Compensated Neutron Tool


High-quality compensated porosity to fully characterize your reservoir


  • Determining porosity and lithology
  • Identifying formation gas, shale volume, and mineral properties
  • Providing input to advanced formation evaluation programs, seismic programs, water saturation calculations, and determination of mechanical properties of rock
  • Providing detailed well-to-well correlation and reservoir delineation

Features and Benefits

  • Measures formation porosity
  • Identifies lithology and detects gas when used in combination with other services
  • Indicates shale volume
  • Operates in openhole and cased-hole environments
  • Provides input for water saturation calculations

Tool Description

The Weatherford compensated neutron tool (CNT) provides a boreholecompensated, high-resolution porosity measurement that can be logged in both open and cased wellbores.

Knowledge of formation porosity is vital to reservoir evaluation. The CNT incorporates an AmBe241 radioactive source, which bombards the formation with high-energy neutrons. As these neutrons disperse throughout the rock matrix, their interaction with hydrogen atoms slows them to thermal energies.

Two detectors, located at different spacings from the source, count thermal neutrons traversing the formation. Count rates measured at the detectors are proportional to hydrogen content of the adjacent formation.

The proprietary source-to-detector spacings of the CNT are designed so that the ratio of count rates at each detector accurately determines hydrogen content compensated for borehole and casing effects.

A set of empirical algorithms converts this ratio into porosity units, assuming one of three rock lithologies. This neutron porosity (øN) is the principal curve displayed during logging.

In the openhole environment, the CNT is typically run with the universal gamma ray (UGR™) tool, advanced formation density (AFD) tool, and a resistivity service to provide triple-combo logging capability. This logging suite, which provides porosity and water saturation analysis, lithology identification, and gas detection, can be combined with other tools for further versatility.

As a cased-hole service, the CNT is commonly run in combination with a UGR tool and casing collar locator. This provides through-casing porosity determination and gas detection. Other services also can be combined, including enhanced gas detection with the monopole-dipole array sonic tool.