|
North Slope seismic goes green Accelerating changes in technology and methods radically reduce environmental impact of North Slope 3-D seismic studies Steve Sutherlin PNA Associate Editor
Over the last 20 years, but more importantly over the last five to 10 years, North Slope seismic techniques and equipment have undergone a radical transformation, resulting in a staggering decrease in environmental impact, says Mike Faust, manager of geoscience for ConocoPhillips Alaska Inc.
Zero tolerance for damage is the norm, Faust said Feb. 27 in remarks to the U. S. Department of Energy/Alaska Oil and Gas Association conference, “Reducing the Effects of Oil and Gas Exploration and Production on Alaska’s North Slope: Issues, Practices and Technologies,” in Anchorage.
In the 1960s and the early 1970s, survey crews plowed their source line with bulldozers. Survey lines from that era are still visible today, Faust said. In the 1980s and early 1990s, he said, there was an attitude that there would be some incidental damage. Contractors made cost-benefit decisions about environmental impacts in the field.
“Now, incidental damage is absolutely unacceptable,” Faust said. “With a zero tolerance for damage, the seismic contractor is forced to come up with a solution to be able to get the data and make their profits, without doing any damage.”
New vehicles tread lightly Early on, vehicles used in seismic shoots were on steel tracks, with skid-steering systems similar to military tanks. When equipment turned, it was difficult to avoid tundra damage.
In the early 1990s companies tried rubber wheels to reduce pressure on the tundra, and articulated steering eliminated the tearing caused by skid steering. Rubber wheels were used on most survey vehicles by 1999.
In 2000, companies took a new look at using rubber tracks. In the past, extreme cold caused rubber tracks to split and fall off vehicles, but new designs and new rubber compounds solved those problems.
Rubber tracks were fully implemented in 2001 on survey vehicles and personnel carriers, Faust said. By 2003, even the 90,000-pound vibrators were equipped with rubber tracks.
The change from steel tracks and balloon tires to rubber tracks has led to a dramatic reduction in tundra damage. The current weight-per-square-inch ratings for much of the equipment is less than 25 percent of the load for the same equipment 10 years ago, Faust said.
New survey design cuts impact New “cross line swath” patterns in seismic surveys allow vehicles to travel for miles without turning — the maneuver that created most damage in the past. Companies are also placing survey lines farther apart. The footprint of the survey has been reduced while the subsurface image has improved at the same time, Faust said. The changes have shrunk the environmental impact of seismic acquisition.
A “button patch” design was tried in 1996 because it was very effective in other states, but it was a good fit for the North Slope, and was abandoned. Faust said. It minimized impacts of vibrators, but caused receivers to make lots of turns, increasing the likelihood of tundra scarring.
“No trace of the seismic activity seen by the third summer is the current standard,” Faust said.
3-D seismic cuts impact over the life of the oil field The use of 3-D seismic early in the exploration process significantly reduces total cumulative impact of oil and gas operations in the sensitive Arctic environment, Faust said. 3-D scans provide information that is useful over the life of an oil field. Before 3-D, one well in 10 hit paying quantities of oil, he said, now 50 percent of wells hit paying quantities. The payoff is better results from fewer wells, aided by better placement of facilities and pipeline corridors.
“We don’t drill in the wrong places now; we don’t put a gravel pad somewhere and find out five years later we should have put it two miles to the east, and put a second pad out,” Faust said.
From the 1960s to the 1980s, 2D seismic was the only method employed.
In the 1980s, and through the mid-1990s, 3-D technology became much more common, and was shot in combination with 2-D views.
From the mid-1990s on, 3-D seismic became the standard. Seismic technology advanced, and equipment designs became more environmentally friendly, Faust said. Operational attitudes changed as well. Industry and regulators have become unforgiving of even small amounts of environmental damage.
In 1996, the 119,000-acre Alpine survey using the turn-heavy button patch pattern damaged 3.2 acres, Faust said. In 2001, a 672,000-acre cross line swath survey resulted in less than one acre of damage, but that damage was unacceptable.
“That crew was terminated, and they lost six or seven million dollars of income that year,” Faust said. “It wasn’t just that they had damaged a half an acre, but they didn’t have a technique in place to keep it from happening again.”
Contractors are now selected based on health, safety and environmental records, Faust said. ConocoPhillips requires its contractors to follow a prescribed checklist at the beginning of each day, to insure that HSE issues are prioritized, and to insure that the database of environmental and archeological hazards is updated. A representative of local communities, with a significant amount of subsistence understanding, travels with the surveyors to pinpoint archeological sites, Faust said.
Competition has developed among contractors, to provide the best HSE innovations and low impact equipment, Faust said.
“We continue to ratchet up the bar for environmental excellence,” he said.
| 