Strauss proved that the rock formations could bear the weight of the foundations and enable the huge bridge structure to be built. The information was provided in a full report to the board of engineers in February 1930 and the bridge was determined to be “feasible economically and structurally.”

This great news meant Strauss and his design team could move on to the next phases of engineering and constructing the Golden Gate Bridge. In gratitude for Longyear’s contribution, Strauss wrote, “The work done by your company, having been entirely satisfactory, and the relations between us and your drillers having been cordial and pleasant, I am glad to make immediate payment of the balance due.” [ii]  

Payments received by the company totaled close to $15,000 for the boring contract. It wasn’t for another three years (January 1933) that construction began and a groundbreaking ceremony for the bridge was held. The Golden Gate Bridge was completed in May 1937 at a total cost of $35,500,000.

Click below images to view larger.

From left to right

Images 1 and 2: “Engineers Speed Plans for Golden Gate Bridge” - A Pacific Street and Road Builder article from March 1930 stating “test borings reveal solid rock foundations and showing a photo of boring operations at the Lime Point side of the bridge in Marin County, California.

Image 3: “Borings Started for Gate Span” – Photos shows in the Vallejo California Chronicle, Sebastopol California Times, and Cresent City Triplicate newspapers on November 29, 1930. The article shows a photo of Longyear’s diamond-tipped drills used for bore sampling the rock at the San Francisco end of the bridge, next to Fort Point.

Image 4: “Getting Down to Bedrock” – A San Francisco Examiner article, dated February 14, 1930, picturing engineers, including Strauss, inspecting boring samples from the Golden Gate Bridge project.

A truck-mounted LS600 sonic rig taking core samples near a dam site.

Shortly after the Golden Gate boring project, the Longyear company became involved with drilling projects for the construction of hydro dams around the country. In the 1930s, Longyear drillers did test borings for several of the twenty planned dams under the jurisdiction of the Tennessee Valley Authority. These dams were part of a comprehensive plan for the reclamation and development of the Tennessee River—covering an area of more than forty thousand square miles and over seven states.[iii]

Later twentieth-century construction-type projects for Longyear drillers included boring for core samples for the Missouri River Project, and the first foundation test borings for the Fort Peck Dam in Montana—the project’s first major hydro dam.

Today, Boart Longyear continues to assist with construction and rehabilitation projects around the world using even more advanced technologies and equipment. The company regularly uses sonic drilling technologies which are ideal for avoiding many of the challenges experienced with conventional drilling methods.

Sonic drilling offers quality control in conjunction with the production and installation of geotechnical construction elements. The sonic method can actually eliminate the need for circulation-type drilling allowing the driller to work safely in situations that involve sensitive structures, vulnerable site conditions, difficult geology, or have restrictive conditions. Sonic drilling also provides measurements and samples to evaluate actual conditions across a given site during the progress of exploration and construction.

A few examples of Boart Longyear’s sonic drilling assistance with tunnel, bridge, and hydro dam projects in the twenty-first century include: [iv]

• Casing installation for the Boston Central Artery / Tunnel Project CO9A4, Massachusetts, USA. As part of the process of installing three jacked tunnels under the 13 railroad tracks at South Station in Boston, specialized sonic drilling was used to install casing through some of the most difficult combinations of historical fill materials—steel rails, brick tanks, woodpiles, granite seawalls, reinforced concrete slabs, track ballast rock, clay, stratified sands, till and weathered bedrock.

• Installation of a grout curtain at Clearwater Dam in Missouri, USA. The project required a drilling method with the ability to penetrate and sample both the body of the dam and its foundation without the use of air or water circulation. Sonic drilling was used to investigate a deep sinkhole and affected a remedial plan involving drilling 15-degree battered grout holes through embankment fill to construct a grout curtain.

• Sonic drilling comparison for a tunnel design pilot study on the Combined Sewer Overflow Control program, Anacostia River Project in Washington DC. Sonic drilling was used to perform continuous soil coring with approximately 100% core recovery and careful installation of multiple piezometers.

• Micro-pile installation testing near the Holland Tunnel in New Jersey, USA. Sonic drilling was compared with conventional drilling to advance micro-piles through silty sand overburden, overlying till, and schist. Not only was the sonic drilling 33% quicker for installation of the micro-piles, waste was also eliminated to nearly the volume of the sonic core, which minimized disposal costs. 

Bridges, tunnels, dams, and even buildings are all safer because of the work done to investigate, test, and secure the foundations. Although considered a small contribution to these engineering marvels, Boart Longyear employees are proud of the heritage the company has earned and its involvement in each part of history.

For more information on Boart Longyear’s construction drilling capabilities, including sampling core, anchoring, micro-piling, jet grouting, and ground freezing, visit the overburden and construction tooling section.

[i] https://www.goldengate.org/bridge/history-research/bridge-construction/joseph-strauss/

[ii] Edmund J Longyear, and Walter R Eastman. 1984. “The Mesabi and Beyond”; Pg 181

[iii] Edmund J Longyear, and Walter R Eastman. 1984. “The Mesabi and Beyond”; Pg 192

[iv] George R Burnhart, Boart Longyear Technical paper. 2006. “Sonic Drilling Offers Quality Control and Non-Destructive Advantage to Geotechnical and Construction Drilling on Sensitive Infrastructure Sites.”

Golden Gate Bridge Photos from historical records, the Golden Gate Bridge, Highway and Transportation District and found here https://www.goldengate.org/exhibits/engineering-the-design/

Golden Gate Bridge Photo courtesy of Umer Sayyam

Edge Drilling director, John Argiropoulos, recently took delivery of a Boart Longyear LS250 MiniSonic rig that is suited to a variety of soft ground, shallow drilling projects including environmental, tunneling, water management, grade control, leach pads, and tailings dams.

The rig delivers faster penetration for nearly undisturbed samples using little or no fluids, said John, and its casing system makes it ideal for a variety of applications including mining, environmental, and infrastructure projects.

The rig provides extremely accurate sampling for unconsolidated formations which makes it suited to mining, but it also eliminates the risk of cross contamination making it ideal for environmental and geotechnical work. It can also precisely drill straight holes at varying angles which ticks the box for infrastructure projects.

“We've already got five months of work lined up with the rig," John told Australasian Drilling.

The idea of acquiring a sonic rig first came to John during a visit to Christchurch in New Zealand where he saw the rigs undertaking post-earthquake recovery sampling work.

“I've been looking at getting into this type of drilling from the first time I saw it,” he said.

“After the earthquake in Christchurch, I saw massive advantages with sonic rigs in drilling overburden and getting near on 100 percent recovery sampling. The rigs were drilling every house in carports or garages and were looking for signs of liquefaction.”

Liquefaction is where the strength and stiffness of soil is reduced by earthquake shaking. If liquefaction was found following testing in Christchurch, the dwelling would be demolished.

“They had conventional rigs at the start including standard diamond drilling, but they weren't getting any core recovery, being glacial fill," John said. "However, the sonic rigs collected everything from pebbles and cobbles, to rock, clay, silt and sand. They were very impressive.”

With work increasing, John eventually took the plunge and invested in a sonic rig.

“We're getting much busier,” he said. “In the space of 12 months, we've gone from two rigs at the start of last year to seven rigs now. We've expanded quite a lot.”

John said work began to resurge since 2016. A big push by Main Roads WA (Western Australia) for testing bridges across the state is creating work from the rollout of the government's METRONET program and is expected to generate more construction activity and geotechnical work in the near future. The METRONET program is one of the largest single investments in public transport that Perth has seen and will involve about 72 km of new passenger rail and up to 18 new stations.

With enhanced capabilities thanks to the new rigs, John is upbeat in his outlook for the business. However, like most contractors, he is feeling the pain of skill shortages. John said he is managing the issue through in-house training.

"I'm a firm believer of training in-house as the best way forward because we can train personnel according to our standards, expectations, policies, and procedures.”

Originally published in Australasian Drilling Magazine, February/March 2020

The drill string’s resistance to deviation—otherwise known as ‘stiffness’—can be determined by its material and mechanical properties. Since all wireline tubular components are made from cold-drawn steel tubing, they all have the same fundamental properties. Specifically, regardless of chemistry, heat treatment, or hardness, all steel grades respond with the same amount of bend to a given load (the ratio of stress (load) to strain (bend) is known as the “modulus of elasticity”). Furthermore, any two steel tubular components with equal dimensions will have equal stiffness, even if produced by different suppliers, regardless of the steel grade, heat treatment, or hardness.

The directional response or sensitivity of the drill string to changes in drilling loads or speeds, or in formation changes, depends heavily on the drill string stiffness. The stiffness of wireline drill rods more than doubles in moving to the next larger system (e.g. BQ to NQ, NQ to HQ, etc.). As a result, larger systems drill straighter but have much more resistance and greater lateral loading when drilling through borehole deviations. Given a typical impregnated coring bit, and constant drilling parameters (assuming no formation changes), the borehole will tend to form a slow helix that is determined primarily by the stiffness of the drill string. With borehole friction, the drill string itself can become unstable, buckling into a helical shape which tightens or loosens with changes in drilling loads and speeds, but then elastically returns straight when unloaded.

The Q wireline core barrel was originally designed to utilize an outer tube with a substantially larger diameter and wall thickness than the unstable string of drill rods behind it. Standard outer tubes provide approximately 40% greater stiffness, and full-hole style outer tubes provide approximately 70% greater stiffness! The outer tube can then act as a stabilizing bearing or collar. The greater the increase in stiffness, the more effective a directional control to resist changes in the formation, drilling parameters, or drill string stability. This control can be enhanced with stabilized reaming shells, stabilized adapter couplings, and stabilized locking couplings.

Consider the directional impact if the outer tube is replaced with another drill rod, completely removing any difference in drill string stiffness, and the related directional control. Originally developed in the 1980’s in an attempt to direct borehole deviations, core barrel configurations, known as “flexi-barrels,” replace the outer tube with an equivalent length assembly of a drill rod and adapters. However, the lack of directional control combined with the lack of directional predictability, typically results in erratic deviations requiring either corrective deviation attempts or reaming to reduce excessive deviations. Therefore, the use of flexi-barrels is not recommended.

When planning holes, consider the potential impact of rod deviation. The stiffness of steel tubes is relatively high, and as mentioned before, increases with system size and section thickness. As a result, the drill string will respond with high side loads against the borehole wall, especially just before and after a deviation. For example, an NQ size drill rod deflected to the recommended maximum deviation of 1.0 degrees over its length produces approximately 9kN (2,000lb) of side load, and an HQ produces 18kN (4,000lb) at only 0.8deg per rod length. Depending on the formation, these high side loads can produce high torque, heavy rod wear or even ‘heat check cracking.’ Additionally, these contact points generate drag and ‘stick-slip’ conditions, which can produce a dynamic response sufficient to permanently deform the drill string into a helical shape. In extreme cases, where the drill string completes enough rotations approaching or exceeding maximum deviation, fatigue failures will occur. Using the minimum deviation possible to hit target and sticking to NQ size rod will reduce the side loads, torque and chances of twisting or cracking rod.

Originally published in Australasian Drilling Magazine, February/March 2020

The COVID-19 outbreak and how it affects everyone’s health and safety is of huge concern for Boart Longyear. Being in an industry that already has many risks due the nature of drilling and manufacturing, employees have learned that fostering a safety culture means that no matter what they do, they always need to take time to make safety part of their daily activities*.

As everyone grapples with the changes and the unfortunate consequences we are seeing and are personally affected by, it is good to take a deep breathe and re-evaluate what you are doing to keep yourself and your loved ones safe and healthy.

The web is full of helpful information on what to look for, how to act, how to respond, and how to give assistance. In regard to the drilling industry, we recently came across this well written article published online by National Driller magazine.

In the article, author Brock Yordy asks, “How do we prepare for abnormal operating conditions?” and responds with, “We start by creating a procedure that minimizes the hazard and prepares our crews to be safe. Next, we implement that procedure by training our people. Finally, we review our procedures and continue to improve as new information arises.” 

Mr. Yordy goes on to compliment the drilling community as we all pull together to provide each other information and figure out the best ways to tackle this crisis. With his research, he interviewed Jeff Williams, former National Ground Water Association (NGWA) president. Mr. Williams and other industry experts have created a guideline for operating procedures during the COVID-19 pandemic. We highly recommend you read this interview and review the findings and procedures set forth.

Read the full National Driller article and excerpts from Mr. Yordy’s interview with Mr. Williams here: What are Best Practices for Drillers During the Coronavirus Pandemic?

Stay safe everyone!

*The employees of Boart Longyear have long prided themselves on a robust safety culture. Embodying a core value of “Safety First” is evident in the company’s recent 2019 safety achievement with the company hitting an incredible milestone of 14.5 million consecutive man-hours worked with no Lost Time Injuries (LTI), and 18 months completely LTI-free. 

Boart Longyear’s Response to COVID-19