RC Drilling: The Art of Saving a Drill String
posted by the Epiroc Exploration and Geoscience team
We did a blog not long ago on reverse circulation drilling compared to diamond drilling, examining the ways in which they differ and are similar. One area where they are similar is the challenge that drillers face when equipment becomes stuck in a hole. Equipment that is stuck is always bad news as it stalls operations and lower productivity. We’ve done a few blogs on stuck equipment in diamond drilling, so let’s look at the world of RC drilling.
In RC drilling, a drill string can become stuck in the ground for a variety of reasons. Oftentimes, it is due to difficult ground, such as fractured ground, or unstable bore hole walls, hammer malfunction and operator mistakes. Whatever the reason, equipment that is stuck causes operations to come to a grinding halt.
Once you are stuck, your options are limited. You can always drill another hole but this represents a lot in terms of lost time and lost equipment, especially if the hole is very deep. For example, the cost of equipment lost in a 120 meter deep hole can range from $30,000 to $50,000 and that number rises the deeper you are in the bore hole. As a result, drillers look for effective equipment that can solve the problem.
In an interesting case, we had a customer who had gotten their drill string stuck in some difficult ground two years ago. The ground held layers of kaolin and very abrasive and hard rock. Water was found at 30 to 50 meters in depth. In this case, operations had to stop for two weeks, while the team tried using different techniques to free the drill string from the ground. They also had to wait to get a new supply of drill steel. Our specialist recommended that they purchase a COP BH 160 back hammer and to keep it for those types of situations. Back hammers are designed to free an RC / DTH hammer and RC /DTH pipes that are jammed. They can also be used to hammer down or to withdraw casings.
This year, the drill string again became stuck at 160 meters of depth. The drill string had a DR thread on pipes whose outside diameter was 102 mm. The customer had been using a COP RC 45 hammer with 133 mm. trubbnos 12 gauge button bits, along with an Explorac 100 drill rig.
The COP BH 160 back hammer is a great product for several reasons. With 30% fewer parts, it is a simpler hammer that is easier to repair and maintain. It is heat treated making it a lot more durable. Despite all this innovation, it is still comparably priced.
This time around the customer had a vastly different experience. Instead of two weeks of downtime, the drill string was freed after two hours. As you can imagine, the customer was very happy with this outcome. They took a video to show the operation and sent it to us. We are sharing that video but keep in mind that this is not a glossy, professional video but a video shot on a smartphone by drillers on the site. Nonetheless, it shows the COP BH 160 in action.
