As state-owned companies, CNPC and CNOOC and the rest are not obliged to sell their oil at market prices to the highest bidder, or even to make long-term contracts with the highest bidder.  

Nevertheless, the economic costs of not responding to the market will be high, as Indonesia is finding.  China will not be able to subsidize domestic oil prices indefinetly, especially since Chinese demand is such a key driver of higher oil prices.  There may be a lag, but it's not long, as we just saw with their decision to reduce purchases for their SPR.  China can't go on ignoring the effects of higher prices and rising demand.

Even if China obtained enough oil reservers to satisy their domestic market today, they cannoe insulate themselves from rising prices.  They would face rising costs for development, extraction, and transportation as the necessary services were bid up in price by the rest of the oil industry when prices rise again.  And, of course, their domestic demand is rapidly growing, requiring a continuing effort to secure new reservers - so they would face the same market pressures anyway because those future reserve purchhses would reflect rising prices, and if they cannot cover their costs because they are subsidizing domestic oil, then they will not be able to afford the additional future reserve purchases.

Remember: if something can't go on, it won't.