It’s an old joke, but it bears retelling.
A bank robber was once asked, “Why do you rob banks?”
His answer:
“Because that’s where the money is.”
Charles Sternbach reminds us that this brings explorers to the Gulf of Mexico, generally, and the giant and super giant fields of the Gulf, specifically.
“It’s where the global resources are,” he said.
And just like banks, these fields in the Gulf have stories to tell.
“They contribute greatly to our understanding and technology that empowers the entire ecosystems of oil and gas fields,” Sternbach said.
The first lesson, however, is how important they are to us.
“When you look at the 79 giant oil and gas fields of the Gulf of Mexico that are greater than 500 million barrels equivalent,” he explained, “they account for more than 51 percent of the conventional reservoirs of the entire Gulf of Mexico – onshore, offshore, U.S. and Mexico.”
“Eight of them are greater than 2 billion barrels – these are called the ‘super giants,’” he added.
Sternbach and his colleague Richard S. Bishop, both AAPG past presidents, believe there are lessons to learn from the Gulf Coast, a marginal sea that’s bordered by five states of the United States and five of Mexico, that will not only help explorationists there but in other parts of the world. To that end the giant fields of the Gulf of Mexico was the topic of a series of presentations they recently made at the GeoGulf23 conference (see related article this issue for more information about the event itself).
According to the Energy Information Administration, the Gulf of Mexico area is one of the country’s most important regions for energy resources and infrastructure. Offshore oil production accounts for 15 percent of total U.S. crude oil production, and federal offshore natural gas production in the Gulf accounts for 5 percent of total U.S. dry production. More than 47 percent of the total U.S. petroleum refining capacity is located along the Gulf Coast, and 51 percent of total U.S. natural gas processing plant capacity.
Considering all that, Sternbach believes the Gulf of Mexico is a great proving ground. The Gulf has produced approximately 145 million barrels of oil equivalent (57-percent oil) of the estimated ultimate recovery of 209 billion barrels of oil equivalent.
“We want to elevate our thinking and look at the Gulf Coast geology and be creative. We must look at the habitat of giants – the commonalities, differences and limiting factors. And then, to dream a little bit,” he said.
Learning from GoM Giant Fields
There is no better way to start doing that than by looking at giant fields as analogs for insights, he explained, because giant fields “have a huge impact, not only on our industry but also on our prosperity and our way of life.”
That didn’t happen by accident.
“You see how technology has been important in their discovery,” he said.
Under favorable economic and accessibility conditions, technology that discovers giant fields flourish.
He said, in researching the 79 giant fields in the Gulf of Mexico for the keynote address he and Bishop presented at the recent GeoGulf23 in Houston in April, “Trap and seal limit the giants, making seismic imaging and integrating geology and geophysics critical.”
And lessons from the Gulf of Mexico don’t just stay in the Gulf of Mexico.
“There has been a resurgence worldwide in understanding both the giants and the super giants. More stratigraphic and combination traps have been found, making up 50 percent of new discoveries,” he said.
These discoveries are noteworthy because stratigraphic trap discoveries have only been around 10-15 percent historically.
In looking at the fields, both he and Bishop determined that the “giants” are 75-percent oil and gas. Few of them are gas alone.
Similarly, “super giants” are some combination of oil or oil and gas, but none just gas alone.
“This suggests a lot of natural gas seepage through the seals and traps over geologic time,” said Sternbach.
Preferential trapping of liquids is consistent with work in Borneo that shows that tall columns can’t support big gas accumulations because the buoyancy pressure exceeds the natural seals. This selective sealing is why giant and super giant fields in the Gulf of Mexico preferentially leak gas and preserve oil and natural gas liquids.
“And as we look at what we call detached structural styles, which are growth faults and salt-associated structures, the giant fields associated with this type of trap average a little more than 650 million barrels, and they seem to limit at about 1.4 billion barrels,” explained Sternbach.
This is consistent when we look at global analogs in Africa, like Nigeria and Angola, or the Campos offshore in Brazil.
The eight super giants fields are a rare breed. These fields all have Cretaceous reservoirs rimming the Gulf of Mexico Basin, Tampico and Campeche. These greatest exploration prizes are associated with basement highs, a late structural sag, an excellent widespread topseal and proximity to source rocks.
Considering that all Gulf of Mexico super giants are Cretaceous reservoirs and that many exciting new global discoveries are being made in the Cretaceous with improved seismic imaging, Sternbach believes there might still be few surprises in the Gulf of Mexico.
“Wouldn’t that be interesting?” he said.
For more information about this topic, see the 2023 GCAGS Transactions and upcoming papers by Sternbach and Bishop: “Gulf Coast giant and super-giant fields (onshore and offshore): Analogs to help us find more,” in GeoGulf Transactions, v. 72, p. 207–213.