Neutron Cross-Section Analysis for Formation Volume
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Solution Overview
Problem
Current neutron well logging techniques face limitations in accurately determining petrophysical properties of subsurface formations, particularly in complex lithologies and environments such as gas-filled porosity, shale, and varying salinity, due to sensitivity to temperature and borehole conditions, and the inaccuracy of thermal neutron porosity measurements in non-water filled or clay-containing formations.
Innovation Solution
The method involves using fast and thermal neutron cross-section values determined from detected radiation events to calculate the fractional volume of formation components, incorporating additional petrophysical parameters and cross-section measurements to improve accuracy, employing a computer system to process data from neutron well logging instruments that emit neutrons at high energy levels and measure radiation events at various distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal neutron porosity measurement is used, then porosity can be determined in water-filled formations, but measurement accuracy deteriorates in gas-filled porosity, shale, and complex lithology formations
Solution Approach 1:
The patent changes the measurement parameter from thermal neutron porosity to neutron cross section (sigma) measurements at multiple energies. By measuring neutron interactions at different energy levels (thermal and fast neutrons) and using cross section values that are less sensitive to environmental conditions, the method achieves accurate determination of formation properties across diverse formation types including gas-filled porosity, shale, and complex lithology where traditional thermal neutron methods fail.
2Measurement precision
If thermal neutron die-away measurement is used, then thermal neutron capture cross section can be determined, but measurement reliability deteriorates due to sensitivity to temperature and borehole conditions
Solution Approach 1:
The patent changes from relying on thermal neutron die-away rates to using neutron cross section measurements at multiple energies. The cross section values, particularly when measured using both thermal and fast neutrons, are less sensitive to temperature and borehole conditions. This parameter change improves measurement reliability while maintaining the ability to determine formation properties.
Solution Approach 2:
The patent employs a multi-functional approach by using both thermal and fast neutron measurements to determine cross section values. This multi-energy measurement strategy creates a more robust measurement system that can reliably determine formation properties under varying environmental conditions, making the method universally applicable across different well logging scenarios.
3Measurement precision
If neutron porosity measurement is used, then hydrogen content can be measured, but measurement accuracy deteriorates in formations with varying salinity and complex lithology
Solution Approach 1:
The patent changes the measurement approach from direct hydrogen content measurement via thermal neutron porosity to cross section measurements at multiple energies. By measuring neutron interactions at both thermal and fast energy levels and using cross section values, the method can accurately determine formation properties including hydrogen content while being less affected by salinity and lithology variations.
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 petrophysical parameter determination, including porosity and fluid saturation, by utilizing thermal and fast neutron cross-sections, which are less sensitive to environmental conditions, thereby improving the reliability of neutron well logging measurements across diverse formation types.
Implementation Method 1
They can be scattered elastically, which means kinetic energy and momentum are conserved
Implementation Method 2
they can be scattered inelastically, which means certain nuclei go into an excited state while kinetic energy is lost
Implementation Method 3
they can also be captured by a nucleus to form a new nucleus
Implementation Method 4
Hydrogen is the most effective neutron moderator among all elements. High hydrogen content can slow down neutrons to thermal energy (0.025 eV at room temperature) before they can travel very far.
Implementation Method 5
The probability of a neutron interacting with a nucleus is measured by the respective interaction cross section
Data Source
AI summary
A method for determining a fractional volume of at least one component of a formation includes entering into a computer a number of detected radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 million electron volts (MeV). The detected radiation events correspond to at least one of an energy level of the imparted neutrons and thermal or epithermal energy neutrons. A measurement of at least one additional petrophysical parameter of the formation is made. The at least one additional petrophysical parameter measurement and at least one of a fast neutron cross-section and a thermal neutron cross-section determined from the detected radiation events are used in the computer to determine the fractional volume of the at least one component of the formation. In another embodiment, the fast neutron cross-section and the thermal neutron cross-section may be used on combination to determine the fractional volume.