Well Development Using Compressed Air

Are you using the right amount of air, tools, or time to properly develop the well?

By Mike Price

Drill Tech Drilling & Pump Inc. drilled a 600-foot, 12-inch well through silt and clay in July in southern Arizona that made approximately 50 gallons per minute. The company gravel packed from top to bottom with 12 cubic yards and airlifted it for eight hours. Photo courtesy Nick Owens, Drill Tech in Chino Valley, Arizona.

There are multiple methods to develop a water well, but the common denominator for each of them is energy. Energy must be produced to develop the well.

Using compressed air is one such well development method. Most of today’s water well drill rigs come equipped with rotary screw air compressors. Reciprocating piston air compressors have been going by the wayside dating back to the mid-1980s.

“Once you know these (rotary screw air) compressors, they’re pretty simple,” says Garth Owens, president of Drill Tech Drilling & Pump Inc. in Chino Valley, Arizona. “It’s not rocket science, but it is a precision unit.”

With approximately 15 rotary screw air compressors (two piston booster compressors) on six drill rigs or as auxiliaries on 10 pump hoists, Owens has learned the mechanical intricacies of them. He has rebuilt the compressors, changed their gear sets, and replaced them on rigs while passing along his knowledge to others in the industry.

“A lot of guys who are drilling don’t even have the right air to develop a well and they’ll throw a pump down there and just try to pump out the mud,” says Garth’s son, Nick, the manager at Drill Tech. “It destroys pumps and you’re never getting that mud wall cake off the walls behind the gravel pack to really get what the well’s producing.”

Nick Owens adds that another common mistake (see shaded box for a full list) contractors make comes down to the drilling products used. “A lot of guys drill with too much polymer and they never get their polymers out of the wells,” he says, “so sometimes you need things like chlorine to break down the polymers.

“You can drill too big of a well to where the annulus is too big, and you can’t get through the gravel pack to get the walls clean. That’s a big problem. A lot of guys think the bigger the hole they go, the more gravel the better, which isn’t necessarily good because you can never get enough annular velocity to get through the gravel pack and get that mud cake off. So, you’ve got to step back and look at the big picture of your annulus to your casing size to your gravel pack.

“A rule of thumb is about 2 inches to 3 inches of gravel pack. If there is more than that, you can’t get enough velocity to develop the well.”

Sizing Rotary Screw Air Compressors

There are drill charts and velocity calculators one can refer to online, but the recommended uphole velocity is about 3000 feet per minute.

“Depending on what size drill pipe, what size borehole, what that annular space is between the drill pipe and the borehole determines the amount of your cubic feet per minute,” Garth Owens explains. “And then your pressure is determined by how deep you’re going to go. Every 2.31 feet of water is one pound of pressure you have to overcome, so basically, it’s a 2-to-1 ratio.

“If you’re going to go 400 feet in the water, you need 200 pounds per square inch (psi). To go 600 feet, you need 300 psi.”

To clean the drill cuttings out of the well, the contractor needs:

  • Gallons per minute (gpm) and pressure when mud drilling
  • Cubic feet per minute (cfm) and pressure when air drilling.

Today’s standard rotary screw air compressor rating is at least 900 cfm or 1000 cfm/350 psi. Thirty years ago, the standard was 450 cfm/250 psi or 600 cfm/250 psi.

For example, a 750 cfm/125 psi compressor is half the compressor of a 750 cfm/250 psi compressor because the contractor is compressing the air twice as tight. Therefore, with a 750 cfm/350 psi compressor, the contractor is compressing the air an additional 50%.

To help visualize it, Garth Owens likens pressurizing the compressor to a scuba tank getting pressurized rather than simply filling a balloon with static pressure.

“Instead of putting 125 pounds in it, in order to put 250 pounds in it, it takes a bigger screw and more horsepower to do that,” he shares. “And then to go to 350, it takes a bigger compressor and more horsepower to do that. So, every compressor has two numbers—cfm, and the second number is the amount of pressure that it puts out at that number.

“For instance, for a 750/125 compressor, it’ll probably take 125 horsepower to run that. You go to 750/250, it’ll take you 300 horsepower. You go to 750/350, it’ll take 400 horsepower to do the exact same thing because you’re compressing tighter, tighter, and tighter it takes more horsepower to overcome that pressure. So, the higher the pressure, the more horsepower you need.”

The water well industry requires compressors rated at extra high pressure (XHP), or extra extra high pressure (XXHP).

“Typically, ballpark rule of thumb, standard compressor is 125 to 150 psi,” Garth Owens says. “High pressure is 175 to maybe 200 psi. Extra high pressure is usually 350 psi and the highest you’ll ever go on a screw compressor is 500 psi. That’d be extra extra high pressure to get to 500 psi. Anything after that you’re running through a piston booster compressor and boosting pressure with a piston.

“When you get into the high-pressure compressors, it takes a lot of horsepower, takes a lot of heat, it builds up a lot of heat, and it burns a lot of fuel, so if the radiators aren’t clean, if the fanbelts are slipping, if the radiator is plugged up. . . .It might run great at 250 pounds; you push it at 350 and 30 minutes later the rig is overheated.”

To decrease the uphole velocity of 3000 feet per minute, some contractors use drill foam to clean the well at half the amount, 1500 feet per minute. “If you’re using foam and you’re filling that void, you’re taking half of that void away,” Garth Owens says. “You’re using half the air because you’re filling that void with an artificial substance. It’s going to foam up and blow out and then it’s going to evaporate and go away.”

Well Development with Reverse Circulation Drilling

Drill Tech conducts simultaneous swab-and-airlift with its double-swabbed development tool that has perforations between the two swabs.

Due to predominately drilling deep large-diameter wells, Drill Tech commonly uses the reverse circulation (RC) drilling
method. With RC drilling, the company primarily develops its wells two different ways.

The company conducts simultaneous swab-and-airlift with its double-swabbed development tool (see right photo) or uses high-velocity horizontal jetting.

The double-swabbed tool has perforations between the two swabs. Airlifting typically occurs through the drill pipe “from which the development swabs are suspended, so as the swabbing action brings suspended solids into the well, they are purged by the simultaneous airlift system,” writes Marvin F. Glotfelty, RG, in his book, The Art of Water Wells.

“The air comes out of the end of the drill pipe, comes up and hits that rubber swab which is the same diameter as the casing,” Garth Owens says, “and therefore all that air has to go out the perforations, blows into the gravel pack, spins that around in there, and cleans the gravel pack and cleans the borehole. Then the water comes up through the gravel pack and comes back to the perforations above your swab and comes out the top of the well.”

Glotfelty writes how this well development method is effective because “it provides both inward and outward energy to break down and remove the wall cake, without forming sand bridges in the adjacent formation.”

“We’ll actually create a vacuum and pull it between sections there,” Nick Owens says. “That’s why there’s a rubber swab above and below the holes. Typically, if you want to do an air swabber, you don’t need the rubbers because you’re just blowing it out through the perforated screen into the formation.”

The company’s high-velocity horizontal jetting tools allow it to adjust the amount of air it needs to push through them. “That way it’s blowing the air through the perforated screen, through the gravel pack, and then we’re trying to develop all that mud off there if it’s a mud hole,” Nick Owens says.

The company has an additional high-velocity jetting ball tool with approximately 20 holes each drilled to 3/16 inches around it. A high-pressure pump is used to pump freshwater down the well at 2000 psi.

“That will not only churn and turn that gravel, but it places that mud thinner all the way back to the borehole to knock off the wall cake,” Garth Owens says, “and once you’re done pressure jetting it, then you’ll come back and re-swab it and RC it all back out of there.”

Drill Tech, which had a backlog of approximately 100 wells and 30 pumps to install as of late July, stresses it all starts with the design of the well, drilling it correctly, using the right products, and not overusing polymers.

“If we’re RC drilling, we’ll mud up the top and then we’ll case the top off,” Nick Owens says. “There’s some wells out here where we live where the top 300 feet is all alluvium and there’s no water in it. We’ll mud those up, we’ll set a 300-foot surface casing, and we’ll RC drill the bottom out with just pure water because it’s just solid rock. So, we don’t use any product.

“We can literally drill a 1200-foot well, pull out, put our casing in it, and gravel pack it. You can trip in as soon as we’re done with zero development and can video the well, it’s that clean. Something of that nature doesn’t take much development because we didn’t put any product in the well. It just depends on where we are.”

To drive home the importance of using the correct amount of product, Nick Owens recalls a large drilling company that installed two large municipal wells 10 years ago in central Arizona. It both drilled with and pumped too much polymer into the wells and was unable to get the polymer out. The wells produced 300 gpm.

“We drilled some other wells near them, and we got 1200 gallons per minute out of the wells and the aquifer just simply because of the development and not using polymers,” he says, “so [it’s] a big thing to make sure of the product when you’re drilling and make sure you’re using the right product that you can get back out—that’s the biggest thing.”

Important Considerations

Garth Owens has noticed a well development trend that shouldn’t be emulated by others in the industry.

“Most guys will just trip their drill pipe straight in, blow it straight up the hole, and they’re done,” he shares. “But you’ll get a lot more water out of your well, you’ll pump a lot less sand, and you’ll have a much better production well with a higher pumping level if you clean that formation out and get every bit of that mud that you put in back out again. The only way to do that is with pressure through the perforations.”

While drilling in July in California, Garth Owens also noticed large amounts of gravel being put into large diameter wells drilled using the mud rotary method. “They think that the bigger the hole is, the more gravel they put in, the better it is, which is not true. What they don’t get is the bigger the hole gets, the worse development job you can do.

“Let’s say you drill a 16-inch hole and put in 6-inch casing, and you’ve got 5 inches of gravel on either side of you, you cannot get enough pressure through 5 inches of gravel to clean the wall cake off the borehole on the outside to get it to produce. The well is still going to produce, but it would be a lot better producing well if it has 2 to 3 inches of gravel and you’ve got enough energy that you can push through that.”

Low-cost gravel too has its disadvantages, with it being crushed and therefore angular. These angular pieces all wiggle together and lock together like chip seal on a highway in the well, according to Garth Owens. This causes a slowdown in the production of water.

“Most people don’t use any chemicals to break down that wall cake because it costs $250 a bucket,” he says, “so we’ll go out and drill a well that will make 500 gallons per minute, and our competition literally on the next lot is drilling 100 gallons a minute. And it’s simply because of the gravel pack and the development process.”

Well development can take multiple hours, so it’s vital to plan and include it in the budget.

“Time is one factor, they want to get to the next job,” Garth Owens says. “Another factor is they don’t want to put a swab in to pressurize the perforations. The third thing is purchasing the cheapest gravel they can because they think they’re going to overcome all that by drilling a hole that’s one or two inches bigger in diameter and now all that other stuff is irrelevant.”

In summary, Garth Owens says the idea in constructing a well to produce is to:

  • Determine the drilling formation
  • Determine the granular size of the ground that one is trying to keep out
  • Install the largest gravel to have the most square inches of opening and the least friction for the water to come through but stop the finest particles of sand.

“You design with maybe a 10 percent passing of sand,” he says, “and then you want to go down there and develop it until that 10 percent gets down to 0.5 percent or 0.25 percent. You want to airlift develop that until you’ve blown out everything, you’ve agitated it, washed out the gravel, washed off the wall cake, and then the ground itself and those fines come out of there.

“The coarser material that’s in the ground will start building its own gravel pack on the backside of your gravel pack. If you do it right, you can go in and develop a well in four or five hours and have a beautiful well.

“If you don’t do it right, you can spend three or four days pumping sand because the gravel is too coarse. You put in too coarse of a filter and the sand just keeps flowing. It takes forever, if it ever does stop. Too coarse of a sand and it’ll never stop.”

Maintenance of Rotary Screw Air Compressors

As mentioned earlier, rotary screw air compressors are simple in nature.

For a high-pressure compressor, there are three gears in the bellhousing and two low-stage screws and two high-stage screws. The simplicity allows the compressor to last for an average of 10,000 hours.

However, unlike with a reciprocating piston air compressor, Garth Owens cautions against closing the downhole valve, build maximum pressure, and jerk the valve open with a rotary screw air compressor.

“Because on a piston compressor, you just have a receiver tank that just holds air,” he says, “and you can pressure it up to 250 to 300 pounds and jerk the valve open and that big surge of air is what blows out silts and rocks when it won’t do it when steady drilling.

“On a screw compressor, when you max out the pressure at say 350 pounds, and you’ve got the same pressure inside the filter as you do on the outside of the filter, when you blast that ball valve open, the pressure differential escapes faster inside than it can equalize. That’s what causes that filter to collapse and blow all your oil down your hose. That’s the one and only thing you don’t do with a screw compressor—build up to max pressure and jerk the valve open—that you can do with a piston compressor.”

For years, automatic transmission fluid (ATF) was the standard for lubrication on compressors. Today, synthetic compressor oil is used because they must run at about 225 degrees to 275 degrees to vaporize the water as it sucks moisture out of the air when drilling. “It sucks all that moisture into it and it rusts up all the bearings and gears,” Garth Owens says, “so by turning the thermostat up so hot, it vaporizes and burns the condensation out of it.

“There’s a water drain on the compressor that you drain every day, and it’s imperative that you keep the temperature up on a screw compressor for condensation reasons.”

The flashpoint for synthetic compressor oil is about 400 degrees; ATF is about 300 degrees.

“You hear about a lot of rigs burning down and compressors burning down, it’s typically because they have old non-synthetic oil because it costs less,” Garth Owens says. “What happens is the tolerances are very tight in a screw compressor.

“Typically, there’s three thousandths max tolerant in a screw compressor, so you really have to keep your air filters clean, your oil filters clean, and your oil good. When that tolerance starts to get loose, when you start getting a bearing wearing out or one of your screws starts wearing into the impeller of the compressor, when that tolerance starts to get loose at all, typically your oil temperatures skyrocket tremendously. It’ll run at 200 degrees for 10 years and then all of a sudden, you’re wondering why it’s running at 275 degrees and trying to cook the hoses off your rig.”

The first indication is typically losing a bearing when the oil temperature begins climbing with the tolerances getting loose. “You either have steel on steel friction, or the tolerance is so loose that after you’ve compressed this air and oil, it scoops up the air and oil and pushes it through the screw,” Garth Owens says.

“Because the tolerance is so loose, it squirts right back out of it and now you’ve built more friction, more heat, and it has to scoop it back up again. So as the screw compressor starts to go out, the volume of air starts dropping and the temperature of your oil starts increasing. Those are your first indications that when the oil temperature is coming up, you’ve got screw damage, and when your cfm of air goes down, you have damage.”

Avoid These 10 Common Well Development Mistakes with Compressed Air

  1. Using too small of an air compressor
  2. No swabbing or jetting tools
  3. Too much polymer used when drilled
  4. Too big of an annulus, resulting in too much gravel between well and casing, or not enough gravel between well and casing
  5. Not using mud thinners
  6. Using the wrong types of gravel that are not well rounded
  7. Not developing the well long enough
  8. Not including time to develop the well in the budget
  9. Not charging the customer enough to develop the well
  10. Not spending time in each zone but just blowing from bottom to the top of the well.

Learn More About Well Development
Marvin F. Glotfelty, RG, discusses various types of well development (including swab-and-airlift) and physical attributes of the well that will be impacted by the various development methods in an NGWA: Industry Connected video.

Click here to learn more about Glotfelty’s book, The Art of Water Wells.

Mike Price is the senior editor of Water Well Journal. In addition to his WWJ responsibilities, Price contributes to the Association’s scientific publications. He can be reached at mprice@ngwa.org, or at (800) 551-7379, ext. 1541.