Seismic Stratigraphic Inversion Using Anamorphosis for Gas Reservoir Monitoring
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Solution Overview
Problem
Seismic imaging for monitoring underground gas storage faces challenges in accurately estimating gas volume due to limitations in seismic frequency band and impedance changes, leading to distorted relationships between impedance and saturation, which affects the quantitative assessment of gas injected or produced.
Innovation Solution
The method involves three-dimensional anamorphosis during stratigraphic inversion of seismic data, constraining impedance changes where they are known to be impossible, and using anamorphosis functions to transform Gaussian impedances into true impedances, allowing for better estimation of gas quantities by preserving the value of impedance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If seismic prospecting is used to monitor underground gas storage, then spatial distribution information is obtained, but measurement precision of gas volume is degraded due to limited seismic frequency band and impedance changes
Solution Approach 1:
The patent applies anamorphosis transformation to modify the impedance parameter space. By transforming the impedance values through a non-linear function, the method preserves the relative variations in impedance that correspond to gas saturation changes, while compensating for the distorting effects of limited seismic frequency band. This parameter transformation allows accurate gas volume estimation despite the inherent limitations of seismic data.
2Measurement precision
If conventional stratigraphic inversion is used, then impedance distribution is obtained, but gas quantity assessment precision is degraded due to unintended impedance changes
Solution Approach 1:
The patent modifies the conventional stratigraphic inversion process by incorporating anamorphosis transformation of the impedance parameter. This transformation changes the parameter space to preserve the physical relationship between impedance variations and gas saturation, preventing the distortion that occurs in conventional inversion. The transformed impedance values maintain a reliable correspondence with actual gas saturation levels.
Solution Approach 2:
The method incorporates a feedback mechanism where the anamorphosis transformation is applied iteratively during the inversion process. The transformation parameters are adjusted based on the relationship between observed impedance changes and expected saturation changes, ensuring that the final impedance distribution accurately reflects the gas distribution. This feedback loop corrects distortion artifacts that would otherwise degrade assessment precision.
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 gas volume estimation by preventing unintended impedance changes, improving the precision of gas quantity assessments in both injection and production scenarios.
Implementation Method 1
Seismic prospecting consists of sending waves into the subsoil from different shooting points, and, using numerous receivers, recording the echoes returned by the boundaries between the geological layers
Implementation Method 2
If gas is injected into a tank, then its acoustic impedance, that is to say the product of the speed of sound and the density, decreases and the echoes are modified
Implementation Method 3
The echoes returned by the discontinuities in the mechanical properties of the terrain are transformed into electrical signals by thousands of sensors called geophones
Data Source
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AI summary
The method involves constructing a cube having seismic wave impedance before gas injection. An anamorphose function is defined by a function comprising a positive lower limit (B1), an upper limit (B4) and an identity interval defined between other two limits (B2, B3). Values of the limits are associated with corresponding cells of the cube. Another seismic wave impedance of the cube is associated with each cell after gas injection, by applying the anamorphose function on the latter impedance. Carbon dioxide gas is injected inside a subsurface zone, by comparing the impedances with one another.