Sonic Logging Casing Wave Inverse-Phase Cancellation
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Solution Overview
Problem
Conventional well logging methods struggle to effectively reduce the impact of casing waves on formation wave analysis, especially when casing wave slowness is similar to formation wave slowness, leading to biased estimates and incomplete data interpretation.
Innovation Solution
A method involving multiple shots of sonic data capture using transmitters and receivers, where auxiliary transmitter positions generate inverse-phase signals to cancel out casing waves at the primary transmitter position, considering both slowness and attenuation to improve formation wave analysis without biasing formation wave slowness estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sonic logging processing methods (STC or DPTS) are used, then formation wave analysis can be performed, but casing waves obscure the formation waves particularly when cement bond index is low
Solution Approach 1:
The patent uses the casing wave itself to eliminate its harmful effects by generating an inverse-phase version of the casing wave from auxiliary transmitter data and subtracting it from the primary transmitter data, thereby converting the harmful casing wave signal into a beneficial cancellation mechanism that reveals the formation wave
Solution Approach 2:
The patent introduces auxiliary transmitter positions as intermediaries that capture casing wave information without the strong formation wave response present in primary transmitter positions, allowing the casing wave to be isolated and removed through inverse-phase subtraction
2Object-affected harmful factors
If F-K filters are used to reduce casing waves, then casing wave suppression is achieved when slowness differs substantially, but the method is ineffective and biases formation wave slowness when slowness is similar
Solution Approach 1:
Instead of filtering out casing waves based on slowness differences, the patent generates an inverse-phase casing wave signal from auxiliary transmitter data and subtracts it from primary transmitter data, converting the harmful overlapping signal into a beneficial cancellation that preserves formation wave slowness accuracy
Solution Approach 2:
The patent segments the wavefield into two components: casing waves captured primarily at auxiliary transmitter positions and formation waves captured at primary transmitter positions, allowing selective removal of the casing wave component without affecting formation wave measurements
3Object-affected harmful factors
If median filter is used to extract casing waves from common-offset array, then casing wave extraction is achieved assuming formation waves arrive at different times, but the method is ineffective when bond condition changes with depth and prevents formation wave analysis in homogenous formation
Solution Approach 1:
The patent segments the measurement system into primary transmitter positions for formation wave detection and auxiliary transmitter positions for casing wave characterization, enabling the method to adapt to varying bond conditions by relying on the consistent casing wave response at auxiliary positions
Solution Approach 2:
The auxiliary transmitter positions serve as intermediaries that provide consistent casing wave information across varying bond conditions, allowing the inversion method to adapt to depth-dependent cement bonding while maintaining formation wave analysis capability
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 accuracy of formation wave analysis by effectively reducing casing wave interference, providing clearer insights into formation properties and cement bond integrity, even in heterogeneous formations.
Implementation Method 1
The one or more transmitters may stimulate an acoustic wave into the geologic formation
Implementation Method 2
auxiliary transmitter positions generate inverse-phase signals to cancel out casing waves at the primary transmitter position
Data Source
AI summary
Reducing casing wave effects on sonic logging data by positioning two or more receivers in a borehole in a subsurface formation; receiving, at two or more receivers in a borehole in a subsurface formation, a first signal associated with a first acoustic signal originating from a first transmitter position; receiving, at the two or more receivers, a second signal associated with a second acoustic signal originating from a second transmitter position; creating a dataset based on the first signal and the second signal; identifying casing wave signals in the dataset based at least in part on the second signal; calculating inverse-phase casing wave signals based at least in part on the casing wave signals and the second signal; and reducing effects of the casing wave signals on the dataset using the inverse-phase casing wave signals.