How does reinforcement help prevent blowouts when drilling deep into the Earth?

[kieyard]

Hello there, just a quick question.
How deep can you drill into the ground before reinforcement is required? Iv watched a video on deep sea drilling and it says they drill down so far then send concrete down for reinforcement then drill again with a smaller drill. So I was just wondering how far down you can go each time before you need the concrete? And does it matter on the diameter of each hole and how deep each hole is?
Thanks in advanced

 

[CWatters]

I don't know the answer but this has a relevant comment...
https://www.damninteresting.com/the-deepest-hole/

The Russian researchers were also surprised at how quickly the temperatures rose as the borehole deepened, which is the factor that ultimately halted the project’s progress. Despite the scientists’ efforts to combat the heat by refrigerating the drilling mud before pumping it down, at twelve kilometers the drill began to approach its maximum heat tolerance. At that depth researchers had estimated that they would encounter rocks at 100°C (212°F), but the actual temperature was about 180°C (356°F)— much higher than anticipated. At that level of heat and pressure, the rocks began to act more like a plastic than a solid, and the hole had a tendency to flow closed whenever the drill bit was pulled out for replacement. Forward progress became impossible without some technological breakthroughs and major renovations of the equipment on hand, so drilling stopped on the SG-3 branch. If the hole had reached the initial goal of 15,000 meters, temperatures would have reached a projected 300°C (572°F).

When drilling stopped in 1994, the hole was over seven miles deep (12,262 meters), making it by far the deepest hole ever drilled by humankind...

 

[Baluncore]

How deep can you drill into the ground before reinforcement is required?

When drilling a deep hole the problem is actually near the surface where there are unconsolidated materials or where weathering has weakened the rock. Once that first section has been drilled oversize, a steel casing is inserted, then the surrounded space will be stabilised with concrete. Drilling can then continue with a smaller diameter drill.

Oil and gas wells can blow out if a high pressure reservoir is encountered while using a low density drilling mud. To prevent escape of gas and oil a blowout preventer is installed. The BOP must be attached to the casing, and that casing must be firmly attached to the solid rock with concrete.