WO1991005135A1

WO1991005135A1 - Phase fraction meter

Info

Publication number: WO1991005135A1
Application number: PCT/GB1990/001499
Authority: WO
Inventors: Nicholas William King
Original assignee: UK Secretary of State for Trade and Industry
Current assignee: UK Secretary of State for Trade and Industry
Priority date: 1989-10-02
Filing date: 1990-10-01
Publication date: 1991-04-18
Anticipated expiration: 1992-04-02
Also published as: GB8922136D0

Abstract

An apparatus for measuring the various fractions of a multi-phase flow system includes a chamber (13) bounded by a casing (12) and by a pipe (10) which defines a passage (11) to which the chamber (13) is connected by a series of perforations (14). Associated with the chamber (13) are means (15a, 15b), such as, for example, floats within the chamber, for defining interfaces of stratified layers (20, 21, 22) of fluid within the chamber (13).

Description

PHASE FRACTION METER

The present invention relates to apparatus for measuring the various fractions of a multi-phase (in which term is included multi-component) flow system, and is particularly concerned with multi-phase flow systems containing gas, oil and water such as issue from oil wells.

It is important that the proportions of gas, oil and water in the output from oil wells be determined at as early a stage as possible, in order to assist in processing of the output and also for fiscal reasons (where it is r. rmally only the oil content of the output which is taxed).

Conventionally this task has been achieved by introducing samples of a well output into settling tanks where the 3 phases have been allowed to settle into separate layers so enabling their individual percentages to be determined. This syβtem is expensive in terms of equipment, and of time. It may also be inaccurate in the case of wells having, as can occur, large fluctuations in the individual fractions of flow. Recently flow measurement systems have been suggested, as for example in US Patent k, 29,581 and UK-A, 8520363, where continuous measurement of the various individual flow rates is attempted. In these systems the total flow rate is measured, and a-sample of the total flow is then diverted from the main flow, passed through a separator where the gaseous and liquid components are separated, after which the liquid components are tested to determine the water to oil ratio (for example by measurement of the density thereof). Such flow measurement systems are complicated, requiring a great deal of complicated measuring equipment. Also the provision of a suitable separator of reasonable size is not easy. The present invention supplies a simplified phase fraction meter.

According to the present invention apparatus for use in a phase fraction meter has a length of pipe defining a fluid passage, a casing defining a chamber surrounding a portion of the pipe and a

SUBSTITUTESHEET plurality of perforations extending the length of the chamber and connecting the passage to the chamber, and is characterised in including means for defining, when the pipe is substantially- vertical and has fluid flowing therethrough, interfaces between stratified layers of fluid within the chamber.

The means for defining the interfaces might include, for example, one or more floats of appropriate density within the chamber, means for measuring differential pressure between various portions of the chamber, and one or more of acoustic, radiative, electrical or nucleonic instruments disposed within, around or axially along the pipe or chamber.

Additionally, means might be provided for measuring the temperature and pressure within an upper most layer of fluid within the chamber. According to a further aspect of the invention a method for measuring the component fractions in a multi-phase or multi- component flow includes the steps of passing the flow through a substantially vertical pipe, a fluid passage through which is connected by a plurality of perforations to a chamber, and determining the position of interfaces between stratified fluid layers within the chamber.

Flow through the pipe can be in either direction. It will be realised that the flow rate through the chamber must be slow, in order for stratification to take place. Only a small fraction of the total flow through the pipe will therefore pass through the chamber. However the percentages of fluids in the chamber at any time will be representative of the total flow.

In GB Patent N° 288,725 an apparatus is described having a chamber surrounding a perforated pipe. A mixture of gas and liquid passing through the apparatus is totally discharged tangentially into the top of the chamber and centrifugal effects cause separation of gas and liquid. Gas passes through perforations in the pipe at the top of the chamber, whilst liquid passes through perforations at the bottom of the chamber, both gas and liquid then flowing downwardly through the pipe. The depth of liquid in the chamber at

SUBSTITUTESHEET any time is, by calibration, related to liquid flow-rate. This apparatus is only suitable for use with a single phase liquid, and can give no indication of the relative percentages of gas and liquid in the total flow. One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing which is an elevation, in section, of apparatus according to the invention.

Apparatus for use in the invention includes a length of pipe 10 defining a passage 11. A casing 12 defines a chamber 13 surrounding a portion of the pipe 10. The passage 11 and chamber 13 are connected by a plurality of perforations, such as those shown at lk. which extend along the length of the chamber 13. At an end of the chamber 13 which, in use, will be at the top are a pressure transducer Ϊ6 and a temperature transducer IT. Also within the chamber 13 are floats 15a, which has a density such that it will settle at an interface between layers of water and oil, and 15b of a density such that it will settle at an interface between oil and gas. In use the apparatus is connected in a substantially vertical position in the output line from an oil well. Fluid flow from the well will pass through the passage 11. Some of this fluid flow will percolate through the perforations l into the chamber 13 and back through these perforations lk to the passage 11. By suitable sizing of the perforations lk the rates of percolation there through can be arranged to be such that the components of the flow, namely water, oil and gas will stratify within the chamber 13 as indicated at, respectively, 20, 21 and 22. The floats 15a, 15b will settle at the interfaces between the water and oil, and between oil and gas respectively. The temperature and pressure of the gas will be measured by the instruments l6, IT respectively. Information regarding the position of the floats 15a, 15b and of the temperature and pressure is passed by a means of communications 18 to suitable analysis equipment. It will be realised that as the fractions of the flow through the passage 11 change, so will the rates of flow into and out of the chamber 13 and so will the positions of the interfaces

SUBSTITUTESHEET k between the layers 20, 21 and 22. The various measurements taken enable the component fractions of the flow to be determined.

It will be realised that within the chamber 13 the pressure in layer 22 will be less than in the layer 21, which will be less than that in the layer 20. The pressure in layer 22 will be less than the pressure within the passage 11, and the pressure within the layer 20 will be greater than the pressure within the passage 11. This ensures that there will be continual flow between the passage 11 and chamber 13. It will be realised that apparatus according to the invention can be positioned at any desirable position within the well outlet line, for example close to the well head or close to the output collection point. Fluid flow through the passage 11 may be either upwards or downwards. The apparatus may advantageously be used in conjunction with a mass flow measurement unit measuring total flow through the passage 11. Such a unit need not necessarily be physically close to the apparatus.

It will be realised that many alternative forms of the apparatus are possible within the scope of the invention. For example the pipe 10 may have a cross sectional shape and area which vary along Its length. The sizes and dispositions of the perforations lk may vary along the length of the chamber 13. Performance of the apparatus might be assisted by the presence of baffles in the passage 11, within the chamber 13 or both. It may, in some instances, be advantageous to provide a homogeniser to thoroughly mix gaseous and fluid flow downstream of the chamber 13. If required, a flushing system might be incorporated in the apparatus to clear any deposits away from the perforations lk. Such a system might consist, for example, of a valve positioned in the passage 11 at some position along the chamber 13 so that greatly increased flow is forced through the perforations llj*.

It will also be realised that many alternative forms of measurement within the chamber 13 may be used. For example the differential pressure between various positions in the chamber 13 might be measured. Alternatively one or more of acoustic,

SUBSTITUTESHEET radiative, electrical or nucleonic instruments may be disposed within or around the pipe, the chamber or both, or disposed axially along the pipe, chamber or both. Suitable sensors might include, for example, the Texaco Microwave Water Monitor, the Endress and Hauser"Aquasyst" Capacitance meter, the ICI Tracereo or the Sarasota Automation Densitometers, and the Endress and Hauser level sensor.

It will be realised that apparatus according to the invention might also be useful for multi-phase or multi-component flows other than those issuing from oil wells and for flows having more than 2 liquid components. When such flows do not contain any gaseous phases there may be no need for instruments such as the pressure sensor 16 and temperature sensor 17.

It will be realised, of course, that use of the apparatus requires that the various fluids be immiscible or that they have only limited, and^' preferably predictable, solubility in one another.

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Claims

CLAIMS What is claimed is:

1. Apparatus, for use in a phase fraction meter, having a length of pipe (19) defining a fluid passage (11), a casing (12) defining a chamber (13) surrounding a portion of the pipe and plurality of per¬ forations (14) extending the length of the chamber and connecting the passage (11) to the chamber (13) characterised in including means (15a, 15b) for defining, when the pipe (10) is substantially vertical and has fluid flowing there-through, interfaces between stratified layers (20, 21, 22) of fluid within the chamber (13).

2. Apparatus as claimed in Claim 1 characterised in that the means for defining interfaces includes one or more floats (15a, 15b).

3. Apparatus as claimed in Claim 1 characterised in that the means for defining interfaces includes differential pressure measurement mea'ns.

4. Apparatus as claimed in Claim 1 characterised in that the means for defining interfaces includes one or more of acoustic, radiative, electrical or nucleonic instruments.

5. Apparatus as claimed in any one of Claims 1 to 4 characterised in including means (16,.17) for measuring temperature and pressure within, in use, an uppermost layer of fluid within the chamber.

6. A method of measuring the component fractions in a multi-phase ormulti-component flow, including the steps of passing the flow through a passage (11) in a substantially vertical pipe (10), the passage (11) being connected to a chamber (13) surrounding a portion of the pipe (10) and connected to the passage (11) by a plurality of perforations (14) which extend the length of the chamber (13), characterised in defining the interfaces between stratified layers (20, 21, 22) of fluid within the chamber-

SUBSTITUTESHEET