Abstract: Assembly for pressure control when drilling underground to locate or produce hydrocarbons; whereby the drilling is done by means of a drill string with fluid circulation down through the drill string and up through an annulus between the drill string and the open hole or casing, as the underground in the open hole may comprise one or both of: areas with formation strength which is unable to withstand the pressure from the fluid circulation without fracturing and areas with formation pressure which cannot be combined with each other or the fluid circulation pressure without the fluid unintentionally leaking in or out from the above-mentioned areas.

Abstract: A method and a system for testing a borehole in an underground formation by the use of so-called closed chamber testing. When carrying out the method, a test or production pipe (5) is carried down the borehole, where the test pipe can be closed at its upper end and at its lower end is provided with a downhole assembly (6) comprising equipment for testing of fluid flow from the formation (3), the annulus (23) between the test pipe (5) and a casing (20) in the borehole being shut off during the test by a gasket (22) at a desired depth, and fluid from the formation being allowed to flow through the test pipe (5) to a collecting tank (9) coupled to the test pipe via a flow head (4) at the upper end of the test pipe (5).