ABSTRACT: Seismic Definition of Sand Lithology by Geologic Setting or by AVO

LANDWER, WILLIAM R., NORMAN S. NEIDELL, and M. SMITH, N. S. Neidell and Associates, Houston, TX

Neidell introduced the idea that sands in relation to shales could occur in three rather distinct environments. The Zone I condition--the bright spot regime--corresponded to young, unconsolidated sands lower in acoustic impedance (density-velocity product) than shales of contemporary age under normal conditions (pressure, temperature, etc.). For Zone III sands (older and consolidated), the acoustic impedance was greater than for shales. Zone II was marked by "inconsistent" relations between sand and shale acoustic impedances. Rutherford and Williams (1989) categorized three sand conditions also showing a relation between amplitude and offset (AVO) in a shale environment. Based on these and other works, many practitioners wish to categorize sands based solely on their AVO responses. He e a detailed prospect-level study involving mapping, seismic inversions with color display, well correlations, and AVO in Grant County, Oklahoma encounters the prospective Bromide (Wilcox) sands. These sands, which are clearly Zone III sands, exhibit Zone II AVO behavior in their host setting of carbonate lithology. Based on this result, it is clear that the definition of sand environments in seismic terms from geologic considerations and from AVO behavior alone are not coincident, and we believe that the geologically based classification is more fundamental.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)