James P. DiSiena¹, Gokay Bozkurt¹, Keith H. Wrolstad¹, Wenlong Xu¹
(1) Unocal Corporation, Sugar Land, TX

Abstract: Understanding seismic sensitivity, including AVO, in 3D to discriminate lithology and fluids

Analysis of the seismic response, which includes amplitude versus offset (AVO) variations, has had limited success in accurately predicting lithology and fluids in the subsurface. Uncertainty can arise from pitfalls in the seismic analysis or from limits in the sensitivity of seismic reflections, (e.g., seismic's inherent nature to only respond to neighboring contrasts in subsurface properties). An important step in this discrimination comes from understanding the sensitivity of the response to geological (shale-sand) setting, thickness, porosity, or fluid variations within the pores. As shown in many attribute or amplitude studies, the incorporation of geological insight, calibration at wells and a 3D perspective into the analysis can often help overcome these inherent limitations. Great strides have been made with modern interpretation software in classifying the apparent seismic facies and mapping these classifications across 3D volumes. Application of these methods to a host of attributes including AVO can become more quantitative when incorporated with our model-based sensitivity approach. While our approach cannot overcome the insensitivity of the seismic response to fluid variations in well cemented/compacted rocks, it has potential to help discriminate thickness/porosity or gas saturation variations over a wide range of sand reservoir conditions. As outlined, our approach attempts to better understand the pitfalls and sensitivity of the seismic response to lithology and fluid variations, while integrating analysis of the pattern and spatial consistencies of these seismic responses within a geological context.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana