presssurized zone was 40metres thick ?, page-22

Lest,

I haven't worked offshore WA so someone more knowledgeable than I could probably answer that one. From what I have seen on land rigs, they control drill for evaluation at 10m per hour down from 30-50m per hour on surface hole. That is if they can achieve that. Sometimes hard formations limit rates of penetration to 1-2m per hour in the zones of interest.

What normally happens is that the operator would request sampling of cuttings at shorter intervals in critical zones. Eg a physical sample and analysis of the cuttings every 2-5m rather than the usual 10m or 20m when drilling the surface hole. You therefore need to slow down the rate of instanteous drilling to ensure the cutting sample correlates better with the depth and to give the mud loggers and geologist time to look at the sample properly.

Coupled with the LWD (logging while drilling) data they are most probably collecting, they would then look at the offset well data and seismics to determine which formation they are drilling in. I think they will have a pre-determined depth in mind for the coring, eg pull out to run in with coring assembly Xm above or after penetration of Calypso sands.

If they keep going into a well control situation, they will also do numerous flow checks which also slows down drilling. This is where they stop drilling and circulating the mud and observe the fluid level in the drill string and tanks to see if they are gaining mud volume, which indicates they are taking a gas kick. This is also confirmed by checking the mud weight. The mud weight drops after a gas kick due to gas being of a lower density and being entrained in the mud. If all is well, they will drill ahead, if they are gaining mud volume, they will stop drilling, circulate the mud through the choke manifold and degasser, maybe decide to weight it up with solid weighting agent. During all this, there will be a steady stream of communication from the rig to MEO who ultimately as operator, decide the next course of action.

Many a time has been spent on rigs waiting on decisions from town as to what happens next.

Just a small insight as to what happens on a rig.