For
drillers, it’s pressure and flow that makes everything go.
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
Air Compressor Selection - Part 1
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