What is it about?

Phase decomposition provides a new way of interpreting seismic data. Thin beds, subtle fluid responses and changes in lithology, otherwise hidden in seismic waveforms, can be amplified on specific phase components. Assuming zero-phase, normal polarity seismic data, seismically thin layers that are high impedance relative to overlying and underlying half-spaces are seen on the +90o phase component, while a relatively low-impedance thin layer will appear on the -90o phase component. In this study, we applied phase decomposition to pre-stack data across gas-bearing channel sand. The results showed that the amplitude-variation-with-angle is magnified on the -90o phase component allowing for a better delineation of the lateral extent of the reservoir when compared to a traditional AVO analysis. These results are corroborated by phase decomposition of fluid-substituted synthetic gathers which shows for the gas-case the same phase component relationships for near and far angle stacks as are observed on the real data. A comparison between the brine-case and the gas-case shows that no amplitude variation is observed on the -90o phase component for the brine-case, while for the gas-case, a strong amplitude-variation-with-angle response is observed for this same component.

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Why is it important?

In a seismically thin layer scenario, where the tuning effect can either lead to a pitfall or masking the gas response, the phase component amplitude-variation-with-angle can be a used as a tool to de-risk prospects and as a direct hydrocarbon indicator. It also can provide a better volumetric estimate of hydrocarbon in place.

Perspectives

I hope this paper can inspire readers, especially geoscientists, to explore and use more the phase component of the data in other to better understand the underneath geology registered by seismic data. Have been working the phase aspect of the seismic trace has opened a new world to me, and I can see many future applications coming from that.

Ph.D. Elita De Abreu
University of Houston

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This page is a summary of: Case study: Phase-component amplitude variation with angle, Geophysics, July 2019, Society of Exploration Geophysicists, DOI: 10.1190/geo2018-0762.1.
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