A. General

Cooperative research by the United States Atomic Energy Commission (AEC) and the United States Bureau of Mines (USBM) under the AEC Plowshare Program, indicates that the use of nuclear explosives (NE) to stimulate low productivity oil and gas reservoirs can be far more effective than present stimulation techniques.1.2,3 This previous work also indicates that the extensive, thick, low-permeability natural gas reservoirs in the Rocky Mountain Region are the most favorable for NE stimulation. A survey of these gas fields and discussion with operators resulted in isolating several locations suitable for a field test.

Proof of the utility of NE stimulation can be determined only by a full-scale field test. Justification for such a test lies in the number and areal extent of lowproductivity reservoirs where the ultimate recovery and the rate at which such recovery occurs may be substantially increased.

As early as 1958, El Paso Natural Gas Company (EPNG) investigated the application of NE stimulation to a gas reservoir by initiating correspondence with the University of California, Lawrence Radiation Laboratory, Livermore, (LRL) in connection with the Pinedale Unit Area, covering approximatley 92,000 acres in Sublette County, Wyoming. Although EPNG did not propose a field test because of technological problems existing at that time, this area is one that should merit consideration for future application.

B. Project Gasbuggy

Project Gasbuggy was instituted to design, conduct and evaluate a NE stimulation experiment in the Pictured Cliffs formation at one of the most promising of the prospective test sites, located on an EPNG oil and gas lease in the San Juan Basin, Rio Arriba County, New Mexico. Project Gasbuggy is a joint undertaking by the AEC, USBM and EPNG to evaluate the feasibility of a test at this location and to execute the test, pending authorization by the policy-making bodies of these organizations.

This report presents the results of the site evaluation

and offers a preliminary design for the experiment. The study was initiated by the AEC San Francisco Operations office. EPNG and USBM, utilizing accepted technology of the industry, performed the necessary calculations and made the engineering evaluations. EPNG furnished the geologic data, ownership and location information, while LRL provided consulting services pertaining to resulting radioactivity in the gas and effects of nuclear explosions.

Performance of this experiment will require drilling and casing an emplacement hole to accommodate the nuclear explosive just below the base of the Pictured Cliffs Formation. The yield of the explosive to be used will not exceed 10 kilotons, the energy equivalent to 10,000 tons of TNT. As an example of its magnitude, the nuclear explosion will generate a force 5,000 times greater than that obtained from 1000 quarts of solidified nitroglycerin, the normal amount of stimulation given a Pictured Cliffs well when the "shot-hole" completion method was practiced.

The energy of the nuclear explosive will be generated in a fraction of a microsecond, vaporizing, melting and crushing the surrounding rock. Within milliseconds, a cavity filled with vaporized and melted rock and debris will be created. The melted rock that initially lines the walls of the cavity will collect in a pool, trapping most of the radioactive fission products as it solidifies. The cavity will be roughly spherical in shape with a radius of approximately 65 feet. Following creation of this cavity, the roof will collapse and a cylindrical chimney of broken rock will develop upward. The radius of the chimney will approximate that of the cavity, and its height is estimated to be 300 feet.

The force of the explosion will also cause fracturing of the rock beyond the cavity and upon this phenomenon rests the success of NE stimulation. Fracturing will cause a gross change in the permeability of the rock in which it occurs, and the number and range of these fractures will determine the extent of permeability change. Production will be accomplished by drilling into the chimney. The plan for this experiment and resultant subsurface effects are illustrated in Figure 1.

A. Criteria for Acceptable Test Site

Criteria for selecting a test site for possible utilization of a nuclear device are as follows:

1. A low permeability depletion-drive reservoir in which conventional stimulative methods are inadequate.

2. Reservoir having sufficient thickness to effectively utilize the anticipated effects of the proposed nuclear explosion. Ideal thickness for a 10 kiloton yield device is approximately 300 feet.

3. Reservoir sufficiently deep to confine the explosion but not so deep as to result in excessive emplacement and testing expenses. Ideally the depth should range from 2000 to 4000 feet.

4. A site reasonably remote from habitation but easily accessible.

5. Sufficient drilling in the surrounding area to provide adequate production and subsurface data, yet not so highly developed as to be subject to heavy liability for possible damage to existing wells and surface field facilities.

6. Uniformity of leasehold ownership and/or withdrawal from leasing of unleased lands adjacent to the test site.

B. Location-Culture-Ownership

The location selected is in the SW/4 of Section 36, Township 29 North, Range 4 West, N.M.P.M., Rio Arriba County, New Mexico, on the eastern side of the San Juan Basin, a structural feature of the Colorado Plateau Province in northwestern New Mexico and southwestern Colorado (Figure 2). Most of the central Basin is open country, broken by occasional low mesas, buttes and wide cuestas, with local relief rarely more than a few hundred feet. The annual rainfall is 8 to 15 inches and only moderate snowfalls occur in the higher elevations.

The location is both remote and uninhabited yet readily accessible by paved highway (Figures 3, 4 and 5). There are no appreciable ground or surface waters in the immediate area. The nearest sizeable town is Farmington, New Mexico, 70 miles to the west, with a population of about 23,000. The nearest community is Dulce, New Mexico, approximately 20 miles to the northeast with a population of about 500. There are no houses or buildings within a five-mile radius.

The proposed test site is within the Carson National Forest and adjacent to the Jicarilla Apache Indian Reservation (Figure 6). Section 36 and the contiguous sections are Federal and Indian lands, some of which are presently unleased. The existing oil and gas leases covering the lands in the immediate area of the test location are held by

EPNG (Figure 7). The area surrounding this site contains mesas, canyons and the usual bench-type topography generally associated with these surface features. The elevation ranges from 6800 to 7500 feet in the general area and from 7000 feet to 7200 feet in the immediate test area. There are no streams of consequence in the area. The San Juan River, at its nearest point, is about 20 miles from the test site and the Navajo Dam about 23 miles away. Vegetation consists of Pinon Pine in the lower levels and Ponderosa Pine and Juniper in the higher elevations. Surface rights are administered by the National Forest Service, with cattle grazing permitted during the summer months. C. Geology of the San Juan Basin

Most of the central part of the Basin is covered by a circular blanket of continental sediments of early Tertiary or very late Cretaceous age. (See Figure 8 for Geologic Time sequence.) The central portion of the Basin is approximately 90 miles in diameter and covers an area of about 10,600 square miles. A roughly circular outcrop of marine and nonmarine Upper Cretaceous formations circumscribes the central part of the Basin. Facies changes within the Basin occur in many formations with intertonguing of marine and nonmarine strata. Overlapping unconformities and local angular unconformities occur in the flanks of the uplifts around the Basin, but in the large central area the beds are generally parallel throughout the section from the deep early Cambrian to the surface Tertiary beds.

Formations in the San Juan Basin range from preCambrian to Eocene, but there was not an uninterrupted sequence of deposition. Some unconformities are present. and to-date no Ordovician or Silurian sediments have been encountered. The total thickness of sedimentary rocks in the center of the Basin ranges from 10,000 to 15,000 feet.

There are eight gas producing formations of Cretaceous age in the central Basin. These formations in descending order are as follows: Kirtland, Fruitland, Pictured Cliffs, Lewis, Mesaverde, Mancos, Graneros, and Dakota. However, the significant production is obtained from the Pictured Cliffs, Mesaverde and Dakota formations, the latter including the Graneros formation as defined by Order of the New Mexico Oil Conservation Commission.

The sequence and thickness of these formations at the test site are shown in Figure 8, based upon the two cross-sections contained in Appendix A. The Pictured Cliffs formation is expected to be 300 feet thick at the test site, exhibiting the characteristics of a low-permeability, depletion-drive reservoir that are specifically described in Section IV-A.