Prismatic Seismic Imaging via Earth Model Perturbation
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Solution Overview
Problem
Seismic imaging in complex subsurface areas, such as near and below salt bodies, often suffers from uneven illumination due to sharp impedance contrasts, making it difficult to interpret steeply dipping salt features and potential hydrocarbon reservoirs effectively.
Innovation Solution
A method involving two-stage seismic imaging using differently perturbed earth models to enhance prismatic energy reflections, where one model alters impedance contrasts at reflectors to generate distinct prismatic amplitudes, allowing for the subtraction of strong background images and revealing weaker prismatic contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional seismic imaging is used in complex subsurface areas with salt bodies, then the imaging process is straightforward, but the illumination becomes uneven and prismatic features are obscured
Solution Approach 1:
The patent applies parameter changes by perturbing the earth model parameters (velocity, impedance) in specific regions to enhance prismatic energy. By modifying the velocity model in the prism region and applying different perturbations to generate multiple images, the method changes the physical parameters to extract prismatic contributions that are otherwise obscured in conventional imaging.
Solution Approach 2:
The patent segments the seismic image into different components by using perturbed and unperturbed earth models. Through differencing of images generated from perturbed models against the original model, the method separates prismatic energy contributions from the background non-prismatic image, effectively segmenting the total image into distinct geological features.
2Loss of information
If the earth model is perturbed to enhance prismatic energy, then prismatic reflections become visible, but the background image becomes distorted
Solution Approach 1:
The patent extracts prismatic energy from the total seismic image by differencing. By subtracting the image from the unperturbed earth model from images of perturbed models, the method takes out the prismatic contributions while removing the background image, isolating the prismatic energy that would otherwise be mixed with and obscured by the strong background signal.
Solution Approach 2:
The method uses controlled parameter changes in the earth model (velocity perturbations, impedance changes) to selectively enhance prismatic energy while maintaining the ability to remove background contributions through differencing. The perturbations are designed to affect prismatic paths differently than non-prismatic paths, allowing selective extraction.
3Loss of information
If multiple perturbed earth models are used to extract prismatic energy, then prismatic features are enhanced, but the processing complexity increases
Solution Approach 1:
The patent uses segmentation by creating multiple perturbed earth models with different perturbations applied to different regions or parameters. Each perturbed model generates an image that, when differenced against the others, isolates specific prismatic contributions. This segmentation approach systematically extracts different prismatic energy components through controlled model variations.
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 improves the visibility of steeply dipping salt flanks and other obscured features by enhancing prismatic energy contributions, enabling better seismic interpretation and hydrocarbon reservoir delineation.
Implementation Method 1
The sources generate seismic waves, which propagate into the geological medium creating pressure changes and vibrations. Variations in physical properties of the geological medium give rise to changes in certain properties of the seismic waves, such as their direction of propagation
Implementation Method 2
The perturbation of the portion of the earth model includes changing an impedance contrast at a reflector for the prismatic energy generation in some way, either directly at the reflector, by changing the properties of the model below the reflector
Data Source
AI summary
A method is described for seismic imaging of complex subsurface volumes using prismatic seismic energy. The method receives a seismic dataset and an earth model. The earth model is perturbed such that prismatic reflections will generate perturbed seismic amplitudes in a target area and seismic imaging is performed using the perturbed model. A second seismic image is generated using a second earth model; the second earth model may be the original earth model or a second perturbed model wherein the perturbation generates different seismic amplitudes in the target area. The two seismic images are differenced to generate a prismatic seismic image that can be used to identify geologic features that are poorly illuminated in conventional imaging. The method may be executed by a computer system.