Method of acquiring and processing neutron log data, and related apparatuses

A method of determining formation porosity in a region in the vicinity of a borehole wall by producing a neutron log using a neutron logging tool that is operable to irradiate the region with a source of neutrons and, using near and far spaced neutron detectors, detecting the neutrons scattered in the formation, the method including the steps of:

• a) operating said neutron logging tool having a first source of neutron radiation, and near- and far-spaced detectors in a borehole in order to acquire neutron log data;
• b) using a processing device to derive from the near-spaced neutron count of the neutron logging tool an approximate, unfiltered, lithology-related characteristic of a formation;
• c) using the processing device to derive a correction for undesirable perturbations that is essentially independent of the lithology;
• d) using the processing device to long filter the correction;
• and
• e) using the processing device to add the resulting, long-filtered correction to the approximate, unfiltered characteristic resulting from step a) in order to derive a compensated characteristic, wherein the method permits the use of said first source having an activity that is less than the activity of a source of neutron radiation of the same type as the first source used in said borehole logging tool or the same type of logging tool as said borehole logging tool operating without carrying out steps b)-e) so as to generate one or more logs of the same statistical counting variability with reference to a particular borehole as said borehole logging tool when so operated.