Drilling through hostile grounds

April 17, 2022

by Mathieu Dionne, President and CEO at Diafor

The Diafor drill site

Diafor Inc. (Diafor) is a diamond drilling company specializing in surface operations and based on the world-class Cadillac Break in the Abitibi region in Quebec, Canada. The company is new, but it is very well organized, has experienced employees and is building a great reputation.  

In the summer of 2021, Diafor was drilling for Laurentia Exploration and Canada Silver Cobalt Works Inc. (CCW) (TSX-V:CCW) on the Graal property. The drill rig was installed for a 2500 m (8200 ft) N-size deep hole, pioneering the depth for this area of Northern Quebec, looking for battery metals. Past shallow exploration in the region had shown very favorable ground for drilling, but this deep hole had surprises in store. 

Responding positively and successfully to great technical challenges like the ones encountered at Graal is one of many occasions for learning, forging a positive attitude in problem-solving and developing innovative solutions. They benefit Diafor employees, the client, and the drilling sector in general. 

The equipment 

Diafor’s fleet consists of AVD’s VD5000 diamond drill rigs. They were well-suited for the job as the main components, shared with the VD8000 model, are known to be frequently used for holes as deep as 3000 m (9843 ft) on parallel-walled N-size rods and were also tested on holes deeper than 3400 m (11 155 ft) on V-wall and W-wall rods. 

The hole 

Within the first few hundred meters of the hole, the team already recognized some geological (or rock-related) particularities that needed to be addressed in order to optimize the drilling process. 

Magnetic rock formations 

The magnetism of the surrounding rock made the whole rod string and all the steel-made downhole equipment magnetized, slowing down the whole drilling process, especially during the descent of the overshot, and of the inner tube. In general, this problem is especially important for deep holes, since, with the depth, those two steps of the drilling process become more and more time-consuming. In order to resolve it, the team replaced some of the critical components on the downhole equipment with brass-made components, which were not influenced by the magnetism and thus increased the speed of descending. 

Diafor’s drill site
Diafor’s drill site

Abrasive, magnetic and heavy drilling cuttings 

The rock was not only magnetic, but it also had a high weight-per-volume, very abrasive part, so the bit life couldn’t get above the 70 to 100 m (200-300 ft) mark. Imagine how difficult it is to flush heavy, magnetic and abrasive cuttings away from the bit, then up the annular space along the drill rods and the wall of the borehole in a deep hole. The team couldn’t get a brass rod string, for obvious economical and physical reasons, so they had to resort to using drilling additives to improve performance; proper lubrication on the diamond tool surfaces, and all along the core barrel and rod string. They also had to reduce the annular velocity (water consumption) needed to lift those heavy and sticky cuttings out of the hole by increasing fluid viscosity. The main goals were to increase diamond tools’ life and protect the core barrel and rod string from excessive wear. The solution came from the Imdex Val d’Or office with their AMC products line. They agreed to make a site visit and propose the ideal recipe of additives. The result was about 10 to 15% extension of tools’ life and an overall improvement to drilling performance of about 2-4%. 

A part of the voids zones, which contained gravel and metallic sand
A part of the voids zones, which contained gravel and metallic sand

The fault 

The team realized that troubles weren’t over yet. The core barrel got stuck at the depth of 1297 m (4255 ft). The drillers couldn’t expect the rock that seemed stable by looking at the fresh core, to suddenly collapse. They had to cut the rods right above the core barrel, set a bypass wedge 50 m (164.04 ft) above the start of the danger zone in solid rock, and prepare for a take-two. 

Knowing that ground conditions were getting more difficult, the team attempted take-two with a single (3 m or 10 ft) round (non-hex) core barrel and a heavier mix of drilling additives with an improved recipe in order to avoid swelling, and to tie the formations so they don’t collapse on the core barrel. The team progressed by raising the bit up to the safe depth before retrieving the inner tube every single time. They also needed to re-drill what had collapsed below to reach the bottom back every time. 

At the depth of 1327 m (4354 ft), things got even more complicated when the team hit voids filled with a kind of heavy metallic sand. It felt like when the bit touched that sand, it was rushing and sticking on the diamond tools and squeezing between the core barrel and the wall of the borehole. This sand created a tremendous amount of torque and a dangerous situation where the rods could snap and jam the equipment again. 

Metallic sand and steel chips from the core barrel and rod string being worn out by the abrasiveness. Caught in the water return with a magnet.
Metallic sand and steel chips from the core barrel and rod string being worn out by the abrasiveness. Caught in the water return with a magnet.

That’s where the team decided to consolidate the borehole from 1297 m (4255 ft) to 1327 m (4354 ft) by using cementation. The drillers had to rely on a permanent consolidation method – not just additives – because they couldn’t take the chance of a later hole collapse, which would bury approximately 1 km (≈ 0.62 mi) of rod string. And they also needed to prepare for moving the wedges through this pass later in the hole. 

The team used a mix of ‘cement fondue’ and developed a new technique allowing to precisely pump the mix at the right place, with almost no dilution with water, and through the bit. Picture using 1.3 km (≈ 0.80 mi) of rod string as a gigantic syringe. The operation was successful, except that the team noticed that the cement was taking twice the usual amount of time to cure. This was probably caused by the chemistry of the surrounding ground, so they had to fine-tune the ‘cement fondue’ recipe to correct the issue. 

Once the drillers got past the cement – only 0.5 m (1.64 ft) – things started to get very difficult once again. There was more of that metallic sand causing problems. The team had to progress as far as they could, just to the point where drilling would become risky, then stop and consolidate the hole through cementation again. 

The drillers were able to progress like this by cementing every 1 to 2 m (3.28 to 6.56 ft). The cement recipe was perfect because not only it was consolidating the borehole and penetrating the loose formations surrounding it, but it also seemed to have infiltrated in the formation around and below, as evidenced by the core retrieved in the inner tube while drilling past the cement. 

Sand formations consolidated by Diafor’s cement mix
Sand formations consolidated by Diafor’s cement mix

The cement mix and the technique used were on point, but there was one major inconvenience when done repeatedly – the curing time. The drillers began looking into accelerating the process without sacrificing reliability and borehole stability. This was where the team at Imdex came into play again with AMC. They recommended using the AMC Bos Tool in order to make Bos Fix product injections in-between cementations to accelerate the pace. The Bos Fix product has the same advantage of being pumped through the bit, but more importantly, it sets almost instantly. The Bos Fix injections accelerated the pace of getting through the voids and sands and the final cementation at the depth of 1332 m (4370 ft) brought a more permanent consolidation of the borehole. 


Passing voids filled with sand is never easy, but this borehole was completely different. Containing metallic sand with coarse granulometry as the surrounding ground formations, core barrels and rod strings were magnetized. This made it a great technical challenge, and a great technical success. Everybody was involved, we were able to transport the equipment needed quickly on-site with the help of Laurentia Exploration, and they also supported and trusted us every step of the way towards this feat. 

About IMDEX: 

At IMDEX our core value is ‘Together We Thrive’, and that’s delivered through our product-leading brands, AMC and REFLEX, which provide a unique, integrated suite of technology and intelligence solutions from exploration to extraction. We partner with our valued customers and know our end-to-end solutions improve productivity, reduce costs and gain access to relevant, reliable information for critical decision making, anywhere and at any time. Learn more about IMDEX here

For more information visit: diafor.ca 

Read Issue 19 here: 

Issue 19/ 2022