CNOOC's $15.1 billion friendly acquisition of Canada's Nexen last month marks not only China's largest foreign takeover to date but signs of a bolder, more sophisticated approach to its overseas expansion.

While much of the headline buzz surrounding the deal has focused on its potential political hurdles in North America, it is Nexen's diversified asset base outside Canada's oil sands that are likely to have piqued Chinese interest. It may also have increased the chance of the deal's success.

With less than a third of its production coming from Canada, one clear difference from CNOOC's failed 2005 Unocal bid or BHP Billiton's scuppered Potash takeover is the global diversity of Nexen's operating portfolio.

While Nexen has oil sands and shale gas operations in Canada, most of its production and cash flow come from outside Canada, notably from the UK North Sea and the US Gulf of Mexico. Nexen is also producing oil in Nigeria and is active in Colombia and Yemen.

But it is China's upstream entrance into UK North Sea for the first time that is of particular interest, a move that--whether by accident or design--came the same day as China's Sinopec's announced plan to take a 49% stake in Talisman's North Sea portfolio.

With the Nexen deal, CNOOC will assume control over the UK's North Sea Buzzard field, the UK's biggest oil field and one of the company's top assets.

Buzzard feeds up to 220,000 b/d into Forties, one of the four crude oil streams comprising the dated Brent benchmark, which is used to price more than half of global crude oil.

With China expected to overtake the US as the world biggest importer of oil within three years, the country's exposure to crude grades priced off Brent is significant. During the first half of 2012, China's share of crude imports priced off Brent made up around 27% of its total oil imports, or some 1.53 million b/d, according to Platts estimates.

This percentage is likely to grow as CNOOC's deals with West Africa bear fruit and the company looks further afield to secure access to foreign oil, making a place at the table of Brent crude owners more valuable.

CNOOC's equity crude from Nigeria will also grow in coming years as Total's large Usan field offshore Nigeria field ramps up. Nexen has a 20% stake in the project. Oil traders have said it is too early to know whether the purchase marks an attempt by China to become more actively involved in the pricing of the Dated Brent benchmark, although it is expected to give CNOOC critical information on North Sea oil supply.

Buzzard has missed a number of production targets since coming on stream, plagued by a number of hitches and, historically, Brent crude values have been supported during outages at the field.

Logically, China would have a vested interest in ensuring that production problems do not push up the price of Brent, especially as the liquidity of the benchmark crude shrinks with future field declines. In Canada, speculation is already rife that CNOOC is playing a long-term strategic card to secure potential future oil sands and shale gas exports across the Pacific if Canada's traditional US markets are unwilling or unable to absorb them.

CNPC, China's other top state oil company, has invested heavily in Central Asia, specifically countries like Turkmenistan and Afghanistan, in a focus on assets that can feed future oil and gas pipelines or shipments to China.

Commerzbank believes the CNOOC move on Nexen leaves scope for the NOC to benefit from the potential influence on the world's two key crude benchmarks; Brent and WTI.

After President Barack Obama's January decision to delay approval of the Keystone XL pipeline that would bring oil from Canada's oil sands to Texas refineries, prices for Canada's crudes are seen remaining depressed.

The prospect of Canada's oil sands finding a future market in China could mean Canadian oil exports would no longer be stranded in the US Midwest. If Canadian oil goes to China and not exclusively to the US, that would mean that the surplus in the Midwest would shrink, so that the discount of WTI versus Brent could decline, analysts at Commerzbank said in the last week.

Nexen also gives CNOOC a foothold in some key exploration catalysts, most notably the BP-operated North Uist deepwater exploration prospect in the UK's West of Shetlands waters, which is due to be completed soon. In the US Gulf of Mexico, Nexen has exposure to Shell's promising Appomattox find.

With or without Canada's likely blessing, the Nexen deal surely reflects China's thirst for knowledge and operational experience in developing diverse conventional, deepwater and unconventional reserves.

This acquisition of transferable expertise will only strengthen CNOOC's hand at home where massive deposits of shale oil and gas await the skills and funds needed to ignite China's own future energy revolution.