I think this is potentially very good news. It is not quite Tom Barnett's scenario - that would imply BP and Exxon buying up Chinese oil firms or building infrastructure to supply the Chinese markets so that they profit (or profit even more) from rising Chinese demand for oil. That is not really happening. China can finance its own oil infrastructure, thank you very much. It also would like to finance the development of the new oil fields needed to meet growing Chinese demand. But that is proving a bit difficult. China has plenty of cash, but much of the oil that is left seems to reserved for the national oil companies of the producing country. Other assets are owned by Western oil companies who got in early and who are not inclined to sell their cash cows right now.
So Chinese firms buying into western oil firms (and buying into their overseas reserves) - or just swapping assets -- is a rather constructive way for China to address its concerns about energy security. Better than cozying up to Iran. Or Richard Clark's scenario.