| Abstrakt: |
A hybrid model for computing the radiation from a borehole while drilling has been developed. A model for modal propagation in a radially layered borehole is coupled with the OASES code for full wave modeling of the resultant seismic wave field. The coupling is performed using the concept of effective sources. First, an equivalent seismic source array that produces the same far‐field radiation as the borehole is determined. This source array is then introduced into the layered earth model and the resulting seismic field is computed. Three propagating modes exist in the borehole in the presence of the drill‐pipe. The individual modes radiate into the formation in a pattern that is dependent on geophysical properties, with the resulting radiation pattern being extremely complex and difficult to interpret physically. Here, visualization and animation in particular has proven to be an extremely useful tool. For example, animation allows the direct identification of the complex arrival pattern recorded on surface mounted geophones. The fundamental differences between the radiation patterns in fast and slow formations are also clearly demonstrated using computer visualization and animation.Standards Committee S12 on Noise. Working group chairs will report on their progress for the production of noise standards. The interaction with ISO/TC 43/SC1 and ISO/TC 94/SC12 activities will also be discussed, with reference to the international standards under preparation. A report will be given on the meeting of ISO/TC 43/SC1 in Pretoria, South Africa, held in February 1996. The Chairs of the respective U.S. Technical Advisory Groups (H. E. von Gierke and E. H. Berger) will report on current activities of these international Technical Subcommittees under ISO. Scope of S12. Standards, specifications and terminology in the field of acoustical noise pertaining to methods of measurement, evaluation, and control; including biological safety, tolerance and comfort and physical acoustics as related to environmental and occupational noise. |
