Mexico tries to save fading Cantarell oil field

Apr 05, 2007 02:00 AM

In March 1971, a Mexican fisherman named Rudesindo Cantarell took a few geologists from state-run oil company Petroleos Mexicanos to this spot, where he had seen oil slicks. Mr Cantarell didn't know it, but he had stumbled across one of the largest offshore oil fields ever found.
A few decades and 12 bn barrels of oil later, the field that bears Mr Cantarell's name is dying, and Pemex, as the state-owned company is known, is struggling to stave off the field's demise. From January 2006 though February 2007, Cantarell lost a staggering one-fifth of its production, with daily output falling to 1.6 mm barrels from 2 mm.

The oil industry was stunned. Cantarell, which currently produces one of every 50 barrels of oil on the world market, is fading so fast analysts believe Mexico may become an oil importer in eight years. That would batter Mexico's economy, which depends on oil exports to fund 40 % of its government spending.
The continued deterioration of the world's second-biggest field by output would also put pressure on prices on the global oil market, where supplies are barely keeping up with growing demand as it is. And it would leave the US even more dependent on Middle Eastern supplies -- and that much more vulnerable to political tumult in that region.

The demise of Cantarell highlights a global issue: Nearly a quarter of the world's daily oil output of 85 mm barrels is pumped from the biggest 20 fields, according to estimates from Wood Mackenzie, a Scotland-based oil consulting firm. And many of those fields, discovered decades ago, could soon follow in Cantarell's footsteps.
It's widely believed that the world's biggest oil fields have already been found. In the decades leading up to the 1970s, the world discovered eight big fields that produced between 500,000 to one mm bpd, according to Matthew Simmons, a veteran oil industry banker. During the 1970s and 1980s, only two were found. Since then, only one -- the Kashagan field in Kazakhstan -- has the potential to easily top the500,000 barrel-a-day mark.

Two decades ago, about a dozen fields produced more than a million bpd. Now there are only four, one of which is Cantarell. The future of two others, discovered more than 50 years ago, remains in question. Some analysts speculate Saudi Arabia's Ghawar, the biggest field by far, could begin a gradual decline within a decade or so. Another, Kuwait's Burgan, is showing signs of maturity. In November of 2005, Kuwait Oil Co. lowered its estimate of the field's sustainable production level to 1.7 mm bpd from 1.9 mm a day.
Replacing big gushers is difficult. Industrialized countries, which tapped out their big fields years earlier, haven't been able to maintain output despite finding large numbers of smaller fields and investing heavily in technology. Alaska production, hurt by declines at the giant Prudhoe Bay field, dropped from 2 mm bpd in 1988 to a current rate of about 900,000 a day.

"The world faces a situation where we have production from smaller and smaller fields tryingto keep up with declines from the big fields like Cantarell," says Mike Rodgers, a partner at industry consulting firm PFC Energy in Houston. "You're on a treadmill trying to keep up, and you get to a point where you can't make any more forward progress."
Some industry veterans are more sanguine. They argue that technology and high prices are helping tap vast sources of so-called "unconventional" crude oil, such as Canada's tar sands. Plus, they say technologies will also delay any decline in big fields by dislodging billions of barrels of additional oil that used to be too costly or difficult to reach. In Texas and California, fields discovered in the late 19th century are still productive.
"The world has managed depending on giant oil fields for the last several decades," says Khalid Al-Roldan, a visiting fellow at the Centre for Strategic and International Studies, based in Washington, DC.

But even if there is enough oil under the ground, the politics above the ground get in the way. The vast majority of the world's remaining big fields are in developing countries and run by government-owned oil companies, which are often less efficient than their investor-owned counterparts.
State-owned companies in many countries, like those in Venezuela and Iran, are milked by their government for taxes, which reduces their ability to invest in new oil technology. Legal restrictions make it hard for national oil companies to work with foreign firms, cutting them off from techniques used in the rest of the industry.

Mexico's Pemex suffers many of these limitations. Its last two chief executives failed to persuade Mexico's Congress to remove foreign investment restrictions, which are embedded in Mexico's constitution and viewed as an embodiment of Mexican nationalism. Mexico's new president, Felipe Calderon, is expected to try to end the investment restrictions, but he too faces long odds.
Cantarell, like all giant oil fields, boasts an unusual geological history. Geologists say it may have been formedthanks to the asteroid that slammed into the Yucatan peninsula some 65 mm years ago -- the same event that is believed to have led to the extinction of the dinosaurs. The impact caused giant cracks underground that allowed oil from previous millennia to accumulate in a single spot.

The field lay unnoticed until Mr Cantarell, the fisherman, kept getting his nets smeared with oil as he trawled for shrimp in the 1960s. Assuming that the oil came from Pemex operations, he regularly hauled his oil-stained nets hundreds of miles to the nearest Pemex offices in neighbouring Veracruz state to seek compensation. Finally, local Pemex officials say, the oil giant grew so exasperated with Mr Cantarell that it went to check out his story.
The find was spectacular. Unlike most oil fields, which have a thin band of oil-rich rock that stretches for miles in every direction, Cantarell is shaped like a massive underground volcano, with huge amounts of oil in a relatively small place. While Saudi Arabia's Ghawar takes upabout 2,700 sq miles, Cantarell is just 70 sq miles. From one platform, one can see the entire field.

Cantarell's formation made the field easy to exploit. It had so much initial pressure that Pemex's first well at the field produced 36,000 barrels of oil a day, compared with a few hundred barrels at most wells. The field is also in relatively shallow waters -- it is 50 yards deep. The water is so calm one can spot barracuda swimming between the platforms and there is no need for expensive deep-sea platforms.
Today, Cantarell needs just 208 wells to produce the equivalent of one-fourth the entire US's oil output, while the US needs hundreds of thousands of wells for a similar haul.

But the field's abundance also bred a sense of complacency. As is the case in many oil-rich countries, Mexico relied on oil to foot its current spending but gave little thought to what happens when the oil runs out. Last year, Cantarell was responsible for some $ 25 bn of the $ 53 bn that Pemex handed over to the government. The steep tax bill has left Pemex chronically short of cash to invest in finding new fields to replace its aging giant.
Cantarell produced about 1 mm bpd from 1980 to the mid-1990s, when the field began to slowly lose pressure. This happens to all fields: They begin with enormous natural pressure because they are buried deeply beneath layers of heavy rock. But from the moment a well pricks a field and the oil is taken out, the pressure eases, like letting air out of a balloon.

So in 1998, Pemex began injecting massive amounts of nitrogen into the field, which was the oil-field equivalent of squeezing a balloon from the bottom. Output more than doubled to a peak of 2.3 mm bpd in 2004. That decision was hailed as a technical success, but it was just a temporary fix: It only sucked the field dry faster and set the stage for a steeper decline.
Now, Pemex's lack of money and technology is a handicap in managing the decline. The company didn't have any machinery on its Cantarell platforms to separate water from oil -- standard equipment for most of the rest of the industry. So when water from an underground aquifer began to creep into wells, a common occurrence in an older field, Pemex had to shut down the wells.

The company closed any well where the water content rose to between 3 % and 5 % of the oil. By contrast, there are wells in Texas that are able to produce with 99 % water.
"The water problem took us by surprise, but we are handling it," says Gustavo Hernandez, Pemex's head of planning at the field. Standing atop an oil platform in the Gulf, Mr Hernandez says the company has overhauled platforms to handle water content of between 8 % and 9 % and is installing an additional water separation plant this year, allowing it to reopen more wells.

Last year, Pemex drilled its first horizontal wells at the field, something investor-owned oil companies have been using since the early 1980s. Horizontal wells bore down into a field like a traditional vertical well, but then spread out horizontally, extending for miles and allowing a single platform to suck up oil from a much larger area. Pemex plans to drill more such wells this year.
Pemex says steps like these, part of $ 2.4 bn in investment in the field this year, will slow the field's decline by about half of last year's pace. Instead of a decrease of 400,000 bpd, Pemex hopes Cantarell will lose some 200,000 barrels of daily output by year's end. After that, the company says Cantarell will probably continue to decline by roughly 10 % a year, down to a daily average of 600,000 in 2013.

Pemex hopes to largely offset Cantarell's decline in the next three years by doing the same kind of nitrogen injection at its second-biggest producer, Ku-Maloob-Zaap, a collection of three fields within eyeshot of Cantarell's platform. (Its Mayan names translate to "nest," "good," and "charcoal.") But Ku-Maloob-Zaap, which is also ranked in the world's top 20 fields, will start its own decline in 2011, according to Pemex.
That leaves Chicontepec, a massive onshore field in eastern Mexico that was discovered in the 1920s, but hasn't been fully developed because it is broken up into tiny pockets of oil that spread out over thousands of square miles in rocky terrain. Pemex says it will need more than 15,000 wells to fully tap the field -- a big stretch for a company that has drilled about 23,000 wells since it was formed in 1938. Developing Chicontepec is also difficult politically; there are scores of nearby towns that may take a dim view of oil production in their backyard.

For now, Pemex is doing what it can to keep Cantarell going as long as possible. A narrowing band of oil means that wells that are drilled at lesser depths have started to hit gas, which is less valuable than oil. Wells that are too deep hit greater amounts of water, which must be extracted from the oil before sale.
"It's a constant game of adjustment," says Mr Hernandez, the field's top planner. In most cases, Pemex tries to replace the production by re-drillingthe same well either higher or lower. Still, Mr Hernandez expects to lose 30 wells this year.

Benjamin Melo, manager of the Akal C platform, tries to assess the future by looking out across the field: "This has been a generous field. And there is still a lot of oil down there.”
“But it won't last forever."

Source: Dow Jones & Company, Inc.
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