Effective Reservoir Characterization using Seismic Amplitudes.

1. TOP 10 TIPS ON USE OF SEISMIC AMPLITUDES
FOR RESERVOIR CHARACTERIZATION
RajeshwaranDandapani,DirectorGeophysics
rajesh@telestoenergy.com
Introduction: Seismic amplitude
analysis plays an important role in
optimum reservoir characterization.
People talk of so many fancy derived
attributes and their uses now-a-days
but sometimes fail to use the basic
measured attribute called amplitude
in an optimum manner for reservoir
characterization. The main reason for
this is because of lack of proper
understanding of whatthat amplitude
represents in terms of reservoir
characteristics.
First and foremost, mistake made by
many is to think that the amplitude is
the direct response of the reservoir.
Amplitude is an interface property
which tells about the impedance
contrast between 2 layers
(overburden and reservoir). The
amplitude can vary if the reservoir
varies or the overburden varies.
Hence amplitude normalization with
background is an important step
before carrying out any meaningful
analysis using amplitudes.
Second common mistake made by
many is to arrive at some relationship
between a reservoir parameter like
thickness, porosity, saturation etc and
amplitude through cross-plot. I don’t
say cross-plotting is bad. My only
request is to understand that seismic
amplitude is the combined response
of all the reservoir parameters put
together. Hence it is better to cross-
plot Net Pay Thickness or Net Pore
Volume and amplitude rather than
individual parameters.
I think with this introduction we are
ready to go to the tips straight away.
Tip-1:
Use the extremum amplitude value
like maximum or minimum instead of
averageor RMS since extremumis the
close representation of reflection
coefficient at any interface. Average
and RMS values over a window length
are contaminated with unwanted
wavelet overprint
Tip-2: Use the formula(ReservoirTop
Amplitude +Reservoir base
Amplitude)/2 to minimize the bias
created due to Coarsening and Fining
upward sequences.

2. Tip-3: The window that is used for
calculating the background amplitude
should be sufficiently long in the
immediate overburden of the
reservoir (Clue: The amplitude
distribution of background window
should be close to Gaussian
distribution)
Tip-4: Perfect Zero Phased data is
ideal for amplitude studies as it is the
true representation of Impedance
contrast but if not possible then the
next best is to use the complex trace
attribute (Amplitude Envelope).
{Complex Trace Analysis is often
mystified by some Geophysicists who
appreciate only the mathematics
without understanding theunderlying
physical significance}. I will deal with
that in detail in a dedicated article to
demystify Complex Trace Analysis.
Tip-5: Find out the Tuning Thickness
of the reservoir by Wedge Modeling
and carry out the Amplitude Analysis
only in the regions where the
reservoir is well above Tuning
Thickness.
Tip-6: You can study the sensitivity of
one particular reservoir parameter to
Amplitude provided you choose
regionswhereyou aresurethat all the
other parameters are more or less
constant.
Tip-7: Always use the Interval
Average value when analyzing
inversion products like (Acoustic
Impedance, Elastic Impedance, Vp/Vs
ratio etc.,) since they are elastic
properties representative of layers
unlike amplitude which is an interface
property.
Tip-8: Use at least 16 bit data to get
reasonable results through amplitude
analysis. 8-bit data is good only for
structural interpretation. Please do
not use it for amplitude analysis.
Tip-9: When dealing with
amplitudes pertaining to different
vintages it is better to evaluate a
quantity called percentage ratio of
anomalous amplitudes to background
which can minimize the disparities
introduced due to dissimilar
acquisition and processing
parameters.
Tip-10: Seismic to Well matching
when done carefully can providegood
calibration of amplitude with actual
reflection coefficient.
Theseare a few tips which cameto my
mind as of now. I amopen for further
discussion and further detailing
depending on the interactions from
the esteemed LinkedIn members.
Telesto Energy Pte Ltd,
#30 Cecil Street, #19-08, Prudential Towers, Singapore – 049712 contact@telestoenergy.com www.telestoenergy.com