Attributes describe seismic data. Seismic is a geophysical technique used to provide information about the subsurface using energy from sound. The technique requires no digging or drilling, but instead, uses a pulse of energy. The data recorded, is the time it takes for the energy emitted to bounce back from layers in the subsurface. Imagine an X-ray image of a slice of cake. This is close to the result!
Seismic attributes are prepared after seismic data collection. They reveal vital information about the seismic, quickly and effortlessly. The data is re-arranged through use of various calculations to help with pattern identification. It takes an experienced geologist or geophysicist to interpret the seismic attributes, as they are still ambiguous representations of the original data. Without the use of attributes, features in the original seismic data can be hidden. There are hundreds of different attributes available, and many of them reveal the same information. The key is choosing the right attribute or combination of attributes for the purpose of the task. It may take some time to find the right one, or combination of many, and you can easily get carried away with just wanting to try another to find an even better result! Attributes are extremely important for understanding seismic and for getting different views of your data, but you have to have an initial understanding of what you are looking for, to be able to choose the best attribute for your interpretation. The end goal is to have a more refined geological understanding of the subsurface. This of course will take some practice.
It is interesting to think about how we, as humans, process visual information. Our visual perception is largely influenced by context and colour. We have a cognitive ability to recognize patterns from what we see and relate them with past experience and knowledge (Paton and Henderson, 2015). For example, Figure 1 (A ): on first sight you see random, disparate shapes, but when the full image is revealed (B) it is then possible to interpret and draw in the missing sections of the image (C). This is context. We all know and recognize pandas! Imagine that the original seismic data (D) is, as though you are looking at the shapes in (A); that, the use of the correct attribute (E) has revealed (B) and that we, as experienced geological and geophysical interpreters, are able to draw the lines to reveal the deeper meaning of the original seismic (C). The lines could be important geological events for example, that were not obvious at first glance.
As a seismic interpreter, I am unable to see any meaningful information in the original seismic (D). Through applying calculations to the seismic data, by use of multiple seismic attributes, I have revealed much more information. I am able to see fractures radiating out from a central point (E). This however, may not be obvious to the non-seismic interpreter. Image (F) gives an alternative view. The photograph gives the viewer further context to understand what the attribute is showing. This is the bottom of a blasting hole, with fractures found in the rock after blasting. The hydro fracturing, as interpreted in (E) – thought to be a result of gas trapped in overpressured sediments – reveals the same fracture pattern as the blasting hole. The use of seismic attributes opens up the opportunity to investigate finer scale geological processes that may uncover details that could be the missing piece in the geological puzzle.
Figure 1 (A) – (C) from Paton and Henderson (2015), (D) original seismic, (E) seismic attribute, (F) from https://www.shutterstock.com/image-photo/bottom-blasting-hole-showing-fracture-rock-687006250
Text and illustration by Frances Cooke