WO2002040911A1

WO2002040911A1 - Damper device for a hydraulic system, where a piston provided with an electric coil and a permanent magnet which propagate a magnetic field, cooperate

Info

Publication number: WO2002040911A1
Application number: PCT/NO2001/000407
Authority: WO
Inventors: Åge KYLLINGSTAD
Original assignee: National Oilwell Norway As
Priority date: 2000-10-09
Filing date: 2001-10-05
Publication date: 2002-05-23
Also published as: NO20005092D0; NO317379B1; AU2002222816A1; NO20005092L

Abstract

A damper device for a hydraulic system of the kind in which an accumulator (2) communicates with a hydraulic system for the purpose of damping pressure variations, and in which a comletely, or essentially, sealingly displaceable piston (16) is disposed in a pipe (4) connecting the hydraulic system with the accumulator (2).

Description

Damper device for a hydraulic system, where a piston provided with an electric coil and a permanent magnet which propagate a magnetic field, cooperate.

The invention relates to a method and device for damping flow rate oscillations in hydraulic systems, especially systems supplying drilling fluid to downhole equipment in an oil well.

Pumps, motors and other equipment that are connected to hydraulic systems cause pressure variations in the hydraulic fluid, and pressure variations are additionally observed as vibrations and acoustic noise. This is particularly noticeable in systems comprising large piston machines, for example said type of system for drilling fluid, as large reciprocating pumps are used such places . Even where so- called triplex-pumps are used, in which three crank-operated pistons work out of phase to achieve a uniform fluid flow, considerable variations occur in the fluid flow.

There are several components contributing all together to variations in flow rate and pressure. A main component is due to the fact that crank-operated pistons provide a sinusoidal course. Even with several pistons working out of phase an even flow rate is not achieved from a reciprocating pump. Another component is due to the fact that liquid is compressible to a certain degree. Other components are due to valves, seals and other elements not being perfect.

It is known to utilize a partially gas-filled pressure accumulator to damp the pressure oscillations caused by the reciprocating pumps in such systems . A drawback of the known solution is that a satisfactory equalizing/smoothening of the flow rate is not achieved, and not a satisfactory reduction in vibrations and noise either, even if a comparatively large accumulator volume is used. Additionally, large accumulators are space-demanding and expensive.

Another drawback results from the fact that the accumulators in question damp all pressure oscillations, also those not generated by pumps . This entails difficulties in picking up and decoding information-carrying pressure pulses from downhole equipment arranged to communicate with surface equipment by means of mud pulse telemetry.

The object of the invention is to provide a device which more specifically dampens undesired pressure oscillations without subduing low energy oscillations of higher frequency, used for signalling.

The object is realized through the features set forth in the following description and the subsequent Claims.

According to the invention a pump is placed between a relatively small pressure accumulator in the hydraulic system, in which the pump is arranged to pump liquid in both directions and to work in time with and in counter-phase to the flow variations which should be damped. By a reduction in the flow from the reciprocating pump, liquid is driven from the accumulator to the hydraulic system to compensate for this reduction. By an increase in the flow, liquid is driven back to the accumulator. The liquid flow to and from the accumulator follows a pattern similar to the one it would have followed without the active pump, but with two important differences. The first difference is that the pump compensates for friction, inertia and change in gas pressure in order to achieve a nearly total damping. The other difference is that pressure pulses generated from sources other than the reciprocating pump will not be damped.

The pump may be realized through a movable piston in a liquid channel connecting the hydraulic system to a pressure accumulator, so that liquid in the hydraulic system acts on one side of the piston, whereas liquid in the pressure accumulator acts on the other side of the piston. The stroke of the piston must be such that multiplied by the area of the piston, it provides a volume corresponding to the volume variations creating the undesired pressure oscillations in the hydraulic system. The piston thus forms a movable partition between two varying volumes of liquid.

Ideally, there is no exchange of liquid between the hydraulic system and the pressure accumulator. In practice it may still be relevant to arrange the piston with a limited liquid passage to achieve pressure equalization between the working pressure of the hydraulic system and the pressure of the accumulator. The object of the invention may be realized in itself, by connecting a reciprocating pump to the hydraulic system and running the piston pump in counter-phase to the undesired flow variations in the system. The solution described above is still to be preferred because the storing of energy in the accumulator allows a partition piston to be driven by a substantially smaller energy consumption. Another condition is that with the preferred solution it is possible to operate with a substantially smaller movable mass and thereby better satisfy the requirements to response times. To damp pressure oscillations generated by a typical drilling fluid pump, the response time should be less than fifty milliseconds.

By controlling the movements of the piston in counter-phase to a known flow variation pattern, only the undesired pressure variations are damped, whereas possible signal- carrying pressure pulses from downhole equipment are not damped.

In addition to damping undesired pulses from reciprocating pumps and other equipment, the pump may also be used to generate pressure pulses, for example for use in two-way mud pulse telemetry.

In the following there will be described a non-limiting example of a preferred embodiment, which is visualized in the accompanying drawings, in which:

Fig. 1 shows, in section, a principle drawing of the invention;

Fig. 2 shows, in section, the details of the pump. In the figures the reference numeral 1 identifies part of a liquid-filled pipe incorporated in a hydraulic system.

A pressure accumulator 2 of a kind known in itself is connected to the pipe 1 through a cylinder pipe 4 which forms the external part of a pump 6. At least adjacent to an end the cylinder pipe 4 is provided with an internal transversal end plate 8. The end plate 8 is provided with fixed or adjustable through ports 10 which allow liquid to flow through the end plate 8.

Between the end plate 8 and a magnet head 12 is arranged a central permanent magnet 14. From the magnet head 12 a radially directed magnetic field, not shown, propagates to the cylinder pipe 4.

The magnetic field follows the cylinder pipe 4 to the end plate 8 and thereby a magnetic circuit is closed. The magnet 14 may be made up of one or more permanent magnets possibly forming a system of magnets .

An annular piston 16 enclosing the magnet head 12 is arranged to be movable axially within the cylinder pipe 4. There is a small clearance between the piston 16 and the cylinder pipe 4, and between the piston 16 and the magnet head 12. Therefore, to some degree, liquid may flow past the piston 16 from the pipe 1 into the pressure accumulator 2 and vice versa.

The annular piston 16 is provided with an electric coil 18 which is connected through wires 20, 20' to a variable power source, not shown. By varying the current within the coil 18, the piston 16 may be moved in the desired axial direction within the cylinder pipe 4. When the piston 16 is displaced, the volumes between the end plate 8 and the piston 16 and between the pipe 1 and the piston 16 change. The magnet 14 and the piston 16 with the coil 18 form an electric linear motor according to principles corresponding to those of a loud-speaker element. Of course, there is nothing to prevent having a permanent magnet in the piston and arranging a coil in the magnet head 12, but it may be a disadvantage that the movable mass will be larger than with the preferred solution.

The cylinder pipe 4 is arranged to be sealingly connected to the hydraulic pipe 1 and the pressure accumulator 2, e.g. by bolts, not shown, through bolt openings 22 in the end plate 8 and in a flange 24.

The movement of the piston 16 is controlled by a control system, not shown, of a kind known in itself. The piston 16 is controlled in such a way that it oscillates in time with and in counter-phase to flow variations which are to be damped. This may be achieved by means of an electrical control signal which varies with a flow profile, known in advance, from a reciprocating pump, not shown. If necessary, the control system may comprise a feedback loop. Such a feedback loop allows a measurement of the position and/or speed of the piston 18 to be used for correcting any deviations from the desired movement.

Claims

C L A I M S

1. A damper device for a hydraulic system of the kind in which an accumulator (2) communicates with a hydraulic system with the purpose of eliminating or damping flow variations, c h a r a c t e r i z e d i n that a completely, or essentially, sealingly displaceable piston (16) is disposed in a pipe (4) connecting the hydraulic system to the accumulator (2 ) .

2. A device according to claim 1, char ac t er i z ed in that a magnetic field circuit comprising the cylinder pipe ( 4 ) , and end plate ( 8 ) , a permanent magnet or magnetic system (14) and a magnet head (12), is arranged to propagate a radial magnetic field from the magnet head (12) to the cylinder pipe ( 4 ) .

3. A device according to one or more of the preceding claims, c har acte r i z ed in that the piston (16) is placed in said magnetic field.

4. A device according to one or more of the preceding claims, char ac t e ri z ed in that the piston (16) is provided with an electric coil (18) connected by wires (20, 20') to a power supply, not shown.

5. A device according to one or more of the preceding claims, c har acter i z ed in that, cooperating with the permanent magnet (14) and other connected components, the piston (16) at the electric coil (18) forms a linear motor, of which the piston (16) forms the pump piston itself.

6. A device according to one or more of the preceding claims, c harac te r i z ed in that the end plate (8) is provided with fixed or adjustable ports (10).