Pulsed Neutron Well Logging Single-Pass Formation Analysis
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Solution Overview
Problem
Current pulsed neutron well logging instruments require multiple passes to obtain various neutron-related parameters of subsurface formations, which is inefficient and time-consuming.
Innovation Solution
A pulsed neutron well logging instrument that uses a combination of neutron bursts and gamma ray spectroscopy detectors to obtain neutron porosity, thermal neutron decay time, capture cross section, and elemental concentrations in a single pass by analyzing gamma ray time and energy spectra, allowing for accurate lithology measurements while moving through formations once.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple passes are used to obtain various neutron-related parameters, then measurement completeness is improved, but logging time and efficiency deteriorate
Solution Approach 1:
The patent combines multiple measurement functions into a single logging pass by using multiple detectors positioned at different distances from the neutron source. Each detector measures neutron porosity, and by combining signals from near and far detectors, the system simultaneously obtains neutron porosity, thermal neutron decay time (SIGMA), and inelastic measurements in one pass, eliminating the need for multiple passes.
Solution Approach 2:
The well logging instrument is designed with multi-functional capability where the same detector system can obtain multiple different neutron-related parameters (neutron porosity, SIGMA, inelastic measurements, lithology) simultaneously during a single logging pass, making the instrument universal for various formation characterizations without requiring separate measurement passes.
2Productivity
If logging speed is increased, then productivity is improved, but measurement accuracy and statistical precision deteriorate
Solution Approach 1:
The patent enables continuous measurement during the entire logging pass by having detectors continuously record neutron-induced gamma rays throughout the single pass through the formation. The system maintains measurement continuity without stopping or slowing down to take multiple passes, thereby preserving statistical precision while achieving high logging speed through efficient single-pass data collection.
3Loss of information
If multiple neutron-related parameters are measured simultaneously, then information completeness is improved, but device complexity deteriorates
Solution Approach 1:
The patent segments the measurement function across multiple detectors positioned at different distances from the neutron source. Each detector is assigned to measure specific parameters, and the segmentation of measurement tasks among near and far detectors enables simultaneous acquisition of multiple parameters while maintaining manageable system complexity through functional distribution.
Data Source
AI summary
A method for well logging includes emitting a plurality of bursts of high energy neutrons into a wellbore and formations surrounding the wellbore. During and for a selected duration after at least one of the plurality of bursts, gamma rays are detected at at least one location spaced apart from the emitting and characterizing an energy of the detected gamma rays. After the last burst, gamma rays are detected and energy spectrum and rates of detection with respect to time thereof are determined. The foregoing is repeated for a selected number of times. After the selected number of times background gamma rays are measured. At least one of the numbers of detected gamma rays during a selected time interval and an energy spectrum of the detected gamma rays during the selected time interval is used to determine selected formation properties.