Systems and methods for evaluating formations having unknown or mixed salinity

A formation evaluation method that comprises:

• determining formation porosity based at least in part on measurements of neutron flux at a distance from a neutron source;
• estimating salt concentration in a formation fluid based at least in part on said measurements of neutron flux and on measurements of hydrogen capture rates at said distance from said neutron source;
• and
• generating a water saturation log display based at least in part on said salt concentration, said formation porosity, and on measurements of formation resistivity.

A salt-compensated logging method that comprises:

• determining a neutron porosity based at least in part on a measurement of neutron flux at a distance from a neutron source;
• combining the neutron porosity with a density-based porosity estimate to obtain a formation porosity;
• estimating salt concentration in a formation fluid based at least in part on the formation porosity and a ratio between said measurement of neutron flux and a measurement of a hydrogen capture rate at said distance from said neutron source;
• correcting the formation porosity based at least in part on the estimated salt concentration, thereby obtaining a salt-compensated porosity;
• and
• providing a log of the salt-compensated porosity.