I don't know if there is some small flow to keep things hot on...

I don't know if there is some small flow to keep things hot on shut down sierra.
My thought is they would have shut off the flow on completion of the 6 week Flow Test at the 'shut off' valve. That would be at the very top of the well head.

The whole thing would just sit there and 'cool off'. There would be virtually little to no cooling down at the bottom of the well (4,500m or whatever it is)and a gradual change would establish itself over the legth to something like ambient ground temps. at the top.
Some thermal circulation would set up with the cooler water sinking from the top and hotter water rising from the bottom. But, a considerable difference between bottom and top temps would come about with appropriate changes in expansion & contraction stresses in the pipe.

This has been discussed in some earlier posts two or three weeks back where it was interesting to hear from some that the sort of streses that this would generate are allowed for in the well design where the initial expansion occuring from 'cold to hot' is to a large part absorbed by the 'stretching' stress imposed on the well pipe during construction due to the pipes just hanging under its own weight!
This equates to some 4m of expansion over the 4,500m length of pipe. Who thought about that? All that weight of pipe just 'hanging'there as it went deeper & deeper.
Then,as the drill breaks into the saturated granite and super hot water is allowed to flow up the pipe it heats up of course to maybe 240degC. Over twice boiling point, and the pipe now expands, maybe eqating to as much as 5m!
This means the initial streching or tension stress just explained is cancelled out and replaced by a smaller level of 'compressive' stress, because remember, the pipe is no longer free to actually move due to it being physicaly locked into the granite below and the massive well head above.
Imagine, if that 'pipe' was just laying out, 4,500m odd long, on the ground and you heated it some 230deg.C. it would grow app. 4.5+ meters in length!

Those sort of expansion/contraction forces have to be dealt with. The forces generated could easily cause a rupture in the pipe and the blow-off event if not controlled.
They are of course anticipated and catered for in the design/construction of the well. Not an entirely new or not understood condition.

Well that is the 'short' decription so I hope it is clear enough. It is a bit amazing but that is about where the case rested here on this topic.

I would be interested to hear further elaboration on all this if anyone who is across it all would care to add.

One extra question has stuck with me.

That is, The drill broke through into a saturated granite strata earlier than anticipated.

Q. Were they drilling in an 'overpressured condition' to provide control against the pressurised water in anticipation of breakthrough at the time?
and, was the well piping cemented into the granite at that stage as I guess would be originally intended when approaching breakthrough. Were plans somewhat compromised at this point?

geojac