Outcrops Book Gives Deep Look
Getting the Big Picture Via ‘Tools of the Trade’
Examples of deep-water outcrops, as examined in the upcoming AAPG Studies in Geology 56.
Coming soon, perhaps to a bookcase near you, is a publication that exposes some exposures that matter a lot to geologists.
And for that reason, it matters a lot to the scientific interests of explorationists everywhere.
AAPG’s Atlas of Deep-Water Outcrops, a detailed, statistical compendium of many of the world’s deep-water outcrops and classic depositional systems, is intended to provide a “vast collection of architectural data that may be used for conceptual models and detailed reservoir modeling,” according to book co-editor Joe Studlick.
That’s for the science.
“It is needed now,” he continued, “because of the current development challenges and expected reserves associated with such deep-water reservoirs.”
That’s for the explorationists.
Or as Studlick put it, “That’s what this is all about.”
Roger Shew, another of the compendium’s four editors, cautions that while the atlas is neither a guide for the general public nor a direct answer to energy policy, it is a significant achievement.
“We wouldn’t have undertaken this work if we didn’t believe there was a need for the book,” Shew said. “We believe we have provided an atlas that is both important for the E&P industry as analog data, but also that is important to the geologic community in understanding deep-water depositional systems.”
Specifically, for the energy industry exploring for and developing deep-water prospects globally, it provides “a comprehensive look” at an important source of analog information.
“That,” Shew said, “should help the geoscientists and engineers more efficiently and economically explore for and develop these costly and often technically difficult reservoirs.
“Understanding the range of reservoir architectural types, baffles and barriers, and properties provide a critical component for deep-water exploration and development.”
The Atlas (Studies in Geology 56), expected to be available this fall, was compiled and edited over a three-year period by the late Tor Nilsen, consultant, former U.S. Geological Survey geologist and a legendary instructor for AAPG; Studlick, senior general manager, Maersk Oil America Inc., Houston; Shew, lecturer, Departments of Geology and Environmental Sciences, University of North Carolina at Wilmington; and Gary Steffens, geological adviser, Shell International E&P, Houston.
Steffens says the compilation, co-published by AAPG and Shell International Exploration and Production, is the “first time that almost all classic turbidite outcrops, as well as many new ones, have been compiled using a standard format (11- x 17-inch) for easy comparison and analysis.
“It was an enormous job both in terms of shear volume of data as well as getting hundreds of authors to agree to a single format,” he added.
True, there have been other articles and even a few atlases on deep-water deposits, but Steffens said that until now there never was a compendium that addressed both qualitative and quantitative aspects on such a diverse number of outcrops around the world – including those on all seven continents and 21 countries.
In all, it has 103 separate outcrops, spanning most of the geologic time scale (from the Neoproterozoic to the Miocene), including those in:
- The Gulf of Mexico.
- The North Sea.
- The Canadian Rockies.
- Offshore Brazil.
- Offshore West Africa.
- South Africa.
- West Texas.
- Southern California.
- The Tibetan Plateau.
“The Atlas had several goals,” Studlick said, “including the primary goal of standardizing statistical data on the outcrops – items such as net to gross, bed lengths, thicknesses, texture and aspect ratios. This statistical data facilitates better reservoir descriptions, which improve geological and reservoir models in all phases of exploration, appraisal and production.”
Steffens underscored that the atlas is not only focused on the sand geometries in the outcrops but also the shale architecture, which is important for understanding baffles and barriers in deepwater reservoirs.
Another realized goal, Shew said, was the standard presentation format of outcrops via photomosaics, lithologic sections, detailed facies and architectural element descriptions.
By doing this, he said, readers will be able to compare various outcrops and subsurface reservoir examples.
“We eliminated those outcrops that are inaccessible, difficult to travel to, little studied, poorly exposed and/or lacking a large 2-D or some 3-D perspective,” he said. “We characterized 75 outcrops by basin setting, age and depositional setting as key selection parameters.”
(Having) The Write StuffMap detailing recoverable resources in BBOE with oil in green oil and gas in red.
There was nothing magical about the number of outcrops featured; in fact, the editors say they started with a wish list of about 25 key outcrops, having personally visited many of them.
As more scientists and researchers became involved in the project, word spread of the work and the number of contributions quickly grew.
Studlick jokes, “It was the power of e-mails.”
The unintended but beneficial consequence was that new outcrops that had heretofore been briefly described or unpublished were now chronicled.
“It was both gratifying and a treat to see and read the many outcrop descriptions that were offered,” Shew said.
Still, there were obstacles along the way – mainly the “shear volume of information.” The atlas is one of the largest on a single geologic topic that has been published.
The breadth of the work was something that AAPG Distinguished Educator awardee Stephan A. Graham, professor and petroleum geologist at Stanford, had long been advocating.
In the preface to the compendium, he wrote, “Outcrops have long been the tools of the trade for geologists trying to better understand the architecture, facies and evolution of deep-water depositional systems.
“Most importantly,” he continued, “outcrops serve as accessible examples of deep-water systems that can be studied at a range of scales as analogs for the buried but economically important deep-water systems that are the targets of modern hydrocarbon exploration.”
Graham, though, echoes the caveat of many scientists: “Given that many deep-water outcrop analogs are derived from foreland basins and other active margin settings, it is frequently questioned whether these analogs can be used in passive-margin subsurface settings where the petroleum industry has focused its activities throughout the past few decades,” he said.
“The value of outcrop data is not questioned, but proper analog usage will only be validated when new generation process modeling and seismic/well studies of near-seafloor-fan systems are integrated and calibrated to outcrop rock data.”
It’s All There
These new processes, Shew said, already are taking place, but he cautioned that the work of the true geologist hasn’t really changed since James Hutton, the father of modern geology, sat on a rock and suggested that the processes occurring in the present were the same processes that had operated in the past.
“We still rely on the ability of the geologist to describe and observe the relationships seen in outcrops, interpret their significance and apply them to other data such as cores, logs and seismic in the subsurface to provide answers on depositional environments and on the heterogeneities that may control reservoir fluid flow,” he said.
“The difference now is that we have numerous programs (visualization software and ‘caves,’ reservoir modeling, etc.) that allow us to create complex models and scenarios that will include more geologic variability for more complete reservoir models,” he said. “Hence the need for more statistically based reservoir data – outcrops and subsurface data. Analogs are still critical.”
Highlighted in the book are some of the new ways that are being used to acquire or analyze data, such as with GPS, LIDAR, range-finding and then, of course, modeling of the outcrop data.
“However, much of the data requires good old-fashioned leg work and descriptions on the outcrop face,” Shew added.
The data, in short, is in better shape than ever – in part because of more efficient means of transporting information between scientists and editors and vice-versa. By converting old 11- x 17-inch format photos to .pdf files, for example, Shew estimates two years of work were saved.
In addition to the hardcopy Atlas, a CD is included in the back of the book with 37 AAPG BULLETIN-style articles on the overview topics and more detailed reviews of selected outcrops.
And other than providing a comprehensive guide to “where” the world’s most significant outcrops are located, the authors agree that perhaps the most important accomplishment is, as Steffens says, “having all the data in one place.”