An approach for minimizing errors in computing effective porosity in reservoir of shaly nature in view of Wyllie–Raymer–Raiga relationship

Effective porosity (ϕE) in clean and shaly formations is evaluated based on a newly introduced formulation that requires acoustic-radiation data and provides superior accuracy over other commonly used formulae based on various porosity tools. This equation, which is termed as a second order acoustic porosity-Vsh model, relates acoustic transit time to matrix and fluid in addition to shale parameters. In both clean and shaly formations, this relationship can be applied safely for evaluating effective porosity specifically for old wells that suffer from insufficient logging data such as density-neutron logs and in the absence of core regardless the differences observed. It can also be considered as a quick-look approach in interpreting the recent exploratory wells before the decision of completing the logging measurements. Successfulness of applying the proposed equation for evaluating “ϕE” to real field data is justified as far as reliability and range of accuracies are concerned.