Corrected porosity measurements of underground formations

Abstract

This disclosure relates to methods and apparatuses for determining the porosity of a formation surrounding a borehole. A drilling fluid penetrates a distance into the formation as a function of time. First and second porosity measurements are taken, both at a first time and at a second time. The first porosity measurement is of a type selected to indicate a different porosity measurement in the presence of a gas as compared to the second porosity measurement. The first and second porosity measurements are selected to have substantially the same depth-of-investigation into the formation and are affected approximately proportionally by the gas.