"FluidSeis" user's guide (a Matlab fluid substitution program)

Ying Zou and Laurence R. Bentley

ABSTRACT

FluidSeis is a Matlab program that performs time-lapse well-log seismic modelling. It calculates fluid and rock bulk moduli, densities and undrained velocities. Given reservoir conditions after fluid substitution, it calculates new bulk moduli, densities and undrained velocities that form new logs. It also calculates the mean changes, standard deviations and percentage changes of the logs and bulk moduli before and after production for time-lapse seismic feasibility study.

The whole program includes three functions. The fluidk.m is for fluid densities and bulk moduli. The rockk.m uses density logs and velocity logs and the results from fluidk.m to calculate dry rock bulk modulus. FluidSeis.m is the main function that uses the results from above two functions to calculate the undrained bulk modulus using Gassmann's equation and calculates the undrained rock density.

FluisSeis can be used to calculate only fluid properties, dry rock properties or calculate the undrained rock properties. The program generates well logs with Vp, Vs and density. The well logs can be used with other software to calculate synthetic seismograms for conditions before and after production. Comparisons can be used in feasibility studies and interpreting 4-D seismic surveys.

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