Marine Seismic Full-Wavefield Inversion Using Wavefield Separation

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Solution Overview

Problem

Current full wavefield inversion methods in geophysical prospecting struggle with accurately modeling free-surface multiples, leading to erroneous subsurface property estimates due to interface errors and the inability to effectively incorporate strong free-surface multiple reflections.

Innovation Solution

The method separates marine seismic data into up-going and down-going wavefields, allowing for simultaneous or cascaded inversion to infer subsurface physical properties, thereby bypassing the need for direct modeling and subtraction of free-surface multiples.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If free-surface multiples are directly modeled and subtracted, then the modeling accuracy improves, but the interface errors increase due to misalignment between numerical grids and interfaces

Engineering Contradiction:

Improvemodeling accuracyVSAvoidinterface errors

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The wavefield is segmented into up-going and down-going components using wavefield separation. This segmentation allows the inversion to process different wavefield types separately, avoiding the need to directly model and subtract free-surface multiples while still utilizing their information content.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of the conventional approach of modeling and subtracting free-surface multiples, the patent inverts the recorded wavefield containing all multiples to directly image the subsurface. This inversion approach naturally handles the multiple reflections without requiring explicit modeling and subtraction steps.

Inventive Principle:

Principle #13The other way round (Inversion)

2Object-affected harmful factors

If only primaries and internal multiples are used for inversion, then the interface errors are reduced, but the information content from free-surface multiples is lost

Engineering Contradiction:

Improveinterface errorsVSAvoidinformation from free-surface multiples

Core Design Contradiction:

Object-affected harmful factorsVSLoss of information

Solution Approach 1:

The patent converts the potentially harmful free-surface multiples into beneficial information sources. By inverting the full wavefield including free-surface multiples rather than removing them, the method transforms what was previously considered noise or error into useful information for subsurface imaging.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The inversion method is designed to handle multiple wavefield types (primaries, internal multiples, and free-surface multiples) simultaneously through a unified inversion framework. This multi-functional approach allows all wavefield components to contribute to the subsurface model without requiring separate processing workflows.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Loss of information

If full wavefield inversion is performed without wavefield separation, then the information content is maximized, but the interface errors from free-surface multiples contaminate the inversion

Engineering Contradiction:

Improveinformation contentVSAvoidinterface errors from free-surface multiples

Core Design Contradiction:

Loss of informationVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS9702998B2Full-wavefield inversion of primaries and multiples in marine environment

Publication Date: 2017.07.11 EXXONMOBIL UPSTREAM RESEARCH COMPANY(US)

AI summary

Method for using the full wavefield (primaries, internal multiples and free-surface multiples) in inversion of marine seismic data, including both pressure and vertical velocity data (21), to infer a subsurface model of acoustic velocity or other physical property. The marine seismic data are separated (22) into up-going (23) and down-going (24) wavefields, and both wavefields are inverted in a joint manner, in which the final model is impacted by both wavefields. This may be achieved by inverting both wavefields simultaneously (25), or one after the other, i.e. in a cascaded approach (35→37, or 45→47), for the subsurface properties (26, 38, 48).