Slim Compensated Neutron Module

The dual neutron module provides an environmentally compensated porosity log in mud-filled open 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, dual induction/ dual laterolog and sonic tools to provide the standard ‘quad-combo’ measurements in a single run.

Principle of Measurement

The dual 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 computer calculations for limestone, sandstone and dolomite.
Fully digital telemetry combines with density,induction and other logging probes
Low-activity source requirements for safe handling and cost reduction
High-resolution measurement.
Maximum data sampling rate is 1cm (0.4”).

Measurements

• Porosity (phi)
• Ratio long/short (NRAT)
• Raw long and short-spacing counts

Applications

• Porosity evaluation
• Lithology identification (in conjunction with other logs)
• Detection of gas or light hydrocarbons
• Correlation between logs

Operating Conditions

• Borehole type: 4” to 12” mud-filled open or cased boreholes