Making waves: Sonic seismic testing helping WPX size up shale project
PARACHUTE — Contractors for an energy company are heading to great heights this winter to help it better understand what’s going on deep underground where it’s been starting to drill in shale for natural gas.
WPX Energy is using seismic testing to better size up and characterize the Niobrara shale formation as it tries to expand on its initial success drilling there. Much of that work is requiring the use of helicopters to ferry crews and equipment to steep, inaccessible mountain terrain to drill holes in which explosives are placed for use in the testing.
Viewed from a helicopter on a sunny but cold December day, crews with WPX contractor Green River Energy, based in Columbia Falls, Mont., were perched on narrow ridges high up cliff sides west of Parachute, where the 42-square-mile project area is centered. On steep, snow-covered terrain marked by the infrequent tracks of intrepid animals, the presence of humans seemed improbable, much less humans firing up diesel-fueled air compressors powering 1,600-pound drill rigs.
Then again, the entire concept of seismic testing seems improbable — the idea of sending down a shuddering shout from the earth’s surface with the expectation of getting back echoes that help describe geology thousands of feet below. But the concept isn’t all that novel, with counterparts to be found in the use of the echolocation navigation employed by everything from bats to submarines, and in the employment of ultrasound in medicine.
“It’s kind of like ultrasound because it’s sound waves we work with,” said Bret Gunneson, a WPX geophysicist.
A stream of echoes from blasts or vibrations on the surface are captured by cup-sized receiver devices that are essentially microphones. The echoes WPX is most interested in might come back within about five or six seconds, from the Niobrara formation. Scientists can know the echoes are from that formation based on characteristics of the sound combined with knowledge of its general depth gained from factors such as nearby drilling. The timing of echoes can help the company better pinpoint the formation’s depth, and the sound waves also can indicate other details such as faults and natural fractures that are considered in making drilling plans.
USE GROWING NATIONALLY
While there’s been some use of seismic testing in western Colorado’s Piceance Basin, Gunneson said its use has become much more commonplace nationally with the increased use of horizontal drilling combined with hydraulic fracturing.
In such drilling, wells are drilled down and then out horizontally to follow what may be thin but rich formations bearing oil and gas.
“The seismic (testing) will tell you where that (formation) is before you drill it, so it will help you guide that horizontal well,” he said.
Most Piceance Basin gas wells have been drilled into the thick Williams Fork sandstone. While those wells might be drilled down at angles, or directionally, they penetrate the pay zone vertically and there’s no missing it.
By contrast, the Niobrara shale sweet spot WPX is targeting might be only 70 feet thick, which makes following that seam challenging and makes seismic data more valuable.
Similar, crucial knowledge comes from drilling actual wells. But drilling and hydraulically fracturing wells are expensive — particularly for horizontal wells, which in the case of WPX’s Piceance Niobrara undertaking could cost $7 million or more apiece even after it gets its initial costs down.
Gunneson said that even with the extensive helicopter work involved, the costs of the seismic job might come out to be about the equivalent of developing one well. But the work will provide WPX information covering 42 square miles rather than just what a single well can reach.
“Then we can plan our wells before we drill them and put them in the right spot,” he said.
That could allow the company to drill more quickly, and develop the resource with potentially fewer wells, resulting in fewer impacts.
THE RATTLING QUESTION
As to what the impacts of seismic work itself might be, one natural question that arises is what kind of damage blast and vibration work might cause. John Stephens, project manager with Green River Energy, said even workers setting off blasts 30 feet away won’t feel the explosion.
“It’s not going to crater out with these big explosions. That’s the last thing we want. We don’t want energy to go out; it goes down,” he said.
The Bureau of Land Management, which manages some of the land WPX is testing, has standards governing the size of charges used and their distance from structures such as pipelines and buildings, Gunneson said. Stephens said landowners also sometimes indicate the minimum distance they want testing to occur from their homes.
Gunneson said past testing in the Rulison area, involving measurements at different distances from charges, studied what’s called peak particle velocity, and was designed to help establish standards to protect buildings and other infrastructure. That work was done in 2001 by Barrett Resources Corp., which later was purchased by Williams, which later yet spun off WPX into a separate company.
Gunneson said WPX has hired peak particle velocity experts for its current job.
He said a train going by a house generates a lot more vibration than seismic testing does. “But you don’t want a railroad going right by your house,” he said in noting the need to be careful in how seismic testing is done.
Stephens said where complaints about seismic testing damage arise, they more typically involve surface issues such as crews causing rutted fields or breaking fence posts, rather than from the seismic vibrations.
Matt Lepore, director of the Colorado Oil and Gas Conservation Commission, said the agency is dealing with one complaint from residents living on the Front Range who believe seismic testing affected their water well. Agency staff determined the testing wasn’t the cause, based on the size of vibrations monitored in real time and the distance between seismic equipment and the well — although he noted that distance is being debated between the resident and the seismic contractor. The residents are asking for a commission hearing on the matter.
CURIOUS ABOUT ‘COPTERS
Lepore said he can’t recall other complaints related to seismic testing, except perhaps one situation in which residents simply were wondering what was going on.
The issue of public awareness arose with the WPX project as well, as residents began asking about the helicopter activity they were seeing. WPX spokeswoman Susan Alvillar gave some details about the work at Garfield County’s Energy Advisory Board meeting early this month and acknowledged it would have been helpful to publicize it earlier.
“I think it was an issue of living in the gas patch and seeing these kinds of things and not having any answers,” said Dave Devanney, a member of Battlement Concerned Citizens in Battlement Mesa. “That was our only issue. I don’t think there’s any other concern, any safety issues or anything, but it would be nice to know what’s going on in our backyard. (Alvillar) took ownership of that problem and that’s fine.”
Lepore said the commission requires that it be notified about pending seismic operations, but not the public. The agency investigates any complaints that arise.
Seismic testing is seeing considerable use on the Front Range as companies do horizontal drilling for oil and gas, also in the Niobrara.
For its local project, WPX obtained surface-use agreements with private property owners, with provisions for covering any damages should they occur, and also got approval from the BLM. Where private agreements can’t be reached, private property simply is avoided and operations are moved, which Gunneson said doesn’t create much of a problem for data gathering, at least in the case of smaller properties. Operations also are shifted to protect other resources as well and the data all averages out, he said.
BLM spokesman David Boyd said the primary concerns the agency wanted addressed in connection with the project were protection of archeological sites and rare plants. These were dealt with through survey work and avoidance of areas of concern. The U.S. Fish and Wildlife Service determined the project wasn’t likely to affect rare plants, such as the Parachute penstemon, under the restrictions the BLM required.
WPX and Green River Energy believe the project’s surface impacts should be reduced because it’s occurring in winter, when plants are dormant, snow provides protection and wildlife has moved down-valley.
Some of the testing, on flatter land, will be done using trucks that place onto the ground a vibrator plate the size of a dinner table and use oversized, low-pressure tires to help minimize surface damage.
Drilling of holes for the project began on private land in October. WPX hopes to have the detonation of charges and use of vibrators begin around the start of the year. Doing that over 4,000 locations should take about a month.
Stephens says he tells people that if they notice anything at all, it will be a dull “dunk” sound as charges go off.
Devanney said that while he hasn’t heard local concerns about the work possibly causing any damage, there’s little public knowledge about it at this point.
“It’s kind of like another fracking (hydraulic fracturing) potential. Industry says this is good for us and everybody, and then you find out after the fact that there may be some hazards that have yet to be discovered,” he said.
He said that so far, the good news associated with the project is that WPX appears to be doing its exploratory work in an unpopulated area, rather than near many homes.