30 STRONG: Exploration rigs more mobile
Alan Bailey
For many years large, powerful and heavy drilling rigs had been the norm for exploration drilling on Alaska’s North Slope. With deep drilling targets in the traditional reservoir rocks associated with the original North Slope oil fields, exploration drillers had tended to use rigs that are equally suitable for oilfield development or exploration.
But a shortening winter drilling season, an interest in prospects some distance from the central North Slope infrastructure and a need to make Alaska exploration more cost effective have been driving a trend toward the use of lighter-weight, purpose-built exploration rigs.
Doyon-Akita rigs Pioneer Natural Resources broke with tradition when in 2005 it commissioned a joint venture between Doyon Drilling and Akita Drilling to build a rig, the Arctic Fox, based on a design that had already been proven for exploration in the Canadian Arctic.
“It is a fit-for-purpose rig, designed to drill exploration on the North Slope of Alaska,” Pioneer’s President Ken Sheffield told Petroleum News.
The rig’s design included a 400,000-pound-rated double mast, rather than the triple mast of a typical Alaska rig. The rig was designed to drill to 10,000 to 12,000 feet, considered an adequate depth for near-vertical exploration wells targeting the type of prospect that companies like Pioneer were pursuing.
The rig’s modular design would enable it to be relatively easily broken down into sections that would load onto a conventional truck for transportation. And that would all translate into an ability to move the rig quickly between drill sites, to enable the drilling of more wells in a single exploration season.
“We’re hopeful that we’ll be able to move this rig in three or four days from location to location,” Sheffield said.
And Pioneer drilled three wells with the new rig in the winter of 2005-06.
In 2006 Akita completed a second purpose-built Alaska exploration rig, the Arctic Wolf, for operation by the Doyon-Akita joint venture. And FEX, Talisman Energy’s Alaska subsidiary, successfully drilled three exploration wells with that rig in the northwestern part of the National Petroleum Reserve-Alaska in the winter of 2006-07.
Nabors rigs The trend towards lighter weight rigs continued in 2007. In February of that year, Mark Hanley, Anadarko’s top official in Alaska, told Petroleum News that the company and its Brooks Range Foothills partners, BG Group and Petro-Canada, had ordered a lightweight drilling rig, Nabors Rig 105, from Nabors Alaska Drilling, “for a multi-year drilling program with extensions options” in the Brooks Range Foothills. Rig 105, which is being built in Alberta, is a “mobile rig, not a wheeled rig, so it can be broken down and transported on rolligons,” Hanley said.
Then in March 2007 Nabors announced that it was building a high-tech lightweight rig, Nabors Rig 106, at the request of Chevron. Chevron plans to use that rig in a multi-year drilling program in the company’s White Hills exploration acreage, southwest of Prudhoe Bay and south of the Kuparuk field. Rig 106 should see service for Chevron on the Kenai Peninsula before moving to the North Slope.
Nabors Rig 105 for Anadarko and Nabors Rig 106 for Chevron will be the first “purpose-built AC rigs for the North Slope,” Dave Hebert, Nabors’ general manager for Alaska, told Petroleum News. An AC rig uses alternating electrical current for power, as distinct from the direct current of a traditional rig.
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