How RC technology Works
In RC technology, the bit has a hole through the center to permit cuttings to travel up the center of the drill pipe, rather than around the drill pipe or casing as in conventional rotary drilling. As in conventional drilling, the air exhaust from driving the hammer is used to force cuttings back up to the surface.
RC technology is ideal for porous formations that take up air easily, because exhaust air travels up the center with the cuttings—maintaining the air pressure and reducing air loss. It is the choice tool for exploration and ore grading. But more than that, it simply makes drilling any hole faster and less expensive.
The Reverse Circulation System
A RC system (shown to the right) is composed of a RC bit, RC down hole hammer (DHH), RC drill pipe, RC Top Head, and a cuttings discharge tube. RC technology can be used with a casing driver, a drive shoe down the hole, or casing rotator. Reverse Circulation also lends itself to holes that don’t need a casing.
It is possible to adapt your conventional system to a partial RC system giving many of the benefits of RC drilling while allowing you to use your current drilling system. Holte RC tools also facilitate Grout Through filling of the hole as the drill is extracted.
Early Pioneer of Reverse Circulation
From the beginning Holte recognized the significant advantages of reverse circulation (RC technology) drilling while out on the job site. Holte’s first true RC hammer, designed in the 80’s, has evolved into an offering of complete RC systems. Matched air channels and cuttings discharge, from top-to-bottom, optimize performance and minimize wear. Ultimately this means the driller can tackle more difficult jobs while using less air, with the added benefit of controlling where cuttings go.
The Reno Retrack project drilled 2000+ holes through Reno, Nevada’s sensitive downtown infrastructure. On the Whitestone Bridge in New York City, 772 mini-piles were drilled with Grout Through, to support the expansion of the I-678 bridge across the East River, connecting the Bronx with Queens.
Expert Tip: When to Switch to RC
6,000-12,000 feet per minute cuttings speed (uphole velocity) is ideal for evacuation. Over 20,000 FPM backpressure makes air find an easier way (through pebbles or sand). The penetration rate drops and the drill can get stuck. Less than 6,000 FPM and it will only be able to evacuate sand; diesel and time get spent pulverizing rocks. If your setup (Bit-Pipe-Compressors) can’t get you into the sweet spot, you’ll need some tricks to get your cuttings out efficiently. Foam can help or sometimes more air is needed. Switching to a Reverse Circulation will provide for the most effective evacuation, penetration rate, and control over the uphole velocity. RC drilling uses significantly less air (and less diesel)to get great evacuation!
- Cuttings Discharge Systems For Reverse Circulation DrillingMichelle2018-10-19T11:24:59+00:00