Combining Inelastic and Capture Gamma Ray Spectroscopy
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Solution Overview
Problem
Current methods for determining elemental concentrations in subsurface formations using neutron activation spectroscopy are limited, particularly in combining inelastic and capture gamma ray measurements to produce enhanced concentration estimates for all elements measured.
Innovation Solution
A method that involves using a well logging instrument equipped with both inelastic and capture gamma ray spectral analysis systems, processing gamma ray yields from both thermal neutron capture and fast neutron inelastic reactions to calculate elemental weight fractions by determining transformation factors depth-by-depth, and combining measurements from both systems to enhance concentration estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If only inelastic gamma ray spectroscopy is used, then carbon and oxygen measurements are obtained, but other elemental concentrations cannot be determined
Solution Approach 1:
The patent combines inelastic gamma ray spectroscopy and capture gamma ray spectroscopy into a unified measurement system. The inelastic system provides carbon and oxygen measurements, while the capture system provides measurements for silicon, calcium, iron, sulfur, and other elements. By merging these two systems and combining their respective gamma ray spectra, the patent achieves comprehensive elemental concentration coverage across all formation components without sacrificing measurement precision for any individual element.
2Quantity of substance
If only capture gamma ray spectroscopy is used, then multiple elemental concentrations are determined, but carbon and oxygen measurements are lost
Solution Approach 1:
The patent merges capture gamma ray spectroscopy (which provides multi-element coverage including silicon, calcium, iron, and sulfur) with inelastic gamma ray spectroscopy (which provides carbon and oxygen measurements). The combination allows the system to determine concentrations of all major formation elements simultaneously, with each spectroscopy method contributing its strength to the overall measurement suite.
3Measurement precision
If separate calibration procedures are used for inelastic and capture spectroscopy, then individual system accuracy is maintained, but overall measurement consistency deteriorates
Solution Approach 1:
The patent employs a feedback mechanism where the calibration transformation factors from one spectroscopy system are used to validate and refine the other system's measurements. The system iteratively adjusts calibration parameters based on the combined performance of both inelastic and capture spectroscopy, ensuring that measurements from both systems are consistent with each other while maintaining individual system accuracy. This feedback loop resolves conflicts between separate calibration procedures and achieves overall measurement consistency.
4Quantity of substance
If comprehensive elemental analysis is performed, then all formation components are characterized, but measurement complexity increases
Solution Approach 1:
The patent segments the comprehensive elemental analysis into two distinct but complementary spectroscopy systems: inelastic gamma ray spectroscopy for carbon and oxygen, and capture gamma ray spectroscopy for other elements. Each segmented system is optimized for its specific measurement goals, reducing the complexity of individual systems while achieving comprehensive coverage when combined. This segmentation allows each subsystem to be calibrated and operated independently according to its specific requirements.
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 more accurate and comprehensive determination of elemental weight fractions in subsurface formations, improving the precision of chemical composition analysis by integrating data from both capture and inelastic gamma ray spectroscopy.
Implementation Method 1
when a formation is bombarded with high energy neutrons (e.g., 14 MeV), from a neutron source deployed in the wellbore, some of the neutrons inelastically scatter upon collision with the nuclei of certain atoms in the formations and as a result generate gamma rays having characteristic energy spectra
Implementation Method 2
At thermal energies neutrons may be captured by the nuclei of certain formation elements, upon which the capturing nuclei emit gamma rays having energies that are characteristic of the specific element
Data Source
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AI summary
A method for determining weight fractions of a plurality of elements in a subsurface formation penetrated by a wellbore includes determining weight fractions of a first plurality of elements using measurements of capture gamma rays made in the wellbore. The capture gamma rays result from bombardment of the formations with high energy neutrons. A weight fraction of a second plurality of elements is determined using measurements of inelastic gamma rays made in the wellbore resulting from bombardment of the formations with high energy neutrons. The weight fraction for the second plurality is determined by setting a transformation factor for those elements common to both the first and second plurality to result in a statistically equivalent weight fraction for the common elements as determined for the first plurality of elements. Weight fractions of elements in the second plurality not common to the first plurality of elements is determined using the set transformation factor.