Pulsed-Neutron Decay PND Spectrum Tool


Provides comprehensive through-casing saturation measurements


  • Determining water saturation in high-salinity formations 
  • Determining oil saturation in formations with low or unknown water salinity
  • Evaluating producing zones for primary and secondary recovery
  • Locating bypassed pay zones
  • Identifying formation fluid contacts (gas, oil, and water)
  • Detecting gravel-pack problems
  • Determining production profile  
  • Identifying sources of water production

Features and Benefits

  • Emits high-energy neutrons at 14.3 MeV. Two spectroscopic detectors measure the resulting gamma radiation, which can be used to determine reservoir properties and fluid saturation.
  • Records inelastic measurements during the burst from a short, fixed-rate pulse of 1,428 Hz. 
  • Records capture data after the burst using a long, variable pulse and variable windows that change with Tau or the formation-decay rate. 
  • Uses the measured formation capture cross section (∑) to determine water saturation in high-salinity formations. 
  • Offers operational flexibility with standard and high-temperature versions of the tool.

Tool Description

The PND spectrum tool is a slimhole pulsed neutron spectroscopy tool that combines conventional pulsed neutron capture, neutron porosity, and inelastic density measurements in one device. When operating in inelastic mode, the tool obtains carbon/oxygen and inelastic density measurements that, combined with capture sigma and neutron porosity, address a broad range of formation-evaluation and reservoir monitoring applications. 
The PND spectrum tool can determine the source of unwanted water production in a flowing well, which informs decisions on isolating pay zones from the water-producing portion of the completion interval. The cased-hole density-porosity measurement differentiates between low-porosity formations and gas-filled-porosity formations, identifies pressure-depleted zones, and locates gas/oil contacts in shale reservoirs.