Seawater gives new life to oil wells in Gulf

TAHITI PLATFORM, Gulf of Mexico – Deep-water drillers are pushing the boundaries of modern technology to help revive the Gulf of Mexico as one of the world’s most prolific oil producers.

In offshore frontiers hit by the 2010 oil spill and drilling moratorium, pioneers are adapting water injection, an old technique for boosting oil recovery, to challenging new environments in the deepest drilling regions of the Gulf. By flushing massive loads of high-pressure water through miles of ocean and earth, they’re stimulating the deepest reservoirs and bringing up more oil.

The technique has been used for decades on land to enhance oil recovery. But applied far at sea, it can be an especially pricey and complex venture. As technology advances, oil companies are applying injection to their the most expensive offshore projects, making deep-water fields more economic by sweeping crude out of reservoirs’ hardest-to-reach crevasses.

“It’s one of the most important things we do in terms of improving oil recovery and extending the life of these wells, in some cases by a decade or more,” said Mukul Sharma, a University of Texas at Austin professor of petroleum and geosystems engineering.

Chevron’s Tahiti project, 190 miles south of New Orleans, took water injection to a new level this year. The company is flooding a reservoir 28,000 feet below the water’s surface – nearly as deep as Mount Everest is tall.

Water injection is part of a $2.3 billion expansion that nearly doubled Tahiti’s price tag. But Chevron says the investment is worth it. Reservoirs naturally lose pressure as oil and natural gas are extracted, causing the fluids to flow more slowly out of wells. Shooting millions of gallons of water underground helps stem the pressure decline and keeps wells producing at a higher rate longer. Chevron expects its water injection operation will extend Tahiti’s life by about 10 years.

‘Pumps didn’t exist’

Tahiti produced its first barrel of crude in May 2009 and gushed 125,000 barrels a day at its peak. Today, it’s producing about 83,500 barrels a day.

Project manager Kevin Ricketts said the reservoir’s pressure declined by 5,000 pounds per square inch within the first two years of production, to 15,000 psi.

“We knew there was a pretty good probability that we were going to need to eventually install water injection at this facility,” Ricketts said. “We didn’t think we needed it right away. And at a reservoir pressure of 20,000 psi, the pumps didn’t exist in the world to inject from day one.”

Water is treated

It took 10 months to assemble on land the 1,250-ton maze of steel tanks and pipes that make up Tahiti’s water injection system. The module was carried by barge and crane-lifted onto the Tahiti platform. It took another four months to get the system hooked up and running. Injection began in February.

Tahiti’s two injection pumps can flush more than 4 million gallons of water into the reservoir each day. The fluid flows through7.5-inch hoses at a record-setting pressure of 8,500 pounds per square inch, about 60 times the power of a fire hose.

While some injection systems reuse the water that’s mixed with the crude, Chevron believed its production wells wouldn’t deliver enough water to feed the immense injection program. So Tahiti’s system pumps seawater from the Gulf.

The seawater goes through a rigorous treatment process to remove bacteria, particles and oxygen. It’s laced with an amalgam of biocides and other chemicals to remove impurities that could corrode the well’s steel or clog the underground water flow.

From a control room aboard the Tahiti platform, workers manipulate equipment more than 20,000 feet below the sea floor to direct the water’s flow through the reservoir.

It’s the deepest use ever of what the industry calls “intelligent well completion” technology, Ricketts said.

Salt poses problems

“It was no small feat to get that equipment to function correctly,” he said. “It’s an uncertain world at that depth.”

To maximize the impact of water injection, Chevron is drilling at least two more production wells, adding to the seven already in operation. That carries a hefty price because the Tahiti reservoir lies below a challenging layer of salt that stretches 8,000 to 15,000 feet thick and is difficult to see through.

“The closer we get to the salt, we had a lot of problems drilling those wells,” Ricketts said. “Every well seems to be a unique experience.”

Other major operators, including Shell and BP, also are investing in water injection technology to extend the productivity of their deep-water Gulf of Mexico projects.

“Because it costs a lot of money, it makes sense to do this where you have really large fields, some of the biggest fields in the Gulf of Mexico,” said Norm Pokutylowicz, a deep-water analyst for research and consulting firm Wood Mackenzie. “You have to make sure it will have an effect. If you improve your recovery, will it pay for the cost?”

More federal permits

Water injection in deep sea environments comes with other challenges as well, including engineering production platforms with the size and heft to handle the equipment.

Even with the ability to get the water underground, geologists and reservoir engineers have the added task of mapping how the water will flow and affect the reservoir.

Chevron received the federal permit for its first Tahiti water injection well in September 2010, during the five-month federal moratorium on deep-water drilling in the Gulf that followed the oil spill at BP’s Macondo well.

The moratorium was lifted a month later and activity in the Gulf has ramped up quickly.

So far this year, federal regulators have approved 90 new deep-water wells in the Gulf of Mexico at depths of 1,000 feet or greater, according to an online database managed by the U.S. Bureau of Safety and Environmental Enforcement. Just 22 had been approved by this point in 2011.

The Gulf of Mexico produces about 1.3 million barrels of oil a day, or about 20 percent of nation’s total crude production, according to federal data.

“You have a lot of work on these larger fields. And in a few years, you’ll have a new batch that will really help production,” said Pokutylowicz. “It’s one of the world’s top regions.”

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