Method and means for providing time delay in downhole well operations
The present invention relates to an apparatus and method for providing hydraulic load compensated time delay in downhole well operations. The apparatus includes a piston stem enclosed by a piston housing. An axial force, acting either in the direction of stretch or in the direction of compression, causes a pressure buildup in one of two hydraulic chambers which are each filled with an incompressible liquid and which are mutually connected through one or more throttle orifices. A sideways floating, supported piston sleeve is arranged between the piston stem and the piston housing. The piston sleeve is adapted to control the differential pressure across the throttle orifice(s) in such a manner that an increasing axial force will, in a predetermined manner, increase the differential pressure across the throttle orifice(s) and hence delay the flow-through of the incompressible liquid from one of the hydraulic chambers to the other chamber, which also causes a predetermined delay of the relative movement between the piston stem and the piston housing.
1. An apparatus for providing a hydraulic load compensated time delay, the apparatus comprising:
a piston housing;
a piston stem having a portion enclosed by the piston housing, the portion of the piston stem and the piston housing defining two hydraulic chambers containing an incompressible liquid located on opposite sides of the portion of the piston stem;
a piston sleeve located between the portion of the piston stem and the piston housing; and
at least one throttle orifice connecting the two hydraulic chambers, wherein
the piston sleeve is adapted to control differential pressure across the at least one throttle orifice.
2. The apparatus of claim 1 , wherein
the at least one throttle orifice is selected from the group consisting of a hole, a slot and a channel.
3. The apparatus of claim 1 , wherein
the at least one throttle orifice is a plurality of throttle orifices, and
the piston sleeve is adapted to close one or more of the plurality of throttle orifices based on increasing axial pressure, and thus increase flow resistance of the incompressible liquid.
4. The apparatus of claim 1 , wherein
the piston sleeve is adapted to reduce a size of the at least one throttle orifice based on increasing axial pressure, and thus increase flow resistance of the incompressible liquid.
5. The apparatus of claim 1 , wherein
the piston sleeve defines at least one channel as the at least one throttle orifice, the piston sleeve being adapted to extend a length of the at least one channel based on increasing axial pressure, thus increasing flow resistance of the incompressible liquid.
6. The apparatus of claim 5 , wherein
the at least one channel has a helical shape.
7. The apparatus of claim 5 , wherein
the at least one channel and the piston sleeve are shaped such that flow of the incompressible liquid through the at least one throttle orifice is laminar at least some of the time.
8. The apparatus of claim 6 , wherein
the at least one channel and the piston sleeve are shaped such that flow of the incompressible liquid through the at least one throttle orifice is laminar at least some of the time.
9. The apparatus of claim 1 , wherein
an area of the at least one throttle orifice is adjustable to allow a constant flow of the incompressible liquid through the at least one throttle orifice, independent of an axial force acting between the piston stem and the piston housing.
10. The apparatus of claim 1 , wherein
an area of the at least one throttle orifice is adjustable to obtain a constant relative movement between the piston stem and the piston housing, independent of an axial force acting between the piston stem and the piston housing.
11. A method for providing hydraulic load compensated time delay in an apparatus including a piston housing, a piston stem having a portion enclosed by the piston housing, the portion of the piston stem and the piston housing defining two hydraulic chambers containing an incompressible liquid located on opposite sides of the portion of the piston stem, a piston sleeve located between the portion of the piston stem and the piston housing, and at least one throttle orifice connecting the two hydraulic chambers, the method comprising:
when an axial force acting between the piston stem and the piston housing causes a relative movement between the piston stem and the piston housing and a pressure buildup in one of the two hydraulic chambers, controlling a flow of the incompressible liquid from the hydraulic chamber having the pressure buildup to the other hydraulic chamber through the at least one throttle orifice by controlling differential pressure across the at least one throttle orifice with the piston sleeve, such that the differential pressure across the at least one throttle orifice depends on a magnitude of the axial force acting between the piston stem and the piston housing, the differential pressure causing the piston sleeve to move axially relative to both the piston stem and the piston housing, the relative axial movement between the piston sleeve and the piston stem and/or the piston housing affecting covering or uncovering of the at least one throttle orifice and the differential pressure across the at least one throttle orifice.
12. The method of claim 11 , wherein
the controlling of the flow of the incompressible liquid comprises adjusting an area of the at least one throttle orifice to allow a constant flow of the incompressible liquid through the at least one throttle orifice.
13. The method of claim 11 , wherein
the controlling of the flow of the incompressible liquid comprises adjusting an area of the at least one throttle orifice to obtain a constant relative movement between the piston stem and the piston housing, independent of the axial force acting between the piston stem and the piston housing.