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Part 1 of 3 – Introduction to Drilling with Dual Tube Reverse Air and Flooded Reverse Methods
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Reverse Circulation Drilling with Air using a Rock Bit (Tri-cone/PDC)
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In recent years, dual tube methods have become a standard practice in mining, water well, and large diameter borehole drilling. Despite their growing popularity, it remains surprising how challenging it can be to find basic information about how these methods operate. This series aims to simplify the concepts behind some of the most common applications of Matrix’s dual tube product line, as utilized by our customers. Please bear in mind that we are not drillers ourselves. We’re a custom manufacturing facility specializing in producing dual tube for the drilling industry. If you have any questions or would like further details, feel free to reach out to us.
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All dual tube projects employ the principle of reverse circulation drilling. This means that the cuttings move up the inside of the pipe instead of the annular space within the borehole. It's worth noting that reverse circulation (RC) drilling can also be achieved with conventional drill rods in several different ways, but these methods shouldn't be confused with the dual tube RC methods we'll discuss here. Dual tube is primarily used in two ways: reverse circulation with air and flooded reverse circulation. Let's delve deeper into these methods and the products Matrix custom manufactures to bring these ideas to life.
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The first method we’ll explore is reverse circulation drilling with air using a rock bit (Tri-cone/PDC), as illustrated in Figure 1. This method involves introducing compressed air into the annular space between the inner tube’s outer diameter (OD) and the outer tube’s inner diameter (ID) via a side-entry air swivel positioned below the top head drive. The air travels down the string and through a rock bit adapter assembly directly above the bit. This assembly includes a wear sleeve that releases the compressed air into the borehole near the bit face. Upon decompression (which happens quite forcefully), the pressure drop sweeps the cuttings across the bit face and up through the center of the API pin-up connection of the tri-cone, into the inner tube. A lift check valve prevents the backflow of air and cuttings into the pipe annulus, which could otherwise obstruct this passage. The cuttings move up the inner tube at high speed and exit through the top head discharge hose. In mineral exploration, these cuttings are typically directed to a collection system that separates the geological materials, allowing samples to be collected and logged. This continuous, real-time sampling method enables the driller to identify the exact depth and formation they're drilling within just a few minutes.
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Figure 1: Sample Flow. Dual Tube Reverse Circulation Drilling with Air using a Rock Bit (Tri-cone/PDC)
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For those eager to learn more, stay tuned for the next two installments of our "Introduction to Drilling with Matrix Dual Tube" series! Part 2: Conventional DTH Hammers and DTH RC Hammers and Part 3: Dual Tube Flooded Reverse Circulation Drilling.
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Disclaimer: The views expressed in this article are the author’s personal opinions, based on engineering education, skills, and experience gained while working with numerous customers in the industry. No part of this article is intended to replace or supersede any information provided by others. The contents of this article may not be used for any form of legal action.
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Additional Note: While the principles described here are generally applicable, specific operational techniques may vary depending on the equipment and conditions encountered during actual fieldwork. Always consult with professional drillers and refer to manufacturer guidelines when implementing these methods.
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