PULSED NEUTRON SYSTEM SERVICES
The Pulsed Neutron Neutron System is a competitive tool for recording the amount of water layer produced.
A burst of high energy neutrons (14,1 MeV) from a neutron generator is emitted into the formation.
Subsequent collisions rapidly slow these neutrons down to thermal energy levels, (0,025 eV), when they are absorbed by nuclei with corresponding emission of capture gamma rays.
The thermal neutron population thus decreases exponentially. The main neutron absorber in hydrocarbon wells is Chlorine from NaCl in the formation water (or brine completion fluid).
The logging tools calculate “Sigma”, the neutron capture cross section.
In fresh water and oil, few neutrons are captured, so the gamma count rate is low. Additionally, there is always a background gamma count, so accuracy in these conditions is poor.
Because the PNN counts the neutrons directly, and in the presence of fresh water, oil and gas, all of which have low values of sigma, the neutron population is numerous, the accuracy of this tool is inherently higher.
Its main advantages are: