PREFACE This report summarizes some of the early, preliminary results from Project Gasbuggy in order to answer the many questions about this unique experiment. No definitive results are available which speak to the primary purpose of the experiment, namely the changes in the deliverability and ultimate recovery of the reservoir gas; these must await the detailed exploration and gas production tests. While every attempt has been made to present accurate data, it must be recognized that they are preliminary and subject to change. Thus the analysis of a complete set of data may point to inconsistencies in individual points which were unsuspected in an earlier analysis. Conclusions based on incomplete data may also turn out to be incorrect, and require correction or modification. The limitations inherent in the results presented here should therefore be clearly kept in mind. GASBUGGY PRELIMINARY POSTSHOT SUMMARY REPORT ABSTRACT The Project Gasbuggy nuclear explosion of nominally 26-kt yield was detonated on Sunday, December 10, 1967, at 12:30:00 Mountain Standard Time. Indications are that the explosive performed satisfactorily. Preliminary information is available on subsurface and surface ground motions, on the extent of the fractures, on the gas pressure in the chimney, and on the concentration of radionuclides. Subsurface ground velocities measured in instrument hole GB-D located 1470 ft from the emplacement hole range from about 1.15 to 1.6 m/sec depending on the gage location. These values are somewhat but not surprisingly higher than expected. Peak surface velocities range from 1.6 m/sec at the surface above the explosion to about 0.4 m/sec 8400 ft away. Both these data as well as preliminary values of ground motion out to a range of 60 miles are in very good agreement with preshot expectations. No damage was sustained by any of the conventional gas wells which were as close as 2600 ft to the explosion, and no structural damage has been reported from the surrounding area. Reentry drilling through the 7-in. casing on which the explosive canister was lowered established connection with the chimney at a depth of 3907 ft below the ground surface. A gas pressure of 833 psi was measured at the surface, and some xenon-133 activity was detected in samples. No other radioactive nuclide has been detected in the gas, although gas samples taken at depth have not as yet been analyzed. Density, gamma-radiation, and caliper logs indicate that a number of breaks or offsets have occurred ranging from 3805 ft down to the void at 3907 ft. These locations are in good agreement with data from fracture instrumentation in GB-1, correlate with preshot rock weaknesses, and compare favorably with predictions. Data from preliminary short term flow tests are not conclusive, and cannot be considered significant relative to either reservoir evaluation or chimney volume determination. Future work should shed light on the connection of the reentry hole with the chimney and on the nature of the chimney itself. INTRODUCTION The Project Gasbuggy nuclear explosive of nominally 26-kt yield was detonated on Sunday, December 10, 1967, at 12:30:00 Mountain Standard Time at a depth of 4240 ft below the ground surface, about 55 air miles east of the city of Farmington, New Mexico. The location of the explosion was 1770 ft from the west line and 1218 ft from the south line of Section 36, Township 29 North, Range 4 West in Rio Arriba County, New Mexico, corresponding to geodetic coordinates of latitude 36° 40'40" North, longitude 107° 12'30" West, at an elevation of 2964 ft above mean sea level. The detonation occurred in the Lewis Shale formation of the San Juan Basin about 40 ft below its contact with the gasbearing Pictured Cliffs sandstone. Indications are that the explosive performed satisfactorily. The purpose of the Gasbuggy experiment is to determine to what extent a lowpermeability natural gas formation can be stimulated by an underground nuclear detonation and to identify the detonationassociated effects which cause the stimulation. Specifically, the experiment was designed to achieve these objectives: 1. To measure the changes in the deliverability and ultimate recovery of the gas, and insofar as possible to identify the changes responsible. 2. To measure any radioactivity of the gas, to study the thermodynamics and chemical reactions of the mixture of gaseous fission products and methane, and to evaluate any necessary control measures. 3. To measure and to evaluate the generation and propagation of seismic energy within the San Juan Basin as part of a continuing study of ground motion and its effect on structures. The preshot program and the preparation for the shot-time measurements were 1 described in the Preshot Summary Report. Since the detonation of the explosive, data analysis and reentry drilling have progressed to the point where preliminary information from measurements taken at shot time is available on the subsurface and surface ground motion, and on the extent and gas pressure of the chimney caused by collapse of the cavity. Some preliminary data on the concentration of radioactivities in the gas are also available. The present report summarizes these data. SURFACE REENTRY AND EFFECTS About 1 hr after the detonation, a limited number of people were dispatched to the recording trailer park and to sur face ground zero to recover data and to monitor the area for radioactive contamination. No obstacle was encountered to normal automobile travel from the control point, and no radioactivity above background level was detected anywhere on the surface. The two radiation meters at depths of 300 and 3000 ft in the emplacement hole also showed only background readings. On the leveled area on the ground above the explosion, very little evidence of any surface disturbance was visible. Figures 1 and 2 show the GB-E and GB-1 wellhead installations as they appeared immediately after reentry. A few minor cracks in the dirt access road were soon obliterated by traffic. A cable reel left some 300 ft from the GB-E well head suffered a bent axle, and there was some minor damage to electronic equipment at the recording trailer park and at the control point. One of the early reentry parties inspected the surface facilities of the gas Fig. 1. GB-E well-head installation immediately after reentry, about 3 hr after shot time. The area is being checked for the presence of gaseous radioactivity; none was found. Fig. 2. GB-1 well-head installation immediately after reentry; photograph taken at the same time as that of Fig. 1. Note that some rather flimsy wires are still in place. wells within 5 miles of the site. At the six closest wells at ranges between 2670 and 6750 ft from surface ground zero, some of the separator-dehydrators had moved between 1 to 3 in. from their original positions, and at the four wells within 1 mile, some cracking of the ground around the well head was observed. In no case was the function of the well impaired. The surface pressure recorders at these well heads continued to operate, and no abrupt changes in the pressure buildup of these wells were observed. No radioactivity or other problems were encountered in retrieving downhole pressure gages which were installed in three of the wells before the detonation. At about 8 hr after the detonation, a small amount of radioactivity was detected at the ground surface in the multiconductor arming and firing cable. This gaseous |