ABSTRACT
Seismic reflections from gas sands exhibit a wide range of amplitude-versus-offset (AVO) characteristics. The two factors that most strongly determine the AVO behavior of a gas-sand reflection are the normal incidence reflection coefficient Ro, and the contrast in Poison’s ratio at the reflector. Of these two factors, Ro, is the least constrained. Based on their AVO characteristics, gas-sand reflectors can be grouped into three classes defined in terms of Ro, at the top of the gas sand.
Class I gas sands have higher impedance than the encasing shale with relativity large positive values for Ro, Class 2 gas sands have nearly the same impedance as the encasing shalt and arc characterized by values of Ro, near zero. Class 3 sands have lower impedance than the encasing shale with negative, large magnitude values for Ro. Each of these sand classes has a distinct AVO characteristic.
An example of a gas sand from each of the three classes is presented in the paper. The Class 1 example involves a Hartshorn channel sand from the Arkoma Basin. The Class 2 example considers a Miocene gas sand from the Brazos offshore area of the Gulf of Mexico. The Class 3 example is a Pliocene gas sand from the High Island oil-shore area of the Gulf of Mexico.
Details:
Author (s): Steven R. Rutherford and Robert H. Williams
Language: English
Pages: 9
Publisher: Geophysics, Vol. 54, No. 6 (June 1989): Pp. 680-688.
File format: PDF
File size: 959 KB
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