Neutron-Absorbing Borehole Fluid for Cleaner Geochemical Logging

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing geological logging tools face challenges in accurately determining the elemental composition of downhole formations due to interference from borehole fluid background neutron flux, which complicates the measurement of neutron-induced gamma rays.

Innovation Solution

The method involves doping the borehole fluid with a neutron absorber having a high neutron absorption cross-section to reduce the thermal neutron flux, allowing for precise measurement of neutron-induced gamma rays using a pulsed neutron logging tool equipped with gamma ray spectrometry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If borehole fluid is used without neutron absorber, then natural gamma ray detection is possible, but thermal neutron flux from borehole fluid interferes with neutron-induced gamma ray measurement

Engineering Contradiction:

Improveelemental composition measurement accuracyVSAvoidborehole fluid background interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

A neutron absorber (such as boron, gadolinium, or cadmium) is introduced as an intermediary substance in the borehole fluid to selectively absorb thermal neutrons. This intermediary component reduces the harmful thermal neutron flux that causes background interference, while allowing the measurement of neutron-induced gamma rays from the formation to proceed accurately.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The neutron absorption characteristics of the borehole fluid are modified by adding neutron-absorbing materials. This changes the physical parameter of neutron flux distribution in the borehole, reducing thermal neutron population and thereby decreasing background interference in gamma ray measurements.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If neutron absorber is added to borehole fluid, then thermal neutron flux is reduced, but additional gamma ray background from dopant may be introduced

Engineering Contradiction:

Improveneutron-induced gamma ray detection accuracyVSAvoiddopant-induced gamma ray background

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The neutron absorber is selected to have specific local properties: high thermal neutron absorption cross-section combined with low or absent gamma ray emission in the energy range of interest. This localized quality ensures that the dopant absorbs neutrons effectively while minimizing the generation of harmful background gamma rays that would interfere with formation measurements.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If separate measurements of neutron-induced and natural gamma rays are performed, then measurement accuracy is maintained, but logging time increases

Engineering Contradiction:

Improvegamma ray spectral analysis accuracyVSAvoidlogging time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The measurement system is designed to simultaneously detect both neutron-induced gamma rays and natural gamma rays using a single pulsed neutron tool configuration. By reducing thermal neutron flux through dopant addition, the tool can perform both measurements concurrently without the need for separate measurement passes, thereby halving the logging time while maintaining spectral analysis accuracy.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances the accuracy of elemental composition analysis by minimizing borehole fluid interference, enabling simultaneous detection of both neutron-induced and natural gamma rays during logging operations, thereby reducing complexity and saving rig time.

Implementation Method 1

doping the borehole fluid with a neutron absorber having a high neutron absorption cross-section to reduce the thermal neutron flux

Methodology Applied

Scientific EffectNeutron absorption: Absorption (physical)

Implementation Method 2

emitting neutrons into a downhole environment

Methodology Applied

Scientific EffectNeutron emission: Radiation

Implementation Method 3

detecting gamma rays from the downhole formation

Methodology Applied

Scientific EffectGamma ray detection: Absorption (EM radiation)

Data Source

PatentUS12535613B2Neutron absorbing dopant for reducing borehole fluid background in geochemical logging

Publication Date: 2026.01.27 HALLIBURTON ENERGY SERVICES INC

AI summary

Disclosed herein are methods and system for determining an elemental composition of a downhole formation using neutron-induced gamma ray spectroscopy and doping the borehole fluid with a neutron absorber to remove at least part of the borehole thermal neutron flux before it can capture borehole nuclei and emit gamma rays within a spectral range of interest. For example, a method for determining the elemental composition includes adding a dopant to a borehole fluid, wherein the dopant absorbs thermal neutrons in the borehole, lowering a logging tool comprising a gamma ray spectrometer, emitting neutrons into a downhole environment, generating neutron-induced gamma rays comprising borehole gamma rays and formation gamma rays, detecting gamma rays from the downhole formation, and extracting the elemental composition of the downhole formation. The dopant may not emit gamma rays above 0.5 MeV or their peaks background should be predictable and/or consistent to be removed during data processing.