  An approximate method to calculate dielectric response and relaxation
functions for water saturated sedimentary rocks is tested for realistic
threedimensional pore space images. The test is performed by comparing the
prediction from the approximate method against the exact solution. The
approximate method is based on image analysis and local porosity theory. An
empirical rule for the specification of the length scale in local porosity
theory is advanced. The results from the exact solution are compared to those
obtained using local porosity theory and various other approximate mixing laws.
The calculation based on local porosity theory is found to yield improved
quantitative agreement with the exact result.
