I would assume they are spending more time setting the concrete...

I would assume they are spending more time setting the concrete than usual due to the high pressure from the gas?
Disclaimer: I am no engineer.

For example, this chart shows that with a specific additive, and at around 60-70°C the concrete will still take >24 hours to reach 25Mpa.



And in the below table, shows combinations of MPa, curing temperature, pressure, and time.
I wonder how much pressure they need to withstand, and if it's from all the gas?

Note: "The results are difficult to compare owing to the variety of different mix designs curing conditions, curing time before testing and sample sizes"




Source: https://www.petroleum.sa.gov.au/__data/assets/pdf_file/0008/272492/20161014_-_UoA_-_Well_Cement_Integrity_and_Cementing_Practices.pdf