Neutron-Gamma Density Logging Standoff Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining the density of underground formations surrounding boreholes face challenges due to borehole effects, particularly when there is a standoff between the tool body and the borehole wall, as signals pass through borehole contents, requiring effective compensation techniques to accurately derive formation properties.
Innovation Solution
The method involves using neutron-gamma density techniques, where a neutron source in a tool body irradiates the formation, measuring gamma-ray flux at two different detector spacings, and applying a spine and rib processing approach to determine the formation density by establishing straight-line relationships and correcting for tool standoff effects, utilizing experimentally derived constants to calculate the density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a tool body is positioned tight against the borehole wall, then the measurement precision is improved, but the device complexity and ease of operation are worsened due to the difficulty of achieving and maintaining contact
Solution Approach 1:
The patent introduces borehole effect compensation as an intermediary computational step that mediates between the imperfect measurement conditions (standoff) and the desired accurate density measurement. The compensation technique acts as a mediator that corrects the signal without requiring physical contact between the tool and borehole wall.
2Measurement precision
If dual-detector compensation is used to compensate for borehole effects, then the measurement precision is improved, but the device complexity increases due to additional detectors and processing
Solution Approach 1:
The patent applies partial compensation by using the difference between two measurements to remove borehole effects, rather than requiring complete elimination of all sources of error. This partial action approach achieves sufficient precision without the complexity of eliminating all possible error sources.
3Measurement precision
If neutron-gamma density techniques are used, then the measurement precision is improved, but the device complexity increases due to the neutron source and gamma-ray detection system
Solution Approach 1:
The patent uses gamma-ray measurements as a copy or proxy for direct neutron density measurements. By measuring gamma rays produced by neutron interactions in the formation, the system obtains density information indirectly, simplifying the detection requirements while maintaining measurement precision.
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 effectively compensates for borehole effects, providing accurate formation density measurements by isolating the deviation due to tool standoff, thereby improving the precision of density determination in neutron-gamma density logging.
Implementation Method 1
measuring gamma rays arising from irradiation of the formation by a nuclear source
Implementation Method 2
neutron irradiation can also lead to inelastic scattering of neutrons with accompanying generation of gamma rays
Implementation Method 3
measuring gamma-ray flux in the tool body at two different detector spacings from the source
Data Source
AI summary
A method of determining the density of an underground formation surrounding a borehole from measurement of gamma rays arising from irradiation of the formation by a nuclear source in a tool body located in the borehole, and measurement of gamma-ray flux in the tool body at two different detector spacings from the source, the method comprising determining a substantially straight-line relationship between gamma-ray flux measurements at each different spacing with respect to the density of the formation for a tool body with no standoff; determining a relationship defining the deviation with respect to tool standoff of the density determined from the measured gamma-ray flux measurements at the two different detector spacings from the density calculated from the straight line relationships; and for a given pair of gamma-ray flux measurements at the different detector spacings, determining the intersection of the relationship defining the deviation with the straight line relationship so as to indicate the density of the formation surrounding the bore-hole; wherein the source is a neutron source and the gamma rays measured in the too! body are neutron-induced gamma rays resulting from neutron irradiation of the formation.