Multi-firing Acoustic Source Dispersion Analysis for Shear Wave Slowness
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Solution Overview
Problem
Existing methods for estimating formation shear wave slowness, such as those used in wireline and logging-while-drilling operations, often face challenges due to noise interference and incomplete data from low-frequency asymptotes, particularly in hard formations or small boreholes, leading to inaccurate results.
Innovation Solution
The method involves using multi-firings of different types of acoustic sources (monopole, dipole, quadrupole, etc.) to generate waveform data, performing multi-mode dispersion analysis, and removing tool waves to determine formation type and initial shear wave slowness, thereby improving accuracy by analyzing fundamental and high-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single mode dispersion analysis is used to estimate formation shear wave slowness, then the measurement process is simple, but the measurement precision deteriorates due to noise interference and missing low-frequency asymptotes
Solution Approach 1:
The patent segments the acoustic source firings into multiple types (monopole, dipole, quadrupole, etc.) and performs separate dispersion analysis for each type. By dividing the analysis into multiple independent measurements with different source characteristics, the method obtains multiple dispersion curves that can be combined to improve estimation accuracy while maintaining manageable analysis complexity for each individual measurement.
Solution Approach 2:
The patent extends the analysis from single-mode to multi-mode dispersion analysis, adding the dimension of multiple acoustic modes (fundamental mode, higher-order modes) to the measurement process. This dimensional expansion allows the system to capture additional information about formation properties that is not available in single-mode analysis, thereby improving measurement precision.
2Measurement precision
If first order flexural or screw waves are used for shear wave slowness estimation, then the measurement process is straightforward, but the measurement precision deteriorates in hard formations or small boreholes where dispersion curves are affected by noise or not well developed
Solution Approach 1:
The patent introduces higher-order acoustic modes as intermediary measurements that are less susceptible to noise interference and development issues in challenging formations. These higher-order modes serve as alternative pathways to obtain reliable dispersion data when fundamental modes are compromised by noise or poor development, thereby maintaining measurement precision without requiring easier operational conditions.
Solution Approach 2:
The patent changes the measurement parameters by utilizing different acoustic source types (monopole, dipole, quadrupole) and analyzing multiple modes rather than relying solely on first-order flexural or screw waves. This parameter diversification allows the system to find suitable measurement conditions even in hard formations or small boreholes where traditional first-order wave analysis fails.
3Measurement precision
If multi-firings of different acoustic sources and multi-mode dispersion analysis are performed, then the measurement precision improves, but the loss of time increases due to multiple measurements and processing steps
Solution Approach 1:
The patent performs preliminary action by acquiring data from multiple acoustic source firings and multiple modes in advance, storing this comprehensive dataset for subsequent analysis. By preparing the multi-dimensional data set beforehand, the system enables efficient processing later when formation evaluation is needed, reducing the time penalty of complex analysis through pre-acquisition of all necessary measurement data.
Solution Approach 2:
The patent creates a universal measurement approach that uses multiple acoustic source types and multiple modes to serve various formation conditions and evaluation needs simultaneously. This multi-functional data acquisition system can estimate shear wave slowness, compressional wave slowness, and formation type classification from the same set of measurements, reducing total measurement time compared to performing separate specialized measurements for each property.
4Measurement precision
If tool waves are not removed from the waveform data, then the processing is simpler, but the measurement precision deteriorates due to interference from tool-generated waves
Solution Approach 1:
The patent extracts and removes tool waves from the waveform data through dedicated processing steps. By separating the tool-generated waves from the formation waves, the system isolates the formation signal for accurate analysis. This extraction process, while adding processing complexity, is necessary to achieve the improved measurement precision in formation wave detection and characterization.
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 enhances the estimation of formation shear wave slowness by reducing noise interference and improving data accuracy, allowing for more precise determination of formation type and shear wave properties, even in challenging logging conditions.
Implementation Method 1
Multi-firings of different types of acoustic sources, including, but not limited to, monopole, dipole, and quadrupole signals are transmitted into a downhole formation
Implementation Method 2
A multi-mode dispersion analysis is performed for each firing of the multi-firings
Data Source
AI summary
Methods to estimate formation shear wave slowness from multi-firings of different types of acoustic sources and multi-mode dispersion estimation systems are presented. The method includes obtaining waveform data of waves traversing through a downhole formation, where the waves are generated from multi-firings of different types of acoustic sources. The method also includes performing a multimode dispersion analysis of the waveform data for each firing of the multi-firings, and removing one or more tool waves generated from the multi-firings. The method further includes determining a formation type of the formation the waves traverse based properties of the waves and determining an initial shear wave slowness estimate of the waves. The method further includes generating a modeling of the waves, and reducing a mismatch between the modeling of the waves and a slowness dispersion of the waves to improve the modeling of the waves.