English to Russian Tech/Engineering Petroleum Eng/Sci Drilling

NOTE: I appreciate everyone's input, and it's a blessing to have KudoZ, but I would like this question to be answered only by those who KNOW closely and specifically what the agreement is talking about. If you don't have a picture of the surface cement plug pumping process, I'd rather come up with a translation myself using all the information available from Multitran, Lingvo and Google. I think I rather need an explanation than a translation. Thank you, everyone!

CONTEXT:

Excerpt from a Well Drilling Services Agreement:

The Operating Day Rate will cease upon, in case of permanent abandonment, when pumping of the surface cement plug is completed: in the case of temporary abandonment, when the cement job (displacement of all cement) on the last string of casing is complete.