Pulsed Neutron Tool Salinity-Independent Elemental Decay Logging
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Solution Overview
Problem
Current neutron logging techniques rely on bulk count rates, which are influenced by salinity, leading to inaccurate determination of subsurface formation properties like porosity and salinity, as they fail to distinguish between elemental contributions in transient decay curves.
Innovation Solution
A pulsed neutron tool that emits neutrons and detects gamma rays to construct elemental decay curves independently of salinity, using near-field and far-field detectors to differentiate between wellbore and formation effects, allowing for the determination of individual elemental decay constants and ratios that are salinity-independent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If bulk count rate from capture mode is used to construct transient decay curve, then the measurement process is simple, but the determination of subsurface formation properties becomes inaccurate due to salinity influence
Solution Approach 1:
The patent segments the bulk count rate signal into individual elemental contributions by detecting characteristic gamma ray energies specific to each element. Instead of treating the transient decay curve as a single bulk signal, the system separates it into element-specific decay curves by identifying and isolating gamma ray peaks corresponding to different elements (e.g., chlorine, formation elements), thereby eliminating salinity interference while maintaining measurement feasibility
Solution Approach 2:
The patent applies local quality by focusing measurements on specific elemental signatures rather than the bulk signal. By detecting gamma ray emissions at characteristic energies unique to each element, the system obtains localized information about individual elements' decay behavior, enabling accurate formation property determination independent of salinity effects
2Measurement precision
If individual elemental decay curves are constructed, then salinity-independent formation property determination is achieved, but the device complexity increases
Solution Approach 1:
The patent employs a single gamma ray detector that performs multiple functions: it detects bulk count rates for traditional transient analysis, identifies characteristic gamma ray energies for elemental discrimination, and constructs individual elemental decay curves. This multi-functional approach achieves salinity-independent measurements without requiring multiple specialized detectors, thereby limiting the increase in device complexity
3Loss of information
If characteristic gamma peaks are traced separately in time, then elemental composition information is obtained, but the data processing complexity increases
Solution Approach 1:
The patent replaces complex mechanical or chemical separation methods with spectral analysis and computational processing. Instead of physically separating elements, the system uses gamma ray energy spectroscopy to identify characteristic peaks and applies mathematical techniques to trace individual elemental decay curves from the composite signal, reducing physical complexity while preserving complete elemental composition information
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 provides accurate, salinity-independent evaluation of subsurface formation properties by decoupling wellbore and formation effects, enhancing the precision of porosity and salinity determination, and enabling more reliable geophysical property assessment.
Implementation Method 1
neutron intensity drop-off with respect to the neutron diffusion due to moderation and capture
Implementation Method 2
neutron intensity drop-off with respect to the neutron diffusion due to moderation and capture
Implementation Method 3
detecting gamma ray emissions generated from a pulse of neutrons
Implementation Method 4
detecting gamma ray emissions generated from a pulse of neutrons
Data Source
AI summary
In some embodiments, a method includes emitting, from a transmitter positioned in a wellbore formed in a subsurface formation, a pulse of neutrons into the subsurface formation and detecting gamma ray emissions at a near field and a far field generated in response to the pulse of neutrons being emitted into the subsurface formation. The method includes determining a single elemental decay for one chemical element of a number of chemical elements present in the subsurface formation based on the gamma ray emissions and determining at least one geophysical property of the subsurface formation based on the single elemental decay of the one chemical element.