If it's going to shift the demand curve, then it's going to shift it out: anticipation of higher supplies in the future will discourage fuel-saving investments (i.e. higher mileage vehicles, housing closer to work, etc). That would put positive pressure on prices.
I think you are referring to the supply curve, rather than the demand curve. Anticipation that more supply is coming in the future might shift out the supply curve today, as producers holding oil in the ground would want to sell more now while prices are still high.
Speculative demand for futures would also shift in, as an announcement of more future supply would signal lower future prices. But that wouldn't have any direct effect on spot prices.
Expectations don't have much of a supply effect. If they did react by supplying more now because they expect future prices to fall, they would just accelerate the price drop.