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Onsite Technical Visits: Large Diameter Bore Holes

posted by the Epiroc Exploration & OreBody Solutions team

May 1, 2019

I often remind our readers that our technical team does onsite visits, but I’ve had a few questions about what they can do while on an onsite visit. There are many types of onsite visits. Sometimes, the team will address a particular problem like poor bit life, or poor water return. Sometimes they will instruct a drilling team how to use a new product, put on a mud school or do core barrel or diamond tool training. Sometimes, a customer simply has a good relationship with a member of the technical team, respects his opinion and may bring him in to pick his brain. I am going to start writing about some actual onsite visits starting with this one in Colorado.

Our customer, San Juan Drilling had a request from their customer to drill a service hole for a water well in Marble, Colorado. As the name suggests, this was a marble mine producing some of the finest marble in the world. It is located at about 11,000 feet in elevation and water can be difficult to come by. The bottom levels of this mine are flooded with about 10,000,000 gallons of water and it cannot be accessed unless it is pumped out.

Our technical team had a longstanding and solid relationship with San Juan Drilling. They were brought in to review the request, and help develop a plan. In Nevada and Colorado, it is common to use large diameters such as HWL 3.830” (HWL oversize). But San Juan Drilling wanted to set some 8-5/8 inch casing in the hole, so they needed a 9 inch hole. Instead of a water well rig, they would be using an Atlas Copco U 6. They would be using this diamond drill rig to give them the accuracy needed to reach the targeted mine drift that was 300 feet below the surface. 

To make the hole large enough, extra-large bits were needed. Specifically, they needed a 3.830 inch core bit, which the Epiroc team had in stock, but in addition they also needed a 4.9 inch hole opener, a 7 ¼ inch and a 9 inch hole opener which needed to be made. Our team in Nevada had come up with custom equipment in the past and after discussions with the head office, they proceeded to build these oversized diamond tools. They then contacted a local supplier, North West Machine in Grand Junction, to do the machine work for the mandrill that would house the bits.

The drill was set up at a - 45 degree angle and a pilot hole was drilled using a 3.830 inch core bit (HWL oversize). The pilot hole was drilled down to 304 feet in depth to break through to the bottom level of the mine where the water was located. The drill rods were removed and a plug was set at the 302 feet depth to keep the water in the hole while they were enlarging the diameter of the bore hole. The larger 7 ¼ hole opener and 9 inch hole opener were then used to drill and open up the hole to a full 9 inches. Everything came together nicely and we had a satisfied customer.

Diamond Tools Fordia 2019 Coring System

In the photo above you see the finished product with 4 components in the assembly. On the bottom is a box thread HWT on the end of the mandrill but this is not visible in the photo. The long steel cylinder is the mandrill and it holds the assembly together. The 3 other components are screwed onto mandrill, starting with the large hole opener with a 9 inch outer diameter (and a 7 ¼ inch inner diameter), then the 7 ¼ inch diameter hole opener is screwed on and finally you screw on the yellow tricone to complete the assembly. The diameter of the tricone is 4 ¾ inches in diameter and acts as the pilot in the 4.900” hole.

 If there is one takeaway from the story above, it is that our technical team is highly knowledgeable with decades of experience amassed between them. They have probably seen everything possible on a drill site. If they haven’t, rest assured that they are out-of-the-box thinkers who can often come up with a new solution to your problem. If you are facing a situation similar to the one describe above, you can contact our technical team for more details about how this project was accomplished.