The fraction (or percentage) of effective (available for continuous fluid phase) pore volume in a total rock volume.
The rock volume
The usual practice is to use relative volumes:
which are measured in V/V units (or fracs) and honor the following constraint:
The relative effective pore volume The log name is PHIE. It corresponds to air porosity of the dried laboratory cores: The relative shale volume
The log name is VSH. The clay bound water
where The total porosity is defined as the sum of effective porosity
The log name is PHIT. The term total porosity is more of a misnomer as it actually does not represent a pore volume for free flow as the clay bound water is essential part of the rock solids. Nevertheles, the total porosity property has been adopted by petrophysics as a part of interpretation workflow where the intermediate value of total porosity from various sensors leads not only to effective porosity but also to lithofacies analysis. On the other hand, the effective porosity itself is also not the final measure of the volume available for flow. It includes the unconnected pores which do not contribute to flow:
Besides the connected effective porosity includes the connate fluids which may be not flowing in the practical range of subsurface temperatures, pressure gradients and sweeping agents:
Finally, the useful porosity which represents a volume available for flow can be
where |