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
