With all the talk about new oil discoveries around the world and new techniques for extracting oil in such places as North Dakota and Texas, it would be easy to miss the main action in the oil supply story: Aging giant fields produce more than half of global oil supply and are already declining as group. Research suggests that their annual production decline rates are likely to accelerate.

The most recent research on giant oil fields has been available since 2009 so it doesn’t attract media attention the way new discoveries hyped by oil company public relations departments do. And yet, that research is far more important to understanding our oil future.

Here’s what the authors of “Giant oil field decline rates and their influence on world oil production” concluded:

The world’s 507 giant oil fields comprise a little over one percent of all oil fields, but produce 60 percent of current world supply (2005). (A giant field is defined as having more than 500 million barrels of ultimately recoverable resources of conventional crude. Heavy oil deposits are not included in the study.) “[A] majority of the largest giant fields are over 50 years old, and fewer and fewer new giants have been discovered since the decade of the 1960s.” The top 10 fields with their location and the year production began are: Ghawar (Saudi Arabia) 1951, Burgan (Kuwait) 1945, Safaniya (Saudi Arabia) 1957, Rumaila (Iraq) 1955, Bolivar Coastal (Venezuela) 1917, Samotlor (Russia) 1964, Kirkuk (Iraq) 1934, Berri (Saudi Arabia) 1964, Manifa (Saudi Arabia) 1964, and Shaybah (Saudi Arabia) 1998 (discovered 1968). (This list was taken from Fredrik Robelius’s “Giant Oil Fields -The Highway to Oil.”) The 2009 study focused on 331 giant oil fields from a database previously created for the groundbreaking work of Robelius mentioned above. Of those, 261 or 79 percent are considered past their peak and in decline. The average annual production decline for those 261 fields has been 6.5 percent. That means, of course, that the number of barrels coming from these fields on average is 6.5 percent less EACH YEAR. Now, here’s the key insight from the study. An evaluation of giant fields by date of peak shows that new technologies applied to those fields has kept their production higher for longer only to lead to more rapid declines later. As the world’s giant fields continue to age and more start to decline, we can therefore expect the annual decline in their rate of production to worsen. Land-based and offshore giants that went into decline in the last decade showed annual production declines on average above 10 percent. What this means is that it will become progressively more difficult for new discoveries to replace declining production from existing giants. And, though I may sound like a broken record, it is important to remind readers that the world remains on a bumpy production plateau for crude oil including lease condensate (which is the definition of oil), a plateau which began in 2005.

One the clearest cases of the study’s key finding is Mexico’s Cantarell oil field, the second most productive in the world, until a steep decline began in 2004. Production from Cantarell stalled in the early 1990s leading Petroleos Mexicanos (PEMEX), the Mexican national oil company, to begin an aggressive drilling campaign and to build what at the time was the largest nitrogen extraction plant in the world. Once completed, the plant captured nitrogen from the air and injected it into the Cantarell field in order to counter falling pressure.

The result was a dramatic rise in production from about 1 million barrels per day (mbpd) in 1995 to above 2 mbpd in 2003, just two years after the nitrogen injection began. But, by the end of 2005 it was evident that Cantarell was in decline. What followed was a breathtaking slide from 2.136 mbpd in 2004 to just 394,000 barrels per day as of March this year. That’s a total decline of 81 percent in just over eight years.

PEMEX has stabilized total Mexican oil output from all fields at about 2.5 mbpd—it was 3.4 mbpd at Cantarell’s peak—by successfully increasing production from its Ku-Maloob-Zap offshore field. But once again the company is using nitrogen injection to achieve the increase just as it did at Cantarell. And so, PEMEX may be on course to repeat at Ku-Maloob-Zap the rapid decline previously experienced at Cantarell.

Four years on from the 2009 study it is possible that the percentage of world oil production from the giants has slipped as just enough production from new smaller fields has been added to keep global production flat. But if, as the study suggests, the decline rate for giant fields accelerates, the record-breaking expenditures and herculean technical efforts now being undertaken by the oil industry just to keep production flat may be overwhelmed.

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Perched on a production plateau, either we are approaching ever closer to a decline in worldwide production of crude oil proper or new developments—that is, ones not yet in evidence—will boost the global rate of production definitively above the current plateau. The weight of the evidence, however, suggests an unfavorable outcome in the decade ahead.

UPDATED 4/9/13: After mysteriously disappearing, the missing PEMEX production report which included the latest production rate from the Cantarell oil field has returned to the company's website. I've now provided a link above.