Abstract: An arrangement and a method to control and regulate the bottom hole pressure in a well during subsea drilling at deep waters: The method involves adjustment of a liquid/gas interface level in a drilling riser up or down. The arrangement comprises a high pressure drilling riser and a surface BOP at the upper end of the drilling riser. The surface BOP havs a gas bleeding outlet. The riser also comprises a BOP, with a by-pass line. The drilling riser has an outlet at a depth below the water surface, and the outlet is connected to a pumping system with a flow return conduit running back to a drilling vessel/platform.

Abstract: An arrangement and a method to control and regulate the bottom hole pressure in a well during subsea drilling at deep waters: The method involves adjustment of a liquid/air interface level in a drilling riser. The arrangement comprises a drilling riser with an outlet at a depth below the water surface. The outlet is connected to a subsea pumping system with a flow return conduit back to a drilling vessel. The intention of the system is to transport the drilling fluid and the formation particles to the surface on the drilling unit prior to setting structural pipe on the seabed and when drilling at least one hole section after the first surface structural casing have been set. The apparatus is used in order to drill all surface hole sections with the riser installed in order to avoid “pump & dump” procedures and to recover all mud and chemicals.