36 FEBRUARY 2023 WorldWide Drilling Resource® Blasthole Drilling by Ronald B. Peterson Drilling Products Specialist, Mountainland Supply Company As mentioned the last time we visited this topic, blasthole drilling is typically a high-energy environment with high pressure and high-volume air. Blastholes are often drilled with an air hammer. Formations which have been previously drilled and blasted tend to be even more unstable than the native ground. The hole must be able to stay open until it is loaded. What you gonna do? The deck seems to be stacked against you. In competent formations, the higher the air pressure and greater the air volume, the faster you can drill. Since this is production drilling, that is the goal, and a big plus. One of the greatest lessons I have learned in life is: “I often hurry faster when I go slow.” When you are in poorly consolidated formations, high air pressure and large air volumes can be a death threat. If you are using an air hammer, you still must maintain enough flow to effectively trip the hammer - no ifs, ands, or buts. Having said this, you can still reduce the air flow to the minimum effective level. When drilling with high pressure and high-volume air, the air is forced into the formation, which results in the implosion of the air back into the hole when the air is shut off. When the air implodes back into the borehole, it brings back the cuttings, as well as any loose formation material. This tends to close off the hole, making it difficult to effectively load it. The first step which can be taken to reduce the implosion effect is to use a drilling foam additive. The foaming additive enables you to clean the hole with reduced air volume, which helps reduce the undesirable implosion effect. The next step that can be taken is to use a stiff foam, which can be accomplished by the addition of a polymer into the injection fluid. This will make the air thicker and more effectively clean the hole with lower air volumes. Either a PAC (polyanionic cellulosic) or a PHPA (partially hydrolyzed polyacrylamide/polyacrylate) polymer is effective in this application. The correct polymer can be added to the injection fluid without causing problems with the hammer or voiding the hammer warranty. The use of foam and stiff foam reduces the amount of air required to clean the hole and helps keep the hole open. Other benefits of reducing the air volume are less wear and tear on the compressor and other drilling components, reduced fuel consumption, and fewer hole problems. If you have any questions on this drilling method, let me know or get with your drilling products provider and ask them. Thanks for reading. As I often say, “A man has to know his limitations.” Working together, it is amazing where we can go. If you have any questions on drilling fluids or if you have another topic you would like me to address, remember this column is ours. Help me make it of value to you. It needs to be an interactive tool. I need your feedback. Please send your suggestions to Michele (below) and she will let me know. Ron Ron Peterson may be contacted via e-mail to michele@worldwidedrillingresource.com EXB For more information call: (270) 786-3010 or visit us online: www.geothermalsupply.com All New! Atlantis-Pro Atlantis-Pro Vault • Traffic-Rated Capable • Simple installation • Trouble-free operation RipSaw from Ulterra is the PDC bit to keep drilling smoothly through changing conditions - limiting torque spikes while delivering consistent engagement to improve performance and maintain the rate of penetration. This is especially difficult to achieve in drilling environments with high interfacial severity between formations. Ulterra engineers devised the award-winning RipSaw technology to anticipate and resist sudden changes in rock properties and adapt the depth of cut to the reactive torque that follows. Its cutting structure brings new meaning for increasing stability and reliability in challenging drilling conditions.
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