bayan
Senior Member

I'm sure there are many possible reasons, but the one that jumps out at me immediately would be as follows;

If you had a situation, where you had a high(er) permeability watered out layer which was preferentially being depleted through production but was connected to an aquifer, over or underlying a lower perm oil zone that supplied the 10% oil, then when you shut the well in, the water zone would recharge pressure meaning (a) other wells connected to the same water zone would see an WC increase and (b) when you put the well back on production you would produce far higher watercuts until you drawdown the water layer to its steady-state pressure again

Just an idea