porosity measurements

Porosity is the space within reservoir rock that can contain fluids, and is generally measured as a percentage of the bulk volume; a formation with no porosity has 0% porosity. Most reservoir rock has a porosity ranging from 6-30%; the greater the porosity, the more fluid the rock can hold. Therefore, petroleum engineers, geologists and financiers are extremely interested in porosity.

If we could directly measure the porosity of the formation as they lie in suit within the earth, petroleum exploration would be simple. Unfortunately, porosity is one of those variables that defies easy determination. Since we cannot measure porosity directly from the wellbore, we must deduce it from other measurements. Because of this, different tools that are used can give a different apparent porosity from the same formation. Sometimes, this can lead to some confusion, but it should be remembered that all of the tools can accurately determine the porosity of the rock under the appropriate conditions.

open-hole porosity determination

2 3/4" Bore hole compensated sonic tool

2 3/4" PTBHC slim hole density tool

3 1/2" Bore hole compensated sonic tool

3 5/8" Compensated neutron tool

4" Compensated density tool

4" Litho-density tool

cased-hole porosity determination

1 11/16" In-line neutron tool

1 11/16" Gamma ray/ccl/neutron tool

2 3/4" In-line neutron tool

2 3/4" Compensated neutron tool