The compensated neutron probe provides an environmentally compensated porosity log in mud-filled open holes. An alternative epithermal detector configuration is available for air/gas filled holes.
The tool design has been optimised to provide good performance at acceptable logging speeds while still using a relatively small 92GBq 241Am-Be source. It is combinable with the litho-density and dual induction log in a single run.
PRINCIPLE OF MEASUREMENT:
The compensated neutron measurement uses two 3He proportional detectors and a side-door-entry sealed neutron source. Fast neutrons emitted by the source are scattered and slowed down by light elements (principally hydrogen) in the formation. The ratio of the neutron flux reaching the detectors depends on the formation hydrogen index/ formation porosity.
Neutron porosity measurements are affected by the borehole environment. These effects are compensated in software by algorithms calculated by Monte Carlo modelling and benchmarked to standards at the Callisto facility in Leicestershire, UK.
FEATURES
Well characterised tool response based on Mont Carlo models
Fully digital telemetry
Combines with densiity, induction and other logging probes
Low strength source requirement for safer handling and reduced cost
Choice of thermal/ epithermal detector
High resolution measurement. Maximum data sampling interval 1cm (0.4")
MEASUREMENTS
Porosity (phi)
Ratio long/short (NRAT)
Raw long and short spacing counts
APPLICATIONS
Porosity
Correlation
Lithology indication (in conjunction with other logs)
Gas/ light hydrocarbon detection
OPERATING
CONDITIONS
Borehole type
Open-hole/ cased-hole fluid filled 4" to 12" diameter
Epithermal tool may be used in air-filled boreholes
