EXPLORATION METHODS USED TO ACQUIRE SEISMIC DATA IN REMOTE AREAS

PRINCIPAL METHODS

There are two types of portable surveys that Conoco would consider when hiring a crew to work in remote and restricted areas. These methods

are:

a. Portable crew, using a surface source (dynamite or primacord)

b. Portable crew using a drilled hole loaded with dynamite (approximately 40' deep).

These "portable" operations have similar characteristics. Both use the same type geophone and cable systems. All equipment is moved along the line of profile by helicopter or by individuals walking. No trucks are used on the line and a trail is not cut.

1. Surface Source - This is the main portable method used in the thrust belt. When using a surface source, the usual method is to suspend five pounds of dynamite three to four feet above the ground. A series of these five pound charges (10 total) are connected together by primacord, forming a source pattern several hundred feet in length. Both primacord and dynamite have greatly improved "flash" characteristics, and at present constitute almost no fire hazard. Two individual contractors, CGG and Seis Port, report that they know of NO fires started this year using this method.

2. Drilled Holes Portable drills are used to drill the holes for this type of survey. These are relatively light weight units that break down into two or three components. Each segment is moved by helicoptor to the drill site and the drill is reassembled as a complete unit, taking only a few minutes.

A routine hole depth that Conoco has used is 40-50 feet. Normally about 40 pounds of dynamite is used. When this explosive is detonated it does not blow out of the hole and is not a fire hazard.

This method gives improved data quality, when compared to the surface method. There is a cost increase of 50-75% over the surface method. It can't be used if drilling is difficult, as it is in some thrust belt

areas.

SUMMARY

The improvements that have been made by the manufacturers of explosives over the past several years have resulted in products with a very low flash point. This has reduced the fire danger to near zero when using the surface source of portable exploration. Holes drilled with portable drills show the

Exploration Methods used to Acquire

Seismic Data in Remote Areas

Page 2

dedication of the industry to a continuing effort to develop methods that have further reduced the impact of seismic exploration in environmentally sensitive

areas.

Other techniques, now primarily in the development stage, will further improve the ability of the industry to conduct exploration surveys with zero effect on the environment. These devleopments show the concern and dedication of management to continue to improve upon the methods used to explore for oil and gas in remote areas.

Pursuant to your request, made during the September 23, 1982 hearing on S. 2801, The Wilderness Protection Act of 1982, submitted herewith is Atlantic Richfield Company's statement regarding the conduct and effects of state of the art seismic survey techniques developed for use in environmentally sensitive areas. We respectfully request that the attached statement be entered into the hearing record as a supplement to our earlier testimony.

Our attached statement is presented in non-technical terms and is, of necessity, brief. We can provide a more in-depth treatise on the subject if needed to enhance public understanding on this issue.

Again, Atlantic Richfield Company appreciates this opportunity to participate in meaningful efforts to resolve the controversy surrounding the wilderness issue.

Atlantic Richfield Company Statement

on

State of the Art

Seismic Techniques in Environmentally Sensitive Areas

Supplementary Testimony on S. 2801, The Wilderness Protection Act of 1982 Before the Subcommittee on Public Lands and Reserved Water of the Senate Energy and Natural Resources Committee

There are four methods of seismic data acquisition that can be used in environmentally sensitive areas. These methods are vibroseis, conventional shot-hole crews, portable shot-hole crews, and surface shot crews. Terrain, topography, and other environmental factors determine which of these methods is employed in any given area. All of these methods apply the same basic technique of sending sound waves into the earth. These sound waves return from the earth and are recorded by a series of sensitive receivers (geophones) that have been placed along the surface of the ground. The differences in these techniques result from the manner in which the sound waves are generated and the mode of transportation used to get to sites.

The vibroseis method of collecting seismic data is exceptionally clean and efficient. In this method, a truck-mounted piece of equipment places a pad against the surface of the earth. This equipment vibrates rapidly, sending a

sound wave into the earth that is returned and recorded by a series of geophones. Because the equipment is truck-mounted, this technique is limited to use in areas which are accessible by vehicle. It is used most often along existing roads, trails or in open fields. In developed areas, operating procedures dictate that the intensity of the vibration be attenuated to preclude damage to nearby structures. During the operation of a vibroseis unit the only noise is that of the truck engines and the only noticeable effect is a shaking of the ground for a brief period. The only possible visible sign that these operations have taken place could occur if the ground is wet; truck tracks might then remain. However, if the ground is soft, alternative seismic techniques will be employed. Otherwise, once the operation is completed there is absolutely no sign any operations have taken place.

Conventional shot-hole crews drill holes in the ground and place small dynamite charges in these holes. The explosion from the dynamite produces the necessary vibrations to record the seismic data. Like vibroseis operations, conventional shot-hole techniques are limited to areas that are accessible by truck. For conventional shot-hole operation, the drills are mounted on light trucks. Holes approximately four inches in diameter and anywhere from ten to 200 feet deep are drilled in a line every one hundred to two hundred feet. After the dynamite is placed in the hole, the hole is packed with either dirt or gravel. When the charges are fired, there is no visible surface expression of the explosion. Like the vibroseis, the only noticeable effect of this technique is a brief period of ground shaking. Prior to leaving an area, the crew will scatter or remove the dirt that was removed in making the hole. heavily wooded areas there may be some small trees and brush which are cut and removed in order for the truck to pass. In extremely environmentally sensitive areas, this pass is restored as necessary.

In

The portable shot-hole crew employs the same technique as conventional shot-hole crews except that light weight portable drills are used instead of drills mounted on light trucks. This technique is used in those locations where trucks are unable to pass or would cause extensive environmental damage if they did pass. The drills, which are normally packed in or are dropped in by helicopter, are very similar to those used to drill fence post-holes. As with the conventional shot-hole crew, the environmental impact of the portable shot-hole technique is minimal. There may be some brush cleared to allow the crew to pass, but there is no opportunity for truck tracks to remain in soft ground.

In certain sparsely populated areas (primarily in the West and Alaska), surface shot crews may be employed. Where appropriate, this technique minimizes the acquisition cost for high quality seismic data. This technique uses a small (one to five pound) dynamite charge that is placed on a stake driven into the ground. Typically, the charge is placed from 1 1/2 to 3 feet above the surface, depending upon surface soil conditions. If adequate snow cover is present, the charge may be placed on top of the snow. Obviously, a loud report is produced when the charge is detonated, but that is the sole environmental impact of this technique. By proper shot placement, even minor root damage to the grass immediately below the shot is prevented. This technique has been carefully studied and approved for use by the U. S. Forest Service in the Bridger-Teton National Forests in Wyoming and the Kootenai National Forest in Montana and by the U. S. Fish and Wildlife Service in the Kenai National Moose Range in Alaska, to cite but three specific examples with which we have direct experience. Long term impacts to wildlife resources have been exhaustively studied and proven undetectable.

These four techniques (vibroseis, conventional shot-hole, portable shot-hole, and surface shot) comprise the normal suite of options available to the geophysicist for obtaining seismic data in environmentally sensitive areas. When properly employed for each specific location, and when conducted in accordance with appropriate permit conditions and stipulations, resulting environmental impacts range from minimal to undetectable.

Senator WALLOP. Thank you all very much. We will move to the next panel, Mr. Adam Schultz, geophysicist, on behalf of the Wilderness Society; Mr. Ed Clark, Virginia Wilderness Coalition; Mr. Patrick Parenteau, vice president of Resources Conservation. Mr. Parenteau is not here, so if the two of you will come up?

STATEMENT OF ADAM SCHULTZ, GEOPHYSICIST, SEATTLE,
WASH.

Mr. SCHULTZ. Mr. Chairman, my name is Adam Schultz. I am a geophysicist for Seattle, Wash. I have come to testify on behalf of the Wilderness Protection Act of 1982. Primarily I will address section 4 of S. 2801.

As has been said before, seismic exploration is used universally throughout the industry as a method of identifying subsurface resource-bearing rock structures. Indeed, seismic control is at the present time considered to be a required part of the evaluation process throughout the oil industry and drilling will rarely occur without seismic work. I would like to review how seismic energy is generated by the detonation of explosives at or near the Earth's surface, or by the activation of airguns or the operation of hydraulically powered vibrator trucks.