Acoustic Array Reflection Extraction via 2D Slowness Beam-Forming
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Solution Overview
Problem
Conventional acoustic processing in subterranean formations struggles to accurately detect and extract secondary reflections from dominant direct arrivals, leading to residual errors and reduced precision in borehole imaging and formation property analysis.
Innovation Solution
The method involves transforming waveforms from the time domain to the frequency domain, selecting a frequency band, computing a beam-former to detect reflection waves, and applying a least squares inversion process to separate direct and reflection waves, using a 2D slowness grid to enhance the detection of secondary reflections and reduce noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional semblance techniques are used to extract formation properties from direct waves, then formation property measurement is achieved, but reflection events are treated as noise and measurement precision deteriorates
Solution Approach 1:
The patent converts the harmful reflection events into beneficial signals by using them as the primary object of analysis. Instead of treating reflections as noise to be eliminated, the method identifies and extracts coherent reflection events from the wave-train to image subsurface features such as bedding planes, fractures, and borehole breakouts, thereby transforming what was previously considered interference into useful geological information
Solution Approach 2:
The patent segments the complex wave-train into distinct components by separating coherent reflection events from incoherent scattering events. This segmentation allows the processing method to selectively enhance reflection signals while suppressing scattering noise, achieving improved measurement precision for reflection-based formation analysis
2Measurement precision
If 1D wave separation is used to estimate direct waves and subtract them, then direct wave estimation is achieved, but residual errors in reflection wave estimate increase due to large amplitude differences
Solution Approach 1:
The patent transitions from 1D wave separation to 2D beam-space processing by incorporating both receiver position and depth as independent dimensions. This dimensional expansion allows the method to separate direct and reflection waves more effectively in the beam-space domain, reducing residual errors that arise from simple amplitude-based subtraction in the time domain
3Measurement precision
If uniform depth spacing is assumed in wave separation, then processing simplicity is maintained, but aliasing errors increase and measurement precision deteriorates
Solution Approach 1:
The patent changes the depth spacing parameter from uniform to non-uniform by explicitly accommodating arbitrary depth intervals between receivers and between tool depths. This parameter modification allows the beam-former to accurately process data from non-uniformly spaced receivers, eliminating aliasing errors while maintaining processing feasibility through the use of depth-weighted beam-space calculations
Data Source
AI summary
Various embodiments include apparatus and methods to extract reflections from acoustic array data collected from a receiver array. A beam-former can be generated to detect a reflection wave in the presence of a direct wave identified from collected waveforms, where the beam-former can be correlated to receiver and depth for the array. The direct wave and the reflection wave can be separated to extract the reflection wave, where the separation is correlated to receiver and depth for the array. The extracted reflected wave can be used to image and/or analyze entities associated with the borehole. Additional apparatus, systems, and methods are disclosed.