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.