Josh Marcus, senior product specialist of Atlas Copco Secoroc down-hole tools, said pneumatic hammer drilling gives drillers an advantage in all but the most extremely soft ground conditions. And when weighted drilling fluid is not required to control the formations, hammer drilling should be the favored technique.
Tom Weller is one of the industry’s leading proponents of pneumatic drilling. Not only does Weller prefer it for carrier-mounted top drive rigs doing surface work, he also takes advantage of its cost-reducing speed on conventional rigs.
“A conventional triple drill rig is great for drilling with the QL 120 hammer,” Weller said. “Hydraulics give perfect control on the break. You can control it with fast reaction to weight on bit. Maintains a constant feed rate.”
Weller was working as a drilling superintendent for an unconventional oil and gas development company at an Ohio pad that required 10 top holes. Using an Atlas Copco Secoroc QL 120 hammer to drill 12 ¼-inch-diameter holes, the rate of penetration exceeded 400 feet (122 m) an hour. Weller said, “We were flying along. In just over 16 hours we drilled 2,550 feet (777 m).”
Weller said the instantaneous ROP read up to 600 feet (183 m) an hour at times. They would pull back for cutting management. “To drill this fast you have to know the formation.”
Pushing the hammer in an abrasive formation could cause premature failure of the bit. Here they were drilling through Onondaga limestone and then a big seam of Oriskany sandstone at 4,100 feet (1,250 m). After that they passed through hard Clinton sedimentary rock before the Queenston shale beds to the resource layers.
The well profile and casing changes were engineered to the formation. After setting 30-inch conductor casing to 100 feet, drill crews isolated the fresh water zone with a 24-inch hole to 500 feet cased with 18 ⅜-pipe.
From there the well profile narrowed to a 17 ½-inch hole to 1,500 feet cased with 13 ⅜ pipe, continuing the next 4,700 feet (1,432 m) to the kickoff with a 12 ¼-inch hole and 5 ½-inch pipe.
The drilling crew vertical-drilled the hole all the way to its 6,200-foot (1,890 m) kickoff point solely with the QL 120. Drilling with air controlled the formation’s water, using flow rates of up to 6,700 cfm with pressures up to 440 psi.
To complete the well for production, drilling crews fluid-drilled through the oil-producing formation after the kickoff point with an 8 ½-inch PDC bit to a total depth of 14,859 feet (4,530 m) cased with 5 ½-inch pipe.
The drill was penetrating so fast it produced 20 tons of cuttings an hour more than rotary had. It took seven people to manage cuttings instead of the usual four.
Total cost of the hole was calculated to split equally, about half for the vertical and half for the lateral. In general, the longer the lateral, the more expensive the hole’s overall cost per foot.
By comparison, mud drilling would have progressed at 400 to 800 feet per day. Pneumatic hammer drilling had been averaging 2,000 feet or more per day.
The final cost analysis includes the operational cost, mostly fuel. For fluid drilling the rig consumes about 1,500 gallons of fuel per day. On air it only uses 400 gallons. Even including fuel used by eight compressors and their generators, with a combined fuel use of 3,680 gallons a day, air cut overall drilling costs in half.