Pulsed Neutron Instrument Borehole Fluid Correction
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Solution Overview
Problem
Measuring formation hydrogen index (HI) and neutron porosity in wellbore environments with varying fluids, such as oil, gas, and air, is challenging due to environmental effects and complexity in interpreting gamma-ray measurements, which are more indirect and affected by multiple factors compared to neutron-based measurements.
Innovation Solution
A pulsed neutron instrument with two or more gamma-ray detectors at different axial spacings is used to measure the response in simulated wellbores filled with various materials, allowing for the calculation of capture gamma-ray ratios and burst ratios to correct for borehole fluid effects and determine formation porosity, thereby characterizing wellbore responses and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If gamma-ray detectors are used to measure formation hydrogen index, then the depth of investigation is increased and count rate is improved, but the measurement precision deteriorates due to indirect measurement and multiple environmental effects
Solution Approach 1:
The patent divides the measurement into two distinct components: fast neutron transport measurement (for porosity) and thermal neutron capture gamma-ray measurement (for hydrogen index). By segmenting the measurement process and using separate detection methods for each neutron energy stage, the system achieves both deep investigation capability and improved measurement precision through ratio-based correction of environmental effects
Solution Approach 2:
The patent introduces a thermal neutron capture gamma-ray measurement as an intermediary to indirectly assess the thermal neutron flux distribution. This intermediary measurement serves as a proxy for the neutron transport conditions, allowing correction of the fast neutron porosity measurement for borehole fluid effects without requiring direct thermal neutron detection
2Productivity
If neutron-gamma porosity measurement is used, then the count rate is increased by more than 1 order of magnitude, but the device complexity increases due to involvement of both neutron and gamma ray transport physics
Solution Approach 1:
The patent segments the neutron-gamma measurement into distinct energy components: fast neutron transport (providing porosity information) and thermal neutron capture gamma-ray emission (providing hydrogen index and environmental effect information). This segmentation allows the system to leverage the high count rate of gamma-ray detection while managing complexity through separate analysis of each neutron energy stage
Solution Approach 2:
The gamma-ray detector serves multiple functions: detecting thermal neutron capture gamma-rays for hydrogen index measurement, providing environmental effect correction data, and enabling deep formation investigation. This multi-functionality justifies the device complexity by extracting multiple valuable measurements from a single detector type
3Measurement precision
If traditional neutron-neutron porosity measurement is used, then the measurement precision is maintained, but the adaptability to complex wellbore conditions deteriorates due to sensitivity to borehole fluid variations
Solution Approach 1:
The patent uses thermal neutron capture gamma-ray measurements as an intermediary to assess borehole fluid conditions. This intermediary measurement provides information about the thermal neutron flux distribution, which is affected by borehole fluids, allowing the system to adapt to complex wellbore conditions while maintaining porosity measurement precision through ratio-based corrections
Solution Approach 2:
The system employs feedback by using the thermal neutron capture gamma-ray measurements to correct the fast neutron porosity measurements. The gamma-ray data provides feedback on the neutron transport conditions and borehole environment, enabling real-time correction of the porosity measurement to maintain precision across varying wellbore conditions
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 method provides more accurate and deeper investigation of formation porosity by reducing the sensitivity to borehole fluid variations and environmental effects, enabling effective determination of hydrogen index and porosity even in complex wellbore conditions.
Implementation Method 1
neutrons can incur a very large energy loss in a single elastic scattering event with a proton (a hydrogen nucleus)
Implementation Method 2
gamma rays from neutron 'capture' interaction (i.e., capture of a thermal neutron by a nucleus of certain atoms having large 'neutron capture cross section' and subsequent emission of a gamma ray)
Data Source
AI summary
A method for characterizing wellbore response of a pulsed neutron instrument includes inserting a pulsed neutron instrument into a plurality of simulated wellbores each filled with materials representing gas and liquid and measuring response of the pulsed neutron instrument in the simulated wellbores.