Gulf of Mexico's Deepwater Oil Industry Is Built on Pillars of Salt  

The NYT has an article on deepwater offshore oil, hidden under salt layers - Gulf of Mexico's Deepwater Oil Industry Is Built on Pillars of Salt.

Not so long ago -- at least, in geological time -- many in the oil game thought the Gulf of Mexico was tapped out.

Financiers called it "the Dead Sea." Nearly a century of production had run its course. Well after deeper well turned up dry, many drilling into thick layers of salt. And where there was salt, most believed, all hope of oil was lost.

Then, 25 years ago, it all began to change.

Exploration geologists discovered that, rather than signaling oil's end, underground salt -- leftovers of repeatedly evaporated seas -- could lead to a horde of new discoveries. And soon, the finds came, with names like Mahogany, Mickey and Tahiti, and the oil majors followed. The salt was obscuring oil, trapping oil or, through its inherently slippery nature, shifting and reordering the Gulf's sedimentary murk.

To understand nearly any deepwater oil find in the Gulf, including BP PLC's runaway Macondo well, requires understanding the salt that provides much of the region's deepest bedrock, geologists say. And, unlike the dull sand and dirt on top of it, carried by various ancestors of the Mississippi River, salt has proven a tricky foundation.

"Do you know the old Bible reference, don't build your house on sand?" said William Galloway, a geologist at the University of Texas at Austin. "Well, building your house on salt goes beyond anything in the biblical expression."

Gulf geology is not only about salt, of course, but scientists' improved take on the rock is one of the best examples of how, for 50 years, the Gulf has served as one of the world's foremost geology labs. Backed by society's endless thirst for oil, geologists have guided drillers to ever deeper and riskier oil reservoirs. But they have also put that money to work, filling in the empty sketch held by most of the vast underground world beneath the ocean floor.

Armed with improved, sonar-like imaging that has begun to reliably sound through salt's uncertain geometries, geologists are discovering oil reserves beneath even foundational salt sheets. (Large recent discoveries off Brazil offer prominent examples.) Not only have these sheets hidden oil, but they have also whisked away the earth's heat, allowing the crude to linger in formations once thought unsuitable.

The global push for salt-hidden oil is only gaining steam, geologists say.

"Salt over the decades has been a difficult rock to seismically image," said Clint Moore, a vice president at ION Geophysical Corp, a seismic technology company. "And we now seem to have solved that problem. And that opens up all kinds of abilities to see the geology of the earth more clearly."

Moore, while at Anadarko Petroleum Corp., was one of the earliest geologists to probe beneath the Gulf's salt, helping discover the Mahogany oil reservoir, the region's first producing subsalt field, after burrowing through 3,825 feet of salt in the early 1990s. The productivity of these salt-based fields could prompt a re-evaluation of peak oil's arrival, he said.

"If the volumes are there, this will be a significant addition to the world's resources," he said.

Of course, there are complications. Deeper wells sit at higher pressures, increasing the risk of blowout. The deepest exploration well, drilled by the ill-fated Deepwater Horizon, is 35,000 feet down, several times the depth of BP's Macondo well. And further oil production will only add to the greenhouse gases humans pour into the atmosphere each year, slowly increasing global temperatures.