Systems and methods for evaluating formations having unknown or mixed salinity

摘要

Systems and methods are disclosed to provide accurate water saturation and/or formation porosity measurements in the presence of unknown or highly variable salinity levels. A logging tool assembly includes a neutron porosity tool augmented with a gamma ray detector configured to measure the rate at which hydrogen nuclei capture neutrons from a neutron source. A processing system is configured to: determine a neutron porosity based on a measurement of neutron flux at a distance from a neutron source; combine the neutron porosity with a density-based porosity estimate to obtain a formation porosity; estimate salt concentration based on the formation porosity and a ratio between said measurement of neutron flux and said measurement of the hydrogen capture rate; correct the formation porosity based on the estimated salt concentration and provide a log of the resulting salt-compensated porosity. The logging tool assembly can also include a density logging tool and a natural gamma ray logging tool to provide a salt independent triple-combo log.