A and B analysis was used to delineate trends in the data, to isolate three different classes of AVO anomalies which suggest the presence of hydrocarbons, and to provide insight as to the rock properties of the interbedded sandstones and shales.Īn AVO analysis was also performed to help evaluate the prospectivity of an area in the Norwegian Hammerfest Basin. In the Fylla area, offshore West Greenland, an AVO analysis focused on large flat spots identified on the seismic data, as part of a licence application. The forward modelling helps validate the processing steps, give clues as to the non-uniqueness of various A and B responses, and integrates the geology into the study. An A plus B section based upon a normalized shale line shows the potential hydrocarbon anomalies at maximum amplitude and the wet sands at minimum amplitude.ĪVO analysis of A and B is generally performed together with forward modelling that generates theoretical responses for intercept amplitude (A) and gradient (B) parameters. Potential hydrocarbon anomalies will then plot as data points with maximum scatter away from the normalized shale line. However, once the empirical background trend or wet trend is established, A and B data can be rescaled such that the shale line takes on a slope of −1. Also, the background trend is empirically defined by the AVO response of shale-on-shale boundaries or shale-on-silt reflectors, and this may not be indicative of the trend line for a shale-on-wet sand response.

Also, A versus B cross plots are easily generated to help define shale, wet sand and hydrocarbon trend lines that better differentiate the anomalies and provide information concerning the geological framework that created the AVO response.ĭetermination of the background trend on an A versus B cross plot is problematic in AVO analysis since variations in lithology and depth are interdependent, with both factors greatly influencing this trend. The creation of AVO intercept (A) and gradient (B) seismic sections allows for a variety of stacks including A, B, A times B, and A plus B. Recent amplitude versus offset (AVO) interpretations in the Norwegian Barents Sea and offshore West Greenland have identified subtle and complex anomalies which are best interpreted using a layer-specific, amplitude and gradient cross plot analysis scheme.

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