posted by the Epiroc Exploration & OreBody Solutions team
August 21, 2021
While many diamond drillers enjoy fishing in their spare time, no one wants to go fishing on the job. Fishing is the process of removing down-hole equipment that has become stuck, lost, or broken off in the hole. It means that operations have ground to a stop and your productivity is being affected.
There are a lot of reasons why a rod string can break. Often, the type of ground is the culprit and can cause your equipment to jam. Clay can swell when water is introduced, squeezing the drill string and barrel. Sand can collapse around the drilling equipment, causing high torque and stuck rods. Sometimes a drill rod can be dropped or the bit can melt and fuse to the rock. Whatever the cause, you will need to try and retrieve the rod, or fish for it. If your hole is deep, you will want to try to get whatever equipment you can from the hole so you don’t have to start over drilling a new hole.
There are different tools you can use but let’s focus on the OWL fishing tool. It is reasonably priced and effective. To use a fishing tool, you lower it into the rod string, well past the broken end. Once inserted into the fish, water is pumped into the rods. The pressure of the water on the internal piston of the tool forces the attached hardened keys down and outwards on the taper of the tool body, to positively engage the fish. The rods are then pulled back, further engaging the keys. Once rod weight is felt on the tool, water pressure can be released. The weight of the rods will now keep the jaws engaged.
Many drillers use a fishing tool but often wonder just how much rod can it pull up out of a hole. That question is hard to answer but a recent case illustrates just how durable and reliable the OWL fishing tool is when it comes to deep holes.
A customer was drilling for nickel in the Sudbury basin and had a borehole that was 2,300 meters in depth when the drill rod broke off at 1,800 meters. No one was sure whether the Owl fishing tool would be able to retrieve that much rod so deep in a hole but it is extremely durable and can fish out much more than you think possible. They figured they had nothing to lose because the fishing tool can be released if you’re not successful. That is a huge bonus.
Think for a moment how much weight that represents. It was a BQ rod. The weight of a 3 meter long BQ rod is about 40 lbs. and we had about 600 of those. So that would make 24,000 lbs. Then you need to calculate how much water was in the rods. There is 13.4 gallons of water per 30 meters, so about 800 gallons of water. A gallon of water weighs about 8 lbs. so another 6,400 lbs. for a total of about 30,400 lbs. That’s a lot of weight for a fishing tool to pull but it worked, and they ended up using the tool again afterwards.
The point of this story is that when tools are made well with quality materials they can do much more than you expect them to be able to do. Our technical team sees innovative solutions to problems on the drill site every day. They can be a very valuable resource when you encounter a drilling challenge so make sure you contact them if you need some creative thinking or advice. Remember our goal is to make drillers’ lives easier and to accelerate the transformation of our industry.
