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b) Verify the validity of these plots by
comparisons with existing Lorentz plots and additional
core data, using statistical (multi-variate analysis)
techniques. This approach has not been tried before and
could have a major impact on linking reservoir simulations
with seismic attribute volumes.
2. Incorporate neutron tool model in a CENPET variable
invasion log interpretation program
Gaby Briceno has just completed her MSc thesis on the
development of a wireline log interpretation program that
uses variable invasion profiles. This method, which was
not tried before, gave very promising results, but suffered
from the shortcomings of wireline tool response models,
especially the model of the thermal neutron tool. I have
arranged that we can use a three energy group diffusion
model, that is part of the Monte Carlo modeling code McBend
(equivalent of MCNP developed by Los Alamos Natlab). The
project would comprise:
a) Verification of the neutron tool model
for our conditions with diffusion equations
b) Link the neutron tool model to the LESA
log interpretation program (which is available on CENPET
computers), with the objective that they can be run in
an iterative mode.
c) Compare the output of this tandem process
with the results that were obtained with existing simplistic
tool models
3. Modeling acoustic wave propagation around a borehole
with a full elastic finite element program
The depth of investigation of conventional borehole sonic
tools confined to a disc around the borehole with a width
of less than one foot. The response of these tools is
therefore strongly affected by the invasion of mud-filtrate.
Sonic tools measure the travel time of compressional and
shear waves that are refracted along the borehole wall.
These waves are assumed to follow the "fastest"
path between source and receiver, but ray tracing is not
very effective, because the dominant wave length and the
dimensions of borehole and invaded zone are similar. For
seismic applications the cumulative travel times are used
to find compressional and shear wave velocities along
the borehole. This can only be performed properly, if
the effect of the invading fluids (mud-filtrate) is removed.
The Gassman "fluid replacement algorithm" is
used with significant success for these corrections, but
it assumes that all movable fluids in the invaded zone
are replaced with mud-filtrate. In reality the invaded
zone often does not have a sharp boundary, and a mixture
or original and invasion fluids is present.
The objective of the project is to use the
"Biot code" that we acquired from the Keldysh
institute in Moscow and was originally used to model our
experiments on core samples in a shocktube. This finite
element code that takes account of all elastic constants
and compressibilities of the fluids, can also be used
to make a 2-D (cylindrically symmetrical) model of the
borehole, the logging tool, and the formation. The idea
is to simulate a smooth invasion profile and compare the
result with calculations of sonic wave velocities using
the Biot equations.
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