Analog traps are an important part of any geoscientist’s tool kit, and there is no better source than understanding how giant fields form and have been found by past and current generations of explorers.
My sojourn into learning about these big fields was in the mid-1980s at Amoco in Denver, part of a task force charged with understanding how to better explore for big, subtle, stratigraphic and combination traps.
Meeting weekly for lunch for several months, a team of us reviewed Amoco’s proprietary “Red Book” – a collection of summaries of giant fields (more than 500 MMBOE) worldwide, which included maps and rock properties, but, more importantly, the strategy used in finding each field. In addition, we pulled heavily from AAPG giant fields publications compiled from hundreds of AAPG volunteers, starting in 1970. Surprisingly, we discovered that it took an average of 11 years to recognize the size of many giant strat traps. Also, their geometry had gone unrecognized, often mistaken for small structural closures that continued to have oil/water contacts or pressure data that went below geometric spill point. Many were simply accidents, but others were found with a careful look at pay behind pipe in old dry holes. Seismic played only a limited role. It became clear that 3-D seismic, workstations and access to much more digital data would potentially revolutionize our ability to see these traps and make sure they were no longer “subtle.”
Data Integration for Understanding Giant Fields
For all of us, a new pathway of data integration – with an emphasis on digital data capture and thinking more quantitatively about migration, charge, free water levels, oil and gas show interpretation married with high-quality 3-D seismic images – became a part of our new tool kit. Gone were the days of isolating geologists from geophysicists. Workspaces and information management fostered creativity. In 1994, my family moved to Egypt with the Gulf of Suez Petroleum Company and implemented many of these practices, which turned around an exploration program that had drilled 32 dry holes from 1989 to1993. We became recognized globally for our success. I’ve spent the rest of my career continuing to hone those skills and have seen successful companies, both big and small, excel with teams that do this well.
For me, it all started with the giant fields, and we were right, back in the 1980s, about the future role of 3-D seismic.
Figure 2 shows the step-change in finding stratigraphic and combination traps in the last 20 years. Halbouty had been right along, urging the industry 50 years ago to understand giants and push for ways to unlock more difficult stratigraphic and combination traps.
These traps traditionally only comprised about 10 percent of giant field volumes. By 2003, however, that number had risen to 15 percent, and by 2020, it has now reached 50 percent.
A Herculean Task
It takes enormous effort to compile and make readily available giant field data, a process that has gone on for 50 years and involved thousands of AAPG authors donating their time and experience. Halbouty worked on the volumes right until his death in 2004. Since then, Robert Merrill and Charles Sternbach have carried the torch with one volume finished and the next one on the way in time for the Denver convention this fall.
Just as importantly, the late Myron Horn captured much of the data from AAPG’s prior publications and made them available in GIS mappable format in both spreadsheet and databases starting in 2003. He then used the data from this compilation to publish several papers. Unfortunately, with his passing in 2016, the database updates ended. That same year, I was asked to give a keynote talk in Oman on strat traps and took on the task of updating the dormant database.
Beware of what you think is easy. Nearly five years later, these data are ready to go back online this fall in conjunction with the 2010-20 giant fields Memoir 125 book. Much has changed in the old database. More than 110 new fields have been added, locations for hundreds of fields corrected and updated (particularly in Russia) and more than 600 older fields updated with more current information. Surface elevation and depth below mudline have been added. More than 1,000 new references, indexed by field name, can be linked in an ArcGIS Personal Geodatabase or searched as separate excel spreadsheets with latitudinal/longitudinal information included.
Several “game changers” show up in the database, beyond the stratigraphic trap successes. The industry is going into progressively deeper water and deeper below mudline to hunt for these fields (figure 3). Drilling 7-10 kilometers below mudline raises some important questions about reservoir preservation and how oil occurs at these great depths rather than gas. In addition, more and more tilted oil/water contacts in hydrodynamically active over-pressured basins – something that mechanically should not be a surprise but has only begun to be recognized as more common than once believed. Further, huge fields have been found over oceanic and highly attenuated continental crust, breaking old industry paradigms.
More Treasures to Find
I am confident more insights and paradigm thought shifts exist in these data, buried in the learning curves that come from actually reading the references and building up that tool kit of analogs. Many companies make their living selling these data for a high price. For the rest of us, tapping into a free, accessible digital data trove like this is a great way to get started and bring those analogs to bear when looking for new fields in old areas or spotting a seismic anomaly in an undrilled basin.
The editors of the upcoming Memoir 125 encourage you to purchase the book and get ready access to this updated GIS database. Better yet, let us know what additional data can be added to it, and any modifications or new references might be added. Doing a “deep dive” into these data is well worth the effort. It would be good to keep this database current annually.
Editor’s note: All of the publications referenced here are in the Memoir 125 bibliography, and a complete bibliography present in the database.