WO1997025594A1

WO1997025594A1 - Improved flow monitoring apparatus

Info

Publication number: WO1997025594A1
Application number: PCT/GB1997/000086
Authority: WO
Inventors: Joseph Calderhead Allan; Andrew Allan
Original assignee: Expro North Sea Ltd
Current assignee: Expro North Sea Ltd
Priority date: 1996-01-13
Filing date: 1997-01-10
Publication date: 1997-07-17
Anticipated expiration: 1998-07-13
Also published as: GB9600699D0; AU1392097A

Abstract

A flowmeter (10; 40; 60) based on the Venturi principle is disclosed in which a flow restrictor insert (14; 42; 62) is located in the bore of a conduit (12) for measuring the flow rate of fluid flowing through the conduit (12). The flow restrictor insert is arranged so that fluid is forced to flow in an annular flow path around the insert. Pressure measurement stations (P1, P2) can be located in the wall of the conduit or in the flow restrictor insert (62). The flow restrictor insert can be permanent or wireline retrievable.

Description

IMPROVED FLOW MONITORING APPARATUS

The present invention relates to flow monitoring apparatus for monitoring the flow of fluids in pipes. In particular the invention is concerned with flow monitoring apparatus in which there are no moving parts and which is based on the Venturi principle. The invention also relates to monitoring the flow rate of hydrocarbon products through a pipeline which carries the products from an underground hydrocarbon reservoir and also to injection-type wells. The hydrocarbon products can be in single-phase flow or multi-phase flow and can be an oil/water/gas mixture or a wet or dry/gas mixture.

For a number of reasons, it is very desirable to be able to measure the flow rate of a fluid in a conduit. It is particularly important to be able to measure the flow rate of the fluid using a flowmeter in which there are no moving parts. This has been done historically using a Venturi flowmeter, particularly in relation to measuring fluid flow through downhole bores and pipelines. The Venturi flowmeter principle is disclosed in U.K. Patent 2186981B in which a constant diameter section of pipe called a gradiomanometer merges smoothly with a converging section of pipe which acts as a Venturi. Applicant's own U.K. Patent No. 2261519B discloses a hydrocarbon flow rate monitor known as a Sureflo device which is able to measure the flow of fluid through a production pipe by using a drill string during drill string testing (DST) of the production pipe. Measurements of pressure are taken from various points from which fluid density and ultimately flow rate of hydrocarbons in the production pipe can be calculated. A modification of this flowmeter was disclosed in applicant's International Patent Application No. W094/16295 where the Venturi flowmeter was provided with pressure measurement stations on either side of the flow restrictor co provide increased flexibility cf use and accuracy of flow rate measurement.

Applicant's existing Venturi flowmeter-based products, which are sold under the Sureflo brand name have three applications: ESP wells (electrically submersible pumps) Sureflo which has a non-retrievable throat; non-ESP wells, such as platform or subsea where the Sureflo (with a remote carrier) has a retrievable throat, and DST (drill string testing) Sureflo. All of these products have the same basic concept, that is a Venturi located within the bore in which the bore is restricted to a throat section which is then widens to a larger bore section. Pressures are measured at the inlet to the Venturi and at the throat of the Venturi and can be measured at a third pressure sensor located upstream or downstream of the carrier to calculate a value for density as disclosed in W094/16295. Various combinations of measurements are made so as to calculate the fluid density and ultimately the flow rate as is set forth in detail in the aforementioned patents.

With existing arrangements, when applied to a wireline retrievable throat design, as shown in Fig. 1 of the accompanying drawings, it will be seen that three sets of seals are used to isolate the Venturi upstream/ throat pressures. Because relatively small pressure differentials are associated with Venturi operation, that is about 10 psi bonded (70 durometer) viton is used. In order to protect the seals from mechanical damage as the wireline assembly is run, it is necessary to include a centraliser on the spacer tube. The inclusion of the centraliser makes it necessary, in turn, to step down from the lock seal bore to the Venturi seal bore. Furthermore, it is also necessary to use a nose piece at the upstream end to provide sufficient flow straightening to minimise turbulence. It should be understood that existing Sureflo device, such as the aforedescribed device, conform to ISO 5167 specification.

However, this tool suffers from a number of disadvantages such as elastomer unreliability, the provision of the step bores reduce the diameter of the through bore, the elastomers require large jarring forces to enter the Venturi seal bore and the wireline assembly is relatively long.

An object of the present invention is to provide an improved flow monitoring apparatus which obviates or mitigates at least one of the aforementioned disadvantages associated with the existing flow monitoring apparatus.

This is achieved in the broadest sense by locating flow restrictor insert in the bore of a conduit or pipe, the flow restrictor insert being arranged so as to create an annular flow path around the insert. In a preferred arrangement the flow restrictor insert has a leading upstream end which is disposed between first and second pressure monitoring stations, whereby pressures measured at these stations can be used to calculate flow rate in accordance with known established methodology.

A remote pressure sensor either upstream of downstream of the insert, but preferably downstream is used in conjunction with one of the pressure sensors at the Venturi, as is well known being disclosed in W094/16295, so as to be able to calculate fluid density p from the pressure difference based on the general formula

P = P_R-P where K is constant

P_R is the remote pressure

P_x is the pressure at the venturi inlet

The remote pressure sensor can be located at any distance from the Venturi and, in practice a distance of 400' (120m) is used.

This value of density can be used to find the flow rate, Q, with the Venturi pressure readings based on the general formula

where K₂ is a constant P₁ is the Venturi inlet pressure P₂ is the venturi bore pressure, p is the fluid density

Alternatively the value of p can be assumed and a remote pressure sensor is not required.

It will be understood that there are simplified versions of general fluid mechanics equations which are well known in the art and which require to be modified to take account of actors such as pipe friction, temperature and hence thermal expansion, the particular dimensions of the pipes and Venturi, discharge coefficients and the like. The general fluid mechanics analysis can be found from the following references: (1) Kay J.M., An Introduction to Fluid Mechanics and Heat Transfer, 2nd Ed., Cambridge U Press, 1968; (2) ISO 5167 (BS 1042), Measurement of Fluid Flow in Closed Conduits, Part 1, BSI; (3) Miller R.W. , Flow Measurement Engineering Handbook, 2nd Ed., McGraw Hill Pub., 1983; (4) Coulson J.M. , Richardson J.F., Chemical Engineering, Vol 1, 2nd Ed., 1970; (5) Gregory, G.A. , Fogarasi M. , Alternate to Standard Friction Factor Equation, Oil & Gas J. April 1 1985, pp 120-127, and (6) Jorissen A.L., Discharge Measurements by Means of Venturi Tubes, Trans ASME, May 1951, pp 403-408.

The flowmeter operates on the Venturi principle but the geometrical arrangement of the structure is radically different from previously disclosed arrangements. The flow restrictor insert is centrally and axially located in the bore and annular flow areas are created between the flow restrictor insert and the conduit bore wall thereby eliminating the requirement for seals. A further advantage of this arrangement is tha the flow restrictor insert may be wireline retrievable as before if used on a temporary basis.

The flow restrictor insert can be oriented in the bore such that the leading end is downstream or upstream. Upstream is preferred as it is easier to retrieve when wireline retrievable assemblies are used.

According to a first aspect of the present invention, there is provided a method of monitoring the flow rate of fluid flowing through a conduit, said method comprising the steps of: providing first and second pressure monitoring stations axially spaced apart along said conduit, said first and second pressure monitoring stations permitting measurement of pressures thereat; disposing within the conduit bore a fluid flow restrictor insert, the leading end of said flow restrictor insert being disposed between the first and the second pressure monitoring stations, the flow restrictor insert being arranged to create an annular flow area in the vicinity of said second fluid monitoring station and to provide a Venturi effect, measuring pressures at said first and said second pressure monitoring points whereby such measured pressures are processed to derive data for determining the flow rate of said fluid.

According to a second aspect of the present invention, there is provided a flowmeter for measuring flow rate of fluid flowing in a conduit, said flowmeter comprising: a flowmeter conduit portion for coupling to upstream and downstream conduits, said flowmeter conduit portion having first and second pressure measurement stations axially spaced along the conduit portion in the wall of the conduit portion; a flow restrictor insert for location in said conduit bore, said insert having a leading end which is disposed when the insert is so located, between the first and second pressure measuring stations, the insert being shaped to cause the fluid to flow through an annular area in the vicinity of the second pressure measuring station passing, whereby a Venturi effect is created by the insert and pressure measurement data from the first and second measurement stations are used to calculate fluid flow rates in the conduit.

Preferably, the flow restrictor insert is wireline retrievable. Alternatively, the flow restrictor insert is secured within the conduit bore.

Preferably also, the flow restrictor insert is coupled to a downstream carrier which is locked to the conduit wall by locking means. Preferably, the insert firstly widens from the carrier towards the conduit wall then reduces in diameter in the upstream direction to the leading end.

The shape of the flow restrictor insert may be varied as long as the combination of the shape and the conduit bore results in a flowmeter which incorporates the Venturi principle.

The flow restrictor is coupled to the bore wall by radial supports and is substantially hydrofoil shaped in side view with the upstream leading end located between first and second pressure sensors and the second pressure sensor being disposed in the conduit wall in the Venturi throat opposite a substantially flat portion of the flow restrictor.

According to a further aspect of the present invention there is provided a flowmeter for measuring the flow rate of a fluid flowing in a conduit, said flowmeter comprising a flowmeter conduit portion for coupling to upstream and downstream conduits, a flow restrictor insert for location within said conduit bore, and having coupling means location securing the insert within the conduit bore, the flow restrictor insert being shaped so as to be disposed substantially centrally in said bore and having a first and a second portion of different diameter extending for respective lengths along said bore, each respective length portion having a pressure measurement station located therein, the insert being shaped to cause fluid flowing downstream to flow through a first annular area in the vicinity of a first pressure measurement station in the smaller diameter portion and through a second smaller annular area in the vicinity of a second pressure measurement station in the larger diameter portion, whereby a Venturi effect is created by the flow restrict insert and pressure measurement data from the first and second pressure measurement stations are used to calculate fluid flow rates in the conduit.

When the first and second pressure sensors are located in the insert, the relatively narrow diameter leading end portion has a first pressure sensor which smoothly connects to the relatively wider portion with the second pressure sensor. With this arrangement there is no need for pressure sensors in the bore wall.

The carrier may be located downstream of the pressure measuring stations or upstream of the pressure measuring stations. Preferably, the insert is centralised in the bore so that the annulus is of a constant size in the vicinity of the second pressure measuring station. Alternatively, the insert is not centralised.

These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:-

Fig. 1 is a cross-section through part of a conduit with a prior art Venturi flowmeter;

Fig. 2 is a similar cross-section through a conduit with a flowmeter in accordance with an embodiment of the present invention incorporated into the conduit, and

Fig. 3 is a perspective view taken of the insert in the tube bore of Fig. 2 showing the structure of the carrier; Fig. 4 is a view of a flow resistor insert, similar to Fig. 2, in accordance with a second embodiment of the present invention; and

Fig. 5 is a view of a further embodiment of a flow restrictor insert where the pressure sensors are located in the insert.

Reference is first made to Fig. 2 of the drawings which depicts a flowmeter, generally indicated by reference numeral 10, which consists of part of a pipeline conduit 12 having two pressure monitoring stations PI and P2 spaced apart axially along the wall of the conduit 10. The conduit 10 is coupled to adjacent pipe sections (not shown in the interest of clarity) . Within the conduit 10 a flow restrictor insert, generally indicated by reference numeral 14, is located. The flow restrictor insert consists of a centralised leading end 16 which is connected by an intermediate portion 18 to a flow restrictor carrier, generally indicated by reference numeral 20. The flow restrictor carrier 20 is located within the bore by means of locking dogs 22 engaging with recesses 24 in the conduit bore 12. The flow restrictor leading end 16 is centralised within the bore by means of centralising buttons, generally indicated by reference numerals 26. Fig. 3 shows that the carrier 20 is generally cylindrical shaped with a cross-piece 21 supporting intermediate portion 18 so that fluid flow passages 28 and 30 are disposed on either side of the portion 18. The intermediate portion is also hollow and has apertures 31 so that fluid can flow into the carrier where it combines with fluid passing through passages 28, 30.

As can be seen from Fig. 2 the flow restrictor insert 16 is generally shaped like a hydrofoil in cross- section with the width of the insert increasing upstream, from portion 18, to a constant width in the vicinity of pressure measurement station P2 and then tapering U_DΞtream to an apex 32 disposed approximately midway between pressure measuring stations PI and P2.

In operation, when fluid flows downstream through the pipe, as shown in Fig. 2, the fluid first of all passes measurement station Pi and pressure is measured. Before the fluid reaches pressure measurement station P2, it encounters the apex 32 of the flow restrictor insert 16 where the fluid is constrained by the insert to travel in the path as shown in Fig. 2 such that in the vicinity of station P2 the fluid flows through an annular area, thus P2 measures pressure of fluid flowing through a much smaller area. The flow restrictor insert 14 creates a Venturi effect which is the same in principle, but with a different structure, to that disclosed in the aforementioned U.K. Patent No. 2261519B. After the fluid passes measurement station P2, it continues to travel through an annular cross-sectional area but which increases as the diameter of the insert decreases until the fluid flow reaches the carrier 20 whereupon it travels on either side of the cross-piece 21, through the passages 28,30 and through apertures 31 and portion 18 before merging within the carrier 20 downstream of the cross-piece 21.

Thus, with the aforementioned device the insert creates a Venturi effect so that the pressures measured stations PI and P2 are different and can be used to calculate flow rate wither with a measured or assumed value of density. Consequently, flow rate as can be achieved as with the Venturi flowmeters of the aforementioned disclosures.

The flowmeter 14 shown in Fig. 2 may be combined with a pressure sensor on a remote gauge carrier (not shown) which can be located upstream or downstream of the flowmeter 14 to provide a further pressure differential using the Venturi inlet pressure (or throat pressure) so that a value of fluid density can be measured as disclosed in W094/16295. If a value of density is assumed then the flowmeter shown in Fig. 2 is all that is needed for measuring flow rate.

Reference is now made to Fig. 4 of the drawings which depicts an alternative embodiment of the invention. In this case the flowmeter 40 has a hydrofoil shaped insert 42 which is located axially within the bore 44 by means of radial supports 46 which lock dogs 46 into bore recesses 48 in the same way as in Fig. 2. It will be seen that the leading end 50 of the insert 42 is located between pressure monitoring stations P_x and P₂ with the insert being flat in the vicinity of P₂ that is, inthe Venturi throat. In operation the flowmeter works in the same way as the first embodiment but requires less length and no carrier is needed. This structure may be permanent or may be wireline retrievable with the downstream end coupling via a mechanism to the locking dogs so that the device can be installed and removed by a wireline tool.

Reference is now made to Fig. 5 of the drawings which depicts a further embodiment of the invention which is similar to Fig. 4. In this case the flowmeter 60 has an insert 62 which has a leading portion 64, located upstream, and a trailing portion 66 located downstream, portion 64 being of smaller diameter (width) than portion 66 and having co-axially directed surfaces 65,67 which are smoothly connected by portion 68. In this case pressure monitoring station P_x is located in portion 64 and pressure monitoring station P₂ is located in portion 66. In this case the monitoring is achieved using known electronic processing circuitry 70,72 to process the signals for storing in memory gauges 74 in the insert or by induction coupling (for a permanent unit) to a wireline lowered unit. A temporary unit in accordance with this embodiment is particularly advantageous if the pressure sensors fail and thus can be readily replaced.

Various modifications may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, all cf the described could be used with or without remote pressure sensors and all of the flowmeters shown could be oriented so that the leading end is downstream instead of upstream. In addition, it will be understood that the flowmeters are described in use in production wells. The flowmeters may also be used in injection-type wells where flow is forced through the pipe in the reverse direction. Thus, the flowmeters can be used to measure flow in both directions. In addition, it will be appreciated that the flowmeter shown in the embodiments of Figs. 3 and 4 may be modified to carry pressure gauges as shown in Fig. 5 so that the tool show in Figs. 3 and 4 would be wireline retrievable. The intermediate portion of flow restrictor shown in Figs 2,3 may not be hollow but could have a solid central portion and side channels, the solid and central portion containing pressure gauge electronics and/or memory gauges similar to those shown in Fig. 5 when the leading end of the insert contains pressure gauges.

It will be understood that the aforementioned structure has many benefits which are believed to be greatest for wireline retrievable tools. Although the ESP Sureflo is assembled in a controlled environment, the improved reliability via seal elimination is considered significant. Therefore, the advantages which this tool has in comparison to the prior art tools are that the seals are eliminated, improving tool reliability and the requirement for step seal bores is eliminated which increases tool through bore. The insert can be located either upstream or downstream of the pressure measuring stations depending on particular requirements.

Claims

1. A flowmeter for measuring flow rate of a fluid flowing in a conduit, said flowmeter comprising: a flowmeter conduit portion for coupling to upstream and downstream conduits, said flowmeter conduit portion having first and second pressure measurement stations axially spaced along the conduit portion in the wall of the conduit portion; a flow restrictor insert for location in said conduit bore, said insert having a leading end which is disposed when the insert is so located, between the first and the second pressure measuring stations, the insert being shaped to cause the fluid to flow through an annular area in the vicinity of the second pressure measuring station passing, whereby a Venturi effect is created by the insert and pressure measurement data from the first and second measurement stations are used to calculate fluid flow rates in the condui .

2. A flow restrictor insert as claimed in claim 1 wherein the flow restrictor insert is coupled to a flow restrictor insert carrier and the carrier and the wall of said conduit portion have locking engagement means such that the insert is securable to the conduit portion, the insert being wireline insertable into the conduit portion or retrievable from the conduit portion.

3. A flowmeter as claimed in claim 1 or claim 2 wherein the flow restrictor carrier is disposed downstream of the insert and is coupled to the insert such that the insert diameter firstly widens from the carrier wall in the upstream direction towards the wall of the conduit portion, stays substantially constant in the vicinity of the second pressure measurement station and then reduces in diameter in the upstream direction towards the leading end.

4. A flowmeter as claimed in claim 1, 2 or 3 wherein the carrier is a substantially hollow cylinder allowing fluid to flow therethrough.

5. A flowmeter as claimed in claim 4 wherein the flow restrictor insert is coupled to a support extending across the conduit by a hollow tube having a plurality of apertures therein to facilitate fluid flow downstream.

6. A flowmeter as claimed in claim 1 or claim 2 wherein the flow restrictor is coupled to the bore wall by radial supports and is substantially hydrofoil shaped in side view with the leading end located between first and second pressure sensors and the second pressure sensor being disposed in the conduit wall in the Venturi throat opposite a substantially flat portion of the flow restrictor.

7. A flowmeter for measuring the flow rate of a fluid flowing in a conduit, said flowmeter comprising a flowmeter conduit portion for coupling to upstream and downstream conduits, a flow restrictor insert for location within said conduit bore, and having coupling means location securing the insert within the conduit bore, the flow restrictor insert being shaped so as to be disposed substantially centrally in said bore and having a first and a second portion of different diameter extending for respective lengths along said bore, each respective length portion having a pressure measurement station located therein, the insert being shaped to cause fluid flowing downstream to flow through a first annular area in the vicinity of a first pressure measurement station in the smaller diameter portion and through a second smaller annular area in the vicinity of a second pressure measurement station in the larger diameter portion, whereby a Venturi effect is created by the flow restrict insert and pressure measurement data from the first and second pressure measurement stations are used to calculate fluid flow rates in the conduit.

8. A flowmeter as claimed in claim 7 wherein the coupling means is provided by radial supports which connect the flow restrictor insert to the conduit wall.

9. A flowmeter as claimed in claim 7 or claim 8 wherein the flow restrictor insert is releasably securable to the conduit wall and is wireline retrievable or insertable.

10. A flowmeter as claimed in any one of claims 7, 8 or 9 wherein the insert is centralised in the conduit bore.

11. A flowmeter as claimed in any one of claims 7 to 10 wherein, in use, the smaller portion is located downstream and the larger diameter portion is located upstream relative to the conduit.

12. A flowmeter as claimed in any one of claims 7 to 11 wherein the flow restrictor insert includes electronic processing circuitry and memory gauges for processing and storing pressure measurement signals.

13. A method of monitoring the flow rate of fluid flowing through a conduit, said method comprising the steps of: providing first and second pressure monitoring stations axially spaced apart along said conduit, said first and second pressure monitoring stations permitting measurement of pressures thereat; disposing within the conduit bore a fluid flow restrictor insert, the leading end of said flow restrictor insert being disposed between the first and the second pressure monitoring stations, the flow restrictor insert being arranged to create an annular flow area in the vicinity of said second fluid monitoring station and to provide a Venturi effect, measuring pressures at said first and said second pressure monitoring points whereby said measured pressures are processed to derive data for determining the flow rate of said fluid.

1 . According to a further aspect of the invention there is provided a method of monitoring the flowrate of fluid flowing in a conduit, said method comprising the steps of, measuring pressures at different axial locations with sensors disposed at first and second pressure measure stations within the insert, the flow restrictor insert being arranged to create different annular flow areas within the vicinity of the spaced first and second pressure measurement stations to create a Venturi effect.