Abstract

A general correlation of cross-well seismic data and surface seismic data is attempted simply by examining a combination of the two major mechanisms of seismic wave attenuation, anelastic Q, and spherical divergence. High-frequency cross-well seismology can be hindered by the assumption that an order of magnitude increase in frequency is accompanied by an order of magnitude decrease in propagation distance such that the anelastic attenuation (described by quality factor Q) remains constant. Such a comparison, however, neglects the effects of geometrical spreading, which is independent of frequency. Through the consideration of both Q and spherical divergence, it is demonstrated that the total attenuation of 2000 Hz energy at a distance of 613 m is equivalent to the total attenuation of 20 Hz energy at a distance of 7000 m. Applications of kilohertz cross-well seismic surveys between wells spaced by over 600 m could be possible with present dynamic-range capabilities in seismic recording systems. Such applications would allow the use of high-resolution cross-well seismic surveys between wells drilled on a 40 acre spacing. One example of cross-well seismic data is shown to demonstrate the high-frequency content (kilohertz) which can be obtained. Theoretical calculations indicate that kilohertz energy could be recorded at distances up to 1 km. The assumptions are that present surface seismology measurements define the dynamic-range capabilities of recording instruments, and that Q with spherical divergence accounts for all attenuation. All calculations neglect the problems of miniaturization required for downhole applications. The goal is that omission of extremely low Q regions near the surface and the noise-free borehole environment can overcome the miniaturization problems.

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