The Fuse

The Long Decline of the World’s Largest Oil Fields

by Nick Cunningham | August 06, 2015

Global oil output continues to steadily increase, topping 93 million barrels per day (mbd) in 2014. But where that oil comes from has changed over time.

All oil fields see their production levels deplete as they age. Shale wells infamously suffer from exponential decline, with their production rates generally collapsing within the first year of coming online.

Large conventional oil fields don’t typically see such dramatic decline rates, but age and maturity still take their toll on output. That means that new discoveries must constantly be logged in order to replace fields that are no longer in their prime.

As older fields fizzle out, they are overtaken by fresh discoveries. Here’s a quick rundown of a few formidable oil fields in their twilight years, powerhouses that are now fading into obscurity.

Brent. The iconic oil field in the North Sea is one of the world’s most famous. That is because it is the basis and namesake for the Brent oil marker, the most important benchmark for international oil prices. Oil prices may vary a bit from region to region, but nearly all markers outside of the United States base their prices on a premium or discount to Brent crude prices.

Behind the benchmark is the oil field itself, which has accounted for 10 percent of all the oil that has ever come out of the North Sea in British territory. However, the field’s days are numbered. Several platforms operating on the Brent field have already terminated production, and Royal Dutch Shell is beginning the process of decommissioning the field altogether, a task that could take a decade and cost Shell billions of dollars.

The entire North Sea is facing an uncertain future, with high costs and declining output. There could still be some life left in the region—BP just announced plans to invest $1 billion to boost production in some of its older North Sea fields. Still, there is little doubt that the entire region’s golden years are a distant memory.

Cantarell. Located in the Bay of Campeche in Southern Mexico, the massive Cantarell oil field has been the core of Mexico’s oil production since it came into operation in 1979. Falling reservoir pressure forced Mexico’s state-owned oil company Pemex to use nitrogen injection to keep output steady. The field, however, peaked at 2.1 mbd in 2004, falling to just 440,000 barrels per day in 2013. Having once accounted for two-thirds of the country’s oil production, its share has plummeted to just 17 percent.

The collapse of Mexico’s oil production over the past decade mirrors the decline of Cantarell, and that is arguably the main impetus for the government of President Enrique Pena Nieto to overhaul the country’s energy industry and open it up to private investment for the first time in over 70 years. Mexico still has a huge upside in terms of oil potential, but higher output in the future will have to come from fields other than Cantarell.

Prudhoe Bay. The oil field on Alaska’s North Slope is the largest oil field in North America, and is in the top 20 worldwide. Discovered in 1968, the Prudhoe Bay oil field originally had about 25 billion barrels in reserves, according to its current operator, BP.

After the 1973 international oil crisis in which OPEC embargoed oil sales to the United States, Prudhoe Bay became a key piece of U.S. energy security. Not only did higher oil prices make production on Alaska’s North Slope much more profitable, but major political support lined up behind the Trans-Alaskan Pipeline, an 800-mile pipeline system that was completed in 1977. That allowed oil from Prudhoe Bay to reach Valdez in southern Alaska, the northernmost ice-free port in North America. Prudhoe Bay has been one of the most important oil fields in the U.S. ever since.

But output peaked long ago. Prudhoe Bay’s oil production has declined from a high-water mark in 1987 at 1.6 mbd. In 2014, Alaska’s entire North Slope saw production dip below 500,000 barrels per day, with further declines expected. That presents significant challenges to the operator of the Trans-Alaska Pipeline. Declining oil throughput in the pipeline means slower oil flows, presenting threats of water freezing. There are fears that the pipeline will be unable to operate at some point in the future. Hopes are now pinned on higher oil production from the Chukchi Sea, where Shell is drilling this summer. But even if successful, oil from offshore Alaska is years away.

Samotlor. Russia is one of the world’s largest oil producers, along with the United States and Saudi Arabia. About two-thirds of Russia’s more than 10 mbd of production comes from West Siberia, and one of the largest oil fields in West Siberia is Samotlor, a massive field that began producing in 1969.

The field was critical to the Soviet Union’s tremendous oil ouput, hitting its peak in the 1980s at over 3 mbd. Samotlor has been suffering from a long period of decline since then, but Russia’s state-owned oil company Rosneft, through significant investment, has managed to limit the decline rate to just five percent per year, lower than the 10 to 14 percent annual decline that other West Siberian oil fields suffer. In the post-Soviet era, the field hit a peak of 635,000 barrels per day in 2006. It is still a critical piece of the puzzle for Rosneft, but its best days are far behind it.

Burgan. The Kuwaiti supergiant oil field is second only to Saudi Arabia’s mammoth Ghawar oil field in terms of the largest oil reserves in the world. The field has been in production for over 60 years, and while data is sketchy (details are considered a state secret), production probably peaked in the 1970s at 2.2 to 2.4 mbd. Still, decline has been gradual, and the EIA estimates that output probably stands near 1.1 to 1.3 mbd. Furthermore, using enhanced oil recovery techniques, Burgan even has the potential to see its production expanded to 1.7 mbd. Although Burgan is past its peak, it has a lot of life left in it, and is in a better position than some of the other oil fields on this list.

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