Method and system for petrophysical quantity estimation from dielectric and neutron capture cross section measurements

A system, comprising:

• a dielectric-measuring tool configured to obtain dielectric measurements;
• a sigma-measuring tool configured to obtain thermal neutron capture cross section measurements;
• a data comprising a processor configured to:
• receive dielectric measurements of a geological formation;
• receive sigma measurements, wherein the sigma measurements comprise thermal neutron capture cross section of the geological formation;
• environmentally correct the dielectric measurements and the sigma measurements;
• jointly invert to fit the corrected dielectric measurements and the corrected sigma measurements to a petrophysical model;
• and
• compute water salinity and water phase tortuosity for medium to high range of water salinity values in a subsurface formation based on the joint inversion.

A tangible, non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to:

• receive dielectric measurements and sigma measurements, wherein the sigma measurements comprise thermal neutron capture cross section of a geological formation;
• environmentally correct the dielectric measurements and the sigma measurements;
• jointly invert the corrected dielectric measurements and the corrected sigma measurements to fit a petrophysical model comprising a dielectric model and a sigma model;
• compute at least water salinity and water tortuosity for medium to high-range of water salinity values in a subsurface formation based on the joint inversion using the petrophysical model.