Ultrasonic Eccentricity Correction via Transit Time Decay Model
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Solution Overview
Problem
Ultrasonic image profiles in oil wells are affected by tool eccentricity, leading to attenuation and distortion of acoustic wave amplitudes, which prior correction methods fail to adequately address, resulting in inaccurate representation of rock properties and introduction of artifacts.
Innovation Solution
A method that corrects ultrasonic image profiles by using a decay model to measure amplitude values in relation to transit time, defined by the equation Aθ=A0·e^(-tθ/τ·Iθ, where τ is the decay correction factor and Iθ is the reflection coefficient, and applies inverse decay correction to rescale amplitudes, effectively removing geometric attenuation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the tool is positioned eccentrically in the well, then the acquisition of ultrasonic image profiles can proceed, but the amplitude of acoustic waves is attenuated due to varying distances from the transducer to the well wall
Solution Approach 1:
The patent applies preliminary action by measuring the transit time of acoustic waves before correcting the amplitude data. The transit time measurements are used to calculate the varying distances from the transducer to the well wall, which then inform the correction factors applied to the amplitude data. This preliminary measurement of transit time enables the subsequent removal of eccentricity effects from the amplitude profile.
2Measurement precision
If prior correction methods are applied to equalize amplitudes, then the geometric attenuation effects are reduced, but artifacts are introduced in regions with high amplitude variance such as fracture zones and caves
Solution Approach 1:
The patent applies parameter changes by using transit time as an additional parameter to guide the amplitude correction process. Instead of simply equalizing amplitudes, the method changes the amplitude values based on the transit time measurements, which reflect the actual distance variations. This parameter-based approach preserves the relative amplitude differences caused by geological features while removing the systematic attenuation caused by eccentricity.
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
The method significantly reduces eccentricity effects, allowing for reliable qualitative and quantitative analysis of geological data, preserving intrinsic rock properties and enabling accurate characterization of reservoirs, especially in the presence of complex geological structures like caves and fractures.
Implementation Method 1
The emission of acoustic waves usually takes place through a transducer, which is a piezoelectric crystal, namely a crystal capable of transforming an electrical pulse into a pulse of mechanical waves
Implementation Method 2
Sound waves are reflected due to the contrasting impedance between the fluid-rock medium
Implementation Method 3
The acoustic pulses are emitted along the entire circumference of the wall of the wells. After they are reflected, these pulses are measured around the entire acquisition tool
Data Source
AI summary
This invention relates to a method of correcting eccentricity of ultrasonic image profiles, measured along a section of rock, including the steps of measuring emitted amplitude values (A0) and measuring transit time values (tθ) of ultrasonic acoustic pulses emitted at a range of default angles (θ), where the amplitude measured at each angle (Aθ) is determined by an amplitude decay model in relation to the transit time (tθ) defined by Aθ=A0e−t<sub2>θ</sub2>/τIθ where τ is the decay correction factor; and Iθ is the reflection coefficient of the rock wall.