GB2296096A

GB2296096A - Flowmeter

Info

Publication number: GB2296096A
Application number: GB9525551A
Authority: GB
Inventors: Stephen Duncan
Original assignee: Wood Group Production Technology Ltd
Current assignee: Wood Group Production Technology Ltd
Priority date: 1994-12-16
Filing date: 1995-12-14
Publication date: 1996-06-19
Anticipated expiration: 2015-12-14
Also published as: GB9525551D0; GB9425463D0; GB2296096B

Abstract

A venturi tube flowmeter which permits the evaluation of the downhole flowrate and density of a fluid flow comprises a first pressure sensor (16) connectable in use to a first pressure port (4), a second pressure sensor (17) connectable in use to a second pressure port (5), and a valve (15) operable to selectively connect each of the first and second pressure sensors (16, 17) to a common pressure source to facilitate sensor calibration. <IMAGE>

Description

XFlowmeterw The present invention relates to a device for use in evaluating characteristics of a fluid flow and particularly, though not exclusively, to evaluating a downhole flow rate of a hydrocarbon flow.

Venturi tubes are well-known for measuring fluid flow.

A venturi tube consists of a tube having a constriction; measurement of the pressure differential produced by a fluid flowing through the constriction allows the flow rate to be calculated. However, harsh conditions which are encountered downhole make use of conventional venturi tubes to measure downhole flow rates of fluid hydrocarbons, for example along a production/injection pipe, problematic.

According to a first aspect, the present invention provides a venturi tube flowmeter having a first pressure sensor connectable in use to a first pressure port of the venturi tube, a second pressure sensor connectable in use to a second pressure port of the venturi tube and one or more valves operable to selectively connect each of the first and second pressure sensors to a common pressure source.

According to a second aspect, the present invention provides a method of calibrating a venturi tube flow meter having two or more pressure sensors each connected to a respective pressure port, the method comprising connecting the pressure sensors simultaneously to a common pressure source and disconnecting the sensors from the pressure ports.

The ability to connect each of the pressure sensors to a common pressure source may allow the first and second pressure sensors to be calibrated with respect to each other. Pressure sensors, especially when used in harsh downhole conditions, will tend to drift from their initial calibration. The ability to recalibrate the sensors in use with respect to each other is intended to increase accuracy of measurement and subsequent calculation of flow rates.

Preferably, each of the pressure sensors is provided by a pressure transducer. One or more of the pressure sensors may be provided by a silicon diaphragm with an associated strain sensor. In this arrangement, the diaphragm will "relax" through time and consequently the output characteristics of the sensor will change or drift over time. Drift of the pressure sensor can be significant, especially if the sensor is installed and used for a number of months, and, if uncorrected, can result in significant inaccuracies.

Each of the first and second pressure sensors may be connected to the same valve. The valve may be operable between a first valve position in which the first pressure sensor is connected to the first pressure port and the second pressure sensor is connected to the second pressure port and a second valve position in which the first and second pressure sensors are connected simultaneously to the common pressure source and disconnected from the first and second pressure ports.

The common pressure source may be a reference pressure port of the venturi tube.

The first and/or second pressure sensors may be adjusted so that they give the same output (within an acceptable tolerance) when connected to the common pressure source. Alternatively, any difference in the respective outputs of the first and second sensors when connected to the common pressure source may be taken into account when subsequent readings of the sensors are used.

The calibration of the flowmeter may be carried out when the flowmeter is located downhole.

According to a third aspect, the present invention provides a venturi tube flowmeter having a first pressure port, a reference pressure port, a pressure sensor and a valve device to selectively connect the pressure sensor to the first pressure port or the reference pressure port.

According to a fourth aspect, the present invention provides a method of evaluating the density of a fluid, the method comprising connecting a pressure sensor to a first pressure port to sense the pressure at the first port, subsequently connecting the pressure sensor to a reference pressure port to sense the pressure at the reference port, and comparing the pressures sensed at the first port and the reference port.

In one preferred embodiment, the flowmeter also has a second pressure port. The pressure sensor may be operable to sense pressure at two of any of the three pressure ports.

The first pressure port may be at a constricted section of the venturi tube, the second pressure port may be spaced along the venturi tube from the first pressure port and the reference pressure port may be spaced along the venturi tube from the first and second pressure ports. In this configuration, the flowmeter may have two pressure sensors. Preferably, one of the pressure sensors is connected to sense pressure at the second pressure port and the other sensor is connected to selectively sense pressure either at the first pressure port or at the reference pressure port.

In use, the reference pressure port is preferably spaced vertically from the first pressure port.

Sensing and comparison of the pressure at the first and reference pressure ports may provide an indication of the density of the fluid flowing through the flowmeter.

The flowmeter may be installed and used downhole.

According to a fifth aspect, the present invention provides a venturi tube flowmeter comprising a mandrel adapted to be installed as part of a flow pipe, a venturi section having one or more pressure ports and adapted to be inserted into the mandrel for use and a securing device adapted to secure the venturi section in use in the mandrel.

The flowmeter may be used downhole. The flow pipe may be a production/injection pipe and the flowmeter may be used to sense characteristics of a hydrocarbon fluid flow.

Preferably, the mandrel is provided with a pressure orifice or pressure orifices adapted in use to cooperate with the pressure port or pressure ports of the venturi tube such that pressure at the or each pressure port may be sensed through a wall of the mandrel. The mandrel may have more than one orifice.

Preferably, the mandrel has an individual pressure orifice associated with each pressure port of the venturi section.

The mandrel may house one or more pressure sensors. It may house one or more valves associated with the pressure sensor or pressure sensors.

The securing device may be provided by a lock mandrel adapted to retain the venturi section in use in the mandrel. The lock mandrel may be attached to the venturi section and may be used to insert and/or position the venturi section in the mandrel.

Preferably, the venturi section is removable from the mandrel. This may allow the venturi section to be removed when no longer required and may allow one venturi section to be replaced by another venturi section, for example when the first venturi section becomes worn or when it is desired to use a venturi section having a different configuration or profile.

The venturi section may be removable by removing the lock mandrel; it may be removable by wireline.

According to a sixth aspect, the present invention provides a method of configuring a downhole flowmeter in accordance with the fifth aspect of the invention comprising the steps of positioning the mandrel downhole as part of a production/injection pipe, inserting the venturi section into the downhole mandrel, aligning the or each of the pressure ports of the venturi section with the or each respective pressure orifice and securing the venturi section at the mandrel for use.

Different aspects of the present invention may be combined in a single embodiment.

An embodiment of the invention will now be described, by way of example only, with reference to Fig. 1 which shows a flowmeter in partial cross-section incorporating a number of aspects of the present invention.

The venturi tube flowmeter 1 of Fig. 1 is intended for use downhole to sense pressure of a hydrocarbon fluid flow passing through a venturi section. Information thus obtained provides an indication of the flow rate of the fluid and may also be used to provide an indication of fluid density.

The flowmeter 1 comprises a venturi section 2 retained within a mandrel 3 by means of a lock mandrel 19. In use, the mandrel 3 is installed as an integral part of a production/injection pipe (not shown). The venturi section 2 is attached to the lock mandrel 19 and is inserted downhole and locked into position within the mandrel 3. The use of the lock mandrel 19 allows the venturi section 2 to be removed by wireline where desired.

The venturi section 2 has three pressure ports. A first pressure port 4 is provided at the venturi section's inlet, a second pressure port 5 is provided at the input to the throat and a reference pressure port 6 is provided spaced vertically from the first and second pressure ports. Each pressure port 4, 5, 6 is connected to a respective first, second and reference pressure port outlet 7, 8, 9, by means of respective pressure port conduits 10 provided by passageways in the body of the venturi section 2. The pressure port outlets 7, 8, 9 are grouped adjacent to each other to facilitate their cooperation with respective first, second and third pressure orifices 11, 12, 13 provided in the body of the mandrel 3.

The mandrel 3 houses a two position valve 15, a first pressure sensor 16 and a second pressure sensor 17.

The valve 15 in this embodiment is a two way, three port ball valve which is solenoid operated with a spring return. Each of the pressure orifices 11, 12, 13 (and thus each of the first, second and third pressure ports 4, 5, 6) is connected to a respective input of the valve 15. A first output of the valve 15 is connected to the first pressure sensor 16 and a second output of the valve is connected to the second pressure sensor 17.

Respective electrical outputs from each of the pressure sensors 16, 17 are conveyed to the surface via a cable 18.

The valve 15 is selectively operable between a first valve position and a second valve position.

In the first valve position, the first pressure port 4 is connected through the valve 15 to the first pressure sensor 16 and the second pressure port 5 is connected through the valve 15 to the second pressure sensor 17.

In this configuration, comparison of the outputs from the pressure sensors 16, 17 allows fluid flow rate to be evaluated and monitored.

In the second valve position, the reference pressure port 6 is connected through the valve 15 to the first pressure sensor 16 and also to the second pressure sensor 17. In this configuration, fluid density can be evaluated by comparing pressure at the first pressure port 4 previously sensed by the first pressure sensor 16 with pressure at the reference pressure port 6 sensed by the first pressure sensor 16. In addition, the outputs of the first and second pressure sensors can be compared (both being connected to a common pressure source) to calibrate their outputs with respect to each other or to take into account any difference in their respective outputs.

Comparison of the outputs of the first and second pressure sensors 16, 17 when connected to a common pressure source may be used to compensate for the sensors' drift from original calibration which would otherwise introduce errors into the pressure measurements. This is enabled by use of the valve 15.

Furthermore, the use of the valve 15 in this embodiment alleviates the need for a third dedicated pressure sensor to sense pressure, for example, at the reference pressure port 6.

The fluid flow may be pre-conditioned prior to its passage through the flowmeter. For example, it may be mixed. This may be desirable for multi-phase flows.

In an alternative embodiment, the reference pressure port 6 may be positioned further up or further down the well. It may be positioned at another section of the production/injection pipe, for example for use of the flowmeter in a substantially horizontal section of a well, so that a suitable vertical height difference is maintained between the first and reference pressure ports.

Claims

1. A venturi tube flowmeter having a first pressure sensor connectable in use to a first pressure port of the venturi tube, a second pressure sensor connectable in use to a second pressure port of the venturi tube and one or more valves operable to selectively connect each of the first and second pressure sensors to a common pressure source.

2. A venturi tube flow meter according to Claim 1, wherein each of the first and second pressure sensors are connected to the same valve.

3. A venturi tube flow meter according to Claim 1 or Claim 2 wherein the valve is operable between a first valve position in which the first pressure sensor is connected to the second pressure port and a second valve position in which the first and second pressure sensors are connected simultaneously to the common pressure source and disconnected from the first and second ports.

4. A venturi tube flowmeter according to any of the preceding claims, wherein the common pressure source is a reference pressure port of the venturi tube.

5. A method of calibrating a venturi tube flow meter, having two or more pressure sensors each connected to a respective pressure port, the method comprising connecting the pressure sensors simultaneously to a common pressure source and disconnecting the sensors from the pressure ports

6. A method of calibrating a venturi tube flowmeter according to Claim 5, wherein the calibration of the flowmeter is carried out when the flowmeter is located down hole.

7. A venturi tube flowmeter having a first pressure port, a reference pressure port, a pressure sensor and a valve device to selectively connect the pressure sensor to the first or the reference pressure port.

8. A venturi tube flowmeter according to Claim 7, wherein the flowmeter also has a second pressure port.

9. A venturi tube flowmeter according to Claim 8, wherein the pressure sensor is operable to sense pressure at two of any of the three pressure ports.

10. A venturi tube flowmeter according to any of Claims 7 to 9, wherein there are two pressure sensors.

11. A venturi tube flow meter according to any of Claims 4, 8 or 9, wherein the first pressure port is at a constricted section of the venturi tube, the second pressure port is spaced along the venturi tube from the first pressure port and the reference pressure port is spaced along the venturi tube from the first and second pressure ports.

12. A venturi tube flowmeter according to Claim 4 or Claim 10 wherein one of the pressure sensors is connected to sense pressure at the second pressure port and the other sensor is connected to selectively sense pressure either at the first pressure port or at the reference pressure port.

13. A method of evaluating the density of a fluid, the method comprising connecting a pressure sensor to a first pressure port to sense the pressure at the first port, subsequently connecting the pressure sensor to a reference pressure port to sense the pressure at the reference port, and comparing the pressures sensed at the first port and the reference port.

14. A venturi tube flowmeter comprising a mandrel adapted to be installed as part of a flowpipe, a venturi section having one or more pressure ports and adapted to be inserted into the mandrel for use and a securing device adapted to secure the venturi section in use in the mandrel.

15. A method of configuring a downhole flowmeter in accordance with the flowmeter of Claim 14, comprising the steps of positioning the mandrel downhole as part of a production/injection pipe, inserting the venturi section into the downhole mandrel, aligning the or each of the pressure ports of the venturi section with the or each respective pressure orifice and securing the venturi section at the mandrel for use.

16. A venturi flowmeter substantially as hereinbefore described with reference to the accompanying drawings.