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4C-ing the future-a word from the "gurus"

	Heloise Lynn

 
The use of anisotropy to obtain additional information has been increasing. I attribute the increased usage to the growing awareness that what has been traditionally termed noise or the problem is in fact signal and the solution.

Heloise Lynn

The increase in clarity in imaged data when the layer anisotropy, or nonhyperbolic arrivals, is explicitly exploited in the code is the first type of improvement realized from the additional information. Our industry is beginning to obtain the same improved clarity in image when the azimu-thal variations in the traveltimes are correctly and explicitly exploited in the processing code.

The second type of improvement is to quantify the nature of the nonhyperbolic arrivals, or azimuthal variation in arrivals, in order to map this quantity, and to interpret this quantity, in the light of the shale:nonshale percentages or unequal horizontal stress field, and/or aligned fractures. To interpret the azimuthal variation in amplitudes, which goes beyond the azimuthal variation in the AVO (amplitude variation in offset), it is necessary to have tracked and documented the azimuthal variation in traveltimes. AVO and AVOA are both good and useful quantities; but beyond these two quantities is the analysis of the azimuthal variation of the near offsets' amplitudes and that of the far offsets'.

Whether one is dealing with PS arrivals or PP arrivals or both, the fundamental question in acquisition is, "Do I acquire limited-azimuth or full-azimuth data?" In many cases, not all, 2-D can be used as "proof of concept," but serious work is conducted as 3-D. The geologic scenario under scrutiny determines which is appropriate. In most of the applications that I can think of, if one is dealing with a long-term asset, one should be dealing with full-azimuth 3-D data. Full-azimuth 3-D also has some superior capabilities, simply to illumine complex structures, . . . [Full Text of this Article]