Abstract: The invention concerns a method for determining the porosity of an earth formation penetrated by a borehole. The method comprises conveying a tool along said borehole, wherein the tool comprises a source of neutron radiation and at least two detectors axially spaced from said source at at least two different spacings. At least one near detector and at least one far detector are selected and a correction computed. The porosity of the earth formation is determined by correcting the far detector porosity with the computed correction.

Abstract: The invention concerns a neutron measurement method for determining porosity of an earth formation surrounding a borehole comprising: conveying a tool along said borehole, wherein said tool comprises a source of neutron radiation and at least one detector axially spaced from said source; generating measured detector response for said at least one detector that is indicative of neutron radiation from said source interacting with said earth formations; operating said measured detector response with a predetermined mathematical equation and thereby obtaining corrected detector response that is independent of the density of said earth formation; and determining porosity of the earth formation surrounding the borehole from said corrected detector response. The invention also relates to a system implementing said method.