Upstream separation is designed for the field as it was at first oil. Over the life of an asset the water cut climbs, gas-oil ratio shifts and slugging gets worse — but the separators, scrubbers and vessels stay exactly the same size.

Offshore that constraint is absolute: deck space and weight are fixed, and new vessels are effectively off the table. The practical route is to raise the performance of what is already installed, which almost always means better internals — an inlet device that absorbs momentum properly, a plate pack that catches the fine droplets gravity cannot, a correctly sized mist eliminator ahead of the compressor.