Spectral Gamma Holdup Tool for Flowstream Lamination
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Solution Overview
Problem
Current production logging tools face challenges in accurately determining gas holdup in wellbores due to limitations in distinguishing between gas and liquid phases, particularly in laminated flowstreams and salinity-sensitive measurements, which are often influenced by the electrical resistivities of oil and gas and water salinity.
Innovation Solution
The Spectral Gamma Holdup Tool (SGHT) employs a low-energy gamma ray source and two scintillation detectors at different spacings to measure gamma ray spectral differences, providing full-bore responses that are less sensitive to fluid salinity and lamination, allowing for accurate determination of gas holdup, salinity, and flowstream stratification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single gamma-ray count rate measurement is used to determine gas holdup, then the measurement is simple and quick, but the measurement is sensitive to flowstream lamination and salinity, making it impossible to resolve three unknown parameters
Solution Approach 1:
The patent segments the gamma-ray detection system into multiple detectors at different axial spacings from the source (first detector at short spacing, second detector at long spacing). Each detector provides a separate count rate measurement, allowing the system to obtain multiple independent measurements simultaneously. This segmentation enables the resolution of multiple unknown parameters (gas holdup, salinity, lamination) by providing sufficient measurement equations, while maintaining rapid measurement capability through parallel detection.
2Measurement precision
If electrical resistivity based production logging tools are used, then the tools can measure fluid properties, but the electrical resistivities of oil and gas are both very high and hard to distinguish, and measurements are strongly dependent on water salinity
Solution Approach 1:
The patent replaces electrical resistivity-based measurement with gamma-ray scattering-based measurement. Instead of using electrical properties that are difficult to distinguish between oil/gas phases and highly sensitive to salinity, the system uses gamma-ray scattering cross-sections which are sensitive to electron density and atomic number. This substitution of measurement physics eliminates the harmful effects of salinity sensitivity and phase distinction difficulty while maintaining the ability to measure fluid properties.
3Reliability
If a low energy gamma ray source is used, then gamma rays are scattered primarily within the borehole fluid making measurements insensitive to outside casing properties, but the single measurement is sensitive to flowstream lamination and salinity in addition to gas holdup
Solution Approach 1:
The patent maintains the low energy gamma-ray source configuration that provides reliability through insensitivity to external casing properties, but segments the detection system into multiple detectors at different spacings. This segmentation allows the system to obtain multiple independent measurements (first count rate at short spacing, second count rate at long spacing) that together provide sufficient information to resolve gas holdup, salinity, and lamination parameters without increasing the complexity of the source or measurement methodology.
4Measurement precision
If two separate gamma ray sources are used for gas holdup and fluid density measurements, then comprehensive measurements can be obtained, but handling, storage, and safety issues arise, and additional capital and operational expenses are required
Solution Approach 1:
The patent merges the functions of multiple gamma-ray sources into a single source system. Instead of using separate sources for gas holdup measurement and fluid density measurement, the invention uses one gamma-ray source with multiple detectors at different spacings to simultaneously obtain all necessary measurements. This consolidation eliminates the handling, storage, and safety issues associated with multiple sources while maintaining comprehensive measurement capability through the multi-detector configuration.
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
The SGHT system achieves improved accuracy and precision in measuring gas holdup, salinity, and lamination, reducing errors associated with prior art methods and providing comprehensive flowstream parameter measurements.
Implementation Method 1
Low energy gamma rays from the source are scattered primarily within the borehole fluid surrounding the tool and the scattered gamma radiation is detected by the gamma ray detector within the tool
Implementation Method 2
any gamma rays that penetrated the well casing and are scatted back toward the detector cannot re-penetrate the well casing due to photoelectric absorption
Implementation Method 3
Two scintillation type gamma ray detectors, such as sodium iodide (NaI) detectors and the associated photomultipliers, are disposed circumferentially near the outer tool casing
Data Source
AI summary
A full bore spectral gas holdup tool that measures gas holdup that is corrected for effects of the flowstream lamination and the salinity of the liquid in the flowstream. The basic methodology utilizes spectral data from two gamma ray detectors at different spacings from a nuclear source that emits gamma radiation. 57Co is the preferred source and the gamma ray detectors are scintillation spectrometers. In addition to a full bore gas holdup measurement, the spectral gas holdup tool also provides indications of the degree of flowstream lamination and the salinity of the liquid in the flowstream. An iterative data processing method optimizes the accuracy of the measured flowstream parameters.