A surefire way to stall operations and lower productivity is to break a drill rod in a bore hole – a too common occurrence in diamond drilling.
A rod string can break, either from too much pressure or by being dropped, or the bit can melt and fuse to the rock. Certain ground conditions can lead to your equipment being jammed. Clay can swell enormously when water is introduced and this swelling can trap the rod and drill bit. Coming across sand can also be harmful as the sand can collapse around the drilling equipment.
Whatever the cause, you will need to try and retrieve the rod, or fish for it. Fishing is the process of removing down-hole equipment that has become stuck, lost, or broken off in the hole. Once you have achieved a significant depth in drilling over a long period of time, it is usually preferable to try and retrieve what equipment you can than to start over drilling a new hole. Different methods and down-hole tools are available depending on the situation.
The choice includes recovery tools, fishing tools, or casing cutters to try and retrieve the rod. If unsuccessful, wedges can be used to deviate from your original borehole. Here are a few of the most common tools available for retrieving a broken drill rod or fish.
4 ways to recover a rod
Recovery Taps: These are among the simplest tools for retrieving lost rods or tooling. They can recover the fish but cannot rotate. If the rod is stuck because the core bit melted and is fused to the rock, it will simply break and you will be no further ahead. The tap is inexpensive but is limited in what it can recover, not a good option if the rods are badly stuck, as it cannot be easily removed once screwed into the fish.
Casing cutters: When equipment lost down the hole is hopelessly stuck in the hole, it may be a good idea to use a casing cutter to retrieve as much of the string as possible. You do this by cutting the core barrel off from the inside in order to save the rods above it.
Bowen spear: This is a robust tool that can be used to retrieve all sizes of tubing, and permits heavy jarring, and pulling strains without distorting the fish. The device resists locking, seizing, or jamming of the tool ensuring easy release. It is a good tool but can be expensive, another disadvantage is that once the fish is engaged, it cannot rotate. Straight pull only.
OWL Fishing tool: The fishing tool is a reasonably priced tool that is very effective. To use it, you lower it into the hole on the drill string. 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.
This is a very good option because, unlike the Bowen spear, it can rotate. More importantly, if the fish cannot be pulled, the fishing tool can be released and disengaged from the fish easily. An added advantage is that it comes in right and left handed versions.
Some guidance in proper hole maintenance is important as the walls of the bore hole should be stable before you attempt to fish a broken rod. Knowing how to use water to improve conditions can also be helpful. Our technical support team can visit a drill site and offer corrective solutions quickly so you are up and running as soon as possible.