Sidetracks are very common especially when you're drilling an exploration well in relatively unchartered waters or the neighbours are not overly forth coming with well data.
The operator would have forecast higher pressure at zone 4 and would have upped the drill mud weight to account for what they theoretically thought the pressure might be. But without well data from previous wells this was unknown territory so its not unusual for the pressure to be at variance with their best estimates based on sparse information.
NEN Price at posting:
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