Compensated Spectroscopy Measurements for Cased-Hole Accuracy
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Solution Overview
Problem
Existing neutron-induced gamma-ray spectroscopy methods struggle to accurately determine elemental concentrations in cased-hole wells due to variations in borehole conditions, as they rely on assumptions that are not valid in such environments, leading to inaccurate results.
Innovation Solution
A system and method utilizing a neutron source and multiple gamma-ray detectors to generate independent measurements from different regions within a geological formation, acquiring and combining energy spectra to determine elemental concentrations, while accounting for borehole and formation contributions using differential sensitivity and timing gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If oxide closure method is used for cased-hole wells, then elemental concentration measurement is simplified, but measurement precision deteriorates due to borehole condition variations
Solution Approach 1:
The measurement is segmented into two independent components: borehole region measurement and formation region measurement. By using multiple detectors with different depths of investigation, the total gamma-ray spectrum is divided into contributions from the borehole and formation, allowing separate analysis and compensation of borehole effects.
Solution Approach 2:
Different detectors are assigned to measure different regions with specific properties. Detectors with shorter source-to-detector spacing are more sensitive to borehole conditions, while detectors with longer spacing are more sensitive to formation properties. This local specialization enables targeted measurement and compensation.
2Measurement precision
If multiple detectors with different depths of investigation are used, then measurement precision improves by distinguishing borehole and formation contributions, but device complexity increases
Solution Approach 1:
The multiple detectors serve multiple functions: they simultaneously measure both borehole and formation regions, provide independent measurements for compensation, and enable depth of investigation differentiation. This multi-functionality reduces the need for separate measurement systems.
Solution Approach 2:
The system uses its own multiple detectors to automatically differentiate and compensate for borehole effects. The detectors themselves provide the data needed for compensation without requiring external correction systems or additional measurement equipment.
3Measurement precision
If independent measurements from different regions are combined, then measurement precision improves through compensation, but processing complexity increases
Solution Approach 1:
The system uses feedback from the borehole region measurements to correct the formation region measurements. The borehole contribution determined from detectors sensitive to borehole conditions is fed back into the analysis to compensate and refine the formation elemental concentration calculations.
Solution Approach 2:
The system performs more measurements than the minimum single measurement by acquiring multiple independent measurements from different detectors and regions. This excessive action provides redundant data that enables compensation and improves precision despite increased processing 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 precise determination of elemental concentrations by distinguishing between borehole and formation components, enhancing accuracy in both open-hole and cased-hole conditions, and enabling effective formation evaluation and well integrity assessments.
Implementation Method 1
emitting neutrons, from a neutron generator placed into a borehole in the geological formation, to cause capture events and inelastic scattering events that generate photons
Implementation Method 2
emitting neutrons, from a neutron generator placed into a borehole in the geological formation, to cause capture events and inelastic scattering events that generate photons
Implementation Method 3
detecting, using one or more detectors, the photons associated with the capture events
Data Source
AI summary
Elemental concentrations in subterranean formations may be determined using neutron spectroscopy. For example, neutrons may be emitted by a downhole tool into the formation and produce gamma rays via inelastic scattering of fast neutrons or capture of slow neutrons. The borehole surrounding a downhole tool may introduce artifacts in the neutron spectroscopy measurement. Embodiments of the present disclosure are directed to techniques that reduce artifacts signals in downhole tools that include one or multiple detectors based at least in part on the inelastic and capture measurements.