Choke valve especially used in oil and gas wells

Abstract

A choke valve specially used for regulating the flow volume and with it the back pressure of liquids or gas while drilling through shallow gas bearing formations from an off-shore drilling platform. The valve comprises a flexible cylindrical valve element (8) positioned in the valve housing (1) flow passage and where the valve is so designed that the valve element's (8) flow area can be reduced by a radial reduction of the valve element. The flow area of the valve element (8) is equal to or larger than the remaining flow area of the valve. The valve has devices (10;22) for constricting the end of the valve element (8) being nearest to the outlet opening (3) of the valve. The valve element (8) is so long that it is possible to compensate for the wear to which the end is exposed by sliding the valve element against the constricting devices (10:22) or by moving the latter along the valve element as the wear proceeds. Only the valve element (8) is exposed to wear and no other parts of the valve being positioned within the wearing zone. The valve element (8) in its withdrawn position has its total diameter free allowing a full flow through the valve. Accordingly the valve do not disturb the flow under normal condition and is not exposed to any wear. At a gas kick the well can be controlled during a long period as it is possible to compensate the wear on the valve element during operation.