What it is
Amplitude Versus Offset analysis, commonly abbreviated AVO, is a seismic interpretation technique that examines how the amplitude of a reflected seismic signal varies with the angle of incidence (or equivalently, the source-receiver offset). The dependence of amplitude on angle is sensitive to the elastic properties of the rocks at the reflector — particularly the contrast in Poisson's ratio — which in turn responds to fluid type and porosity.
In a classical "Class II" or "Class III" AVO response, amplitudes increase with offset in the presence of hydrocarbons (especially gas), producing a diagnostic signature that helps distinguish hydrocarbon-bearing reservoirs from brine-saturated ones.
Why it matters
AVO is one of the primary seismic-derived direct hydrocarbon indicators. In combination with other techniques (inversion, rock-physics modelling, flat-spot detection), it materially improves pre-drill commercial-success rates relative to structural seismic alone.
When it works, when it doesn't
- Works well. Clean, thick, gas-bearing sands in younger basins. Good acquisition SNR. Calibrated rock-physics models.
- Works poorly. Thin beds (tuning effects dominate). Complex lithologies. Weathered or carbonate intervals. Old or low-fold 2D data.
Remote substance classification methods (see DHI) are increasingly used alongside AVO to cross-validate seismic fluid interpretations, especially in basins where AVO's classical assumptions break down.