Regulations designed to protect the fragile Arctic tundra and shorter winters have given Alaska North Slope operators both economic and environmental impetus to develop clever ways to extend their drilling seasons.
One such innovation is insulating drilling pads to prevent them from thawing during the short Arctic summers. This technology succeeded in extending exploratory drilling seasons as much as 50 percent, and earned recognition from the U.S. Department of Energy as one of the Alaska oil and gas industryís best practices.
Currently, Arctic drilling seasons are restricted to 135-170 days, at best lasting from late November until mid-May. Operators not only must quickly build temporary ice roads to drilling sites, they also are required to construct ice pads, often as large as an acre. Drilling rigs and the remote camps that support them rest on these pads.
Drilling crews confine their activities to these islands of ice all winter and are careful to not stray onto the tundra beyond them. By mid-May, all traces of the rigs, camps and equipment must be removed to non-sensitive areas.
In the 1970s, regulations on the North Slope were less strict and the first ice roads invariably ended at a drill rig resting on a gravel pad. In very remote locations, a gravel airstrip also might be nearby.
The approach resulted in a potential loss of eight to 10 acres of tundra habitat, and should the drilling program end with a dry hole, state regulators said operators could show no economic benefit from the lost habitat.
Shift to ice pads in 1980sOperators switched to drilling pads made of ice in the 1980s, recognizing them as less costly and environmentally intrusive than their gravel predecessors. Still, by the 1990s, conventional ice pads were no longer meeting the needs of operators because they melted in spring and had to be rebuilt the following winter.
Adding prefabricated insulation to ice pad construction made ice pads last for multiple seasons. It enabled operators to build ice pads before a winter drilling season started, and preserve the site through the summer thaw for re-use the following winter.
More importantly, the technique gave the companies up to a two-month head start on conventional technology. Insulated ice pads, in effect, extended the available drilling season to 205 days and effective well operations to 160 days. This enabled drillers to complete at least one exploratory well, and sometimes two penetrations in a single season, operators say.
Whatís the allure of single-season completions?
Completing a multimillion-dollar exploratory well in one season cuts mobilization costs considerably, not to mention reduces related environmental effects. It also shortens the time between initial investment and return on that investment, and gets valuable subsurface data to exploration teams sooner than otherwise would be possible. Such speedy feedback enhances planning, operators say.
DOE cites BP ice pad successWhen a BP Exploration (Alaska) Inc. engineering feasibility study indicated that constructing an insulated ice pad in March 1993 at Yukon Gold No. 1 on the North Slope would significantly extend the winter drilling season, BP built a 390-by-280-foot ice pad covered with nearly 600 wind-resistant insulating panels. Summer visits confirmed that the ice beneath the panels remained sufficiently frozen. When the panels were disassembled in October 1993, they had not bonded to the resting surface, or scattered, and nearly 90 percent were in excellent condition and reusable.
BP began drilling in mid-November, two months ahead of conventional Arctic practice. With such an early start, Yukon Gold No. 1 was completed and the company had time to begin drilling at nearby Sourdough No. 2, where the insulated panels were placed under the drilling rig to give BP the option of leaving the rig on location over the summer and avoiding remobilization if the well wasnít completed before seasonís end. This proved to be unnecessary since the Sourdough well also was completed during the same season.
Overall, BP netted a cost savings of more than $2.3 million from the two single-season well completions, according to DOE. In addition, the tundra endured significantly less impact than would have been the case had BPís crews been required to move seasonal equipment back and forth between two or more drilling seasons.
DOE also reported that subsequent site monitoring showed no long-term environmental impacts from use of the insulated ice pads.