Hammering out the curve

February 10th, 2014 | Posted by in TD 90 hammer

First-of-its-kind directional air drilling system cuts unconventional oil drilling time, costs in half

The quest for cost-effective directional drilling tools for unconventional oil has finally produced a reliable system for the job. It didn’t require new technology, just modifications on existing, proven tools and the persistence of directional drilling experts dedicated to turning the corner with percussion.

Air drilling expert Tom Weller described the benefits of the new bottom hole assembly (BHA): “Even on our worst day, we’re two times faster than rotary and saving $100 a drill foot.”

The breakthrough percussion drilling technique was developed from Atlas Copco Secoroc TD 90 hammers and jet subs, as well

Weller’s interest in air began in the 1980s in the Appalachian Basin before he left on a career that took him around the world. Upon returning to the United States to work in the Marcellus Shale in the spring of 2011, he discovered that the progressive trend toward air drilling in the U.S. had stalled out. In some places where air had been introduced, companies had gone back to tricones.

Weller said, “I believe 20 percent or more of oil drilling in the U.S. should be done with air, but when I came back I was only seeing 5 to 10 percent.”

He also noted that down-the-hole drilling was still vertical, in comparatively shallow holes. Weller’s vision was to create a faster, better drilling technique through the use of DTH hammers capable of directional drilling. Although some companies were already successful steering rotary tools on air, Weller said, “I knew we could do much better with percussion.”

Keystone Drilling sales representative Ed Teel coordinates support for drilling companies throughout the Marcellus region from Keystone’s Wycox, Pa., center. The center keeps Atlas Copco Secoroc bits and hammers on hand and has a maintenance and repair shop that provides 24/7 service.

Teel said he first met Weller on site at a drill pad. “He asked me about air applications that were beyond me. He has all this experience with air from all over the world. So I told him he should contact Jeff White.”

Jeff White is an Atlas Copco down-the-hole tools specialist for oil and gas. When the two met, it was flint meeting steel. Weller said, “Jeff was a man after my own heart. I knew right here I had found an ear, and I didn’t want to use anyone else.”

Weller credited White, who has an engineering background, with working out the air hydraulics for the system. White said the answer was simple, but “it just needed a champion like Tom Weller.”

White and Weller believed pneumatic direction tools would drill holes more than twice as fast and at half the cost of rotary. Together they developed the patented solution that’s turning hammer drilling on its side.

Simple solution

White said, “I thought we could make modifications to existing Atlas Copco Secoroc technology.” The ability to turn would be provided by an air-driven motor.

“Atlas Copco already had jet subs to handle the air. We have the Hydrocyclone to handle fluid. We have EDGE to monitor performance. All we needed were a few changes to the hammer.” White said a side benefit of using modified technology rather than inventing technology is the ability to use existing complementary products such as fluids, foams and Hydrocyclone. “We have something for every situation.”

The successful hammer candidate was an off-the-shelf 8 ½-inch Atlas Copco Secoroc TD 90 pneumatic hammer. The modified version has been renamed the TD 90 DT for “TD 90 Directional Tool.”

White said air flow issues came primarily from the need to put far more air in the hole to clear out cuttings than was necessary to run the hammer. Atlas Copco jet subs were a key component of the solution, diverting a significant portion of the 3,000 cfm airflow from the drill string before it reached the hammer, strategically spacing the subs to move cuttings up the annulus. The other part of the solution was fine-tuning the hammer’s blow-down sequence. Together the solutions provided sufficient air for evacuating cuttings without overworking the hammer.

Vibration and lateral loading were other obstacles to overcome. Weller said putting a hammer on its side raises G-forces “by about two orders of magnitude,” or 100 times greater than vertical operation.

One of the solutions seemed at first counter-intuitive: Weller had the shock sub removed. He said it was making vibration worse and obscuring communications with monitoring systems. “The shock sub was actually causing excessive shocks,” Weller said. He added that by not having to rent it, they would realize a savings of a half million dollars a year.

To increase the radius of turns, the additional length of adding a hammer was accommodated by shortening the mud motor’s driveshaft.

Josh Marcus, Senior DTH product specialist at Atlas Copco Secoroc, said that the over-rotation of the motor when the hammer was lifted off bottom also had to be addressed. From an engineering standpoint, he said, the solution was quite simple. The key was to make sure the hammer used the same air while it was off bottom as it did when it was cycling on the bottom.

Once the formula for the blow down sequence proved itself in the TD 90 DT, directional drilling capability spread across the entire Atlas Copco Secoroc range of hammers. Deep hole offerings now include the QLX 100 DT, QL 120 DT and QL 60 HF HC.

Up to 15 times faster

The first wells were drilled to 7,000 feet (2,130 m), 20 feet apart, at 15 degrees for collision avoidance measures. With the modified BHA and a new Atlas Copco 8 ¾-inch bit configured especially for this application, the entire 7,000 feet of hole length to the kick off in the sandstone cap could be drilled without tripping out.

“We had been tripping out three times a hole,” Weller said, “with connections every 30 feet. It took up to 11 hours per trip.”

The new bits make a difference. “We used to use three bits per hole. We get two holes per bit now.” He said penetration rates are now up to 15 times faster.

Weller said it’s still a learning process, and changing to new personnel after the winter furlough slowed the process’s evolution. “This is not written down. Each crew has to be taught. Drilling this way is as much art and touch as it is science in development.”

Two of the things the crews have learned are to clean the hole and “don’t break stuff,” Weller said. “Drilling at a 25 to 30 degree angle in a dirty hole can be a problem.”

Weller said the rest is learning to slow down. “We’re at 26 rpm on the bit. We were at 60 rpm but were experiencing motor failure. It’s important to get the hammer, motor and jet sub working together to flush the hole and turn the corner. When we reduced pressure, we doubled the rate of drilling on this hole.”

Each hole unique

On this day Weller’s crew was building the curve near Tunkhannock, Penn. Target depth for the top drive rig was 7,400 feet. A conventional rig would complete the hole to 16,500 feet total depth.

This hole required an 8-inch, 1.25 degree fixed motor with a 12-inch hammer. Air was first supplied by three compressors and a booster, adding a fourth compressor nearer the bottom. Air was controlled by throttling the booster up or down. At 3,880 feet the flow was 2,600 cfm at 150 psi. Standpipe pressure was 425 psi. By 7,000 feet, Weller said, air flow would be 3,400 cfm.

One-third of the air was leaving the jet sub before the hammer, and a jet sub was set in the drill string 130 feet off the bottom to help with evacuation.

The hole was angled at 5 degrees to 1,683 feet (513 m) and then turned 26 degrees to 3,400 feet (1,036). The hole was kept at 26 degrees through 6,400 feet with the oiler injecting 3.5 gph, every third joint receiving an extra half gallon to keep the inclined hammer sufficiently lubricated.

White said the technique in some locations has been up to 15 times faster, but a more reasonable expectation is anywhere from two to five times faster. In this location rotary drilling had been progressing at about 40 to 50 feet per hour. Percussive drilling in the same area had to be held back to 300 feet per hour out of concern the assembly would outpace the operator’s ability to keep weight on bit.

Weller said the number of days to drill 12,000-foot (3,658 m) holes start to finish have been cut from the upper twenties to 13 or less through the use of top hole rigs. These “spudder rigs” start the hole and build the curve out to the 7,000-foot kickoff in as little as six days. Weller estimated that directional hammer drilling is now saving the company “half the days and more than half the cost” of rotary. “Save days, dollars follow.”

For White, the directional hammer system is the fulfillment of a dream that just needed the right people to make it come to life: “Every person who’s seen it, without exception, admires it for its simplicity. Simplicity is the beauty of it.”

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