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Dual Neutron Probe

The dual neutron probe provides an accurately calibrated borehole-compensated neutron porosity measurement in mud-filled open holes. It is the probe of choice for quantitative formation-fluid studies, including shallow oil and gas prospects.

Principles of Measurement

The dual neutron measurement uses two 3He proportional detectors and a detachable, sealed neutron source. Fast neutrons emitted by the source are scattered and slowed by light elements (and principally hydrogen in the formation) until they reach thermal energy levels. The ratio of the flux of thermal neutrons reaching the near and far detectors depends on the Hydrogen Index and porosity. Use of the two detectors and a ratio method provides a porosity measurement which is independent of borehole size over a range of hole diameters.

Features

  • Wide porosity range (0 to 60% sandstone equivalent)
  • Compensation for borehole diameter using dual detectors
  • Real-time porosity measurement with Videologger and Micrologger systems
  • Option of natural gamma for correlation
  • Option of CCL for casing inspection

Measurements

  • Compensated porosity
  • Raw long-spaced neutron
  • Raw short-spaced neutron
  • Count ratio
  • Natural gamma
  • Casing collar locator

Applications

Water

Lithology identification

Engineering

Location of aquifer and aquitard

Minerals

Shale content

Fracture analysis in coals

Correlation between open and cased-hole logs

Strata correlation between wells

Operating Conditions

Borehole type:

Open/cased, water-filled (qualitative measurements are possible in air-filled boreholes)

Centralisation:

Excentralised with bowspring