Pulsed Neutron Generator Inelastic Spectrum Isolation
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Solution Overview
Problem
Current downhole measurement systems face challenges in obtaining a pure inelastic spectrum of gamma rays due to the interference from prompt capture gamma rays, which obscures the detection of inelastic scattering gamma rays during the burst gate period.
Innovation Solution
The system employs a pulsed neutron generator that emits high-energy neutrons for a short burst period, followed by a waiting period allowing thermalization, and then records data during a capture gate period when thermal neutrons are predominantly absorbed, thereby reducing the interference and enabling the acquisition of a pure inelastic spectrum without subtracting the capture spectrum from the total spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If neutron generation unit emits neutrons continuously, then measurement data can be recorded continuously, but inelastic spectrum cannot be isolated from capture spectrum
Solution Approach 1:
The system uses periodic pulsed neutron generation with alternating burst gates and capture gates. During burst gates, neutrons are emitted and inelastic scattering data is collected. During capture gates, neutron emission is halted and capture gamma data is collected. This periodic alternation enables separate measurement of inelastic and capture spectra, resolving the spectral interference problem while maintaining efficient data acquisition through systematic time-multiplexed operation.
Solution Approach 2:
The measurement process is segmented into distinct time periods: burst gates for inelastic scattering measurement and capture gates for capture gamma measurement. By dividing the continuous measurement process into discrete segments with different neutron emission states, the system can isolate and measure different spectral components separately, eliminating the mixing problem that would occur with continuous emission.
2Measurement precision
If waiting period is extended to allow thermalization, then inelastic spectrum purity is improved, but measurement time increases
Solution Approach 1:
The system implements periodic measurement cycles with optimized burst gate and capture gate durations. By carefully controlling the timing and duration of each gate type, the system achieves sufficient thermalization for pure inelastic spectrum measurement during burst gates while limiting the overall cycle time through efficient alternation with capture gates, balancing spectral purity requirements with measurement speed.
Solution Approach 2:
The system rushes through the thermalization process by using short, intense burst gates followed by immediate capture gates. Rather than allowing prolonged thermalization that would extend measurement time, the system captures the inelastic scattering signal quickly during the burst gate before significant thermalization occurs, then immediately transitions to capture gate mode to measure the capture component separately.
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 improves measurement quality by isolating the inelastic spectrum from the capture spectrum, reducing the likelihood of thermal neutron interference and enhancing the accuracy of wellbore characteristic analysis.
Implementation Method 1
The fast neutrons may cause inelastic scatter that is detected as gamma rays
Implementation Method 2
neutron capture for many prompt gamma reactions also preferentially captures thermal neutrons
Implementation Method 3
those neutrons are then thermalized, over time, to interact at a lower energy
Data Source
AI summary
Embodiments of the present disclosure include a method that includes activating a neutron generation unit operable to emit neutrons toward a target for a first period of time. The method also includes recording first measurement data, via a detection unit, during the first period of time. The method further includes deactivating the neutron generation unit after the first period of time. The method also includes processing at least a portion of the first measurement data after the first period of time, the first measurement data being correlated to burst gate. The method includes recording second measurement data, via the neutron detection unit, during a second period of time, the second measurement data being correlated to a capture gate.