Unless it coinsides with them finding Angola's oil earlier, it wouldn't really. Outside of Guinea Bissau Portugal already was winning. To my understanding, it was the economic strain of managing such a massive war (especially relative to the wealth and population of Portugal) that brought about the collapse of military and civilian support for the conflict and the regime. Give Portugal an excess of oil wealth and the conflict is more sustainable (more money in the budget for soldier's salaries, equipment purchases, infrastructure programs in the colonies, as well as a greater importance of the colonies to Portugal, potential higher standard of living in Portugal to shore up support for the regime, ect...).
The war was being won in Angola and being placed under control in Mozambique.
More oil means more money for the war effort and some civilian development (mostly in the colonies), but that only delays the fall of the regime. The economic development would not be able to answer the desire for democracy that was growing every year on both sides of the political spectrum. However a better living standard with less inequalities would change the flavour of the fall of the regime (a revolution more visibly centrist than in OTL).
A large Portuguese Population could impact referendums when the issue of independence is inevitably brought. Depending on the way the transition to independence is done, it might be gradual, with a Commonwealth like structure, or rapid, with some assurances that tranquilize the Portuguese living there against political radicalism. A gradual transition implies a more normal revolution (without so much visibility for the far-left minority). In the case of a more moderate revolution and gradual transition of the colonies to independence, some of the smaller colonies (like Cabo Verde) might want to stay part of Portugal.
Depending on the level of radicalization between both sides of the population in the colonies, it could lead to UDI situations (most likely in Mozambique). But this would be unsustainable in the long term.