Patent ID: 7544929

Claim:
A method for determining standoff of a tool disposed within a borehole, the method comprising: (a) disposing an isotopic neutron source within said tool; (b) measuring a response of a first thermal neutron detector disposed within said tool at a first axial spacing from said source; (c) measuring a response of a second thermal neutron detector disposed within said tool at a second axial spacing from said source; (d) measuring a response of an epithermal neutron detector disposed within said tool at a third axial spacing from said source; (e) computing a thermal neutron porosity by combining said first and second thermal neutron detector responses; (f) computing an epithermal neutron porosity from said response of said epithermal neutron detector; and (g) computing the difference of said thermal neutron porosity and said epithermal neutron porosity and combining said difference with a measure of borehole diameter and mud weight and lithology to obtain said standoff.