AVA Analysis Illumination Correction for Complex Overburden
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Solution Overview
Problem
Seismic surveys in complex geological areas, particularly those with subsurface salt features, face challenges due to uneven illumination and distortion of seismic wavefields, leading to unreliable Amplitude Versus Angle (AVA) analysis and well placement risks.
Innovation Solution
The method extends zero-offset or stacked wave-equation illumination analysis into the angle-gather domain, creating an angle gather with a perfect AVA response for demigration, which separates illumination effects from actual rock properties, enabling AVA confidence analysis and improved well placement decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional seismic survey methods are used in complex geological areas with subsurface salt features, then the seismic survey can be conducted with standard equipment and procedures, but the illumination becomes uneven and the wavefield is distorted, leading to unreliable AVA analysis
Solution Approach 1:
The patent introduces an intermediary process (wave-equation illumination analysis extended into the angle-gather domain) that acts as a mediator between the raw seismic data and the final AVA analysis. This intermediary step separates illumination effects from rock property effects, allowing the harmful illumination irregularities to be identified and compensated before performing the final AVA interpretation.
Solution Approach 2:
The patent extracts the illumination effects from the seismic data by creating a separate illumination model through wave-equation analysis. By taking out the illumination component, the method allows users to distinguish between amplitude variations caused by illumination irregularities and those caused by actual rock properties, thereby improving the reliability of AVA analysis in complex geological areas.
2Reliability
If standard seismic processing is applied, then the processing workflow remains simple and familiar, but the distortion of seismic wavefields by complex overburden cannot be adequately compensated, resulting in poor AVA response
Solution Approach 1:
The patent applies preliminary action by performing wave-equation illumination analysis and creating an illumination model before the final AVA processing step. This preliminary step prepares the data by separating illumination effects, so that when the actual AVA analysis is performed, the results are not contaminated by illumination irregularities. The method extends this preliminary action into the angle-gather domain to specifically address AVA analysis needs.
Solution Approach 2:
The patent transitions the illumination analysis from the conventional depth or time domain into the angle-gather domain. By changing the dimensional perspective and analyzing illumination effects as a function of angle rather than just depth or time, the method provides new insights into wavefield distortion and enables more accurate separation of illumination effects from rock property effects in AVA analysis.
3Measurement precision
If conventional illumination analysis is used, then the analysis remains in the traditional depth or time domain, but it cannot adequately assess the effects of complex overburden on AVA response
Solution Approach 1:
The patent extends the illumination analysis into the angle-gather domain, adding the angular dimension to the traditional depth or time domain illumination analysis. This dimensional extension allows the method to specifically assess how illumination varies with angle of incidence, which is critical for AVA analysis. The angle-gather domain provides a more precise measurement of illumination effects that are relevant to AVA interpretation.
Solution Approach 2:
The patent applies local quality by making the illumination analysis specific to different angular ranges and angle gathers. Rather than providing a single overall illumination assessment, the method evaluates illumination effects locally for each angle gather, allowing for more precise and nuanced assessment of illumination conditions that are specific to different viewing angles and geological structures.
Data Source
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AI summary
According to a preferred aspect of the instant invention, there is provided herein a system and method for extending zero-offset or stacked wave-equation illumination analysis into the angle-gather domain, where it becomes an appropriate tool for assessing the effects of complex overburden on AVA response. A preferred method for doing this involves first creating an angle gather that has a perfect AVA response (i.e. a constant amplitude as a function of angle). This gather is then preferably used as a reflectivity map that is fed into a demigration process which creates modeled data that by construction carries with it a completely flat reflectivity signature. Remigration of such a data set then results in a gather on which any amplitude variation is more likely to be a measure of illumination effects alone. The resulting AVA signature on the gather can then be used to assess the validity of the AVA response on modeled or actual data, resulting in a useful AVA risk analysis.