Downhole Tomographic Imaging via Compton Backscattering
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Solution Overview
Problem
Conventional methods for detecting defects in cement behind oil and gas well casings, such as acoustic logging and ultrasonic imaging, are limited by micro-annulus decoupling and thick casing issues, leading to incomplete defect detection.
Innovation Solution
The use of downhole photon tomographic imaging via Compton backscattering, where a photon source emits photons that are detected by slant-hole or pin-hole collimators, allowing for the creation of tomographic images that reveal density anomalies in the cement, unaffected by micro-annuluses or coatings, and capable of inspecting cement behind thick-walled casings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acoustic logging is used to detect cement defects, then cement quality can be assessed, but the method fails when micro-annulus or shear film coating is present due to decoupling
Solution Approach 1:
The patent replaces acoustic/mechanical measurement systems with a photon-based imaging system. Instead of using acoustic waves that are decoupled by micro-annulus, the system uses photons that can penetrate through the casing and cement to image defects directly, eliminating the decoupling problem inherent in acoustic methods.
Solution Approach 2:
The patent introduces photon backscattering as an intermediary mechanism to detect cement defects. Photons serve as the intermediary that can penetrate the casing and cement matrix, providing imaging information without being affected by the micro-annulus interface, thus mediating the detection process in a way that acoustic waves cannot.
2Measurement precision
If ultrasonic imaging tools are used, then cement defects can be detected, but the technique is limited when heavy mud or thick casing is used since reflected signals decay quickly
Solution Approach 1:
The patent substitutes mechanical ultrasonic wave propagation with electromagnetic photon propagation. Photons can penetrate much thicker materials than ultrasonic waves, allowing imaging through thick casing and heavy mud without the signal decay that limits ultrasonic methods to about 0.59 inches of casing thickness.
Solution Approach 2:
The patent changes the fundamental detection parameter from acoustic wave reflection to photon backscattering. This parameter change enables the system to penetrate deeper into the earth formation through thick casing and mud, as photons are not subject to the same attenuation limits as ultrasonic waves in these conditions.
3Measurement precision
If conventional imaging methods are used, then cement defects can be detected, but the methods are affected by micro-annulus and shear film coating that break the bond between cement and casing
Solution Approach 1:
The patent replaces mechanical/acoustic detection with optical/photon-based detection. Since photons are not mechanical waves, they are not affected by the decoupling effect of micro-annulus or shear film coatings that interfere with acoustic wave transmission. This substitution eliminates the harmful decoupling effect entirely.
Solution Approach 2:
The patent uses photon backscattering as an intermediary that is not blocked by the micro-annulus interface. Unlike acoustic waves that require good contact between cement and casing, photons can scatter off the cement matrix through the micro-annulus, providing imaging information that is independent of the bond quality between cement and casing.
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 method effectively detects and assesses cement defects, providing clear radial and azimuthal information, enabling accurate evaluation of cement quality and structural integrity without the limitations of prior techniques.
Implementation Method 1
the number of backscattered photons coming from an object placed in front of a photon source is a function of photon energy and the backscattering angle
Data Source
AI summary
A tomographic imaging apparatus utilizes Compton backscattering to evaluate cement behind the casing. The imaging apparatus includes a slant-hole or pin-hole collimator coupled to a series of detectors in order to count the number of photons that backscatter off from the cement. The number of backscattered photons is proportional to the density of the cement behind the casing. Using the photon count, an image processing unit of the imaging apparatus generates a 2D or 3D tomographic image of the borehole.