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GCSobel Filtering Brings Edges into Sharp Focus*
Satinder Chopra¹ and Kurt J. Marfurt²
Search and Discovery Article #41511 (2015)
Posted January 12, 2015
*Adapted from the Geophysical Corner column, prepared by the authors, in AAPG Explorer, January, 2015. Editor of Geophysical Corner is Satinder Chopra ([email protected]). Managing Editor of AAPG Explorer is Vern Stefanic. AAPG © 2015
¹Arcis Seismic
Solutions, TGS, Calgary, Canada ([email protected])
²University of Oklahoma, Norman, Oklahoma
Mapping of geologic edges such as faults or channel levees forms a critical component in the interpretation on 3-D seismic
volumes. While the more prominent features often can be easily visualized, smaller features important to understanding the structural and depositional environment can be easily overlooked. Careful manual interpretation of such features is both tedious and time consuming. A
seismic
coherence
attribute
that enhances edges not only accelerates the interpretation process, it also provides a quantitative measure of just how significant a given discontinuity is in relation to others.
Since the seismic
coherence
attribute
extracts all subtle features in the
seismic
amplitude volume, then preconditioning the data to enhance geologic edges and minimize edges due to acquisition and processing is key to accurate analysis. We find that the application of a Sobel filter to energy-ratio coherence volumes significantly sharpens faults and channel edges of interest. We demonstrate this simple cascaded workflow with examples from Canada, where one of the objectives is to provide improved attributes for subsequent automatic fault plane extraction.
♦General statement ♦Figures ♦Method ♦Examples ♦Conclusions
♦General statement ♦Figures ♦Method ♦Examples ♦Conclusions
♦General statement ♦Figures ♦Method ♦Examples ♦Conclusions
♦General statement ♦Figures ♦Method ♦Examples ♦Conclusions |
Sobel filters are one of many filters that are commonly distributed when one purchases a digital camera. For a flat photograph containing pixels of a given amplitude aligned along the x and y axes, the classical Sobel-filtered image is simply obtained by running a process equivalent to the square-root of the sum of the squares of derivatives of the amplitude in the x and the y directions. Unlike a photograph, In Figure 1 we show the application of Sobel filtering on a 3-D Since the classical Sobel filter is routinely used in sharpening photographic images, we hypothesize that we can do the same by applying it to edge-sensitive The data going into coherence computation are usually preconditioned using structure-oriented filtering, reducing the risk of enhancing aligned noise showing up as edges. In Figure 2 we show a similar comparison of coherence run on a 3-D In Figure 2b we show the result of applying the Sobel filter to the coherence volume. Notice the crisp definition of the channels on this display. Besides the main channels, many of the narrower channels are seen clearly. Invariably, the definition of all the channels on the display is very prominent. In Figure 3 we show a comparison of time slices from a 3-D Such convincing displays of the application of Sobel filters to coherence volumes suggest that discontinuity features – such as channels as well as faults – can be enhanced, resulting in crisper and more focused images. We believe such images provide superior input to modern object extraction software application, as well as in visualizing the channel features clearly. The present exercise can be easily extended to other features of interest, such as faults, which would be a useful input for automatic fault extraction software applications. Such applications would definitely help with the geologic understanding of the subsurface area of interest. |