The determination of hydrocarbon saturation in shaly sands has produced a plethora of methods and bound-less measure of discussion around these methods for over 30 years. Due to the complexity of determining the resistivity of a bed in a shaly sand reservoir (Kennedy), we may have to accept that setting bounds will have to be "good enough". Any errors introduced during saturation determination for a shaly sand reservoir pale in comparison to those due to uncertainty in areal extent when we consider the propagation of error in the computation of reserves. These relative permeability data must reflect the moving phases in the reservoir, thus the fluid saturations must be based upon effective porosity. The definition and determination of effective porosity has provoked a longer and even more heated debate than that of saturation determination. The best definition and discussion of the effective porosity conundrum was written by Jeffrey Hook in his tutorial in Petrophysics, "An Introduction to Porosity". We agree with these definitions and only wish to supplement them. In particular, in his Table 1, "Summary of Terms", the very last paragraph states, "No direct technique to measure this ", in reference to determining effective porosity used in reservoir simulations. In our paper we propose such a technique to determine effective porosity and can defend the method with physical principles.
Effective porosity is defined as ??? That is the conundrum: there are simply too many definitions each having their passionate champions and defenders. These definitions and their resulting mathematical relation-ships, either classic theory or empiric, are used indiscriminately with scant regards to the historical path resulting in the currently accepted practice, i.e. one uses the equation without understanding its derivation, underlying assumptions, range of applicability and envelope of error, random and systematic.
