The point of carbon sinks is to reduce CO2 levels in the atmosphere.
The process you're suggesting is:
- Pull a bunch of oil out of the ground
- Crack it into smaller hydrocarbons (using energy from burning other oil derived hydrocarbons)
- Polymerize those smaller components into plastics (using more energy from burning hydrocarbons)
- Bury the plastic
That doesn't take CO2 out of the atmosphere, every single part of the process is adding more.
For a carbon sink to be useful you need to be taking carbon that is already part of the carbon cycle and sequestering it, not pulling up carbon that has been buried for millions of years and then sending half of that into the air and the other half into a landfill.
The process you're suggesting is:
- Pull a bunch of oil out of the ground
- Crack it into smaller hydrocarbons (using energy from burning other oil derived hydrocarbons)
- Polymerize those smaller components into plastics (using more energy from burning hydrocarbons)
- Bury the plastic
That doesn't take CO2 out of the atmosphere, every single part of the process is adding more.
For a carbon sink to be useful you need to be taking carbon that is already part of the carbon cycle and sequestering it, not pulling up carbon that has been buried for millions of years and then sending half of that into the air and the other half into a landfill.