ROSS, CHRISTOPHER P., and MARK A. SPARLIN , Hampson-Russell, Houston, TX

Amplitude-versus-offset (AVO) crossplotting is a widely employed AVO analysis technique that has gained acceptance in the geophysical community over the past decade. Crossplotting AVO attributes such as the AVO intercept (A) and gradient (B) has proven useful in hydrocarbon diagnostics in unconsolidated clastic basins worldwide. Improved interpretation of the crossplot results can be obtained through 3D visualization of the AVO crossplot.

AVO crossplotting, which typically uses the intercept and gradient, abets standard AVO analysis techniques by identifying background trends and anomalous responses that may or may not be associated with hydrocarbons. Using the A and B data volumes and small target specific windows where VpVs are nearly invariant, a background trend can often be determined which defines the wet-sandshale interfaces and other similar lithologies. A-B pairs lying off the trend are considered anomalous, and through interactive testing, with a priori information through modeling, and with geological integration of the basin geology, can be used to assess hydrocarbon-bearing strata or key lithologies. In light of the aforementioned, crossplotting has evolved to be a crucial component in AVO analysis.

The 3D crossplot display has many advantages over the composite-summary 2D displays traditionally used. By visualizing the seismic data in 3D space, the resulting interpretation is more reliable. Modeled and observed 3D crossplots through visualization techniques demonstrate the improved recognition of background trends and AVO anomalies which in turn improve interpretation and analysis.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas