PNL

Question 1

Name two types of PNL.

Answer 1

• Pulsed Neutron Capture (PNC) - SIGMA

- Pulsed Neutron Spectroscopy (PNS) - Inelastic-Capture

Question 2

Describe the principle of PNC.

Answer 2

• high energy neutron pulse slowed down by collisions
• thermal neutrons captured by Chlorine
• measures decay rate of thermal neutrons (Sigma = 4550/Tau)
• calculate Sw from Sigma (get Sigma_ma, Sigma_hc and Sigma_w from charts/lab measurements)
• can also calculate change in Sw by comparing Sigmas in subsequent runs

Note: works best in high salinity water and in time lapse mode (no shale effects)

Question 3

Describe the principle of PNS.

Answer 3

• in the inelastic-capture mode, each measurement cycle contains one neutron burst and three timing gates for collecting spectra.
• the first gate measures total GR spectrum during the neutron burst, which contains both inelastic and capture spectra.
• the second gate measures an early capture spectrum following the neutron burst, which is used to subtract the capture background from the previous inelastic spectrum, yielding the net inelastic spectrum.
• the third gate measures a capture spectrum after the neutron burst.

Inelastic spectrum yields the relative concentrations of C and O which are used to determine So. Other elements are also determined during inelastic neutron scattering such as Ca, Si, Fe, S and Mg. The neutron capture spectra also provide elemental yields.

Note: Salinity-independent and works well in low or variable salinity environments.