PNN – 1400.0000 PULSED NEUTRON NEUTRON TOOL

PNN measures Sigma, the ability of material to capture thermal neutrons, in capture units (c.u.).

PNN counts directly the thermal neutrons reaching the detectors after their interaction with the surrounding formation; therefore, the usual inference applied by common Thermal Decay tools—where gamma rays are counted and high counts indicate high Sigma values—is inverted with the PNN tool, where high counts correspond to low Sigma values. This has the significant advantage of reducing statistical uncertainties, particularly for low Sigma values.

This direct measurement approach allows better differentiation in environments with low Sigma values, such as formations containing fresh water, oil, and/or gas in the pore spaces, effectively overcoming the low-salinity formation water limitation commonly associated with standard Thermal Decay Time tools. Additionally, neutron readings are less affected by neutron activation; therefore, time-driven stop-check logging in areas of interest can further reduce statistical uncertainties at any desired depth.

All of this makes the pnnPlus tool, in conjunction with our PNN processing and analysis, a highly competitive behind-casing formation evaluation tool for high to moderate water salinity formations, and the ultimate thermal decay solution for evaluating lower salinity and lower porosity formations.

PNN Application 

• Determination of water saturation behind casing
• Porosity evaluation
• Estimation of remaining hydrocarbon reserves
• Identification of oil–water, gas–water, and gas–oil contacts
• Monitoring of reservoir dynamics and fluid movement
• Evaluation of low-salinity formations
• Applications in geothermal energy projects

PNN technology is particularly effective in complex reservoir conditions where conventional thermal decay tools face limitations, especially in low-salinity and low-porosity environments.

PNN Operation

The formation is bombarded with pulses of high-energy neutrons (14 MeV) generated by the tool. These neutrons interact with the surrounding atoms, and during the time interval between successive pulses, the population of thermal neutrons reaching the detectors is measured.

The tool uses two neutron detectors, each with 60 time channels, to sample the thermal neutron population over time. The neutron counts recorded in each channel are used to compute the decay rate, which is equivalent to measuring how quickly thermal neutrons are absorbed by the formation.

The greater the ability of the formation fluids and minerals to capture thermal neutrons, the higher the resulting Sigma value.

PNN TOOL SPECIFICATIONS: