EMAT Sensor Halbach Array for Downhole Cement Bond Evaluation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing downhole tools face challenges in evaluating the integrity of wellbore casing bonds due to limitations in coupling efficiency, especially in low-density fluids and the presence of debris, which affects the accuracy of cement bond logging.
Innovation Solution
The use of electromagnetic acoustic transducers (EMATs) with optimized coil and magnet configurations, including a Halbach array, to generate and detect acoustic waves within the wellbore casing, enhancing transduction efficiency and signal quality for evaluating cement bond integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional transducers are used in downhole tools, then acoustic energy can be transmitted and received, but coupling efficiency deteriorates in low-density fluids and presence of debris
Solution Approach 1:
The patent replaces traditional mechanical contact transducers with electromagnetic acoustic transducers (EMATs) that use electromagnetic fields to generate and detect acoustic waves. The EMAT system uses a magnetic field source and conductive coil to induce eddy currents in the casing, which interact with the magnetic field to generate acoustic waves without requiring mechanical coupling or couplant, thereby eliminating the harmful effects of low-density fluids and debris on coupling efficiency.
2Measurement precision
If EMAT device uses conventional coil and magnet configurations, then transduction can occur, but signal-to-noise ratio and dynamic range are insufficient
Solution Approach 1:
The patent applies local quality by creating an asymmetric magnetic flux distribution using a specialized magnet configuration where the magnetic flux is concentrated on one side of the array (the side facing the casing) while being substantially zero on the opposite side. This is achieved through specific magnet orientations and arrangements that direct the magnetic field primarily toward the casing, improving transduction efficiency and signal quality while minimizing interference and noise from the opposite direction.
3Reliability
If magnetic flux is distributed evenly on both sides of magnet array, then magnetic field coverage is maximized, but transduction efficiency to the casing decreases
Solution Approach 1:
The patent employs asymmetry by designing the magnet array to produce unequal magnetic flux distribution on opposite sides. The magnetic flux is intentionally concentrated on the first side (facing the casing) while being substantially zero on the second side (opposite side). This asymmetric configuration ensures that the magnetic field energy is directed where needed (toward the casing for effective transduction) rather than wasted in unnecessary directions, thereby improving transduction efficiency.
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 EMAT system improves the accuracy and reliability of cement bond evaluation by increasing signal-to-noise ratio and dynamic range, providing effective acoustic wave propagation and reception without the need for couplant, even in harsh environments.
Implementation Method 1
When a wire is placed near the surface of an electrically conducting object and is driven by a current at a suitable ultrasonic frequency, eddy currents are induced in a near surface region of the object
Implementation Method 2
If a static magnetic field is also present, these eddy currents experience Lorentz forces. These forces cause an acoustic excitation in the object
Implementation Method 3
a magnet array comprising magnets arranged with a corresponding direction of magnetization of each magnet oriented according to a configuration producing a greater magnetic flux on a first side of the array than on a second side opposing the first side
Implementation Method 4
In a reciprocal use, an electric signal will be generated in the wire as a result of acoustic excitation in a metal placed close to a permanent magnet
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3C
AI summary
Systems, devices, and methods for estimating a value of a downhole parameter of interest. Aspects include an apparatus for evaluating a tubular. The apparatus may include a sensor including an electromagnetic acoustic transducer (EMAT) device configured to be conveyed into the tubular. The EMAT device may include measurement circuitry comprising at least one conductive coil; and a magnet array comprising magnets arranged with a corresponding direction of magnetization of each magnet oriented according to a configuration producing a greater magnetic flux on a first side of the array than on a second side opposing the first side. The magnetic flux produced from the second side may be substantially zero. In embodiments, the configuration of magnets comprises at least a first set of permanent magnets in a linear Halbach configuration.