Patent application title: FLOW MEASUREMENTS IN AN OIL RESERVOIR
Sam Simonian (Paris, FR)
Class name: Measuring and testing borehole or drilling (e.g., drill loading factor, drilling rate, rate of fluid flow) pressure measurement
Publication date: 2012-11-08
Patent application number: 20120279292
The present invention provides for a down-well fluid measuring
arrangement, and related methods, having at least one surface defining
part of a fluid path, the at least one surface having first and second
ports each arranged to deliver fluid to a single pressure gauge (28), one
of the ports being provided in the region of an obstruction formation
(30) provided in the fluid path, the arrangement further including switch
means (34) arranged to change the port delivering fluid to the gauge so
as to allow for determination of a pressure difference of the fluid at
the said ports and a third port located either upstream or downstream of
the first port delivering fluid the gauge to allow of determination of a
pressure difference and hence volume fraction.
1. A down-well fluid measuring arrangement having at least one surface
defining part of a fluid path, the at least one surface having first and
second ports each arranged to deliver fluid to a single pressure gauge,
one of the ports being provided in the region of an obstruction formation
provided in the fluid path, the arrangement further including switch
means arranged to change the port delivering fluid to the gauge so as to
allow for determination of a pressure difference of the fluid at the said
2. An arrangement as claimed in claim 1 and comprising an annular arrangement.
3. An arrangement as claimed in claim 2 and comprising a cylindrical arrangement having the parts provided on the inner or outer surface of a cylindrical section.
4. An arrangement as claimed in claim 1 and comprising an element of production tubing to be employed as one functional element of a production tubing string.
5. An arrangement as claimed in claim 1, wherein the pressure gauge comprises a combined pressure temperature gauge.
6. An arrangement as claimed in claim 1, wherein three ports are provided each of which is arranged to be switched, in turn, to the pressure gauge.
7. An arrangement as claimed in claim 1 wherein a separate switch valve arrangement is provided with each port and which feed respective conduits leading to a connector block or delivering fluid to the gauge.
8. An arrangement as claimed in claim 1 and including conduits from each of the ports leading to a multi-way valve switch arranged to be controlled to determine which of the ports delivers fluid to the gauge.
9. An arrangement as claimed in claim 7, wherein the switch(es) is/are arranged to be controlled in a cyclical manner to allow for repeated delivery of fluid from each of the ports in a repeated cyclical manner.
10. An arrangement as claimed in claim 1, including three ports wherein a first and second of the ports are located in a relatively close manner, with the third port being remote therefrom.
11. An arrangement as claimed in claim 10, wherein one of the first and second ports is provided at the throat of or just after the obstruction formation, and the other at the inlet thereof.
12. An arrangement as claimed in claim 10, comprises an elongate tubing section with the said third port being spaced in the order of one to two metres from the obstruction formation.
13. An arrangement as claimed in claim 1 wherein the obstruction formation is arranged to exhibit a degree of flexibility and resilience.
14. An arrangement as claimed in claim 1 and further including means for facilitating communication of data from the pressure gauge in a wired, or wireless, manner.
15. An arrangement as claimed in claim 1 and including packer means provided interspersed on an outer surface of the arrangement.
16. An arrangement as in claim 1, further comprising a down-well tubing string.
17. An arrangement as defined in claim 1, wherein the obstruction formation comprises a venturi or orifice formation.
19. A method of down-well fluid measurement, including introducing fluid to first and second parts of a measuring arrangement switching in a cylindrical manner the parts into, and out of, fluid communication with a single pressure gauge to obtain pressure readings at the parts by means of the said gauge.
20. A down-well two-phase fluid sensor device arranged to be exposed to fluid in an open hole section of a producing well and having a sensor element arranged to be exposed to the fluid and to determine the volume fraction of the two phases in the fluid, the sensor element also being located so as to sense fluid external of the device and in the generally annular space between reservoir rock and the outer device surface.
21. A device as claimed in claim 20 and including a flow rate detector.
22. A device as claimed in claim 21 wherein the flow rate detector comprises a pressure-drop detector employing an obstruction formation.
23. A device as claimed in claim 22 wherein the obstruction formation comprises a flexible and resilient member arranged to allow passage of down-well tools.
24. A device as claimed in claim 20, wherein the sensor comprises one of a capacitive sensor or resistive sensor.
25. A device as claimed in claim 20, and packer means provided interspersed between sensor elements including means for facilitating communication of output derived from the sensor can be provided and such communication means can comprise wired or wireless connection means.
27. A down-hole production tubing string comprising a fluid sensor device as in claim 20.
 The present invention relates to the measurements to be taken in a
down-hole environment such as that of a producing oil well.
 Known arrangements are available for taking down-well measurements and can comprise pressure and temperature gauges located along the production tubing with a retrievable or fixed venturi for measuring downhole flowrates and volume fractions. The typical arrangement has been to use three separate pressure and temperature gauges; two of which are provided to measure the pressure drop across the venture, and third of which is located typically 100 meters downstream the first two gauges for measuring the volume fraction.
 The differential pressure measurement has historically been made by two individual pressure gauges measuring the inlet and throat pressures across a venturi shaped restriction. By subtracting the inlet and throat pressures, the differential pressure is measured or calculated. The third of the gauges is, as noted above, employed in relation to volume-fraction measurement.
 The present invention relates to down-well measurements and, in particular, to the measurement of fluid flow particularly of two-phase fluids such as for example those comprising oil and water phases, or liquid and gas phases within a producing oil well where liquid should be understood as either oil or water or a combination of oil and water.
 According to the first aspect of the present invention there is provided a down-well fluid measuring arrangement having at least one surface defining part of a fluid path, then at least one surface having first and second ports each arranged to deliver fluid to a common pressure gauge, one of the ports being provided in the region of, or just after, an obstruction formation provided in the fluid path, the arrangement further including switch means arranged to change the port delivering fluid to the gauge so as to allow for determination of a pressure difference of the fluid at the set ports. A third port located some distance downstream or upstream of the first port (this is the port just before the obstruction in the flow path) is arranged such that the same switch means can be employed to deliver fluid from the third port to the gauge.
 The invention can prove particularly advantageous insofar as forming a basis for any required flow and/or volume fraction measurements in a reliable, efficient and easily maintained manner within the down well environment.
 A particular advantage of the present invention over the prior art employing two or more individual gauges is that manufacturing differences (such as thermal drift, pressure accuracy) between the two or more gauges are eliminated; hence eliminating any drift or accuracy differences between the gauges.
 Advantageously, the arrangement can comprise an annular arrangement and which can offer a substantially cylindrical form.
 The ports can be provided in an inner or outer surface of such a cylindrical arrangement which, as a particular advantage, is adapted to form part of a pipe section of a production string. The gauge, switch valve and associated downhole electronics can be either mounted onto a gauge-carrying mandrel which in turn can be welded onto a standard production string, or by the mandrel can comprise a "stand alone" carrier such that it can be threaded in a correspondingly similar manner to the production string and can be added as an "extra" section of the production string.
 The arrangement can therefore advantageously take on the form of production tubing to be employed as one functional element of a production tubing string for achieving the appropriate hydrocarbon recovery but whilst also providing the fluid measurement functionality.
 In particular, the pressure gauge can comprise a combined pressure temperature gauge.
 Of course, it should be appreciated that the arrangement can comprise any appropriate number of ports as required to achieve the requirement measurement scenarios.
 In one particular functional arrangement, which can nevertheless be provided in a relatively compact manner, three ports are provided each of which can be switched, in turn, to the pressure gauge.
 Of course, any variety of switching arrangements can be provided.
 For example, a separate switch valve arrangement can be provided at each port and which feed respective conduits leading to a connector block or delivering fluid to the gauge.
 The switches are controlled in turn such that only one port can deliver fluid to the gauge at any one time; however the switch controller can open a combination of ports to allow `bleeding` or `stabilization` of the pressure contained within the system.
 As will be appreciated, in order to achieve the appropriate measurements, a series of measuring results are built up so as to arrive at an average value. In this manner, the switches can be controlled in a cyclical manner to allow for repeated delivery of fluid from each of the ports in a repeated cyclical manner.
 Alternatively, conduits from each of the ports can lead to a multi-way valve switch which is controlled to determine which of the ports delivers fluid to the pressure gauge.
 Again, the multi-way switch valve can be controlled in a cyclical manner so as to achieve the required repeated measurements at each of the ports and thus the calculation of an average value if required.
 In one arrangement, for example with three ports, first and second ports are located in a relatively close manner, with the third port being remote therefrom.
 Advantageously the obstruction formation can comprise an inner annular member which can be arranged as a venturi or orifice formation.
 One of the first and second ports can be provided at the throat of the obstruction formation, or just downstream therefrom, and the other at the inlet thereof. One particular embodiment of the present invention comprises an elongate tubing section with the said third port being spaced in the order of one or two metres from the obstruction formation; however, the tubing section could be as long as the standard production tubing length which is typically 30 ft.
 Advantageously, the overall longitude dimension of the arrangement is slightly greater than the separation between the third port and the obstruction formation. A particular further advantage of the present invention is that the obstruction formation exhibits a degree of flexibility and resilience.
 In this manner, although the obstruction formation effectively represents a reduction in internal diameter of the tubing section, down well tools can nevertheless pass through insofar as they can cause the obstruction formation to flex so as to allow passage thereby.
 The arrangement can further comprise means for facilitating communication of data from the pressure gauge and which can comprise wired communication means.
 Alternatively, wireless connection means can be provided. It should also be appreciated that the present invention can provide for a down well sensor string comprising a plurality of arrangements such as those discussed above.
 If required, packer means can be provided interspersed on an outer surface of the arrangement.
 The invention can further provide for a method of determining two-phase flow and including steps of the controlled alternating activation of accessing of pressure gauge devices of a sensor string as noted above.
 Of course, the method can include the controlled interrogation of the pressure gauges and, in particular, the retrieval of reading there from in a cyclical manner.
 Yet further, the invention can comprise oil well production tubing including an arrangement as defined above
 Thus, a down hole production tubing sting can be provided comprising one or more of the said arrangements as required.
 According to another aspect of the present invention there is provided a down-well two-phase fluid sensor device arranged to be exposed to fluid in an open hole section of a producing well, and having a sensor element arranged to be exposed to the fluid and to determine the volume fraction of the two or single phases in the fluid, the sensor element also being located so as to sense fluid external of the device and in the generally annular space between reservoir rock and the outer device surface.
 As will be appreciated, this aspect of the present invention is particularly useful for measuring the volume fraction of the two or single phases of the fluid flowing within the open hole section but outside of the production tubing.
 The device can also include a flow rate detector and can further comprise, or include, a carrier member on which the detector and element are mounted.
 As should be appreciated, the flow rate detector can comprise a pressure-drop detector and, in particular, a pressure gauge employing an obstruction formation and a switch valve mechanism to switch between the ports in a cyclic manner as required similar to above.
 Further, the detector can be associated with a flow diverter or flow restrictor or indeed any obstruction formation serving to affect the smooth flow of fluid in relation to the device.
 Advantageously, the obstruction formation comprises a flexible and resilient material arranged to allow passage of down-well tools thereby or therethrough.
 The sensor can comprise one of a capacitive sensor or resistive sensor. Preferably, the carrier member can comprise a substantially tubular member such that the device can effectively form an integral part of a production tubing string.
 Means for facilitating communication of output derived from the sensor can be provided and such communication needs can comprise wired or wireless connection means. The invention can again comprise a down well sensor string comprising a plurality of devices such as those defined above and mounted in series of long string.
 Advantageously, packer means can be provided interspersed between the sensor devices.
 The invention can also provide for method of determining two-phase flow and including the steps of the controlled alternating activation or accessing of sensor devices of the string such as that defined above.
 Advantageously, the method includes the controlled interrogation of the sensor devices and, further, includes taking readings from each of the sensors both for a predetermined period in turn, and, in particular, in a cyclical manner.
 Yet further, the invention can provide for a down hole production tubing string comprising a plurality of devices as defined above.
 It will therefore be appreciated that a particular aspect of the present invention is the provision of an apparatus for, and related method of, measuring two-phase (oil and water or liquid and gas) in a producing oil or gas well. The apparatus can be permanently installed into a producing well without limiting down-hole access for tools etc. As naturally occurring reservoir fluids flow from the reservoir to the surface, the apparatus firstly detects the amount of oil and water (in an oil/water well) or gas and condensate (in a gas well) and secondly the flow rates of the two-phase mixture. The apparatus is also capable of measuring single phase low rates e.g. flow of injected water. The apparatus is made up of a single downhole pressure and temperature gauge which is used to measure the pressure at certain points along the apparatus.
 A device and arrangement embodying the present invention is typically located above the production packer and can form part of the production tubing which runs to the surface. A single electrical cable from the surface can be deployed with the apparatus which forms the communication and power controls from the surface to the apparatus located downhole. In one specific example, the arrangement can include a single downhole Quartz pressure and temperature gauge along with a solenoid actuated valve along with a flexible venturi or orifice section.
 The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which:
 FIG. 1 is a schematic sectional view of a producing well employing an embodiment of the present invention;
 FIG. 1A is a schematic sectional view of a producing well employing an embodiment of the present invention;
 FIG. 2 is a schematic sectional view of a producing well employing another embodiment of the present invention;
 FIG. 3A is a schematic sectional view of a sensor arrangement according to an embodiment of the present invention;
 FIG. 3B is a schematic sectional view of the gauge and switch arrangement of FIG. 3A but in greater detail;
 FIG. 4A is a schematic representation of a tubing member embodying one aspect of the present invention;
 FIG. 4B is a schematic representation similar to that of FIG. 4A but illustrating a different example of an obstruction formation of an embodiment of the present invention;
 FIG. 5 is a schematic representation illustrating the hydraulic arrangement of FIG. 4;
 FIG. 6 is a schematic representation of an alternative hydraulic arrangement to that of FIG. 5;
 FIG. 7 is a schematic illustration of an electrical connection arrangement exhibited by an embodiment of the present invention;
 FIG. 8A and FIG. 8B are perspective views of one example of a flexible venturi member according to the further embodiment of the present invention;
 FIG. 9 is a perspective view of a single mandrel arranged to embody an example of the present invention;
 FIG. 10 is a perspective view of a pipe tubing section, forming one part of a production string, and employing a mandrel such as that of FIG. 9; and
 FIG. 11 is a perspective view of an obstruction formation according to another embodiment of the present invention.
 Various different examples of different embodiments of the present invention are discussed below with reference to the above mentioned drawings and, in particular, in relation to a producing well which is experiences two-phase fluid flow.
 The embodiment illustrated with reference to the FIGS. 1.-3. relates to a producing well extending through gas, and into oil, varying rock structures and which comprise an initial vertical section and then a long generally horizontally extending section.
 Turning now to the FIG. 1, it should be appreciated that the apparatus can be permanently installed into a producing well 10 having an openhole section 12 and, production tubing string 14. As natural occurring reservoir water or injected water moves towards the producing well 10, the apparatus firstly detects the presence of water and secondly the flow rates for the oil and water. The apparatus is made up of resistance or capacitance sensors 16, located on the outside of a production tubing string 14.
 It is an important aspect of this initial embodiment of the present invention that the sensors are positioned as noted insofar as this allows volume fraction measurements within the generally annular space between the production tubing string 14 and the inner face of the openhole section 12.
 The readings for the sensors, and indeed the powering and control thereof, is achieved by way of a surface acquisition system 20.
 The communications between the sensors 16 and the surface acquisition system 20 can be by way of a wired connection or by way of a wireless arrangement.
 Referring now to FIG. 1A, there is illustrated a schematic sectional view of a producing well having a generally horizontal open hole section 11 from which fluid flows in the direction of arrow 13 into the production tubing 15. A standard production packer 17 is employed to instill that all of the fluid flow during retrieval from the open hole section 11 is via the production tubing 15 so as to impinge on a flow meter 19 such as that described herein and which receives power and control data, and delivers measurement data, from/to surface by way of cable 21--it should be noted that the measurement of data and control to the meter can be wireless.
 Referring to FIG. 2 there is illustrated a similar schematic sectional view of a producing well but including a wireless communications pod 22 allowing for wireless communication with each of the sensors and which can then communicate with the surface acquisition system 20 using any wired, or wireless, manner as appropriate.
 Turning now to FIG. 3A, there is illustrated further detail of a sensor arrangement according to a further embodiment of the present invention. As with the earlier example, an openhole section 12 of the producing well has a production tubing string located therein with the openhole packers 18 serving to securely locate the production string within the openhole section 12 and to compartmentalise a section of the reservoir.
 A volume fraction sensor 26 is again located outside the tubing string and the body of this section of the tubing string can comprise a single element in which a pressure gauge 28, switch valve 34 and related controller electronics are located. The pressure gauge 28 is in fluid communication by way of two pressure ports at different points along the inner surface of the production tubing sting. The switch valve 34 can be activated such that fluid from one port provides a pressure-reading at one particular time and the switch valve 34 is arranged to behave in a cyclic manner as also described further herein.
 In the region of these ports, there is provided an obstruction formation which, in this example, takes the form of a relatively shallow annular ring member forming, again in this example, a venturi obstruction 30.
 With regard to FIG. 3B, further detail of the gauge 28 and switch valve 34 arrangement is illustrated, and in particular the manner of switching access to the pressure gauge 28 for each of the two pressure ports associated with an inlet, and throat, of the obstruction formation comprising in this example a venturi arrangement. As clearly illustrated, the switch valve 34 can be controlled in an alternating cyclic manner such that each of the two ports in turn, and in a repeating the manner, communicates fluid pressure through to the single pressure gauge 28.
 As illustrated, one of the pressure ports opens into the inlet of the venturi obstruction assuming fluid flow in the direction of arrow A, and a second of the ports opens into a throat of the venturi obstruction.
 The venturi obstruction 30 causes a pressure difference between the two ports which is indicative of the speed of movement of the fluid along the production tubing.
 As will be appreciated therefore, the speed of movement of fluid can be readily determined and such information combined with the volume fraction measurements.
 Indeed within this illustrated example in FIGS. 3A and 3B, a further volume fraction sensor 32 is provided on the inside of the production tubing string.
 However, in an oil/gas reservoir, the resistance sensors can be replaced by capacitance sensors since the capacitance sensors will be able to measure the volume fraction of the oil and gas. By using a similar ring arrangement in the tube with a pressure gauge, the total rate of oil and gas is measured. Knowing the volume fractions from the capacitance sensor, the individual phase rates are calculated. The sensors are connected to the surface data acquisition unit 20 which can also power and receives data from the downhole sensors.
 In further detail, and in their simplest form, the capacitance sensors operate by measuring current flow from the sensor. Any change in fluid type between the plates of the capacitor would affect the dielectric constant of the capacitor and thus the capacitance thereof. A change in capacitance would result in a change in the amount of current flow and would therefore indicate a change in die-electric material between the plates and so from the Bruggeman law:
m = oil ( 1 - β ) 3 ##EQU00001##
.di-elect cons.m=Relative Permittivity of mixture .di-elect cons.oil=Relative Permittivity of oil β=Water fraction
 The water fraction can then be determined.
 An example of the resistance sensor is made of two plates that are mounted on the outside of the tubing between the annular space (between tubing outer diameter and wellbore inner diameter) and the reservoir (wellbore inner diameter). Now from application of the Ramu Rao law:
σ m = σ w 2 β 3 - β ##EQU00002##
σm=Conductivity of mixture σw=Conductivity of water β=Water fraction
 As noted, a particular feature of the method of this invention is that a volume fraction value is measured in the annular space between the reservoir rock face 12 and the outside of the tube 24 although if required volume faction measurements inside the tubing can be taken. By having sensors measuring the volume fraction on the outside of the tubing, it proves possible to provide the user with information on exactly where the water or gas is entering the lower completion. It should be noted that the arrangements of the present invention is particularly appropriate for long horizontal wells and can be placed in openhole segments divided by openhole packers 18. The structure is intended to be `multi-dropped` on a single wire from surface to the last sensor set. Another method could be to package the sensors with acoustic or radio-frequency communications such that the sensors along the horizontal well communicate with central receiving pod located in the upper completion which in turn is connected to the surface via a wire.
 As will be appreciated, in this illustrated embodiment of the invention, it is proposed to chill a producing well in a conventional manner; either vertical or horizontal. The producing well will be cased to a certain depth thereafter will comprise a vertical openhole section and/or horizontal openhole section. The sensors for detecting water or gas and the two-phase rates will be placed on the tubing which can be deployed into the well. The tubing diameter will be smaller than that of the casing and the openhole section. The array of sensors will be deployed in the openhole section and will be separated by openhole packers. These openhole packers can be either swellable or mechanical packers as an example. The purpose of the packers is to compartmentalise the vertical or horizontal openhole section.
 Each sensor is electrically connected in a `daisy chain` fashion across the openhole section either by wire or a wireless communication system e.g. acoustics or radio-frequency. The last sensor is directly connected to the surface via an electrical cable or communicating with a wireless pod located some distance downstream of the sensor--such as illustrated at 22 in FIG. 2. This wireless pod communicates with the sensors in the lower completion and in turn sends the signals/data to surface via a wired connection. At the surface wellhead, an electrical connection is made between the electrical wire that runs downhole and connects all sensors to the surface data acquisition system. This surface system powers and sends signals to the downhole sensors to be switched. Once a sensor is switched `on` a series of measurements are taken and the data is sent to the surface acquisition box. Thereafter that sensor is switched off and the next sensor is switched on. This switching on & off and taking a measurement from each sensor is a continuous process. Using software, a surface display of whether water is present in a compartment is given to the user.
 The sensors can be mounted onto a sub which can be either metallic or fibre-glass. The sensors and sub are screwed onto the main tubing and deployed into the well. Once the downhole equipment has reached the bottom of the well, the packers are set (if mechanical) or swell with time to form the compartments. The sensors are exposed to the wellbore fluid; hence if water was to arrive at the wellbore, then sensors will detect the presence of water. Also, the two-phase rate will be calculated for each of the flowing components. This illustrated embodiment of a sensor assembly relating to this invention comprises four main components. First, the sensors (e.g. either capacitance or resistance, or combination thereof, and a pressure gauge). Then a carrier such as a sub on-which the sensors are mounted with centralisation system. Next there is the downhole switching electronics and finally the surface data acquisition system and display
 The sensors are mounted circumferentially onto the sub. Electrical connection between the sensors and the switching electronics is made. The sensors are exposed to the wellbore fluid. The sensors are made up of stainless steel plates formed around the circumference of the sub. If the sub is metallic, then insulation will be required between the sensor and the sub. Since this technology is to be used in producing wells, cost effective tubular material e.g. fibre-glass can be used as the sub. In this case insulation will not be required.
 The sub can comprise a carrier for the sensors and the switching electronics. The sub can be metallic or non metallic. If metallic then insulation is required between the sensors and the sub body. If non-metallic then insulation is not required. The sensors are mounted on to the sub and fixed in position. Electrical connections are made between the sensor and the switching electronics.
 As noted, the downhole switching electronics are housed inside the sub and connections are made (top and bottom) between subsequent sensors and the cable to surface. The switching electronics is also connected to the sensors which power and measure from the sensors.
 The surface data acquisition system 20 serves to power and read data from the downhole sensors. Electrical signals are sent from the surface box 20 downhole to the switching electronics. Each switching electronic has its own distinct signature such that when a signal is sent from the surface box to the switching electronics that particular switch is activated and in turn the sensor. The measured voltage/signal from the sensor is sent to the surface data box which in turn interprets the data and graphically displays the information for the user.
 Turning now to FIG. 4A. there is provided a schematic cross section of a fluid monitoring device according to another embodiment of the present invention and which generally takes on the configuration of a tubing section that, in addition to providing the fluid monitoring/measurement required, also forms an integral part of a production tubing string.
 Thus, the arrangement is generally of a tubular section configuration arranged to be located in line with production tubing sections or similar tubing section arrangements offering the monitoring functionality illustrated.
 Within FIG. 4 therefore there is provided a tubular pipe section 32 within the casing in which is provided a hydraulic and electrical system 34 providing the required functionality as to be discussed further below.
 For further illustration, a production packer 36 is illustrated around the outside of part of the tubing section 32 so as to illustrate the manner of secure location of the arrangement within a cased section of a producing well (see FIG. 1A).
 When producing, the two-phase flow is arranged to travel in the direction of arrow B and, as illustrated, this passes along the inside of the tube 32 and via an obstruction arrangement 38 which in the illustrated example comprises an annular venturi formation 38. This appears in cross-section in FIG. 4 and as will be appreciated comprises an elongate annular configuration which includes the throat arranged to offer an abrupt reduction in diameter on the upstream side of the arrangement 38, and a more graduated increase in diameter in the downstream direction. An alternative arrangement of such an obstruction can be formed by using an orifice type formation as discussed in further detail below.
 FIG. 4B is a view similar to that of the flow-detector/sensor arrangement of FIG. 4A but wherein a flexible orifice member 39 is employed in place of the venturi arrangement 38 of FIG. 4A. Further specific details of an example of a flexible orifice member such as that 39 is described later with reference to FIG. 11. As will be appreciated from the positioning of the flexible orifice member 39 relative to the ports 40, 42, the "throat pressure" is now actually measured just downstream of the obstruction formation in the FIG. 4B embodiment.
 It is a particular feature of the present invention that the venturi, or orifice, structure can comprise a flexible member offering an appropriate degree of rigidity but also resilient deformability. In one example, the venturi can be formed from a polyethylene/nitrile material. This has the particular advantage that, while offering appropriate impedance to the fluid flow B generally by way of a decrease in effective diameter of the pipe section 32, the flexible venturi can nevertheless deform when abutted by, for example, a downhole tool so as to allow the tool to pass through the throat of the venturi structure 38 and further along the pipe string as required. Quite commonly, a production logging tool is required to measure the performance of a well and will require access below the production packer, and thus the likely location of the venturi section. Historically, the venturi section will have to have been removed to allow for the passage of the logging tool to its required downhole location. This aspect of the present invention however allows for resilient deformation of the venturi section and thus the ready access of, for example, logging tools beyond the packer and to any required location
 At present, it is necessary to pursue a disruptive and costly process of removal of the venturi arrangement so as allow such a downhole tool to pass deeper into the production string as and when required.
 In the present invention, there is no such need for any "down time" and related expense and the flexible venturi structure 38 can simply remain in place as the tool is urged to be passed through, and then back again, as required.
 The illustrated embodiment of the present invention in FIG. 4 is arranged to provide for volume fraction, and flow rate measurements of the two-phase fluid flowing in the direction of arrow B. To this end, there are provided three ports within the inner surface of the tube section 32 such as ports 40, 42 and 44.
 As will be appreciated, port 40 is located at the inlet of the venturi section 38, port 42 is located in the throat of the venturi section 38 while port 44 spaced some distance further along the tubing section 32.
 As a general example of the dimensions of such a tubing section, and the spacing of the various ports, ports 40, 42 are located generally close to each other so as to allow for pressure difference measurements and thereby determination of the rate of flow of the two-phase fluid. Port 44 however is located in the order of one to two metres away from the venturi section 38.
 The overall longitude dimension of the venturi section is therefore in the order of just over two metres (the venturi is typically 4 inches in length, the distance between the inlet & throat pressure ports is 2 inches and the orifice is 1 inch in length).
 As will be appreciated further, provision of the third port 44 allows for volume fraction measurements and so the appropriate measurements for determining the rate of flow of each of two phases within a two-phase fluid can be obtained by way of the relatively compact structure of just over two metres in length.
 As is already known, the flow rate within the tube is determined by the pressure differences at the ports 40, 42, and the further measurement away from the venturi system of the pressure at port 44 allows for the volume fraction measurements.
 To this end, conduits 46, 48, 50 lead respectively from each of the ports 40, 42, 44 and lead into a downhole solenoid switch 42 which is controlled such that any one of the ports and related conduits 46, 44, 50 at any one time is open to a single downhole pressure and temperature gauge as discussed with particular advantages further.
 The downhole solenoid switch valve 52 is controlled by way of electrical signalling delivered from control wire 54 leading from a connect block 56 which likewise connected to a cable 58 leading to the surface and which carries a variety of control wires or can be a single wire.
 While, as noted, three inlets 46, 48, 50 are provided to the downhole solenoid switch valve 52, a single outlet 60 is provided and which delivers fluid from either of the ports 40, 42, 44 to the single downhole pressure and temperature gauge 62. Readings are taken from the gauge 62 by way of a cable 64 which leads into the connector block 56 and previously mentioned and then into the single cable 58 leading to the surface.
 Turning now to FIG. 5 there is provided clear illustration of the hydraulic arrangement of the present invention insofar as only one wall of the tubing section 32 is shown along with the position of the three ports 40, 42, 44 and the related input conduits 46, 48, 50 to the downhole solenoid switch valve 5, a single outlet conduit 60 leading to the single pressure and temperature gauge 62.
 FIG. 5 therefore illustrates a particularly advantageous aspect of this invention in that, through use of the switch ports 40, 42, 44 and respective conduits 46, 48, 50 it becomes possible to require only a single pressure and temperature gauge 62 in order to achieve all of the appropriate pressure difference measurements or flow rate and volume fraction measurements.
 Appropriate electrical control of the solenoid switch valve 52 dictates that only one of the three ports can communicate with the pressure temperature gauge 62 at any one time however the switch controller can open a combination of ports to allow `bleeding` or `stabilization` of the pressure contained within the system.
 The switch valve 52 is therefore arranged to switch, in a cyclical manner, each of the conduits 46, 48, 50 in turn to provide pressurized fluid to the pressure temperature gauge for an appropriate length of time, and for appropriate number of separate measurements, in order to build up a volume of results that can be analysed as appropriate to determine an average figure or otherwise.
 Employing just a single pressure temperature gauge in this manner proves particularly advantageous insofar as there is no need for any recalibration between gauges, nor likely for any drift in the readings nor any inaccuracies that will otherwise arise between the use of three separate gauges, or a differential pressure gauge.
 There are of course also associated advantages over cost and simplicity of use and maintenance.
 The particular example of FIG. 5 is in no way limiting and any variety of control arrangements can be provided in order to switch, in turn, each of a plurality of ports to a single pressure and temperate gauge.
 Merely as a yet further example, reference is therefore made to FIG. 6 which again illustrates just one sidewall section of a tubing section of the present invention and in which similar features to those appearing in the previous diagrams employ similar reference numerals.
 Thus, there is again provided a series of three ports 40, 42, 44 each leading to a respective conduit 46, 48, 50.
 However, in the example of FIG. 6, rather than leading to a single downhole solenoid switch valve, each of the ports leads to its own separate two-way i.e. open/close switch 66, 68, 70 as illustrated.
 Further conduits then lead from the outlets of each of the switches 66, 68 and 70.
 It is these outlet conduits 72, 73, 74 for each of the three switches 66, 68, 70 respectively that leads to a four-way connector block 76.
 As illustrated, the four-way connector block has three inputs faired respectively by each of the conduits 72, 73, 74, and a single output conduit 60 which leads to the single pressure temperature gauge 62 of the present invention.
 Thus, rather than achieving the switching controlled functionality at the connector block 76, each port is associated with its own control switch 66, 68, 70 to determine which of the ports communicates via the connector block 76, with the conduit 60 and thus the single pressure and temperature gauge 62.
 No switching is provided within the connector block 66 and appropriate cyclical control of each of the switches 66, 68, 70 is provided by electrical means such that only one of the ports 40, 42, 44 can communicate through to the single pressure and temperature gauge at any one time however the switch controller can open a combination of ports to allow `bleeding` or `stabilization` of the pressure contained within the system. Such open and closing occurs in a repeated cyclical manner so that, as before, a series of measurements can be built up and an appropriate volume of data established. In the illustrated example, switch 70 is open such that port 44 is in communication with the pressure and temperature gauge 62 by way of the conduits 50, 74, the connector block 76 and the conduit 60.
 The pressure being experienced at port 44 within the tube section is therefore determined at the pressure and temperature gauge 62.
 As with the hydraulic arrangements, a variety of electrical arrangements can be provided although only one example is found in FIG. 7 but a clear illustration of the arrangement employed within the embodiment of FIG. 4.
 Firstly, there is illustrated the downhole solenoid switch valve 52 connected to control cabling 54 through which appropriate control signals are received so as to establish the switched timing of the solenoid switch valve so as to achieve the required cyclical series of pressure readings at each of the three ports: The signals being fed via the connect wire 54 and connect block 56 to the cable 58 which runs further with the downhole pipe string to the cable and the surface-located electronic management/measurement system.
 Likewise there is illustrated the single pressure and temperature gauge 62 which comprises a transducer member experiencing the pressure provided at each port in turn and producing an electrical signal delivered by way of electrical connector cable 64 to the connector block 56 and then into the cable 58 rising to the surface.
 Reference is now made to FIGS. 8A and 8B which comprise perspective illustrations of an annular flexible venturi arrangement 38 such as that illustrated in FIG. 4.
 FIG. 8A is shown in the direction of fluid flow into the annular venturi arrangement 78 and shows clearly the steeper incline 80 presented on the inlet side of the arrangement.
 FIG. 8B illustrates the annular venturi arrangement 78 from the opposite side and the somewhat more gentle incline 82 presented by the outlet side is clearly illustrated.
 Also illustrated within FIGS. 8A and 8B, although not shown in a schematic representation of FIG. 4, are longitudinal fin sections 84 upstanding along the length of the venturi arrangement and serving to stabilize the flow of fluid through the venturi and to allow `stand-off` between a production logging tool passing through the venturi--this will allow fluid flow between inlet and outlet of the venturi section and hence create zero differential pressure between inlet and outlet, as a production logging tool passes through it.
 Turning now to FIGS. 9 and 10, there are illustrated by way of perspective views, a single mandrel, of lengths in the order of 8 ft, and which is arranged to have mounted their on a switching/sensing arrangement such as that discussed herein. The mandrel itself can be threaded such as to be screwed into a production tubing string or the mandrel itself is mounted onto a section of production tubing string comprising tubing section such as that of FIG. 10 and having a length in the order of 30 ft.
 Finally, reference is made to FIG. 11 which comprises perspective illustrations of another embodiment of obstruction formation 86--and comprising an example of the flexible orifice 39 illustrated in FIG. 4B. This example of an obstruction formation 86 embodying the present invention comprises an annular body 88 having four inwardly extending thin segments 90-96 separated from each other as illustrated so as to flex independently. It should be appreciated however that any appropriate number, and configuration, of inwardly directed flexible things can be provided. Generally, the degree of flexibility and strength will determine the number of fins employed. As with the venturi arrangements discussed above the orifice formation 86 forms a partial obstruction to the flow of fluid within the production tubing so as to produce a pressure difference which can be determined by the pressure gauge. The gap between the fins are there such that fluid can flow between inlet and outlet, and hence create zero differential pressure between inlet and outlet, of the orifice during the passage of a production logging tool.
 While a tubing section can be provided with such an orifice arrangement, or indeed a venturi section, formed integrally therewith such arrangements/sections can be retrofitted or at least removable and replaceable as required. In this manner, and with specific reference to the orifice formation 86, the outer diameter thereof is arranged such that it can be securely received at appropriate location within the tubing section. Indeed, the said appropriate location of the inside of the tubing section may include a formation for engaging with the perimeter of the formation 86.
 As mentioned previously, a particular feature of the present invention is that the venturi structure can be provided from a flexible and resiliently deformable material so as to allow for the passage in, and out, of downhole tools. In the current art use of known venturi formations upstream of the venturi arrangement would otherwise require initial removal of the pipe section offering the venturi structure which of course would prove a particularly time consuming, expensive and complex operation.
 Typically, the system will measure the pressure and temperature at one port position for 6 hours and then switch to the next position. After 24 hours of measuring, analysis of the data is performed by the surface acquisition system where P1-P2=differential pressure across the venturi which in turns gives the total flow rate and P1-P3=gradiomanometer pressure which in turn gives the volume fractions between the two-phase fluids. Of course, if a single phase fluid is flowing eg 100% water, then no need to calculate P1-P3.
Patent applications by Sam Simonian, Paris FR
Patent applications in class Pressure measurement
Patent applications in all subclasses Pressure measurement