Addressing several key outstanding issues and extending the capability of the inverse scattering subseries for internal multiple attenuation, depth imaging, and parameter estimation
Liang, Hong 1984-
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The objective of seismic exploration is to determine the physical properties of the Earth's subsurface in order to detect potential hydrocarbon accumulations. The inverse scattering series (ISS) is a multi-dimensional direct method that can perform all of the tasks associated with inversion only using the measured data and a chosen reference medium. This is achieved in stages using task-specific subseries that accomplish: (1) free-surface multiple removal; (2) internal multiple removal; (3) depth imaging; and (4) parameter estimation. This dissertation provides deeper comprehension of current ISS strengths and shortcomings for internal multiple removal, and caveats and understanding of ISS depth imaging and parameter estimation, which can be used to progress and develop further capability as part of a strategy to address the current outstanding challenges in exploration seismology. This dissertation is composed of three topics. The first topic extends the capability of the current ISS internal multiple attenuation algorithm by addressing one of its shortcomings. The current ISS internal multiple attenuator has provided added-value compared to other demultiple methods for complex media where multiple generators are not easy or able to be identified. However, this single term has its own strengths and limitations. Under certain circumstances, spurious events can be produced by the ISS leading-order attenuator. In this dissertation, higher-order terms in the ISS that address the spurious events generation from the leading-order attenuator are identified. Adding the higher-order terms to the current algorithm provides a more capable ISS internal multiple attenuation algorithm, which retains the benefit of the original algorithm and addresses the shortcoming due to spurious events. This work is part of the strategy to provide further capability for internal multiple attenuation in onshore or complex offshore exploration areas. The second project focuses on the generation and prediction of internal multiples in thin-layer models. A new method (named the reflector spectrum) based on the reflectivity forward modeling is presented to illustrate where internal multiples are generated in thin layers. The modeling of sub-resolution internal multiples leads to the concept of effective primaries. By comparing the modeling and prediction of internal multiples, it is shown that sub-resolution internal multiples cannot be predicted by the ISS internal multiple attenuator and internal multiples generated by resolvable reflectors can be accommodated by the ISS method. The third topic in the dissertation studies and evaluates the impact of matching or mismatching between the earth model type (e.g., acoustic, elastic, isotropic, anisotropic earth) that generates the data and the assumed model type behind the processing methods for ISS depth imaging and parameter estimation. Numerical results show that for ISS depth imaging and inversion applications, when the model type assumed in the processing algorithm is less complicated than the model type that generates the data, there are errors in the results. The tests and conclusions provide a caveat concerning the consequences of a model mismatch between the model type that generates the data and the model type assumed in processing methods and motivate the need to develop model-type independent ISS imaging methods.