Alfred H. Balch

Theoretical seismic wave radiation from a fluid-filled borehole

This paper concerns far‐field radiation of compressional P and shear S waves into the surrounding medium from a fluid‐filled borehole in an infinite medium and tube waves propagating along a borehole, using a low‐frequency approximation. Two kinds of sources are considered: (1) a volume displacement point source acting on the axis of a borehole, and (2) a uniform radial stress source acting on the wall of a borehole. When the tube‐wave velocity is close to the shear‐wave velocity, the effect of the borehole fluid on the P‐wave radiation pattern and on the S‐wave radiation pattern is substantial.

The use of vertical seismic profiles in seismic investigations of the earth

During the past 8 years, the U.S. Geological Survey has conducted an extensive investigation on the use of vertical seismic profiles (VSP) in a variety of seismic exploration applications. Seismic sources used were surface air guns, vibrators, explosives, marine air guns, and downhole air guns. Source offsets have ranged from 100 to 7800 ft. Well depths have been from 1200 to over 10,000 ft. We have found three specific ways in which VSPs can be applied to seismic exploration. First, seismic events observed at the surface of the ground can be traced, level by level, to their point of origin within the earth. Thus, one can tie a surface profile to a well log with an extraordinarily high degree of confidence. Second, one can establish the detectability of a target horizon, such as a porous zone. One can determine (either before or after surface profiling) whether or not a given horizon or layered sequence returns a detectable reflection to the surface. The amplitude and character of the reflection can also ...

Computer processing of vertical seismic profile data

Vertical seismic profiles (VSP) are a powerful tool in a variety of seismic exploration situations. Only after extensive computer processing of the raw field data, however, can the full value of this tool be realized. With the help of processing, relations between important rock parameters and acoustic properties can sometimes be established and highly reliable ties from well logs to surface seismic profiles can usually be obtained. The basic theory of the processing techniques is well known. However, the techniques used in processing standard surface seismic profiles usually must be modified to adapt them to the unique conditions associated with VSPs. Processing procedures, and their relevance to the interpretation of VSP and surface seismic profile data, are described.

Radiation from a downhole air gun source

This paper describes some characteristics of a downhole air gun as a source of seismic energy for a vertical seismic profiling (VSP) experiment at Salt Valley, Utah. The major emphasis is on primary radiations from the air gun source and secondary radiations from the bottom of the source hole. The observed primary radiation pattern agrees very well with theory developed for a volume displacement source acting on the axis of a fluid-filled hole. The observed secondary radiations, whose amplitudes were much stronger than the primary radiations, can be explained by calculating the wave field resulting from the application of an equivalent point force in an infinite medium, which was caused by the reflection of a tube wave at the bottom of the source hole. The experimental data also indicate that high-amplitude compressional and shear wave multiples are generated between the bottom of the source hole and the air bubble. (Author)

Seismic amplitude anomalies associated with thick First Leo sandstone lenses, eastern Powder River basin, Wyoming

Several new discoveries of oil production in the Leo sandstone, an economic unit in the Pennsylvanian middle member of the Minnelusa formation, eastern Powder River basin, Wyoming‐Nebraska‐South Dakota, have renewed exploration interest in this area. Vertical seismic profiles (VSP) and model studies suggested that a measurable seismic amplitude anomaly is frequently associated with the thick First Leo sandstone lenses. To test this concept, a surface reflection seismic profile was run between two wells about 12 miles apart. The First Leo was present and productive in one well and thin and barren in the other. The surface profile shows the predicted amplitude anomaly at the well where a thick lens is known to exist. Two other First Leo amplitude anomalies also appear on the surface seismic profile between the two wells, which may indicate the presence of additional lenses.

EXPLORATION GEOPHYSICS IN THE U.S.S.R.

Five American exploration geophysicists visited the USSR for a month during the late summer of 1971 as members of an official U.S.-USSR exchange program. The group was hosted by the USSR Ministry of Geology and saw 15 technical activities in six cities: Moscow, Leningrad, Tyumen, Kiev, Krasnodar, and Baku. During their stay, the Ministry of Geology assisted the American delegation in participating in the Proceedings of the 15th General Assembly of the International Union of Geodesy and Geophysics held at Moscow State University.