If yuan becomes a reserve currency, can we expect the petrodollars to be swapped with petroyuans given china's ever increasing mammoth demand for energy resources?
Yuan will certainly appear in the reserves of oil exporting countries. The question is how much of it?
China still has many problems with its currency and a long way to go until it becomes as appealing as dollar or even Japanese yen. Whether countries include a currency in their reserve basket ultimately depends on how predictable and stable it is compare to other currencies. It is also preferred that the currency appreciates in the long term. Living in China myself and holding my savings in yuan, I try to keep an eye on factors and risks that may move it up or down in medium to long term. Here are the most important in my opinion:
China is still a huge and rapidly growing economy, expanding at least 4% a year (~7% being the official figure). As long as it produces so much goods and services that can be bought with its national currency, yuan will be appealing to investors.
China's population is growing and with recent cancellation of a one-child policy, it will continue to grow even faster. Growing population generally leads to economic expansion.
There are still market reforms to be made that, if implemented, will make the currency even more appealing. For example allowing banks to set lending and deposit rates freely would send yuan sky high.
China's state owned enterprises (SOEs) have trillions of dollar-denominated debt on their balance sheets. If yuan were to depreciate considerably, they would go bust being unable to service debt. It limits the freedom of Chinese government to devalue yuan.
China still has a lot of work to do before yuan becomes a full-fledged reserve currency. It is still not freely convertible, there are capital controls in place for Chinese citizens, the People's Bank of China (China's central bank) is not independent of China's government, etc.
China's economy is slowing and the reforms that are being done are not enough. To reach growth targets and maintain social stability, the Chinese government may continue the policy of devaluing yuan to boost exports. Chinese corporate sector is certainly betting on it: http://www.marketwatch.com/story/chinese-companies-are-betting-on-further-yuan-weakness-2015-11-18
China packs a lot of political risk. It is not a democratic state with thick censorship of every media outlet. If it starts the process of democratization, it may become politically unstable with disastrous consequences to the economy and its currency. If it continues the path of one-party rule with a tight grip on the economy, it may lead to prolonged stagnation and slow devaluation of yuan.