Which property do neutron logs primarily measure to estimate porosity?

Which property do neutron logs primarily measure to estimate porosity?

• A. Electrical conductivity of the rock.
• B. Porosity inferred from hydrogen content.
• C. Hydrogen content in the formation.
• D. Thermal conductivity of the rock.

Answer: (C)

Neutron logs primarily respond to hydrogen content in the formation. The tool emits fast neutrons and detects how they slow down when colliding with nuclei; hydrogen nuclei are especially effective at slowing neutrons, so the neutron response is closely tied to how much hydrogen is present. Since pore spaces are filled with fluids (water, oil, gas) that contain hydrogen, the hydrogen content serves as a proxy for how much pore space exists, i.e., porosity. In practice, you translate that hydrogen signal into porosity, but the fundamental measured property is the hydrogen content of the formation. Electrical conductivity and thermal conductivity are measured by other rock-property tests and are not what the neutron tool primarily detects, and while porosity can be inferred from hydrogen content, the direct measurement is hydrogen content itself.

Neutron logs primarily respond to hydrogen content in the formation. The tool emits fast neutrons and detects how they slow down when colliding with nuclei; hydrogen nuclei are especially effective at slowing neutrons, so the neutron response is closely tied to how much hydrogen is present. Since pore spaces are filled with fluids (water, oil, gas) that contain hydrogen, the hydrogen content serves as a proxy for how much pore space exists, i.e., porosity. In practice, you translate that hydrogen signal into porosity, but the fundamental measured property is the hydrogen content of the formation. Electrical conductivity and thermal conductivity are measured by other rock-property tests and are not what the neutron tool primarily detects, and while porosity can be inferred from hydrogen content, the direct measurement is hydrogen content itself.