Fracture Detection Using Offset Acoustic Array Reflections
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Solution Overview
Problem
Current methods for fracture imaging and detection in subsurface formations, particularly in shale fracturing and drilling, face challenges due to low acoustic contrast in healed fractures and limited applicability of electrical resistivity tools, making it difficult to locate and optimize fractures for hydrocarbon extraction.
Innovation Solution
An acoustic array system with a transmitter and receivers radially or longitudinally offset is used to broadcast and receive acoustic signals, inferring fracture presence based on travel times and coherency, allowing for real-time or post-processing imaging and orientation determination of fractures using sonic or ultrasonic frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electrical resistivity tools are used to locate fractures, then fracture detection is achieved in certain wellbore environments, but applicability is limited to specific conditions
Solution Approach 1:
The patent replaces electrical resistivity measurement tools with acoustic wave-based detection tools. The acoustic tool uses a transmitter to generate acoustic waves and receivers to detect reflected waves from fractures, substituting the electrical field-based method with an acoustic field-based method that is not limited by wellbore environment or mud type.
2Measurement precision
If acoustic measurements are used to detect fractures, then detection capability is improved, but healed fractures with low acoustic contrast become difficult to detect
Solution Approach 1:
The patent employs multiple receivers positioned at different radial and longitudinal offsets from the transmitter, creating a three-dimensional detection geometry. This multi-dimensional approach allows detection of subtle acoustic reflections from healed fractures by analyzing signal arrivals from multiple angles and positions, enhancing the ability to detect low-contrast features.
Solution Approach 2:
The patent uses multiple receivers to create multiple copies of the acoustic signal from different positions. By comparing and correlating these copied signals, the system can enhance weak reflections from healed fractures through signal processing techniques that identify consistent patterns across multiple receiver copies.
3Loss of information
If acoustic signals are broadcast to detect fractures, then fracture imaging is achieved, but signal interpretation becomes complex due to multiple reflections and noise
Solution Approach 1:
The patent segments the acoustic signal analysis by processing reflections from different receiver positions and time windows separately. Each receiver's signal is analyzed independently to identify specific reflection events, then results are integrated to build the complete fracture image. This segmentation reduces the complexity of interpreting the full signal by breaking it into manageable segments.
Solution Approach 2:
The patent implements signal processing workflows where received acoustic signals are analyzed, interpreted, and used to guide further measurement or processing decisions. The system provides feedback on fracture detection quality and can adjust processing parameters or suggest additional measurements to reduce ambiguity in complex signal environments.
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 detects and images fractures, including healed and conductive ones, independent of mud type and borehole conditions, providing valuable data for well completion strategies without the need for nuclear sources, across a range of frequencies.
Implementation Method 1
an acoustic signal is broadcast using the transmitter and a portion of the emitted signal is reflected by a reflector and received by the receivers
Implementation Method 2
An acoustic signal is broadcast using the transmitter and a portion of the emitted signal is reflected by a reflector and received by the receivers
Implementation Method 3
Inferences are based on travel times and/or coherency of the received signals
Data Source
AI summary
An acoustic array includes an acoustic transmitter and acoustic receivers radially or longitudinally offset from the acoustic transmitter. The acoustic array is disposed in a wellbore penetrating a subsurface formation. An acoustic signal is broadcast using the transmitter and a portion of the emitted signal is reflected by a reflector and received by the receivers. The presence or absence of fractures in the subsurface formation is inferred based on the received acoustic signal. Inferences are based on travel times and/or coherency of the received signals. Images can be made and fracture orientations determined. Frequencies in the sonic or ultrasonic range may be used. Measurements may be made while-drilling or while performing post-drilling operations. Processing may be done in real-time or post-processing may be performed on recorded data.