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Doyon meets exploration challenge Rig 19 gets sliding drill floor for transport to remote exploration wells Kristen Nelson Petroleum News Editor-in-Chief
By sliding the drill floor and mast onto a “rig floor transporter” and moving it separately from the rig's sub base, Doyon Drilling was able to move rig 19 from the Alpine on Alaska’s North Slope, across an ice bridge to a remote exploration drilling site; a move which would have been impossible for the entire 2.3 million pound rig.
Doyon Rig 19 — formerly rig 9 — was built in 1997 for extended reach and horizontal drilling at the ConocoPhillips Alaska-operated Alpine field on the western side of the North Slope, adjacent to the National Petroleum Reserve-Alaska. To meet 10-foot well spacing at Alpine, Doyon had a new sub base built and also beefed the rig up, enabling it to drill extended reach wells.
The rig has a sliding drill floor that allows the floor to be cantilevered into position over wells.
But there was a downside to this innovation. Lloyd Andrews, Doyon Drilling senior engineer, said that with the new sub base the rig weighed 2.3 million pounds. A sea-ice road was required to move it to Alpine, and, without the rig floor transporter, another sea-ice road would have been required at the end of drilling to de-mobilize the rig back to Prudhoe.
Then NPR-A was opened up for leasing. Rig 19 was the closest rig for exploration work, but it was too heavy — by a million pounds — to cross the ice bridges needed to reach most exploration sites, especially those in NPR-A.
Alpine field operator ConocoPhillips did use the rig for a couple of winter exploration wells that could be reached without ice bridges, Doyon Drilling's general manager, Ron Wilson, told Petroleum News June 23, but the company wanted a rig that could compete for exploration drilling in NPR-A.
It was clear, Wilson said, that the industry was going to be drilling more extended reach and horizontal wells, and “we wanted to make sure that we positioned ourselves with this rig to be able to do that.” The versatile cantilever The work done on rig 9 to turn it into rig 19 included a sliding drill floor. Think of the rig substructure as a box-like structure, Andrews said. The rig backs up to the wellhead and “the cantilever on the drill floor actually slides over the well.” When drilling is complete, the cantilever slides back over the wheels for rig moves. The sliding drill floor was added because the wells at Alpine are 10 feet apart, Wilson said, and Doyon Drilling didn't have a rig available that could drill wells on 10-foot spacing.
Rig 19 has drilled more than a million feet of hole at Alpine, 250,000 feet of horizontal hole (see story in June 8 issue of Petroleum News), including recent wells that were drilled and completed in 12 days. Weight a factor in moves But Doyon Drilling wanted rig 19 to be useable for exploration work, and rig weight is a factor in moves to exploration locations on ice roads, with ice bridges the big problem for rig weight. Ice bridges can't be grounded, Wilson said, there has to be flowing water to allow for fish passage, so “weight became a factor for getting across the ice bridges.”
It was a concern for Doyon Drilling, he said, because as the company looked at acreage that had been leased, it was evident that exploration drilling would take place in the NPR-A, and the company wanted “to make sure that this rig has an opportunity to stay working, especially in the NPR-A or other fields that are developed that require ice bridge crossings.”
Ice bridges are the critical path on ice road construction, Andrews said, and the lighter the rig, the less ice you have to put into that arch across a creek, reducing both the time and the cost. Ice bridges are built up in arches, he said, and they just keep building a big arch and “the weight of the ice compacts down until the arch compresses in and forms a bridge.”
Rig 19 weighed in at 2.3 million pounds. The weight limit for ice bridges was 1.275 million pounds. What comes off Doyon Drilling discussed how to reduce the rig weight for moves, but couldn't get it down to the weight needed by just taking the mast and certain equipment off for rig moves. Wilson said he commented to Andrews and Todd Driskill, Doyon Drilling's operations manager, that the only way they could get down to the necessary weight was to take off the whole rig floor and mast. The next thing he knew, Wilson said, they were on the phone discussing taking off the whole rig floor and mast with Alberta, Canada-based rig fabricator Dreco, the company which built the rig 19 sub base.
“The whole thing that made this possible,” Andrews said, “was the fact that the floor slides. That whole concept was already there.” Since you could already slide the rig floor over the well, why couldn't you just slide the whole rig floor, with the mast up, off the sub base for moves?
The test came earlier this year, when the rig was moved from Alpine to drill a winter exploration well.
It worked, Wilson said: “we were able to take the thing off in 12 hours and that's about the time it takes you to just unpin and remove a derrick — and that also requires cranes and other equipment that we didn't have to have out there.”
The fact that the drill floor and derrick of rig 19 can be cantilevered and slid onto the new rig floor transporter for moves without cranes means huge cost savings, Andrews said. The rig move can be done with the derrick up, but even if the derrick has to be removed, it is just lifted off for the move without the need for a crane.
The old technology of moving rigs with cranes used very large Manitowoc cranes, and required cranes to build the cranes, he said. The Manitowoc cranes would be taken apart at Prudhoe and trucked to the drilling site, and then reassembled with a boom crane. Then the big Manitowoc cranes took the rig apart — and the cranes, as well as the rig parts, had to move to the new site to reassemble the rig.
“That was a huge cost and huge time implications,” Andrews said. Disassembly-reassembly in 12 hours The drill floor and mast are transported on a rig floor transporter, a trailer-mounted, scissors-jack lifting device that can accept the entire rig floor as a unit, the company said. The heaviest load would then be no more than 1.275 million pounds, and the cost of the project would pay for itself because a sea-ice road would not be required to demobilize the rig back to Prudhoe.
Dreco, which built the new substructure, did detailed engineering and construction, with work beginning in the third quarter of 2002. Rig modification parts were fabricated and delivered to the rig with a Hercules C-130 airplane while the rig floor transporter was still under construction in Edmonton, Alberta. The rig floor transporter was dismantled, moved to the North Slope and reassembled. It was moved to Alpine by ice road, and can move at 25 miles per hour when not loaded.
Once the rig floor and derrick were loaded onto the transporter, it was lowered to the ground and moved to its new location ahead of the substructure. Doyon said that on a flat road the transporter moves five to 10 miles per hour, compared to the substructure which mores at about three mph.
After a 40-mile ice road move the substructure and rig floor were reunited.
“We were able to take the thing off in 12 hours — and that's about the time it takes you to just unpin and remove a derrick and that also requires cranes and other equipment that we didn't have to have out there,” Wilson said.
If you disassembled a rig with cranes to get it down to the required weights it would take two weeks to dismantle — “a month to disassemble and reassemble and we've got it down to 24 hours where you can take it off and put it back on,” Wilson said.
In the old days, said Andrews, a move with cranes would have cost millions, “versus what we're doing now, which is relatively nothing” in cost. Halfway to exploration Because rig 19 is at Alpine, Wilson said, the rig is already halfway out there for winter exploration, so “they can get a jump on their exploration season.” In addition to the advantage of location, rig 19 is a big rig based on hook load, Andrews said. Doyon rig 141 is a mobile exploration rig, but its hook load is 750,000 pounds, compared to a million pounds for rig 19, Andrews said. “So we are equivalent in moving weight to a rig which is not nearly as capable. It's kind of like putting a Sumo wrestler in ballerina shoes,” he said.
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