Compensated neutron correction for contributions outside the petrophysical model

An apparatus for estimating at least one property of a volume of interest of an earth formation from a compensated thermal neutron porosity measurement, the volume of interest surrounding a borehole intersecting the earth formation, the method comprising:

• a carrier having a tool disposed thereon and configured for conveyance in a borehole, the tool configured to make radiation-based measurements including a compensated thermal neutron porosity measurements;
• at least one information processing device configured for estimating a correction factor by processing compensated thermal neutron porosity measurements taken in a fluid-saturated rock matrix, the processing comprising:
• modeling each measurement of the compensated thermal neutron porosity measurements of the log as resulting from at least:
• i) a first contribution correlated to an absorbance of a first portion of neutrons produced by irradiation of the volume attributable to interactions in the volume indicative of pore space in the matrix, and
• ii) a second contribution correlated to an absorbance of a second portion of the neutrons produced by the irradiation of the volume attributable to trace elements of at least one dominant neutron absorber in the formation
• iii) a third contribution correlated to an absorbance of a third portion of the neutrons produced by the irradiation of the volume attributable to dry minerals in the matrix other than dominant neutron absorbers;
• estimating the second contribution and determining the correction factor from the second contribution;
• and
• correcting a compensated thermal neutron porosity measurement using the correction factor to produce a corrected compensated thermal neutron porosity measurement.