It could also mean that the oil at U4 cannot easily get to the...

It could also mean that the oil at U4 cannot easily get to the wells that have produced the 1 million bbls .
There may not be a high permeability pathway between U4 and U1 and 2.
They are going to drill horizontal wells to try and link up parts of the field with good reservoir quality .
The reservoir may be quasi compartmentalised because of changes in reservoir quality from good vuggy fractured reservoir to poorer quality reservoir horizontally .They have been musing about this problem for a while now .
squidgy is by far our most knowledgeable poster on this stuff.
Can you give us your opinion when you have time ?