It's been a constant in the ongoing story of seismic stratigraphy: New types of data have always sparked quantum leaps of geologists' understanding of the discipline.
If that's true, get ready for another leap.
Can you say, "geomorphology"?
That's the word -- and the concept -- being advanced by Henry W. Posamentier, with Veritas Exploration Services in Calgary -- an AAPG Distinguished Lecturer who just presented an SEPM award-winning paper on the topic at the recent AAPG annual meeting in New Orleans.
In his words, the explosion of 3-D seismic data over the last decade has taken seismic stratigraphy to new heights by providing the potential for directly imaging discrete elements of entire depositional systems.
The first major leap in the discipline occurred in the 1960s with the advent of multi-channel seismic reflection data.
"At that time we saw a virtual explosion in our understanding of how basins fill," Posamentier said. "In the 1980s we recognized that the same principles we had developed based on seismic data were applicable to other forms of data. Outcrops, well logs, biostratigraphy and chemostratigraphy, for example, could now be integrated into a sequence stratigraphic analysis -- evolving the discipline from seismic stratigraphy, as it had been known up to that time, to the more general sequence stratigraphy."
The 1990s brought "a massive push in 3-D seismic data," he continued, "and in my mind that will offer us the next opportunity for a quantum leap in our understanding of how basins fill."
Up to now, he said, geologists have had an emphasis on the architecture and geometry of the rock layers in a 2-D sense. Three-D seismic data allows geologists to not only slice the earth in profile but also in plan view, "which gives us an image of paleogeography -- a direct visualization of the paleogeography," he said.
"Although seismic resolution decreases with depth, a broad range of depositional elements can nonetheless be imaged from the sea floor down to basement through analysis of a combination of seismic reflection and seismic interval attributes," he said. "Integration of 3-D based analyses of the spatial and temporal distribution of depositional systems with classical sequence stratigraphic concepts will elevate these concepts to the next higher level.
"We are now looking at plan view images, whether it's through slicing, interval attributes or reflection attributes," he said -- and this yields a mass view of the subsurface at a succession of different levels.
"Modern 3-D seismic is becoming more and more amenable to this approach as resolution continually improves," he said. "It opens incredible vistas of the subsurface to us."
'A Whole New Discipline'
Posamentier said in order to maximize the potential stratigraphic insights afforded by 3-D data, the interpreter's required skill set must evolve from an understanding of stratigraphic architecture to an understanding of paleo-geomorphology and depositional systems.
"I see a whole new discipline evolving -- seismic geomorphology as opposed to seismic stratigraphy," he said.
"We are now extracting geomorphic insights from 3-D seismic data," he added, "and injecting those geomorphic insights into what we know as sequence stratigraphy will dramatically advance our understanding."
Obviously, geoscientists will require training in the interpretation of landforms and their stratigraphic significance if they want to maximize the insights that can be gleaned from ever-higher resolution 3-D seismic data.
"Seismic geomorphology will require specialized training," he said, "just as its predecessor seismic stratigraphy did."
So how do geoscientists train for this new approach?
Posamentier said taking a course in geomorphology is a good start, but field training is also essential. Field trips and flights over modern depositional settings are critical to a greater appreciation of landforms and how to extract stratigraphic information.
"Geoscientists need to be aware of what modern systems look like from the air, because that is essentially what you are looking for in the subsurface. The scale factor, that is, the size of various depositional elements, as well as map paterns are brought home this way," he said.
"Pattern analysis based on geomorphic insights is where the next breakthroughs will be."
One of Posamentier's mandates with Veritas is to develop a catalog of aerial photos and satellite imagery, integrated with seismic images, which can be used as reference when studying the subsurface with 3-D seismic data. He said geoscientists can do the same thing, that is, develop their own catalogs of observations, to dramatically improve their level of understanding of the subsurface.
"In order to maximize the information extracted from 3-D seismic data the geoscientist needs to be attuned to watch for geomorphologically significant map patterns," he said. "Further, in order to do this, he needs to build up his experience base with a catalog of land forms and an understanding of how they evolve."
Looking Deeper
This new technique has tremendous potential in some of the hottest exploration regions in the industry today -- deep water.
"We know very little about deep water systems. Why? Because we can't walk on them," he said. "Also, most of these deep water systems aren't active today -- they were active in the Ice Age when sea level was 100 to 120 meters lower than it is today, so we are really hamstrung when we try to develop models for deep water systems.
"This is where seismic geomorphology has tremendous growth potential."
He said there are two ways to approach seismic geomorphology.
"One is to look at the near surface down to about 400 meters, where seismic resolution and data quality is typically higher, and develop expertise and understanding on how different depositional systems can be imaged and what kind of stratigraphic insights we can draw from that," he said.
"Then, after gaining that experience in the shallower zones, we can do the same sorts of things deeper where you have fewer pieces of the puzzle.
"The data are sketchier and require more interpretation in deeper horizons," he continued, "but with experience we are starting to make some pretty dramatic observations at depth and that's where it will impact exploration success."
And exploration success is what seismic geomorphology is all about. So what if it's a new way of looking at things?
"The integration of 3-D seismic," he said, "will shift the emphasis of seismic stratigraphy from exclusively identifying stratigraphic discontinuities and discrete seismic facies to direct identification of depositional elements that depend on plan view interpretations."
Next step? Posamentier's already in mid-stride.