Acoustic Array Processing for Dispersion-Compensated Slowness Estimation
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Solution Overview
Problem
Existing acoustic array processing methods for estimating formation properties in subterranean operations face challenges due to dispersive wave propagation, which complicates the estimation of true shear formation slowness, especially when using advanced techniques like point-to-point time domain coherence analysis, and requires accurate wellbore diameter, fluid properties, and formation slowness inputs.
Innovation Solution
A method and system that perform modal analysis using calculated parameters like wellbore diameter, fluid properties, and formation properties to create masks that isolate the actual dispersion phenomenon, allowing for accurate estimation of formation slowness by tracking the dispersion curve to its lower asymptote, free from wellbore environment effects, and using algorithms like Multiple Signal Classification (MUSIC) or Matrix Pencil for frequency semblance analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acoustic array processing is used to estimate formation properties, then measurement capability is improved, but dispersive wave propagation complicates the estimation of true shear formation slowness
Solution Approach 1:
The patent segments the acoustic signal into different frequency components and processes each frequency band separately using frequency-dependent slowness filters. This allows the system to handle dispersive wave propagation by treating each frequency component independently, where dispersion effects are more manageable, and then combines the results to obtain the true shear formation slowness.
Solution Approach 2:
The patent introduces an intermediary processing stage that uses theoretical dispersion curves as a reference framework. By comparing measured acoustic signals against these theoretical curves at multiple frequencies, the system can identify and eliminate the effects of dispersive wave propagation, effectively using the theoretical model as a mediator to separate true formation properties from dispersion artifacts.
2Measurement precision
If theoretical models are used to correct formation shear slowness, then measurement precision is improved, but the process becomes complicated and burdensome due to multiple input requirements
Solution Approach 1:
The patent applies partial action by using only the essential frequency-dependent slowness information from theoretical models, rather than requiring all possible input parameters. The system selectively uses frequency-slowness relationships that are most critical for correcting dispersion effects, omitting less important inputs to reduce complexity while maintaining correction accuracy.
Solution Approach 2:
The patent transforms the correction process by changing from a static single-frequency correction approach to a dynamic multi-frequency approach. By varying the frequency parameter and observing how slowness estimates change across frequencies, the system can identify the true shear slowness as the frequency-independent value, eliminating the need for complex multi-parameter theoretical model inputs.
3Measurement precision
If higher frequency signal excitation is used, then slowness estimation is improved, but tool mode effects and unwanted signatures are enhanced
Solution Approach 1:
The patent employs periodic action by using frequency sweeps that systematically vary the excitation frequency over time. By periodically exciting the formation at multiple frequencies and analyzing the frequency-dependent response, the system can distinguish between true formation slowness (which remains relatively constant) and tool mode effects (which vary with frequency), thereby eliminating harmful artifacts while maintaining estimation precision.
Solution Approach 2:
The patent adds a frequency dimension to the slowness estimation process. Instead of relying on a single high-frequency measurement that is contaminated by tool modes, the system measures slowness across a spectrum of frequencies, creating a two-dimensional frequency-slowness space. True formation properties appear as frequency-independent values in this space, while tool mode effects appear as frequency-dependent anomalies that can be identified and eliminated.
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 enables more accurate and reliable estimation of formation properties, such as slowness, by eliminating unwanted signatures and tool mode effects, improving the precision of formation property determination in both real-time and post-processing applications for wireline, LWD, and MWD environments.
Implementation Method 1
An acoustic signal is transmitted by the acoustic source and received at the receivers of the acoustic tool
Implementation Method 2
one of the major hurdles for estimating the formation properties is the natural phenomenon of dispersive wave propagation along the wellbore
Data Source
AI summary
A system and method for effective estimation of properties of a formation using acoustic array processing is disclosed. An acoustic tool is directed to a zone of interest in the formation and generates a first signal. Real data corresponding to the first signal is then received. One or more basic parameters are provided as input. The basic parameters may include parameters relating to the acoustic tool or parameters relating to the zone of interest. A time semblance shear slowness and a frequency semblance shear slowness are determined using the basic parameters. A mask is then selected using the determined time semblance and frequency semblance shear slowness values and used to isolate a dispersion curve. A shear slowness value is selected from the dispersion curve and quality control is performed on the selected shear slowness value.