Borehole Acoustic Transducer Array for Deep Formation Penetration
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Solution Overview
Problem
Existing acoustic interrogation methods for rock formations around a borehole are limited by the size and power of practical sources, with high frequency signals having short penetration and low frequency signals requiring large sources, leading to weak and diffuse signals that do not penetrate deeply into the surrounding rock formation.
Innovation Solution
A method and system using an array of transducers within the borehole to generate two acoustic signals of different frequencies, which undergo three-wave mixing in the non-linear rock formation to produce a collimated low-frequency signal that can penetrate deeper, allowing for effective characterization of rock properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency acoustic signals are used, then the penetration distance is short, but the signal resolution is improved
Solution Approach 1:
The patent transforms high frequency acoustic signals into low frequency signals through non-linear mixing in the rock formation. By changing the frequency parameter from high (original signals) to low (difference frequency), the system achieves both deep penetration and maintained resolution through the collimated beam effect.
Solution Approach 2:
The rock formation itself acts as an intermediary medium that performs non-linear mixing of the two high frequency acoustic signals. This intermediary process generates a new low frequency signal that would be difficult to produce directly, resolving the contradiction between penetration distance and signal resolution.
2Length of stationary object
If low frequency acoustic signals are used, then the penetration distance is improved, but the source size must be large
Solution Approach 1:
Instead of directly generating low frequency signals that would require large sources, the system generates high frequency signals from compact transducers and transforms them into low frequency signals through non-linear mixing in the formation, achieving deep penetration without large source size.
Solution Approach 2:
The rock formation serves as an intermediary that converts high frequency signals from compact sources into low frequency signals. This intermediary transformation allows the system to achieve the penetration benefits of low frequency signals while using only small, practical transducer sizes.
3Length of stationary object
If low frequency acoustic signals are generated by conventional means, then the penetration distance is improved, but the signal strength becomes weak and diffuse
Solution Approach 1:
The system generates high frequency signals with strong power from compact transducers, then transforms them into low frequency signals through non-linear mixing. The resulting low frequency signals maintain the directional collimation and strength characteristics of the original high frequency signals, avoiding the weak and diffuse problem.
Solution Approach 2:
The non-linear mixing process in the rock formation acts as an intermediary that preserves the power and directional characteristics of the original signals while transforming the frequency. This maintains signal strength and collimation that would be lost in conventional low frequency generation methods.
4Shape
If an array of transducers is used, then the device complexity increases, but the ability to generate collimated beams is improved
Solution Approach 1:
The system uses phase parameter control of the transducer array to generate collimated high frequency beams. The same phase control parameters then determine the direction of the resulting low frequency beam through non-linear mixing, achieving collimation without additional hardware complexity.
Solution Approach 2:
The transducer array serves multiple functions: generating the acoustic signals, controlling beam direction through phase modulation, and determining the characteristics of the resulting low frequency beam. This multi-functionality achieves collimation without requiring separate control mechanisms.
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 system generates a collimated low-frequency beam that can propagate considerable distances into the rock formation, enabling effective characterization of non-linear properties and improving the depth of penetration and resolution in acoustic logging.
Implementation Method 1
generating a first acoustic signal at a first frequency; generating a second acoustic signal at a second frequency different from the first frequency
Implementation Method 2
combining the first and the second acoustic signals by a three wave mixing process to generate a collimated third signal in the rock formation, wherein the collimated third signal propagates through the rock formation in a same direction as an initial direction of the first and the second acoustic signals and has a frequency equal to a difference of the first and the second acoustic signals
Implementation Method 3
High frequency signals have a relatively short penetration distance, while low frequency signals generally require large sources, clamped to the borehole wall, to maximize energy transfer to the formation
Implementation Method 4
receiving the third signal at one or more receivers after it has reflected or backscattered from an inhomogeneity in the formation
Data Source
Figure 1
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Figure 3A
AI summary
A compact array of transducers is employed as a downhole instrument for acoustic investigation of the surrounding rock formation. The array is operable to generate simultaneously a first acoustic beam signal at a first frequency and a second acoustic beam signal at a second frequency different than the first frequency. These two signals can be oriented through an azimuthal rotation of the array and an inclination rotation using control of the relative phases of the signals from the transmitter elements or electro-mechanical linkage. Due to the non-linearity of the formation, the first and the second acoustic beam signal mix into the rock formation where they combine into a collimated third signal that propagates in the formation along the same direction than the first and second signals and has a frequency equal to the difference of the first and the second acoustic signals. The third signal is received either within the same borehole, after reflection, or another borehole, after transmission, and analyzed to determine information about rock formation. Recording of the third signal generated along several azimuthal and inclination directions also provides 3D images of the formation, information about 3D distribution of rock formation and fluid properties and an indication of the dynamic acoustic non-linearity of the formation.