Neutron Activation Formation Imaging
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Solution Overview
Problem
Current well logging methods face challenges in obtaining high-resolution azimuthal and axial measurements, particularly with nuclear logs, due to limited statistical precision and the need for radioisotopic sources, which are impractical and environmentally concerning. Additionally, existing methods struggle with background interference from oxygen activation and natural gamma rays, affecting the accuracy of formation imaging and geosteering.
Innovation Solution
The method involves using a downhole tool equipped with a neutron source and gamma ray detectors to measure formation activation caused by neutrons, correcting for variations in neutron output and oxygen activation, and subtracting background contributions from natural gamma rays to obtain high-resolution azimuthal and axial images without the need for radioisotopic sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radioisotopic sources are used for neutron activation imaging, then formation imaging capability is achieved, but environmental harm and practicality deteriorate
Solution Approach 1:
The patent removes the harmful radioisotopic source from the system and replaces it with an electronic neutron generator. The neutron source is extracted from the traditional radioactive material-based approach and substituted with a non-radioactive electronic device that can be controlled and regulated, thereby eliminating environmental harm while preserving the neutron activation imaging capability.
Solution Approach 2:
The patent changes the fundamental parameter of the neutron source from radioactive material to electronic generation. This parameter change transforms the system from one with inherent environmental harm to one with controllable, non-harmful operation. The electronic neutron generator can be turned on and off, regulated in intensity, and eliminates the need for radioactive waste management.
2Measurement precision
If neutron activation measurement is performed, then formation activation signal is obtained, but background interference from oxygen activation deteriorates measurement precision
Solution Approach 1:
The patent converts the harmful background interference from oxygen activation into a useful measurement capability. By detecting the oxygen activation signal and using it as a reference, the system can correct for borehole effects and improve the precision of formation activation measurements. The previously problematic oxygen activation becomes a tool for calibration and correction.
Solution Approach 2:
The patent implements feedback by continuously monitoring the oxygen activation signal and using it to correct the formation activation measurements. The system uses the known response of oxygen activation to normalize and correct the formation signals, thereby removing the harmful background interference and improving measurement precision.
3Manufacturing precision
If high-resolution azimuthal and axial measurements are obtained, then formation imaging quality improves, but statistical precision deteriorates due to limited counting statistics
Solution Approach 1:
The patent applies preliminary action by performing neutron activation before the actual imaging measurement. The formation is activated in advance, allowing the activation signal to build up and stabilize before detection begins. This preliminary activation step ensures that sufficient statistical precision is achieved while maintaining high-resolution azimuthal and axial imaging capabilities.
Solution Approach 2:
The patent maintains continuity of useful action by keeping the neutron source active and the formation continuously activated during the measurement process. This continuous activation ensures that statistical precision is maintained throughout the imaging process, providing sufficient counting statistics while preserving high-resolution imaging quality.
4Quantity of substance
If natural gamma ray background is present, then measurement completeness is maintained, but accuracy of formation imaging deteriorates
Solution Approach 1:
The patent extracts and separates the natural gamma ray background signal from the formation activation signal. By using spectral analysis and signal processing techniques, the system identifies and removes the natural gamma ray contribution, thereby maintaining measurement completeness while improving the accuracy of formation imaging.
Solution Approach 2:
The patent introduces an intermediary processing step that separates the natural gamma ray background from the formation activation signal. Through spectral filtering and signal processing, an intermediary analysis is performed to isolate the true formation activation signal, removing the interfering natural gamma ray background while preserving measurement completeness.
Data Source
AI summary
A method for determining azimuthal formation information using neutron activation, wherein the formation is activated by a neutron source and the activation signal is measured by at least one detector trailing the neutron source during the logging operation. The number of detected gamma rays as a function of the detector azimuth may be used to provide azimuthal information for determining an image of the formation surrounding the borehole.