June 2008 Edition

VERTICAL MACHINING CENTERS

Stringing Along Energy Development

Pipe strings down oil well bores have to be stabilized with collars cut from huge forgings. A manufacturer of the stabilizers incorporated new machines to do the job.

Drilling for oil has never been as technically challenging as it is today; yet, petroleum exploration has never been more ambitious. Armed with new high-tech tools and groundbreaking technologies, crews are drilling deeper – much deeper – than ever before.

Previously impossible wellbores are routinely sunk in North African deserts, South American jungles, Nordic ice fields, and Caribbean ocean floors. The scope of complex drilling is worldwide, but much of the new technology originates in the Gulf Coast crescent of Louisiana and Texas.

"We’ve developed and built a lot of the specialized downhole tools on which modern oil drilling is based," Pat McJimsey, production manager of Stabil Drill in Lafayette, LA, said. "But, our primary products are drill-string stabilizers."

For almost 20 years, the company has been one of the industry’s major players. With manufacturing and machining facilities along the Gulf Coast, as well as distribution centers in Newfoundland and Scotland, the company has an international reputation. Now, as a subsidiary of Superior Energy Services, Stabil Drill’s products are an integral part of many oilfield operations around the world.

"The technology has grown over the years," McJimsey said, "both out in the field and here in the shop."

Supervising the first run of a VS-3 vertical machining center from Haas Automation, Oxnard, CA, McJimsey said the large-capacity machine and the size of the forgings, 18" in diameter by 100" long, indicate the new trend.

“Instead of taking 30 to 34 hours to machine, we now cut the largest units in 12 to 14 hours.”

"As wells go deeper, the upper casings get bigger – and so do the stabilizers we make."

Deep bores expose the drill string to unpredictable working pressures and temperature extremes. They also penetrate more thermally unstable and potentially violent rock formations than ever before. This is where Stabil Drill’s primary product comes to the fore.

Stabilization is the Answer

Since drill pipe has a smaller diameter than the boring bit, a long pipe string can sometimes vibrate or "whip around" inside the larger-diameter borehole. This can distort the borehole’s shape, tighten the wall clearance or cause other problems. Unstable rock formations can make the situation worse. The answer is to stabilize the pipe by placing finned spacers along the drill string at regular intervals. The stabilizers center the pipe in the borehole, yet let the drilling mud flow up to the surface. In practice, the solution can become considerably more complicated.

Modern drilling crews include engineering teams who decide the exact deployment of stabilizing tools along the lengthening string. The stabilizers have diameters up to 26", and can weigh as much as 3,700 lb each.

"Stabil Drill didn’t invent the downhole stabilizer," McJimsey said. "They’d been around, in one form or another, since the 1950s. But, our founder – now president and CEO – Sammy Joe Russo, saw a better way to make them. In 1986 he started this company."

Now, the firm designs and manufactures a range of downhole tools, including weighted drill collars, hole openers and reamers, and an array of stabilizers.

Most new stabilizer designs have integrally machined spiral blades instead of the welded-on straight fins used on the original stabilizers. The spiral blades help clear debris that can "tighten" – reduce the diameter of – a hole.

By machining the part from a single large forging, Stabil Drill eliminates the possibility of a broken weld stranding a multi-million-dollar drill string down an expensive borehole.

"We make sizes larger than ever before," McJimsey said. "Since they often go through deep water, our clients want to make sure nothing can break off. The big one-piece integral-blade units are stronger and more uniform; but to machine them, we have to remove huge amounts of metal. As the parts got bigger, we transitioned the milling from manual equipment to the Haas CNC machines."

A Machine Suited for the Job

With travels of 150"×50"×50" – in the X-, Y-, and Z-axes – and a 10,000 lb table weight capacity, the CNC machine handles the forgings required for the larger stabilizers. Stabil chose an open-enclosure machine to simplify loading and setup of the large workpieces.

"Full access to the entire table makes life easier," McJimsey said. "The cost benefits of getting this size machine at a good price made our choice easy."

The machine’s large table – 146"×40" – and the Haas control’s full 4th-axis capability let Stabil integrate a large rotary table and tailstock into the setup, allowing full machining of the blades in 3D. The VS-3’s gear-driven 50-taper spindle provides 450 ft-lb of cutting torque to the large-diameter cutting tools through an array of hardened materials.

"Stabilizers are mostly 4245-4145-H steel," McJimsey said. "But, for applications with measurement-while-drilling telemetry, we use hard, non-magnetic material like NMS-100 or -140 stainless."

The biggest units start as 5,500 lb stepped-diameter cylindrical forgings. By the time the three spiral blades are precisely sculpted, the forgings are reduced by a third.

"The big forgings are expensive and hard to get," McJimsey said. "Lead times are anywhere from six months to a year for the steel, and even longer for the non-magnetic. With manual cuts, each time we put a forging on a machine, we had the opportunity to make a very expensive piece of scrap.

"Believe me, no one wants to scrap a part of these proportions. The Haas CNC machines have all but eliminated that worry. Once we get a part perfected, we know every one that follows is going to be the same. We can trust these machines."

The VS-3 that mills the large stabilizer was bought to replace one of Stabil’s manual horizontal machines.

"The VS-3 is easier to use. That makes a difference in our efficiency," McJimsey said. "Milling the blades in 3D instead of cutting pockets with a large shaped tool, as we had to do before, speeds everything."

Improvements All Around

"Simultaneous 4th-axis machining is a better way to do this job. The spirals are uniform, and the total time is reduced," McJimsey said. "Instead of taking 30 to 34 hours to machine, we now cut the largest units in 12 to 14 hours.

"Since one person can run two mills at once – each with two-and-a-half times the efficiency – we see a five-fold increase in productivity."

“The ability to program and maintain consistent feedrates and spindle loads on the Haas control...saves time and money”

Because the cycle times on the 3D parts are long, the machinists are able to start the machines’ cycles then do other jobs.

Stabil Drill uses the ceramic cutting-tool technology that has inserts set at a flatter angle. Instead of cutting with just the edge of the insert, it cuts the hardened steel forgings with the entire land. The tooling is cooled with through-spindle air instead of liquid coolant, to reduce the risk of thermal shock to the cutting edge.

The high-tech inserts still require some attention and periodic replacement, but the ability to program and maintain consistent feedrates and spindle loads on the Haas control lets the machinists run at 250 ipm without worrying about pushing the inserts to failure. The company saves time and money, because the inserts do not need replacing as often.

The VS-3 is Stabil Drill’s third Haas vertical machining center. It’s used both VF-9 and VF-11 models to produce smaller products.

"I have all Haas CNCs here in the production shop," McJimsey said, "and we’re about to order more to keep up with demand. But, our rental department shop is still all manual, due to the large volume of repair work they do to used tools. That’s going to have to change," he said. "The labor pool here is barely large enough to support us at our current level. Experienced manual machinists are getting hard to find.

"We train most of the new workers," McJimsey said. "Students with good math and mechanical abilities, who aren’t interested in college, are interested in this industry – once they find out that modern CNC machinists don’t swing hammers and crank handles all day. The PlayStation generation wants to play with computers. CNC is the definite future here." Haas Automation, Inc.

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