Method and system for testing a borehole by the use of a movable plug

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). In the downhole assembly (6) at the lower end of the test pipe (5) there is releasably retained a pig (30) forming a barrier between formation fluid and a lightweight damping fluid (7) filling the test pipe above the pig, the pig (30) being released at the start of the test and being moved in a controlled manner upwards in the pipe (5) as a result of a positive pressure difference between the fluids below and above the pig.

Dependencies are inferred from the claim text.