The Gass venting pump does not want to vent/void vanilla Petrolium gas.
I think there is a void-petroleum-gas recipe missing.

Factorio version 0.17.32
Bobs's Metals, Chemicals and Intermediates version 0.17.3

It was left out on purpose, and I have no plans to add it, but I could be persuaded to. Reason below if you're interested.

the gas venting is only designed for you to vent gasses that could be considered useless... these are mainly ones added from my own mods, such as Nitrogen, Oxygen, Chlorine and Hydrogen, all of which are produced in at least combinations of 2, and can't be transformed into something else. (Well, you can burn Hydrogen or make solid fuel out of it, but the others can't be used in such a way). Sulfur Dioxide is also on the list because it's a byproduct that can be awkward (you need to research how to turn it into sulfur or sulfuric acid in another research than what produces it).
Petroleum gas itself is a fuel(can be burned in oil burning entities, like oil boilers), and typically when you have it, already have the option to turn it into fuel blocks. You can also turn it into Hydrogen.

I can see that it can be considered a shame to waste potential fuel by venting petrolium gass.
However i feel that it is inconsistent becaues we can already vent Hydrogen and that can be made into solid fuel.

The problem, for me, comes when trying to balance out production.
Several things that we need in very large amounts for research packs, require some byproducts oil processing, but not the other byproducts (or not in a perfectly balanced way), so I'm often left with trying to dispose of large amounts of light oil or petrolium gas.

Take Logistics Science packs for example.
They require Express transport belts and express filter inserters, which both require cobalt steel.
Cobalt steel can afaik by default only be obtained from Copper plate+cobalt oxide, unless cobalt ore is enabled before generating the world.
Cobalt plate requires sulfuric acid, and then what do i do with all the light oil and petroleum gas i get from creating Sulfur dioxide?
Right now I have to convert 5 petroleum gas into 250 Hydrogen (2.5 second) and THEN vent the Hydrogen. And that is a slow process that requires a lot of room, gas vents and high tier chemical plants.

I was unaware that it was possible to burn petroleum gas in oil burners. How can we see that in-game? Perhaps rename the "Oil burning boiler" to "Oil and gas burning boiler"?
Can Oil burners burn light and heavy oil as well? and what about Hydrogen?
Burning hydrogen should be a pollution free process, so that would be an alternative to nuclear?

I'm soon switching all my power generation over to nuclear because it generates 0 pollution, so then i can't even burn petroleum gas.

Could it be an idea to add a way to turn petroleum gas in to light oil and light oil into heavy oil?
I mean, its already possible to convert from heavy to light to gas just by adding water. Perhaps we can convert the other way by means of evaporation?

As it stands in the game right now, all fluids with a fuel value can be burned as fuel in an "Oil" burning generator. the game will tell you if the fluid has a fuel value when you point to a pipe or storage tank containing the fluid.

what the game doesn't tell you is how much pollution each fuel will generate. Some like petroleum gas don't produce much, others like crude oil create LOTS of pollution.