The expansion blueprints of Chinese oil companies overseas are currently facing "unprecedented challenges", which means that the State-owned enterprise giants should prepare for the unexpected, according to a former executive of China National Petroleum Corp.

Both geopolitical and economic risks have surged recently, a situation China has not encountered in recent decades, and have slowed the oil companies' pace of expansion overseas, said Chen Geng, a deputy of the National People's Congress (NPC) and the former general manager of CNPC.

"It is now a good time to launch mergers and acquisitions overseas, because the rising oil price is lifting the market value of public companies, adding to costs and potential risks," said Chen.

In 2011, the total mergers and acquisition value of China's three biggest oil companies CNPC, China Petrochemical Corp and China National Offshore Oil Corp, reached about $20 billion, the second highest level in the country's history, following on from 2010, according to a report from CNPC's Economics and Technology Research Institute.

The overseas journey of China's oil companies started in 1993. Those 18 years of overseas experience has played an important role in establishing the energy security system, said Chen.

"It will be much more difficult for the oil giants to take the traditional investment model purchasing oil concessions in the coming years," said Chen.

Wu Mouyuan, a researcher with the CNPC Economics and Technology Research Institute, predicted that China's total overseas equity-based oil and gas production volume may increase by 5 to 10 percent this year.

Last year, the offshore equity-based oil output of Chinese companies was 90 million tons, 20 million tons more than in 2010, said Wu. "Globally, 11 percent of oil production came from Chinese producers in 2011."

"We should not only see the potential for rapid growth, but should also be aware of the potential risks," said Chen.

Currently, some oil construction and production projects have ceased in Sudan, CNPC's biggest overseas destination for oil exploration, and there is no sign of them restarting because of political issues.