Acoustic Logging Tool Behind Casing Seismic Velocity
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Solution Overview
Problem
Measuring seismic velocity behind casing in subterranean wellbores is challenging due to interference from guided, dispersive waves, which complicates the estimation of formation properties like rock strength, porosity, and pore pressure, and existing methods are invasive or require additional equipment like fiber optics that may not be installed in existing wells.
Innovation Solution
An acoustic logging tool with directional transmitters that control the angle of incidence to reduce interference, using a method that involves obtaining waveform data sets at different propagation paths, determining Green's functions, and generating a reduced-noise wavefield to estimate formation compressional wave speed, allowing for non-invasive measurement of seismic velocity behind casing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional acoustic logging is used to measure seismic velocity behind casing, then formation property estimation is possible, but measurement precision deteriorates due to interference from guided dispersive waves
Solution Approach 1:
The patent extracts and removes the harmful guided wave components from the total acoustic signal through signal processing techniques. By identifying and separating the dispersive wave patterns from the formation wave arrivals, the method isolates the useful formation velocity information from the interfering casing-generated waves, thereby improving measurement precision behind casing.
Solution Approach 2:
The patent introduces an intermediary signal processing framework that acts as a mediator between the raw acoustic signal and the formation velocity measurement. This intermediary process involves cross-correlation analysis, wavefield decomposition, and selective filtering that transforms the contaminated signal into clean formation velocity data without requiring physical modification of the wellbore or casing.
2Reliability
If invasive methods are used to measure behind casing properties, then measurement reliability improves, but device complexity and operational difficulty increase due to requirements for perforation and patching
Solution Approach 1:
The patent enables the acoustic logging tool to perform behind-casing measurements using its own transmitted acoustic signals and the natural wavefield responses. The method utilizes the casing and formation themselves as the measurement medium, eliminating the need for external modifications like perforations or fiber optic installations. The tool serves itself by generating the necessary acoustic energy and processing the returning signals to derive formation properties.
Solution Approach 2:
The patent replaces mechanical/invasive measurement approaches (perforation, physical contact with formation) with a non-invasive acoustic wavefield analysis method. Instead of mechanically altering the wellbore to access formation properties, the method uses acoustic wave propagation and signal processing to remotely determine formation velocity and other properties through the casing, thereby reducing operational complexity and device requirements.
3Adaptability or versatility
If additional equipment like fiber optics is installed to measure strain behind casing, then measurement capability improves, but ease of operation deteriorates due to installation requirements in existing wells
Solution Approach 1:
The patent creates a universal acoustic logging method that can measure formation properties both in open-hole and behind-casing environments using the same tool and methodology. The acoustic tool and signal processing framework are designed to adapt to different wellbore conditions without requiring specialized equipment or installation procedures, making the system universally applicable across various well types and stages of development.
Solution Approach 2:
The patent creates a virtual model of the formation velocity profile by analyzing acoustic wavefield responses. Instead of physically installing sensors in the formation, the method uses acoustic signaling and cross-correlation analysis to generate a digital representation of formation properties behind casing, thereby obtaining measurement capability without physical installation of additional equipment in existing wells.
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
Enables accurate and non-invasive measurement of seismic velocity and formation properties, reducing interference from dispersive waves and not requiring additional equipment like fiber optics, thus improving well integrity and operational efficiency.
Implementation Method 1
one or more acoustic or ultrasonic transmitters configured to sample different propagation paths between the transmitter source and an array of acoustic receivers
Implementation Method 2
one or more directional acoustic or ultrasonic transmitters configured to sample different propagation paths between the transmitter source and an array of acoustic receivers
Data Source
AI summary
Apparatus, methods, and systems for determining acoustic velocity behind casing or tubing in a subterranean wellbore. A method may include obtaining a plurality of waveform data sets corresponding to a plurality of propagation path regimes and obtaining a total wavefield across the receiver array. The method may also include determining a Green's function representing each of the plurality of propagation path regimes and determining a noise wavefield by convolving the Green's functions and a known transmitted pressure signal corresponding to the plurality of waveform data sets. The method may also include generating a reduced-noise wavefield by subtracting the noise wavefield from the total wavefield and estimating the acoustic velocity of a formation behind the casing or tubing from the reduce-noise wavefield.