1. AVO
(Amplitude variation with offset)
AAPG ASUSC . ‫بالبريمة‬ ‫انزل‬ PROSPECT GENERATION . SEISMIC INTERPRETATION SESSION
Early practical evidence that fluids could
be seen by seismic waves came from
‘bright spots’ - streaks of unexpectedly
high amplitude on seismic sections– often
found to signify gas. But hard rocks
produce high amplitude look the same as
those of hydrocarbons. Only AVO analysis
can distinguish lithology changes from
fluid changes.
The variation in the amplitude of a
seismic reflection with source-geophone
distance depends on the velocity, density
and Poisson’s ratio contrast. AVO is used
as a hydrocarbon indicator for gas
because a large change in Poisson’s ratio
(as may occur when the pore fluid is a
gas )tends to produce an increase in
amplitude with offset. pore-fluid
identification is the ultimate goal of AVO.
AVO principles:
The AVO technique for DHI is based on
two principles:
1.When gas replaces brine in reservoir
rocks Poisson’s ratio (lateral strain/axial
strain) decreases.
2.When Poisson’s ratio decreases Rc and
amplitude becomes more negative with
increasing offset.