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Full Wavefield Inversion (FWI) for Simultaneous Source Data Considering Earth Attenuation

IP.com Disclosure Number: IPCOM000252454D
Publication Date: 2018-Jan-12
Document File: 2 page(s) / 42K

Publishing Venue

The IP.com Prior Art Database

Abstract

Seismic energy attenuates when it propagates through the Earth. Transmission losses, geometrical divergence, and absorption are the main causes of the seismic energy attenuation. Absorption is the conversion of kinetic energy in the seismic waves into heat, or kinetic energy associated with the Earth's atoms. The quality factor Q is used to describe this attenuation property. Q alters both the amplitude and phase of seismic events as a function of frequency. In conventional processing, the seismic data itself is often compensated for these phase and/or amplitude alternations by various means. Processed shot gathers with this background Q compensation can provide a good input dataset for full wavefield inversion (FWI). In this scenario, FWI does not need to account for the background Earth attenuation as part of the earth model because the data itself has been compensated during preprocessing. Unfortunately, Q-compensation methods only apply to shot gathers generated by a single shot. They cannot be applied to a simultaneous source dataset because energy from multiple active shots will have traversed very different paths corresponding to different traveltimes only to arrive at the receiver at the same time. There are two ways to account for the Earth's attenuation with simultaneous-source FWI: 1) deblend the simultaneous source dataset, apply Q compensation separately and apply FWI process, optionally re-blending the Q-compensated data; and, 2) include Q in the FWI Earth model, account for it during FWI simulation with an initial guess of Q, and optionally update Q if there is enough information about Q in the simultaneous source dataset. This manuscript is focused on method 2), which is to include Q as a part of Earth models of FWI process

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Full Wavefield Inversion (FWI) for Simultaneous Source Data Considering Earth Attenuation

Introduction

Seismic energy attenuates when it propagates through the Earth. Transmission losses, geometrical divergence, and absorption are the main causes of the seismic energy attenuation. Absorption is the conversion of kinetic energy in the seismic waves into heat, or kinetic energy associated with the Earth’s atoms. The quality factor Q is used to describe this attenuation property. Q alters both the amplitude and phase of seismic events as a function of frequency. In conventional processing, the seismic data itself is often compensated for these phase and/or amplitude alternations by various means. Processed shot gathers with this background Q compensation can provide a good input dataset for full wavefield inversion (FWI).  In this scenario, FWI does not need to account for the background Earth attenuation as part of the earth model because the data itself has been compensated during preprocessing.

Unfortunately, Q-compensation methods only apply to shot gathers generated by a single shot.  They cannot be applied to a simultaneous source dataset because energy from multiple active shots will have traversed very different paths corresponding to different traveltimes only to arrive at the receiver at the same time.  There are two ways to account for the Earth’s attenuation with simultaneous-source FWI: 1) deblend the simultaneous source dataset, apply Q compensation separately and apply FWI process, optionally re-blending the Q-compensated data; and, 2) include Q in the FWI Earth model, account for it during FWI simulation with an initial guess of Q, and optionally update Q if there is enough information about Q in the simultaneous source dataset. This manuscript is focused on method 2), which is to include Q as a part of Earth models of FWI process

Method

A seismic trace from simultaneous source acquisition contains seismic events from the subsurface corresponding to the energy from multiple different shots. Furthermore, the multiple number of shots could fire at randomly chosen different times. The multiple shots and timings are two reasons why it is very difficult to apply Q-compensation in a simultaneous source shot gather. Conventional Q-compensation methods only apply to shot gathers generated by a single shot.  They cannot be applied to a simultaneous source dataset because energy from multiple active shots will have traversed very different paths corresponding to different traveltimes only to arrive at the receiver at the same time. 

The FWI process is to find an Earth model that matches the measured seismic data with the simulated dataset by iteratively updating the model to improve the match. Attenuation is one of Earth properties that affect seismic wave propagation. Thus it should be taken into account during FWI process to describe seismic data better. Q compensation of shot gathers is one way to consider attenuation for FWI,...