I recently started a new game with rainbow ores enabled with all other resources removed (besides the trees for power poles), and I noticed on the tech tree that in order to "mine" crude oil from rainbow ore you need a chemical plant, but unfortunately that tech is locked behind the milestone of actually mining crude oil. Would it be possible to change the recipe so that it can either be made in a mk2 assembler by adding a barrel to the recipe to make a barrel of crude oil as opposed to piping it out (as both techs are already available before oil processing), or give the player a free chemical plant so that they can complete the required milestone of mining oil?

Good catch, have just released an update that should fix this.

Chem plant is unlocked along with the conversion recipes when mining the ore for the first time, and you can get the rest of the oil machines like normal when you craft your first oil. Same goes for Uranium.