Less weight means less hydrostatic pressure until it sets, but will accept down hole gas as it exits the bottom of the casing to the outside well bore on the way back up.
They would have also collected cement samples during the job (did in the 80's) for the customer.
Sounds like you’ve been around a cement job or two.
What’s your opinion of nitrifying (adding compressibility) to the cement in a well full of 14+ ppg very viscous OBM. Cement has to serve two functions, 1) get the mud out by laminar displacemet requiring well tuned friction and density heiarchy and 2) set up hard pretty quick after placement.
I seriously doubt BP did not make HAL leave a field blend around for testing. But I guess that went down with the rig. Thats the one that really matters. Everyuting else is pilot belend and not necessarily representative of actual blend, rig water & liquid adds the day, time and palce of the disaster.
My guess, BP loses this one.