GB2524800A

GB2524800A - Volume sensing accumulator

Info

Publication number: GB2524800A
Application number: GB1406013.1A
Authority: GB
Inventors: Peter John Davey; Julian James Jefferis; Robert John Gough; Chad Sankey
Original assignee: GE Oil and Gas UK Ltd
Current assignee: Baker Hughes Energy Technology UK Ltd
Priority date: 2014-04-03
Filing date: 2014-04-03
Publication date: 2015-10-07
Also published as: WO2015150478A2; WO2015150478A3; GB201406013D0

Abstract

A hydraulic accumulator assembly 1 in which a hydraulic accumulator 2 is associated with at least one sensing device 4 configured to provide an indication of the displacement of an internal divider 3 within the accumulator to provide an indication of the volume of gas within the hydraulic accumulator. The sensor can be mounted either perpendicularly or parallel to the direction of displacement of the divider and the internal divider can comprise an ultrasound or electromagnetic radiation reflection sensor. The accumulator can also comprise a pressure and temperature sensor (9 fig. 4) that can be used to calculate the quantity of energy stored in the accumulator. The internal divider can be a piston 3, a bladder (10 fig. 5) or a diaphragm and the accumulator can be used in an underwater extraction well facility. Also claimed is a method for providing an indication of the volume of gas within a hydraulic accumulator by sensing the displacement of an internal divider.

Description

Volume Sensing Accumulator

Field of the Invention

The present invention relates to hydraulic accumulators, for example a hydraulic accumulator in an underwater (e.g. subsea) fluid extraction well facility.

Background to the Invention

Prior art subsea hydraulic accumulators only have means to measure the pressure in the accumulators, and have to assume that the gas remaining in the accumulator is the same as when it was initially pre-charged. The hydraulic accumulator assembly of the present invention can be used to verify if that assumption is valid or if the accumulator has leaked gas, indicating that it cannot be relied upon and should be replaced. This may reduce instances of failure to supply sufficient hydraulic pressure to the subsea equipment to which it is connected.

FR2585086 discloses a hydraulic accumulator assembly in which a hydraulic accumulator is associated with at least one means responsive to the weight of the accumulator to provide an indication dependent on the weight of the accumulator.

As further prior art there may be mentioned EP2653731, in which a hydraulic accumulator located in an underwater fluid extraction well facility is associated with at least one means responsive to the weight of the accumulator to provide an indication dependent on the weight of the accumulator.

Summary of the Invention

In accordance with a first aspect of the invention there is provided a hydraulic accumulator assembly in which a hydraulic accumulator is associated with at least one sensing device configured to provide an indication of the displacement of an internal divider within the accumulator to provide an indication of the volume of gas within the hydraulic accumulator.

In accordance with a second aspect of the invention there is provided a method of providing an indication of the volume of gas within a hydraulic accumulator in a hydraulic accumulator assembly, comprising the steps of: a) mounting at least one sensor on the hydraulic accumulator; b) providing an indication of the displacement of an internal divider within the hydraulic accumulator with the at least one sensor; and c) using the measured displacement to provide an indication of the volume of gas within the hydraulic accumulator.

At least one sensing device could be mounted with its sensing direction perpendicular to the direction of displacement of the internal divider.

At least one sensing device could be mounted with its sensing direction parallel to the direction of displacement of the internal divider. In this case, the at least one sensing device mounted parallel to the direction of displacement of the internal divider could comprise an ultrasound sensor or an electromagnetic radiation reflection sensor.

At least one magnetic, electromagnetic radiation or radiological source could be attached to the internal divider.

The assembly could further comprise a pressure and temperature sensor. In this case, displacement, pressure and temperature values could be used to calculate the quantity of energy stored in the hydraulic accumulator.

The internal divider could comprise a piston, a bladder, or a diaphragm.

The hydraulic accumulator could be a hydraulic accumulator in an underwater fluid extraction well facility.

Brief Description of the Drawings

Fig. 1 is a schematic diagram of a first embodiment of this invention; Fig. 2 is a schematic diagram of a second embodiment of this invention; Fig. 3 is a schematic diagram of a third embodiment of this invention; Fig. 4 is a schematic diagram of a fourth embodiment of this invention; Fig. 5 is a schematic diagram of a fifth embodiment of this invention; Fig. 6 is a schematic diagram of a sixth embodiment of this invention; and Fig. 7 is a schematic diagram of an underwater fluid extraction well facility comprising hydraulic accumulator assemblies according to the invention.

Fig. 1 schematically shows a hydraulic accumulator assembly 1 according to a first embodiment of the invention, comprising a cylindrical hydraulic accumulator 2 connected to a hydraulic circuit 5. Hydraulic fluid may enter and exit the hydraulic accumulator 2 through a T-junction. As such fluid moves in and out of the hydraulic accumulator 2, an internal divider, i.e. a piston 3, which separates the hydraulic fluid from a pressurised gas, is displaced in response. For the purpose of consistency, the amount of displacement is defined as being zero when the piston 3 is at the top of the cylinder of the hydraulic accumulator 2 as shown in Figs. 1-4, the amount of displacement increasing as the piston 3 moves downward.

A sensing device 4 is mounted on a side wall of the hydraulic accumulator 2. The sensing device 4 has a sensing direction which is perpendicular to the direction of displacement of the piston 3 to detect the piston 3 as it passes across the sensing device 4. As the cross-sectional area of the cylinder of the hydraulic accumulator 2 is known (and, in this case, constant), the amount of the displacement is proportional to the volume of gas within the hydraulic accumulator 2.

With a sensing device 4 mounted on the side wall of the hydraulic accumulator 2, it is also possible to perform an alternative method whereby the composition of the contents of the hydraulic accumulator are sensed through the side wall. When the sensing device 4 senses a change from liquid to gas (or vice versa), it provides an indication that the piston 3 has passed in front of the sensing device 4 at that point.

As a further alternative embodiment (not shown), the sensing device 4 may comprise a transmitter on the side wall of the hydraulic accumulator 2 and a corresponding receiver located diametrically on the opposite side of the hydraulic accumulator 2. A link can be established between them, e.g. via electromagnetic radiation, which is readily transmitted through the medium of liquid or gas, but which is interrupted by the piston 3. An indication of the piston's displacement can be provided at the point at which the link is interrupted.

The sensing device 4 is connected to a communication bus 6. Through the communication bus 6, the sensing device 4 can communicate with other sensing devices on other hydraulic accumulators in an underwater fluid extraction field, and other components of an underwater fluid extraction well facility, for example a subsea electronics module in a subsea control module. As subsea electronics modules can be monitored from a topside control centre, usually via an umbilical, this allows the volume of gas within the hydraulic accumulator 2 to be monitored from the surface.

Although only one sensing device is shown in Fig. 1, more sensors may be used in practice.

Fig. 2 schematically shows a hydraulic accumulator assembly according to a second embodiment of the invention. Like reference numerals have been retained where appropriate. In this embodiment, a sensing device 7 has been mounted on the top of a hydraulic accumulator 2. The sensing device 7 has a sensing direction which is parallel to the direction of displacement of a piston 3, and the sensing device 7 monitors the extent to which the piston 3 moves towards, or away from, the sensing device 7. In this embodiment, the sensor may comprise an ultrasound sensing device or an electromagnetic radiation reflection sensor. Again, while only one sensing device 7 is shown, more sensing devices may be used in practice. Also in this embodiment, the sensing device 7 may be sensitive to the substance reflecting the ultrasound / electromagnetic radiation. This can be used to give an indication that the accumulator is leaking, e.g. if the reflecting substance is fluid then the accumulator is leaking.

Fig. 3 schematically shows a hydraulic accumulator assembly according to a third embodiment of the invention. Again, like reference numerals have been retained where appropriate. In this embodiment, pair of sensing devices 4, 7 is mounted on the outside of a hydraulic accumulator 2. A first sensing device 4 is mounted to have a sensing direction which is perpendicular to the direction of displacement of a piston 3, and a second sensing device 7 is mounted to have a sensing direction which is parallel to the direction of displacement of the piston 3 within the hydraulic accumulator 2. Both sensing devices 4, 7 are connected to a communications bus 6.

While only one perpendicular sensing device 4 and one parallel sensing device 6 are shown, a plurality of each type of sensing device may be used in practice.

Fig. 4 schematically shows a hydraulic accumulator assembly according to a fourth embodiment of the invention. Again, like reference numerals have been retained where appropriate. This embodiment is similar to that shown in Fig. 3, however a marker 8 has been attached to the piston 3 to increase its visibility to the sensing devices 4, 7. The marker 8 may comprise, for example, a magnetic, electromagnetic radiation or radiological source. Although only one has been shown, a plurality of markers may be used to increase the accuracy of the displacement sensing.

Also shown in Fig. 4 is a pressure and temperature sensor 9 attached to the hydraulic circuit 5. Values of pressure and temperature measured by the sensor 9 may be combined with the measured piston displacement value to calculate the energy stored within the hydraulic accumulator 2. The stored energy is particularly important information for hydraulic accumulators in underwater fluid extraction well facilities, as the stored energy must be kept above a minimum threshold to ensure that safety critical systems may be operated in case of an emergency requiring shutdown of the well.

Fig. 5 schematically shows a hydraulic accumulator assembly according to a fifth embodiment of the invention. Again, like reference numerals have been retained where appropriate. In this embodiment, an internal divider of the hydraulic accumulator 2 comprises a bladder 10 (this embodiment could also operate with an internal divider comprising a diaphragm). A pair of sensing devices 11, 12 on the top of the accumulator 2 is used to measure the displacement of the bladder 10 at the centre of the hydraulic accumulator 2, and at a point offset from the centre. These two measured values provide an indication of the volume of gas within the hydraulic accumulator 2 by indicating the size and shape of the bladder. As an alternative embodiment, a single sensing device could be used to measure displacement, for example at the centre of the hydraulic accumulator 2, and a computer model could estimate the shape of the bladder from this measurement. However, it is preferable to use a plurality of sensing devices to provide a more accurate indication of shape.

Fig. 6 schematically shows a hydraulic accumulator assembly according to a sixth embodiment of the invention. Again, like reference numerals have been retained where appropriate. In this embodiment, the hydraulic accumulator 2 contains an internal divider comprising a piston 3. A stiff but flexible cable 13 (e.g. a Bowden cable) is attached to the piston at one end, and is attached to a magnet 14 at the opposite end. The magnet 14 moves in response to the movement of the piston 3, and a sensor 15 measures the movement of the magnet 14 to provide an indication of the movement of the piston 3.

Fig. 7 is a schematic diagram of an underwater fluid extraction well facility. A pair of hydraulic accumulator assemblies 16, 17 according to the invention is disposed in an underwater fluid extraction well facility on the sea bed. The sensing devices of the hydraulic accumulator assemblies are connected to a communications bus 18. The communications bus 18 is connected to a subsea control module (SCM) 19 which houses a subsea electronics module (SEM) 20. The SEM is in communication with a topside control centre via an umbilical 21. This allows the volume of gas in each respective hydraulic accumulator assembly 16, 17 to be monitored from the surface.

Advantaaes provided by the invention An advantage of the hydraulic accumulator assembly provided is that it can be used to detect whether or not the accumulator has leaked gas, indicating that it cannot be relied upon and should be replaced. This may reduce instances of failure to supply sufficient hydraulic pressure to the subsea equipment to which it is connected.

Various alternatives and modifications within the scope of the invention will be apparent to those skilled in the art. For example, while the above embodiments have been described with reference to sensing devices having a sensing direction, this is not intended to preclude the use of omnidirectional sensors, provided they are capable of producing an indication of the displacement of the internal divider. As another example, the sensing devices in the above embodiments are all external to the hydraulic accumulator, however this is not intended to preclude the use of sensors internal to the hydraulic cylinder itself, for example, mounted on the inside of the cylinder wall, or located within the internal divider itself.