They will never need oil. Any hydrocarbons can be synthesized entirely artificially, or in bioreactors.

You have water, and you have carbon, because you can grow plants. They may use plants to generate oxygen because it's convenient, and they get food as a byproduct, but they don't have to--if you just wanted oxygen, it would be more energy-efficient to produce oxygen directly by electrolysis, so as not to waste energy on all the other stuff that plants do to keep themselves alive. Similarly, you can get carbon and hydrogen as byproducts of water or CO2 electrolysis.

Most likely, however, you don't even need to go that far. If life never evolved, so there's no atmospheric oxygen, there is almost certainly atmospheric methane. That can be extracted from the air and dehydrogenated. If there somehow isn't atmospheric methane, you can just use agricultural waste; dump manure into and inedible plant waste into a bacterial digester with bacteria artificially selected to maximize methane and oil production, and you'll be set. You don't need and can't use petroleum for energy (since there's no atmospheric oxygen to burn it with), so all you need to replace is chemical feedstocks, and that takes a far lower volume of material, which your colony should have no trouble synthesizing indefinitely if they don't start out dependent on large quantities of oil and thus don't need to transition away from it.

They will never need oil.

Any hydrocarbons can be synthesized entirely artificially, or in bioreactors.

You have water, and you have carbon, because you can grow plants. They may use plants to generate oxygen because it's convenient, and they get food as a byproduct, but they don't have to--if you just wanted oxygen, it would be more energy-efficient to produce oxygen directly by electrolysis, so as not to waste energy on all the other stuff that plants do to keep themselves alive. Similarly, you can get carbon and hydrogen as byproducts of water or CO2 electrolysis.

Most likely, however, you don't even need to go that far. If life never evolved, so there's no atmospheric oxygen, there is almost certainly atmospheric methane. That can be extracted from the air and dehydrogenated. If there somehow isn't atmospheric methane, you can just use agricultural waste; dump manure into and inedible plant waste into a bacterial digester with bacteria artificially selected to maximize methane and oil production, and you'll be set. You don't need and can't use petroleum for energy (since there's no atmospheric oxygen to burn it with), so all you need to replace is chemical feedstocks, and that takes a far lower volume of material, which your colony should have no trouble synthesizing indefinitely if they don't start out dependent on large quantities of oil and thus don't need to transition away from it.