Last
month’s feature on air compressors addressed pressure, flow and environmental
concerns; this month, we continue our compressor discussion with Devin Biehler,
Arkoma (Arkansas/Oklahoma) region manager for Keystone Drill Services
LLC.
I asked Biehler to comment on pitfalls and/or things occasionally forgotten by
drilling contractors. “One of the things that drillers sometimes get into
trouble with is when they’re drilling at higher altitudes,” he replies. “If
you’re drilling up in the mountains, your air compressor is drawing in that
thinner air. You need to account for that. You’re losing approximately 1
percent of your compressor capacity for every 300 feet of elevation. That can
change the uphole velocity significantly enough that you have to use an
additional air compressor when drilling at altitude.”
Another consideration: Does the compressor have an after-cooler? Biehler says,
“The after-cooler cools the discharge air of the compressor, of course, but it
also removes additional condensation and oil content out of the air. That means
less compressor lubricant going down the drill string, and cooler temperatures
on the bit. And if you’re feeding air from the compressors into a booster,
you’ll want to know if the booster has a pre-cooler. If it doesn’t, you for
sure need to have after-coolers so that air going into the booster is cool.”
That can be rather handy if you’re in a situation where you’re in a pinch and
need to rent a booster. Anybody who’s been around the block more than once can
tell you that the odds of that rental unit having a pre-cooler are directly
proportional to whether your compressor has an
after-cooler.
Can you ever have too much air? “That’s a subject of some debate,” Biehler
notes. “That gets into the operation of the air hammer. Some people want as
much air as possible because they believe that that works the hammer better and
gets cuttings out faster so they can drill faster. But, in reality, if you
talked to the hammer experts, they’ll tell you that there’s a certain balance
between the weight on the hammer’s bit and the cushion of air that is under it
so that it can achieve its maximum blow energy into the formation during drilling.
Too much air actually produces more of an air cushion, and that hammer isn’t
able to work as well as it is designed to. But that doesn’t come up too often.
The drilling contractors look to us to say, ‘Here’s really the optimal amount
of air you need, and if you buy more air, you’re just wasting equipment,
energy, fuel, maintenance, etc.’ If drillers want to use more air because they
want to clear the hole, they can adjust the choke in the hammer to bypass the
functioning part of the hammer, and the air just blows out and upward above the
bit. So all that extra capacity is clearing the hole and not going into the
workings of the hammer.”
It’s all about efficiency. Let’s suppose a particular project requires 3,000
cfm. If you put 4,000 cfm of compressors into it, you’ve got 33 percent too
much air. In that situation, “the compressors are going to unload slightly,”
Biehler explains. “They’re going to run at less than full capacity, and that’s
a very inefficient way to run a screw compressor. The compressors consume a
tremendous amount of fuel – even when they are unloaded. More than half of the
total horsepower still is being consumed by the compressor when it’s unloaded.
The most efficient way to run a screw compressor – the workhorse of the air drilling
industry – is to try to max them out. Another consideration is if a booster can
only take two compressors and you’re giving it three – you’ve got the same
situation.”
Let’s talk lubricants. The fluids that compressor manufacturers recommend have
been extensively tested and approved. Outside the normal warranty period, the
compressor owners can use whatever they want. But using fluids that are
marketed as compressor fluids but don’t have the correct additive package or
other things that were specifically designed to extend the life of the
compressor can lead to problems. “In many cases, these products don’t hold up
as well to the heat and pressure of the operations,” Biehler warns. “The oil
can oxidize faster, which means less lubrication for the bearings. The
properties of the oil change, and in a worst-case scenario, can contribute to
flash fires inside the compressor. When a compressor goes down at the drill
site, it can be very, very expensive.”
He also stresses that compressor operators should have a meticulous service
program in place. “They should be maintaining the compressors to keep them in
optimum working condition at all times,” he says. Just follow the
manufacturer’s recommendations – which are spelled out quite clearly – and your
compressors will lead long and prosperous lives.
ND