Downhole Elemental Analysis Using Geochemical Constraints
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Solution Overview
Problem
Current well logging techniques face inaccuracies in determining elemental concentrations and lithology, leading to unreliable assessments of hydrocarbon reservoir productivity and reserves, due to limitations in measuring gamma-ray spectra and lack of linear independence in elemental standards.
Innovation Solution
A method and apparatus that utilize a logging tool to obtain multiple energy spectra, apply geochemically-based constraints, and decompose these spectra using a weighted sum of monoelemental standards to accurately determine elemental concentrations, which are then classified to identify the lithotype of an earth formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gamma-ray spectra are measured using conventional logging tools, then elemental concentrations can be determined, but measurement precision deteriorates due to lack of linear independence in elemental standards
Solution Approach 1:
The patent segments the spectral decomposition process by separating accurate and inaccurate elemental yield determinations. Accurate yields are used to constrain inaccurate yields through geochemical relationships, dividing the problem into manageable parts where each element's contribution can be independently evaluated and constrained by geological knowledge
Solution Approach 2:
The patent changes the parameters of the spectral decomposition by introducing geochemical constraints as additional parameters. Instead of simply decomposing spectra into elemental standards, the method incorporates geological relationships (e.g., fixed ratios between certain elements) as constraints that modify the decomposition process, thereby improving measurement precision
2Reliability
If inaccurate elemental yields are used in lithology determination, then processing simplicity is maintained, but reliability deteriorates due to propagation of measurement errors
Solution Approach 1:
The patent implements feedback by using accurate elemental yields to constrain and correct inaccurate yields. The geochemical relationships provide a feedback mechanism where the measured spectral data is continuously adjusted based on geological knowledge, ensuring that final lithology determinations reflect both measurement data and geological reality
Solution Approach 2:
The patent applies preliminary action by establishing geochemical constraints before performing the final lithology determination. These constraints are pre-established based on geological knowledge and are applied during the spectral decomposition process, preventing inaccurate yields from propagating through subsequent analysis
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 enhances the accuracy of lithology determination by constraining inaccurate elemental yields and applying external geological constraints, resulting in more reliable estimates of hydrocarbon reservoir characteristics.
Implementation Method 1
The instrument, such as a spectrometer, can measure gamma-ray spectra to extract from them yields of various elements
Implementation Method 2
each energy spectrum having at least one of a natural gamma-ray spectrum, a fast neutron-induced inelastic spectrum, and a thermal neutron induced capture spectrum
Data Source
AI summary
A method for estimating a lithotype of an earth formation, the method includes: obtaining at least two different energy spectra of radiation received from the earth formation using the logging tool, each energy spectrum having at least one of a natural gamma-ray spectrum, a fast neutron-induced inelastic spectrum, and a thermal neutron induced capture spectrum; establishing at least one geochemically-based constraint related to elemental spectral yields to be determined; determining the elemental spectral yields from the at least two different energy spectra by decomposing the at least two different energy spectra over weighted sum of monoelemental standards wherein at least one weight is constrained by the at least one geochemically-based constraint and each weight represents a proportion of one monoelemental standard; converting the elemental spectral yields to elemental concentrations; and using a classifier to receive the elemental concentrations as input and to provide a lithotype as output.