Neutron logs are used to determine which properties?

• A. moisture content and porosity
• B. permeability
• C. grain size
• D. mineralogy

Answer: (A)

Neutron logs measure hydrogen content in the formation, which makes them ideal for estimating porosity and moisture content. The tool emits fast neutrons that collide with nuclei, especially hydrogen, slowing them down. The detector then records the slowed (thermal) neutrons, and the response increases with hydrogen abundance. Since pore spaces filled with fluids contain hydrogen, a higher neutron response indicates more pore space or higher moisture content in saturated formations. If the pores contain hydrocarbons rather than water, the hydrogen distribution changes, but the primary use remains estimating porosity (and moisture content when water is present). Permeability, grain size, and mineralogy aren’t directly inferred from neutron response, which is why those properties aren’t the best match for what neutron logs determine.