GB2237646A

GB2237646A - Pressure transducer for submerged items of petroleum exploration and exploitation equipment

Info

Publication number: GB2237646A
Application number: GB9023320A
Authority: GB
Inventors: Jose Fernando Vigano; Silva Fabio Barbosa E
Original assignee: Pirelli SA Compania Industrial Brasileira
Current assignee: Pirelli SA Compania Industrial Brasileira
Priority date: 1989-10-30
Filing date: 1990-10-26
Publication date: 1991-05-08
Anticipated expiration: 2010-10-26
Also published as: FR2653881A1; IT9021850A1; IT9021850A0; IT1244067B; GB2237646B; GB9023320D0; BR8905638A

Abstract

The transducer comprises a protective pressure resistant casing 1, a capacitative sensing element 4, an interface to an electrical connection 2, a pressure interface to the fluid to be measured 3 and an electronic processing circuit 5. Sensor diaphragm 12 moves between fixed electrodes 17 under the influence of an internal fluid which is isolated from the fluid to be measured and the interior of the sensor by isolating diaphragms adjacent inlets 13, 15. The casing is constructed to contain any leakage of petroleum. <IMAGE>

Description

PRESSURE TRANSDUCER FOR SUBMERGED ITEMS OF PETROLEUM EXPLORATION AND EXPLOITATION EOUIPHENT Pressure transducers are items of equipment which convert the pressure value of a fluid into a suitable form (electrical signal for example) for transmission, monitoring, recording or simply visualisation of this information. They are used in virtually all areas of knowledge such as, for example, space, industry, medicine, etc.

The application of pressure transducers in the areas of petroleum exploration and exploitation is wide. They have been used at the well bottom, at the well head (Christmas tree), in submarine production manifolds and on the actual platform. The pressure information has been used to survey the capacity of deposits, to estimate and maximise the working life of the wells, to plan the application of artificial petroleum exploration mechanisms, to estimate future production, etc.

This invention is concerned with pressure transducers for submerged items of petroleum exploration and exploitation equipment, such as Christmas trees, submarine production manifolds, 'templates', etc.

Pressure transducers used in submerged items of petroleum exploration and exploitation equipment are subjected to fairly unfavourable environmental conditions. They are submerged in salt water, at depths which may exceed 1,000 metres of head of water and at an ambient temperature varying seasonally, with latitude and with the depth and conditions of installation. The process fluid, normally composed of petroleum, gas and water, whose pressure it is desired to monitor, may be at above 1000C. The conditions of installation make maintenance procedures for these transducers in the field difficult if not impossible.

Maintenance procedures normally require use of divers or remotely operated vehicles when production is not interrupted. Therefore, stability over time and accuracy are essential parameters for a good pressure transducer in this type of application.

The transducers which have traditionally been used employ pressure sensor elements (such as strain gauges, for example), which, although advantageous because of their small size, are defective in terms of reliability and, principally, stability over time of measurement.

An object of the present invention is to provide a pressure transducer for use with a submerged item of petroleum exploration or exploitation equipment which is more stable over time and more accurate than the above-mentioned traditional transducers.

In broad terms the invention meets this object by employing a capacitive sensor element. Capacitive sensor elements may have great stability over time, and may permit the manufacture of pressure transducers for this type of application, with high reliability and low maintenance costs.

The invention includes a pressure transducer for use with a submerged item of petroleum exploration or exploitation equipment, comprising a protective casing provided with a pressure interface and an electrical interface and accommodating a sensor element of the capacitive type and an electronic circuit for conditioning a signal from the sensor element.

The sensor element may comprise a cell having a high pressure inlet connected to said pressure interface and a low pressure inlet connected to the interior space of the casing, a sensor diaphragm disposed in said cell and deflectable therein in response to a pressure differential thereacross caused by the pressures at said inlets, deflection of said diaphragm altering the capacitive value of said sensor element.

Preferably an isolating diaphragm is positioned in said cell for being subjected to the pressure at said high pressure inlet and isolating said sensor diaphragm for the fluid media thereat.

Advantageously, a further isolating diaphragm may be positioned in said cell for being subjected to the pressure at the low pressure inlet and isolating said sensor diaphragm from the fluid media thereat. In this case the cell may contain a fluid through which the isolating diaphragms transmit the pressures at the pressure inlets to the sensor diaphragm.

The sensor element may be an electrode of a capacitive device. In this case the sensor element may be disposed between two fixed electrodes of said capacitive device.

Electrically conducting wiring may be used for interconnecting said capacitive device to said electronic circuit.

The casing of the transducer is preferably constructed to contain any leakage of petroleum therein.

In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a schematic longitudinal crosssection of a pressure transducer for use with a submerged item of petroleum exploration or exploitation equipment; Figure 2 is a cross-section taken along the line A-A in Figure 1; Figure 3 shows the transducer with a mount therefor; and Figure 4 shows the transducer with an alternative form of pressure interface which also mounts the transducer.

The illustrated transducer comprises a casing 1, an interface 2 to an electrical interconnection system, an interface 3 to the fluid whose pressure is to be measured, a capacitive sensor element 4 and an electronic circuit 5 which conditions a signal from the sensor element.

The casing 1 is formed by a metal body which protects the internal elements from water and from the pressure of the external medium. It mechanically supports the interface 2 to the electrical interconnection system and the interface 3 to the pressure contact. It may optionally be constructed with a sacrificial anode 6 for preventing corrosion of the casing itself. It may optionally be constructed in order to contain the leakage of petroleum to the ambient medium in the event of internal explosion due to failure in the sensor 4 or in the hydraulic connection 9 to the capacitive sensor element.

The interface 2 to the electrical interconnection system enables (a) the capacitive sensor element 4 and the electronic circuit 5 which conditions the signal to be fed with external electrical energy, and (b) a standard signal, containing information on the pressure being monitored, to be transmitted by the electrical interconnection system.

The interface 3 to the fluid whose pressure is to be measured comprises a metal body which, as shown in Figures 3 and 4 may have various forms in accordance with the specific requirements of each item of submarine equipment whose pressure is being monitored.

The interface 3 comprises a hydraulic connection 7 to the submarine item of equipment, a hydraulic line 8 for transmission of the pressure and a hydraulic connection 9 to the capacitive sensor element 4.

The capacitive sensor element 4 comprises two flanges, or walls 10 which demarcate a capacitive cell 11 on opposed sides thereof. The cell has a high pressure inlet 13 connected to the connection 9 to the pressure interface 3 and a low pressure inlet connected to the interior space of the casing 14. In the centre of the cell 11 is the sensor diaphragm 12.

This diaphragm 12 has the function of deflecting in response to the difference in the pressures on the high pressure side and on the low pressure side thereof. These pressures are applied directly to respective isolating diaphragms adjacent the pressure inlets 13,14,15. In turn the isolating diaphragms transmit the pressures to the sensor diaphragms 12 via a filling fluid 16, causing the deflection of the sensor diaphragm.

The sensor diaphragm 12 is a movable electrode and is disposed between two metallised surfaces 17 which are fixed electrodes. The amount of deflection of the sensor diaphragm 12 is ascertained via the variation in the capacitance between the two fixed electrodes and the movable electrode; and, by means of electrical wires 18, the deflection is recorded and transmitted to an electronic circuit board 5 which conditions the signal.

The electronic circus which conditions the signal 5 measures the capacitance of the sensor element 4. This capacitance is conditioned in the form of a standard electrical signal which contains the pressure information. The standard electrical signal is transmitted via the interface to the electrical interconnection system.

Figure 3 shows the transducer provided with a mount comprising two saddle members 20,22 which cooperate to circumscribe the casing and which are clamped together at opposed flanges 24,26 by means (not shown), the saddle member 22 being provided with an extension 28 and mounting base 30.

An alternative mount is shown in Figure 4 and comprises a flanged extension 32 of the pressure interface 3 which is connectable to a mating flange (not shown) of the item of submerged equipment by threaded fasteners schematically illustrated by centre lines 34.

In summary, the pressure transducer described above is an assembly which permits the remote monitoring of the pressure of petroleum in submerged items of exploration and exploitation equipment. The pressure 'value' is converted into an electrical signal via the capacitive sensor element. As capacitive pressure sensors have great stability over time, there is a drastic reduction in the frequency of submarine operations for the maintenance or replacement of these transducers, as well as greater reliability in pressure measurements. The electrical signal, produced by the capacitive sensor is conditioned, via an electronic circuit, to a suitable standard signal.

Claims

CLAIIIS :

1. A pressure transducer for use with a submerged item of petroleum exploration or exploitation equipment, comprising a protective casing provided with a pressure interface and an electrical interface and accommodating a sensor element of the capacitive type and an electronic circuit for conditioning a signal from the sensor element.

2. A pressure transducer as claimed in claim 1, wherein the sensor element comprises a cell having a high pressure inlet connected to said pressure interface and a low pressure inlet connected to the interior space of the casing, a sensor diaphragm disposed in said cell and deflectable therein in response to a pressure differential thereacross caused by the pressures at said inlets, deflection of said diaphragm altering the capacitive value of said sensor element.

3. A pressure transducer as claimed in claim 2, wherein an isolating diaphragm is positioned in said cell for being subjected to the pressure at said high pressure inlet and isolating said sensor diaphragm from the fluid media thereat.

4. A pressure transducer as claimed in claim 3, wherein a further isolating diaphragm is positioned in said cell for being subjected to the pressure at the low pressure inlet and isolating said sensor diaphragm from the fluid media thereat.

5. A pressure transducer as claimed in claim 4, wherein the cell contains a fluid through which the isolating diaphragms transmit the pressures at the pressure inlets to the sensor diaphragm.

6. A pressure transducer as claimed in any one of claims 2 to 5, wherein the sensor diaphragm is an electrode of a capacitive device.

7. A pressure transducer as claimed in claim 6, wherein said sensor diaphragm is disposed between two fixed electrodes of said capacitive device.

8. A pressure transducer as claimed in claim 6 or 7, wherein electrically conducting wiring interconnects said capacitive device to said electronic circuit.

9. A pressure transducer as claimed in any one of the preceding claims in that the casing is constructed to contain any leakage of petroleum therein.

10. A pressure transducer substantially as hereinbefore described with reference to Figures 1 to 3 or 1 and 2 as modified by Figure 4.