I’m a driller, and I need air; what should I do? That question was posed to Devin Biehler, Arkoma (Arkansas/Oklahoma) region manager for Keystone Drill Services LLC, and he walks us through some of the basics of the process.
“First, I need to know what types of drilling you’re doing,” Biehler explains. ”Are you drilling top-hole vertical? Are you drilling the entire vertical section to TD using air? Are you going to be doing horizontal or directional drilling? Do you want air specifically for air drilling or are you going to be doing aerated fluid or are you going to be doing mist drilling or do you just need air for a parasite string?
“If you’re simply doing vertical air drilling, and it’s not reverse circulation, you need to have enough air velocity to lift the cuttings out of the hole. That is a calculation of the borehole diameter minus the drill pipe diameter, giving you the annular area. In order to properly lift those cuttings, the rule of thumb is you need at least 3,000 feet per minute of uphole velocity. Then, you back-calculate from that what CFM of total compressor capacity you need to clear the hole as you drill. That tells you how much air capacity you’ll need, whether you’ll need one, two or three air compressors.”
Biehler adds that the formula pretty much holds true for horizontal/directional drilling as well. “But there are other considerations,” he advises, “such as if you have a downhole directional air motor. There are specific parameters regarding how much air that air motor will require.”
Turning our attention to the hammer doing all that work, Biehler says, “The hammer needs a certain amount of pressure available to operate; typically, that’s around 250 psi. So, if you have a 350-psi compressor, you only have 100 psi left over to lift any cuttings or water that might get in the hole. If you’re going to encounter water, which, in most cases, you will, you’ll need additional air pressure to lift the weight of the water that’s coming in from the formation. You’ll either have to go to a higher-pressure compressor or use an air booster so you don’t water out. The air booster is a type of compressor, but it’s not drawing in air from the atmosphere, it’s being fed air by the primary air compressor and raising the pressure further.”
Relative to pressures, Ted Flatt, who’s in charge of strategic accounts, portable compressors for Doosan Infracore Portable Power, tells us, “There has been an increased demand for going to higher pressures in the primary feed compressors. The industry standard used to be 350 psi, but in a lot of applications now – in underbalanced drilling and other applications – it’s gone up to 500 psi. That puts it in a niche where there are fewer players in the market that can provide that type of equipment, but it can help make for a more efficient and effective method of drilling.” Flatt says things have been trending this way over the past two or three years. “Especially as you get into deeper and deeper wells, the higher pressure is needed,” he explains. “As you get deeper into these wells, you have to continue to flush the core cuttings out; the deeper you go, the more pressure you need to keep the hole clean. But you don’t always need that higher pressure, so you’ll have dual-pressure compressors that can operate at either 350 psi or 500 psi.”
When it comes to basic maintenance and repair issues, drillers often are working in very hostile environments; there’s a lot of dirt and dust. “You want to keep your heat exchanger packages clean so that you operate properly,” Flatt advises. “Clogged coolers will lead to overheating and your unit will shut down. Routine maintenance is something that people can sometimes overlook. You get into these situations where you’re running a compressor and you’re running your drill and you’ve got your crew there – if your compressor goes down, you’re losing a lot of money very quickly.” The lesson: Change that oil and clean that cooler package.
There are certain features being built into compressors these days that are fairly new. A lot of them have to do with the operation of the compressor – operating your oil temperatures so that you optimize your oil life. “Electronic oil temperature control valves, which are sort of like a thermostat in your car, control the temperature much more precisely,” Flatt notes. “This maximizes the life of the oil; you can extent the life of the oil – which is expensive – up to 15 percent.
“Also, environmentally friendly compressors that allow you to contain any spillage of diesel fuel or oil or antifreeze or anything are very important in some areas. These units keep any possible contaminants from getting into the ground, and this is something that more and more people are paying attention to.” ND
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