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    Micro-seismic Imaging Using a Source Independent Waveform Inversion Method

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    Name:
    Hanchen Wang - Thesis - Final Draft.pdf
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    12.29Mb
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    Type
    Thesis
    Authors
    Wang, Hanchen cc
    Advisors
    Alkhalifah, Tariq Ali cc
    Committee members
    Hoteit, Ibrahim cc
    Wu, Ying cc
    Program
    Earth Science and Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2016-04-18
    Embargo End Date
    2017-05-15
    Permanent link to this record
    http://hdl.handle.net/10754/609461
    
    Metadata
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    Access Restrictions
    At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis became available to the public after the expiration of the embargo on 2017-05-15.
    Abstract
    Micro-seismology is attracting more and more attention in the exploration seismology community. The main goal in micro-seismic imaging is to find the source location and the ignition time in order to track the fracture expansion, which will help engineers monitor the reservoirs. Conventional imaging methods work fine in this field but there are many limitations such as manual picking, incorrect migration velocity and low signal to noise ratio (S/N). In traditional surface survey imaging, full waveform inversion (FWI) is widely used. The FWI method updates the velocity model by minimizing the misfit between the observed data and the predicted data. Using FWI to locate and image microseismic events allows for an automatic process (free of picking) that utilizes the full wavefield. Use the FWI technique, and overcomes the difficulties of manual pickings and incorrect velocity model for migration. However, the technique of waveform inversion of micro-seismic events faces its own problems. There is significant nonlinearity due to the unknown source location (space) and function (time). We have developed a source independent FWI of micro-seismic events to simultaneously invert for the source image, source function and velocity model. It is based on convolving reference traces with the observed and modeled data to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. To examine the accuracy of the inverted source image and velocity model the extended image for source wavelet in z-axis is extracted. Also the angle gather is calculated to check the applicability of the migration velocity. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity in the synthetic experiments with both parts of the Marmousi and the SEG Overthrust model. On the other hand, a new imaging condition of natural Green’s function has been implemented to mitigate the effect of the unknown velocity model. It is based on putting receivers in a horizontal well close to the micro-seismic events so that only a small part of the velocity model is required for the imaging. In order to focus the multi scattering energy to the source location, as well as to suppress the influence of the noise in the data, we introduced a new method to compensate the energy in the receiver wavefield. It is based on reflection waveform inversion (RWI) theory. We simply migrate for the scatters (reflectors) in the medium, and set the image as a secondary source to compensate for the multi scattering energy in the receiver wavefield. By applying the same imaging condition, the energy of those scattering events can be traced to the source location. Thus the source point has higher energy in the source image. A simple two-layer medium test demonstrates the features.
    Citation
    Wang, H. (2016). Micro-seismic Imaging Using a Source Independent Waveform Inversion Method. KAUST Research Repository. https://doi.org/10.25781/KAUST-5J3A0
    DOI
    10.25781/KAUST-5J3A0
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-5J3A0
    Scopus Count
    Collections
    MS Theses; Physical Science and Engineering (PSE) Division; Earth Science and Engineering Program

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