Oil supply is effectively infinite. By that I mean there is so much available that we will have destroyed the planet before we remove it all. We extract as much as there is a demand for. If you lower the demand then you lower the amount being extracted
Shell’s new US-based plant [1] is expected to pump half a million cars worth of CO2 exhaust into the air a year. I haven’t seen any data suggesting that plastics production reduces the net amount of CO2 in the atmosphere.