Pulsed Neutron Tool Single Detector Density Determination

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Solution Overview

Problem

Existing wellbore logging tools, such as neutron-neutron and gamma-gamma tools, are challenging to use in cased hole applications due to their shallow depth of investigation, and methods for determining porosity and bulk density using a single detector of a Pulsed Neutron Logging (PNL) tool are needed.

Innovation Solution

A method and system using a Pulsed Neutron (PN) tool with a single detector to determine the bulk density of a formation by binning gamma photon counts into specific bins corresponding to different neutron interactions and using these bins to calculate the bulk density through fractional contributions and density formulas.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If neutron-neutron or gamma-gamma tools are used, then porosity and bulk density can be determined, but the depth of investigation is shallow making them difficult to use in cased hole applications

Engineering Contradiction:

Improvedepth of investigationVSAvoidapplicability to cased hole logging

Core Design Contradiction:

Length of stationary objectVSAdaptability or versatility

Solution Approach 1:

The patent introduces gamma photons as an intermediary to indirectly measure formation properties. Instead of directly detecting neutrons (which have shallow penetration), the system detects gamma photons produced by neutron interactions in the formation, enabling deeper investigation through cased holes while still obtaining porosity and bulk density information

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct neutron detection mechanical system with a gamma photon detection system. By measuring gamma photon counts at different time gates after neutron pulsing, the system achieves deeper depth of investigation suitable for cased hole applications while determining formation properties

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If multiple detectors are used in PNL tools to determine porosity, then measurement accuracy improves, but device complexity and cost increase

Engineering Contradiction:

Improveporosity measurement accuracyVSAvoidnumber of detectors

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the gamma photon detection process into multiple time gates (first time gate and second time gate) after neutron pulsing. By analyzing gamma photon counts in different time segments, the system achieves accurate porosity and bulk density measurements using only a single detector, eliminating the need for multiple detectors

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses periodic pulsed neutron generation with corresponding periodic time-gated gamma photon detection. The neutron source is pulsed at regular intervals, and gamma photons are detected in specific time windows after each pulse, enabling accurate formation property measurement with simplified single-detector hardware

Inventive Principle:

Principle #19Periodic action

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 allows for a deeper depth of investigation, suitable for cased hole applications, and provides accurate measurements of bulk density with improved depth resolution compared to multi-detector systems.

Implementation Method 1

a source configured to issue bursts of fast neutrons, thereby irradiating the formation with neutrons

Methodology Applied

Scientific EffectNeutron production:

Implementation Method 2

at least one detector configured to detect gamma photons resulting from the irradiating and arriving at the detector

Methodology Applied

Scientific EffectGamma photon detection:

Implementation Method 3

When fast neutrons are slowed down by collisions with hydrogen, their energies are reduced to epithermal or thermal state

Methodology Applied

Scientific EffectNeutron moderation:

Implementation Method 4

making them available to be captured by surrounding atoms where such an action results in production of gamma photons

Methodology Applied

Scientific EffectNeutron capture:

Data Source

PatentUS12326535B2Determination of neutron porosity and bulk density from a pulsed neutron tool

Publication Date: 2025.06.10 WEATHERFORD TECHNOLOGY HOLDINGS LLC

AI summary

Methods and systems for determining bulk density and/or neutron porosity of a formation are described herein. The methods and systems use a pulsed neutron (PN) tool and may be performed with a tool having a single gamma detector though tools with multiple detectors may be used as well. The PN tool may be a geochemical logging tool. The methods and systems involve partitioning the time spectrum into pluralities of bins that are indicative of non-clay mineral elements and of shale/clay to the overall bulk density.