high pressure oil/gas, page-4

Redal,

Size of the rig was not an issue, at least not at the depth they encountered the high pressure aquifer.

The problem here was surprise at encountering it at this shallow depth when it was not even evident in Duhat-1 just 440 mts away, nor on any of the seismic they had.

They were probably drilling ahead monitoring wellbore pressure when the bit suddenly penetrated the high pressure aquifer.
The monitored pressure beforehand probably gave little warning (happened too quick) that would've had them increasing mud weight to match wellbore pressure...result, big pressure kick in the wellbore which could have all sorts of consequences if not controlled.

Read this primer to understand what process they may be going through...you'll see it's not that simple.
Managing Drilling Risk