Azimuthal Cement Density Imaging via Short-Spaced Gamma Logging
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Solution Overview
Problem
Existing gamma ray density tools are not optimized to accurately measure cement properties in cased wells, as they are designed to optimize sensitivity to formation density rather than cement density, and lack azimuthal sensitivity to provide accurate cement density and thickness measurements.
Innovation Solution
A nuclear density logging tool with a gamma ray source and detectors positioned closer together than traditional tools, optimized for cement measurement sensitivity, and capable of scanning all azimuth angles to generate cement density images, using a tool design with a gamma ray source and detectors spaced less than 12 inches apart, and optionally mounted on a rotating device or multiple pads to provide high-resolution azimuthal data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional gamma ray density tools are used with standard source-detector spacing, then sensitivity to formation density is optimized, but sensitivity to cement density in cased wells deteriorates
Solution Approach 1:
The patent changes the source-detector spacing parameter from traditional large distances (optimized for formation density) to small distances (less than 12 inches, preferably 4-8 inches) to optimize sensitivity to cement density in cased wells. This parameter modification allows the tool to penetrate the casing and detect cement properties effectively.
Solution Approach 2:
The patent adds azimuthal dimensionality by incorporating multiple detectors positioned at different azimuthal angles around the source. This transforms the measurement from a single-point density reading to a three-dimensional cement density image, enabling detection of cement quality variations around the wellbore.
2Measurement precision
If traditional density tools with single or few detectors are used, then tool simplicity is maintained, but azimuthal sensitivity and cement density image capability are lost
Solution Approach 1:
The patent segments the detection function by placing multiple detectors at different azimuthal positions around the source. Each detector measures density in a specific azimuthal sector, and the combined data creates a comprehensive cement density image. This segmentation enables azimuthal sensitivity while maintaining manageable system complexity.
Solution Approach 2:
The patent transitions from one-dimensional (single-point) or two-dimensional (radial) measurements to three-dimensional azimuthal imaging by adding the azimuthal angle dimension. Multiple detectors positioned at different azimuthal angles capture density variations around the wellbore, enabling full circumferential cement evaluation.
3Measurement precision
If existing density tools optimized for formation density are deployed in cased wells, then formation density measurement capability is preserved, but cement property measurement accuracy deteriorates
Solution Approach 1:
The patent modifies key tool parameters including source-detector spacing (reduced to less than 12 inches), detector positioning (multiple azimuthal positions), and energy window selection to optimize sensitivity to cement density rather than formation density. These parameter changes enable the tool to effectively measure cement properties through the casing.
Solution Approach 2:
The patent creates a multi-functional tool that can measure both cement density and formation density by incorporating multiple detectors at different positions and configurations. The same tool platform can be adapted for different measurement objectives through software configuration and detector selection, enhancing versatility.
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
Enables accurate cement density and thickness measurements in cased wells, reducing uncertainty in cement bond interpretation and detecting fluid contaminations or channels within the cement sheath, while maintaining tool integrity in hostile downhole conditions.
Implementation Method 1
measuring gamma ray count rates at each detector and using them to calculate an estimated cement thickness or density
Data Source
AI summary
Well logging method and logging tool for measuring cement density and thickness at different azimuth angles for a cemented, cased well. The method uses a gamma source, a short-spaced detector, a long-spaced detector, and preferably a backscatter detector, where the detector-to-source spacings are designed for calculating (93) thickness and density of the cement annulus (94) from the detector count rates (91).