Neutron Gamma Formation Evaluation with Hydrogen Capture Removal
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Solution Overview
Problem
Neutron-gamma porosity measurements are challenging due to loss of porosity sensitivity, especially at high fractional volumes of pore space, and are susceptible to environmental effects, making it difficult to interpret and accurately determine formation properties using conventional gamma ray detector analysis.
Innovation Solution
A method involving the use of a computer system to process detected gamma rays from neutron interactions, removing counts attributed to hydrogen capture and calculating formation properties, which enhances porosity sensitivity and accuracy by excluding hydrogen-related gamma rays from the analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If neutron-gamma porosity measurements are used, then porosity can be determined in various formation conditions, but porosity sensitivity is lost especially at high fractional volumes of pore space
Solution Approach 1:
The gamma ray energy spectrum is segmented into multiple energy windows, with different windows optimized for detecting gamma rays from different elements. By dividing the spectrum analysis into distinct energy ranges, the method can selectively measure gamma rays from specific elements (e.g., calcium, silicon, hydrogen) while filtering out others, thereby maintaining porosity sensitivity across various formation conditions including high porosity cases.
Solution Approach 2:
Different energy windows are assigned different quality characteristics for detecting specific elements. The method applies element-specific detection parameters and calibration factors to each energy window, allowing optimized local measurement quality for each element type. This enables accurate porosity determination even in high porosity formations where conventional single-window methods fail.
2Object-affected harmful factors
If conventional gamma ray detector analysis is used, then environmental effects can be measured, but interpretation difficulty increases due to susceptibility to environmental effects
Solution Approach 1:
The patent introduces computational algorithms and correction factors as intermediaries between the raw gamma ray measurements and the final formation property interpretation. These computational tools act as mediators that automatically account for environmental effects (such as borehole conditions, casing, and tool positioning) by applying pre-determined correction models, thereby simplifying the interpretation process while maintaining accuracy in measuring environmental effects.
Solution Approach 2:
The method transforms the complex interpretation problem into a series of parameter adjustments by changing detection parameters (energy window thresholds, counting statistics weights) and applying correction factors for various environmental conditions. This parameter-based approach converts difficult qualitative interpretation into systematic quantitative adjustments, reducing interpretation difficulty while preserving environmental effect measurements.
3Quantity of substance
If hydrogen capture gamma rays are included in analysis, then total gamma ray counts increase, but porosity measurement accuracy decreases
Solution Approach 1:
The method extracts and separates hydrogen capture gamma rays from the total gamma ray spectrum by identifying and isolating the specific energy range characteristic of hydrogen capture events (approximately 2.2 MeV). By taking out the hydrogen component as a separate measurement, the remaining gamma ray counts from other elements (calcium, silicon, etc.) can be used for porosity calculation without the confounding influence of hydrogen capture events, thereby improving porosity measurement accuracy.
Solution Approach 2:
Instead of treating hydrogen capture gamma rays as a harmful interference that reduces measurement accuracy, the method converts this previously problematic signal into a useful component by measuring it separately. The hydrogen capture gamma ray counts are now used to determine hydrogen index and water saturation independently, while the remaining gamma ray spectrum provides clean porosity information. This transforms a harmful factor into a beneficial additional measurement capability.
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 improves the accuracy and computational efficiency of porosity and fluid content determination in formation pore spaces, offering results comparable to neutron-neutron porosity measurements while overcoming the limitations of neutron-gamma porosity methods.
Implementation Method 1
They can be scattered elastically, which means kinetic energy and momentum are conserved; they can be scattered inelastically, which means certain nuclei go into an excited state while kinetic energy is lost
Implementation Method 2
They can also be captured by a nucleus to form a new nucleus
Implementation Method 3
it is also possible that the neutron interaction causes a nuclear reaction resulting in the emission of one or more nucleons from the target nucleus
Implementation Method 4
The neutron porosity measurement is very sensitive to the hydrogen content in the formation because hydrogen is the most effective neutron moderator among all elements found in earthen formations
Data Source
AI summary
A method for evaluating a formation includes determining a number of detected gamma rays resulting from imparting neutrons into a formation. The detected gamma rays are each characterized by an energy level thereof. The gamma rays are detected at a first distance from a position of imparting the neutrons into the formation. Those of the detected gamma rays attributable to neutron capture by hydrogen nuclei are removed from the number of detected gamma rays. The number of detected gamma rays having hydrogen neutron capture gamma rays removed therefrom are used to calculate a property of the formation.