Publications

While attenuation zones (dim-spots) have been visually noted on seismic sections associated with some hydrocarbon accumulations for almost twenty years (Taner and Sheriff, 1977, Anstey, 1977, Dobrin, 1984), early attempts at measuring attenuation in the laboratory and from seismic data met limited success. Work during the mid eighties set the stage for further investigation and development of these ideas, including discussions of a frequency dependent attenuation model by Terry Jones (1986) and experimental work by Bourbie et al. (1986) demonstrating that gas attenuates more P wave energy than water in rock pores.Factors affecting the spectral character of the seismic data generally fit into two categories (Dilay and Eastwood, 1995). The first is a lithological factor where the spectral character changes in response to time-thickness variations within a formation or a group of formations. The second is a petrophysical factor where spectral attributes can also be used to estimate the attenuation characteristics of a certain formation. It has been experimentally established that fluid-bearing porous rock formations attenuate seismic waves preferentially (i.e. higher frequencies within the seismic band are more severely attenuated than lower frequencies). Generally, gas attenuates seismic energy more than oil, and oil attenuates more than water.Spectral analysis was used to measure the attenuation of seismic frequencies beneath the Badak oil and gas field, located in the Sanga-Sanga PSC in East Kalimantan, Indonesia. This study utilized recently developed techniques for spectral and attenuation analysis (Maher, 1988). The spectral analysis method employed in the study contains several proprietary algorithms to overcome some limitations of previous methods for measuring attenuation from stacked seismic data. Comparison with AVO attributes indicates that spectral analysis provides additional information necessary to characterize the deeper reservoirs.