Under what logic does "Remove oil from the ground, process it into something, and then bury that something" count as actual carbon sequestration? You've not removed anything from the atmosphere in any plastic cycle I'm aware of, and you've used an awful lot of energy in the process of going from "ground" to "ground." You'd have been better off, in every possible way, just leaving that oil in the ground in the first place.
Except for the important way, which is corporate profits.
I agree but the same logic applies to "remove oil from the ground, burn it, capture the carbon from the smoke using expensive equipment, then bury the smoke" which describes all major carbon sequestration plans if I understand correctly.
I think that both forms of sequestration (sequestering gaseous CO2 (or a solid-stabilized form of it) vs sequestering plastic) are worse than not drilling the oil to begin with, but better than letting the CO2 end up in the air.
Climeworks is doing some work with atmospheric capture and sequestration in basalt via underground water injection (I believe they site with hydroelectric plants which gives them the reinjection well infrastructure mostly for free).
You can do the same thing by grinding basalt and spreading it on fields, which... given that I live on a pile of basalt, might be useful eventually. I keep collecting the stuff to make a greenhouse with, though.
It may be better than leaving it in the air, but given all the other biological activity of plastic, I'd really rather we not use the stuff in the first place at this point.