Prognosis and Venturi Meters (wet gas application)

Prognosis and Venturi Meters (wet gas application)
Oil and Gas Focus Group Meeting Weds 11th May 2011, Norwich Prognosis and Venturi Meters (wet gas application) by Jennifer Ayre, Swinton Technology Welcome ladies and gentlemen. I would like to present our paper detailing Application of and Advancements in Differential Pressure Meter Diagnostics, with focus on a Venturi meter application for Petronas.

DP Meter Diagnostics – the Theory
One Meter body P1 t1 t2 DPt Traditional DP Traditional flow rate prediction equation Over the last year a new concept to provide self diagnostic capabilities to any generic DP meter in single phase applications has been developed into an industrially available system. The theory behind the system was presented by Dr Richard Steven at the NSFMW in 2008 and 2009 and is detailed in full in those papers. I will now briefly summarise this theory: Traditionally the flow rate through the meter is predicted using the ISO 5167 standard equation which uses the inlet Pressure (P1) and the TRADITIONAL DP (as we can see here in this simplified Venturi diagram) NOTE: Although the subject of this paper is a Venturi meter, the diagnostic concept can be applied to any generic DP meter Simplified Venturi meter diagram

One Meter body , 3 DP readings P1 t1 t2 t3 DPt Additional downstream tapping The diagnostic concept relies on having a third tapping downstream of the meter body. With this third tapping we are able to read three DPs......

One Meter body, 3 DP readings P1 t1 t2 t3 DPt DPppl DPr Recovered DP PermanentPressure Loss .... that is the TRADITIONAL DP plus the RECOVERED DP and the PERMANENT PRESSURE LOSS as shown in this diagram DPt is the Differential Pressure between the inlet pressure tap (t1) and the pressure tap positioned at the point of low pressure (t2) We refer to this DP measurement as DPt or the ‘traditional DP’. DPr is the DP between the downstream (t3) and low (t2) pressure taps or the “recovered” DP DPppl is the DP between the inlet (t1) and the downstream (t3) pressure taps i.e. the permanent pressure loss, sometimes called the “PPL” or “total head loss”

One Meter body, 3 DP readings P1 t1 t2 t3 DPt DPppl DPr ‘Permanent Pressure Loss’ flow rate prediction equation ‘Recovered DP’ flow rate prediction equation Using the same physical principles as ISO 5167 (i.e. mass continuity and energy conservation), it can be shown that one meter with three separate DP readings provides two further flow rate predictions, [CLICK] one using just the ‘Recovered DP’ (DPr) and one [CLICK] using the ‘Permanent Pressure Loss’ (DPppl). [CLICK] Hence every Venturi meter body is in effect three flow meters: the traditional meter, the ‘recovered DP’ meter and the ‘Permanent Pressure Loss’ meter.

One Meter body, 3 DP readings provides: 3 flow rate predictions! So we have THREE flow rate prediction equations! The traditional flow rate prediction equation using the traditional DP and the traditional meter’s discharge coefficient (top equation) The other two equations require their own flow coefficients (Kr and Kppl) All three flow coefficients (point to Cd, Kr and Kppl) [CLICK] can be found during meter calibration and their uncertainties set (hence the uncertainties of the flow rate predictions can be set). Flow coefficients found during meter calibration

One Meter body, 3 DP readings provides: 3 DP ratios As well as these three flow rate predictions, we also have three DP ratios defined as shown It can be shown that all three DP ratios are constant for any set meter geometry operating single phase flow. [CLICK] These DP ratios can also be found during the same meter calibration as the flow coefficients are found and their uncertainties set. Note: ISO 5167 states that the PLR is constant for any set meter geometry operating single phase flow. Because of the relationship between the three DPs (i.e., the ‘sum’) it follows that all three ratios are constant for any set meter geometry operating single phase flow DP ratios found during meter calibration

One Meter body, 3 DP readings provides: 3 flow rate predictions AND 3 DP ratios SO for ONE meter we have three flow rate predictions and three DP ratios

One Meter body, 3 DP readings provides: 3 flow rate inter-comparisons So what do we do with this information? Well taking the flowrate predictions first of all, we make inter-comparisons between them... By making inter-comparisons between the three flow rate prediction equations, we are in effect comparing the DPs directly. We obtain 3 percentage difference values (the ‘a’ values above) which can each be compared to the equation pair’s summed uncertainties (x,y,z) [CLICK] The pairings are shown here & & & comparable uncertainty

One Meter body, 3 DP readings provides: 3 DP ratio comparisons (actual v calibrated) For the DP ratios, we compare the calibrated DP ratios with the actual DP ratios from the DPs being read from the field, hence obtaining 3 more percentage difference values (the ‘b’ values above), again each is in effect a comparison of two DPs which can be compared to the associated DP ratio calibration uncertainty (a,b,c). & & & comparable uncertainty

One Meter body, 3 DP readings provides: 6 diagnostic results (and comparable uncertainties) DP pair flow rate comparison DP ratio comparison & So we have 6 diagnostic results and comparable uncertainties. We can pair up these results based on the DP pair in question. & &

One Meter body, 3 DP readings provides: 3 PAIRS of normalised diagnostic results DP pair normalised flow rate comparison normalised DP ratio comparison & By dividing each percentage difference by its comparable uncertainty we obtain 3 pairs of ‘normalised’ diagnostic results: Each pair of (x,y) values represents a comparison of one ‘DP pair’ in two different ways. The normalization allows us to easily interpret the results because [CLICK] as long as each diagnostic result is between -1 and +1, all predictions are within allowable uncertainties and the traditional meter’s standard single phase flow rate prediction can be trusted. & & Correctly operating meter: each result between -1 and +1

One Meter body, 3 pairs of normalised diagnostic results, plotted on a Normalised Diagnostic Box (NDB) (-1,1) (1,1) (x1,y1) & (x2,y2) & y - normalised DP ratio comparison In order to visualize the results, we plot the three pairs on an x,y axis: the normalized flowrate prediction comparisons along the x-axis and the corresponding normalized DP ratio comparisons along the y-axis. By super-imposing a 1x1 box around the origin, we have a very clear real time monitoring system: if all points are inside the box, there is no reason to question that the meter is operating correctly, in compliance with ISO5167 and to within its allowable uncertainties; but if any points are outside of the box then there is a problem and that meter’s traditional (or any) single phase flow rate prediction cannot be trusted. (x3,y3) (-1,-1) (1,-1) & x - normalised flow rate comparison

DP Meter Diagnostics – Prognosis
Now a commercially available system (software + I/O gathering) (-1,1) (1,1) Live Field Trials: BP and ConocoPhillips, Orifice meters North Sea Flow Measurement Workshop Paper 2010 (-1,-1) (1,-1) Swinton Technology have developed this theory into a commercially available system which includes software and I/O gathering Following development of the system it has now been tested at two independent test facilities AND trialled at two major UK gas terminals, one operated by BP and the second operated by Conoco Phillips – both field trials were performed on Orifice meter streams and the findings were presented at the 2010 NSFMW.

Petronas Carigali Metering Team challenge...
Can we utilise the Prognosis system (designed and proven for single phase flows) to provide real time monitoring and indication of change in liquid loading of wet gas? Petronas questioned whether the single phase DP Meter Diagnostic solution could be used to provide a real time tool that would identify when there is a change in liquid loading in wet gas applications. Swinton Technology were aware that the DP Meter Diagnostic solution was very sensitive to liquid in gas; however it had not considered using the system as a tool to identify when the liquid loading has changed within a wet gas Swinton Technology were aware that the DP Meter Diagnostic solution was very sensitive to liquid in gas as this renders the system ‘out of balance’ with its ‘normal’ operating conditions of dry gas – it was understood that any significant change in liquid loading would produce a large ‘shift’ in the diagnostic results; however it had not considered using the system as a tool to identify when the liquid loading has changed within a wet gas; (i.e. a gas and liquid flow which has a Lockhart Martinelli parameter of < 0.3) Not before considered

Challenges When Measuring Wet Gas
The ‘apparent’ wet gas flow rate must be ‘corrected’ using a correlation method – requires a spot check to determine the liquid flow rate and Lockhart Martinelli parameter Wet gas is a hostile environment for transmitters – integrity of DP readings is a big issue Saturated DP transmitters are common Transmitters often damaged – drift Water ; hydrates, salt deposits and scale often block impulse lines There are a number of specific challenges that operators face when measuring wet gas: The primary issue associated with measuring wet gas is that the ‘apparent’ wet gas flow rate must be ‘corrected’ using a correlation method. This requires a spot check to determine liquid flow rate in order to calculate Lockhart Martinelli parameter. Such spot checks can be costly and time consuming. The operator needs an accurate indication of when one is needed. The integrity of DP transmitter readings is also a big issue. Liquid presence can cause a huge increase in DP readings so saturated transmitters are common. Wet gas often has slugs which subjects transmitters to damage and a shift in their reading. Hydrates, salt deposits and scale can build up and block impulse lines. Any correlation used to calculate the ‘corrected’ gas flow rate requires the flow’s Lockhart Martinelli (XLM ) parameter. The liquid flow rate is usually determined by spot methods external to the Venturi meter, e.g., tracer dilution methods. With the liquid flow rate the correlation can predict the Lockhart Martinelli parameter and with it the actual gas flow rate. An important question is, with the liquid flow rate measurement being a set input from a spot check, how can the operator know when the liquid flow rate has changed? That is, when does the meter operator know when an update on the liquid flow rate spot check is required? Carrying out tracer dilution is expensive and time consuming and the operator / regulator has to balance this cost against the potential mis-measurements incurred due to a change in liquid loading. The operator does not want to perform the test when it is not required (i.e. when the liquid loading has not changed) but wants to perform it when the liquid loading has changed such that there is a significant mis-measurement and the Lockhart Martinelli parameter needs to be changed. NOTE: Wet gas is a very hostile environment for transmitters – the integrity of the DP readings is a key issue. Liquid presence in a gas can cause a huge increase in the DP readings – you can get a 225% increase in DP with a Lockhart Martinelli parameter of just 0.3. This means that DP transmitters will be saturated if the liquid loading is a little higher than originally expected. Wet gas often has slugs – this causes dp’s to spike dramatically and subjects the transmitter diaphragms to sudden shock increases in pressure which in effect punches the diaphragm and after a short while the transmitter drifts. Wet gas flows are dirty and often contain water as well as light oils. Water is bad news which can form hydrates when mixed with the methane in the gas, water also contains salts and scaling chemicals. Hydrates, salt deposits and scale deposits can (and do) block impulse lines so resulting in erroneous dp readings. In addition on export systems it could identify when exported product is off spec, as a consequence of a large increase in the level of liquid. I will be talking today about a wet gas venturi application on the Petronas Kinarut platform where and the correction approach selected by Petronas was De Leeuw

Petronas Carigali Offshore Platform
Petronas operates the Carigali Offshore Platform which is located offshore about 100 km North-West of KotaKinabalu, Sabah, East Malaysia 100 km North-West of KotaKinabalu, Sabah, East Malaysia

Petronas Carigali Offshore Platform
Operating since 2004 The platform has 4 Venturi meters measuring wet gas Throughput averaging 30 mmscf/d per flow line Hydraulic workover campaign - Production increase from 30 mmscf / d to 72 mmscf / d on two of the flow lines The platform has been operating since 2004 and has 4 Venturi meters measuring wet gas averaging around 30 MMScf/d each. A Hydraulic workover campaign is planned which will increase throughput from 30 MMSCFD to 72 MMSCFD per meter stream. For this reason Petronas require the replacement of the current Venturi element on one of the flowlines The production fluid will flow under reservoir pressure from KINDP-A to Erb West via a subsea pipeline. The well fluid is separated and dehydrated at Erb West before commingle with the Erb West production for export to shore.

Petronas Wet Gas Application
New 6”, 0.7 beta ratio Venturi meter to replace one existing DP Meter Diagnostic solution (Prognosis) applied to new Meter to help identify when liquid loading changes Tracer dilution + wet gas correlation to correct the apparent gas mass flow rate This requires the two flow lines to be upgraded, one with a new meter and the other by using two existing venturis in parallel. A new 6”, 0.7 beta ratio Venturi meter manufactured by DP Diagnostics was selected. Petronas also opted to apply the Prognosis system to the new meter to help determine when there is a change in the liquid loading. Their procedure would then be to take a tracer dilution spot check to determine Liquid mass flow rate and use a wet gas correlation to determine the Lockhart Martinelli parameter and correction factor for the actual gas mass flow rate

Meter to be replaced This is the Venturi which was to be replaced

New 6”, 0.7 beta ratio Venturi meter to be dry gas calibrated And wet gas tested to find Discharge Coefficient (Cd) + all diagnostic parameters to assess the suitability of the Prognosis solution for detecting change in liquid loading In line with best practice (and advice given in ISO 5167 ), Petronas had the meter calibrated. This was to enable the Discharge Coefficient to be found and at the same time to find all other diagnostic parameters for the application of the diagnostics. Petronas also decided to have the meter wet gas tested to a) verify that the meter performs in line accepted theory and published data when measuring wet gas and b) to establish the suitability of the DP Meter Diagnostic solution for this application. The traditional flow rate prediction equation requires knowledge of the meter’s discharge coefficient. ISO 5167 Part 4 states that within a certain geometry range and a certain flow condition range the discharge coefficient has a constant value of Cd = (+/-1%). However, as the Kinarut Venturi meter’s application range is outside of these ranges, Petronas followed the advice given in ISO 5167 and had the meter calibrated. [limitations of the use of Cd = are 50 mm (2”) ≤ D ≤ 250 mm (10”), 0.4 ≤ β ≤ 0.75 and 200,000 ≤ Inlet Reynolds Number (Rey) ≤ 1,000,000] to prove wet gas performance in line with accepted theory

Dry Gas Calibration and Wet Gas Tests CEESI Colorado
I will now present the findings during the Dry Gas Calibration and Wet Gas Testing of the Petronas Venturi meter and the DP meter Diagnostics system.The Dry Gas Calibration and Wet Gas Testing of the system was performed at CEESI’s facilities in Colorado USA.

Dry Gas Calibration CEESI air blow down facility
The Kinarut Venturi was calibrated by CEESI in an air blow down facility up to a Reynolds number of 20,000,000, thereby covering the application’s required flow range (which is 16,000,000). CEESI air blow down facility Reynolds number of up to 20,000,000

Dry Gas Calibration - Results
This graph plots the flow coefficients found over the application’s Reynolds number range The meter’s discharge coefficient was found to be a constant value with an uncertainty of +/-1%. In fact all three flow coefficients were found to be constant with low uncertainties Meter flow coefficients found during calibration Discharge Coefficient = (+/-1%)

This graph plots the DP ratios found during calibration. We can see that the PLR is set at a constant (i.e. the meter only loses 6.7% of the DP created for flow measurement). Also (as expected) the other two DP ratios were found to be constant with relatively low uncertainties Meter DP Ratios found during calibration PLR = (+/- 4%)

Reading of all 3 DPs during calibration enabled identification of all diagnostic parameters All found to be constant with low associated uncertainties The table at the bottom here shows the dry gas calibration results Reading of all three DPs during calibration also enabled the identification of all diagnostic parameters and associated uncertainties required for the DP Meter Diagnostics solution. All were found to be constant with relatively low associated uncertainties NOTE: Because the PLR is so small, a 4% uncertainty means a tiny change in actual terms, hence the uncertainty is low relative to the value.

Prognosis Response to Dry Gas
All single phase flow calibration data plotted on mass on NDB Low DPppl (relative to the other 2 DPs) means more scatter of points that include DPppl We will now look at the Prognosis response to dry gas All the single phase flow calibration data can be plotted on mass on the NDB as shown here. The permanent pressure loss is very small relative to the other 2 DPs, hence there is more scatter in its reading and more scatter in the diagnostic points that include the PPL All points are inside the box, which is trivial as this is the data we are using to set uncertainties. What is interesting is what happens when there is a problem. The following examples show various common problems that can arise when using Venturi meters. If we look closely we can see that the traditional & recovered DP pair results (yellow circles) are clustered closer to the origin than the other two DP pairs. The other two DP pairs both include the PPL. Note that with a PLR of 6.7% the PPL is much smaller than the other two DP’s. Hence, when reading the smaller PPL there is naturally more scatter in the result than for the other two higher DP readings. This explains why the two DP pairs that include the PPL are seen here to have more scatter than the traditional to recovered DP pair. However, note that all points are within the box. In itself this is a trivial result, as we are using this same calibration data to set the uncertainties. Hence, by definition, the points must be inside the box. Baseline Single Phase Diagnostic Results

Prognosis Response to Wrong Pipe ID (wrong schedule)
Pipe ID set too high at 14.63cm (schedule 80) Approx measurement error -2.5% Using all the data gathered from the dry gas calibration, we are able to see the Prognosis response to some common problems. Here we see the diagnostic response (all dry gas data plotted together) when the wrong Pipe ID is entered into the software, in these examples we have pipeID corresponding to the wrong Pipe Schedule entered. In a real life application, the Prognosis software will read constants and characteristics from the stream’s Flow Computer, traditionally there is no way other than due diligence to know that the Pipe ID is accurate. Clearly Prognosis is sensitive to this issue. Too high a pipe ID results in an inlet area that is too large and a subsequent under-reading Too low a pipe ID results in an inlet area that is too small and a subsequent over-reading Pipe ID set too small at 13.18cm (schedule 160) Approx measurement error +4.4% Actual pipe ID cm (schedule 120)

Prognosis Response to Wrong Throat Diameter
Throat diameter too low at ” (9.5268cm) Approx measurement error -6.6% Throat diameter too high at 10cm Approx measurement error +6.1% Similarly with wrongly entered Throat Diameter... Too low a throat diameter results in a throat area that is too small and a subsequent under-reading Too high a throat diameter results in a throat area that is too large and a subsequent over-reading Actual throat diameter cm (3.8506”)

Prognosis Response to Wrong Cd
Cd set too high at Approx measurement error +2.7% We also simulated what the diagnostic response would be to a wrong in-use discharge coefficient On the left we see when the ISO nominal discharge coefficient value (0.995) is used in the flow rate calculation instead of the precise value (1.014) found by the calibration On the right we see when the discharge coefficient is wrongly entered as (instead of 1.014). [CLICK] Hence the need to calibrate a meter to find the correct Discharge Coefficient! On the left we see when the ISO nominal discharge coefficient value (0.995) is used in the flow rate calculation instead of the precise value (1.014) found by the calibration. The result is a discharge coefficient that is too small (1.9% too small) being used in the flow rate calculation and an associated measurement error of approximately -1.9% will occur On the right we see when the discharge coefficient is wrongly entered as (instead of 1.014). The result is a discharge coefficient that is too high (2.7% too too) being used in the flow rate calculation and an associated measurement error of approximately +2.7% will occur Cd set too low at (ISO Nominal Discharge Coefficient!) Approx measurement error -1.9% Illustrates need to have meter calibrated to find correct Discharge Coefficient Actual Cd (+/-1%)

Wet Gas Testing CEESI wet gas flow loop
Once fully calibrated the meter was ready for the wet gas flow tests. Here we see the meter installed on the wet gas flow loop at CEESI, with a Petronas representative who was witnessing the testing Fluid was natural gas and different amounts of a light hydrocarbon liquid (exxsol D80 - kerosene substitute) The first of the tests on the wet gas flow facility were with dry natural gas at 35bar and 75bar with flows within the Reynolds number range of the previous air calibration. Therefore, since fluid type is independent of venturi meter performance, it was theoretically sound to use the results of these tests to double check the air calibration data. These results showed good agreement with the dry gas calibration results as required by theory. CEESI wet gas flow loop Fluid: natural gas and a light hydrocarbon liquid (exxsol D80 - kerosene substitute)

Wet Gas Parmeters XLM = Lockhart Martinelli parameter (dimensionless representation of liquid loading) Wet Gas Definition: gas and liquid flow such that 0< XLM < 0.3 Petronas wet gas application: XLM ≈ 0.02 DR = gas to liquid density ratio (dimensionless representation of pressure) Frg = gas densimetric Froude number (dimensionless representation of flow rate) Just to introduce some Wet Gas parameter definitions as we will use these to describe the conditions of the tests: Xlm is the Lockhart Martinelli Parameter, it represents liquid loading Wet gas is defined as having a Xlm of less than 0.3 (the Petronas application is expected to have Xlm of approx 0.02) DR is the Gas to Liquid Density Ratio and represents the Pressure Frg is the Gas Densimetric Froude number and represents the Flow Rate

Wet Gas Testing Conditions
Pressures of 35 bar and 75 bar Gas flow rates up to 12 m/s 0 ≤ XLM ≤ 0.12 Wet Gas Testing Conditions DR Pressure (bar) Flow rate (m/s) Frg 0.034 35 3.3 1.3 4.3 1.7 0.078 75 5 1.4 7.4 2.0 9.7 2.7 Frg = gas densimetric Froude number (dimensionless representation of flow rate) DR = gas to liquid density ratio (dimensionless representation of pressure) Testing was performed at 2 different pressures at different flow rates and different Lockhart Martinelli parameters up to 0.12 The different pressures and flowrates are depicted here by the ‘Gas to Liquid Density Ratio’ (DR) and the ‘Gas Densimetric Frouds Number’ (Frg) and these were used when analysing the test data The Kinarut liquid loading was estimated to be in the region of Lockhart-Martinelli parameter of 0.02

Wet Gas Testing – Meter Response
The higher the liquid loading (XLM), the larger the over-reading The larger the pressure (DR), the lower over-reading Venturi meters with wet gas flow tend to have a positive bias or over-reading on their gas flow rate prediction. Here we see a plot of all the Kinarut meter wet gas test data, Xlm against % over-reading. Clearly data agrees with established theories: any liquid loading produces an over-reading, the higher the Xlm the higher the over-reading the lower the gas to liquid density ratio (DR) the lower the over-reading for all other parameters held constant Petronas meter wet gas data agrees with established theories

The higher the Xlm the higher the PLR The higher the Pressure (DR) the less an increase in PLR Here is another plot of the data, Xlm against PLR Again, the data shows trends that agree with established wet gas theories Any liquid loading produces an increase in PLR The higher the Xlm, the higher the PLR The higher the DR, the less an increase in PLR for all other parameters held constant A principal first introduced by de Leeuw (which has since been confirmed by independent research) is that an increasing liquid loading (Xlm) produces an increase in Pressure Loss Ratio (PLR) And hence monitoring the PLR can indicate shifts in liquid loading. Another established theory of wet gas flow through DP meters is that for all other parameters held constant, the higher the pressure, the less an increase in PLR. The graph shows PLR vs. Lockhart Martinelli parameter with the set pressure (density ratio) data sets separated out. Hence the Kinarut meter is performing in agreement with established theory and in line with all published data Petronas meter wet gas data agrees with established theories

The Petronas meter is performing in agreement with established theory and in line with all published data Hence monitoring PLR can indicate shifts in liquid loading and instigate a new spot check (a well established technique) So the Kinarut meter is performing in agreement with established theory and in line with all published data Therefore, the well established technique of monitoring PLR can be used to monitor the flow for changes in the liquid loading. (In other words traditionally, a shift in PLR is interpreted as a change in liquid loading. Therefore, a monitored shift in PLR can instigate a new spot check of liquid flow rate and the correction is duly updated. ) But what is the diagnostics response to wet gas and can it be used to detect changes in liquid loading? What is Prognosis response to wet gas and change in liquid loading?

Prognosis Response to Wet Gas
The left hand side plot shows diagnostic response to all wet gas data. It takes very small amounts of liquid in a gas stream for the NDB plot to register a significant issue. In fact, the diagnostic system is so sensitive to wet gas flow that the points are so far away from the NDB that the NDB is just seen as a green dot at the origin. Even at very low liquid loadings (i.e., a Lockhart Martinelli parameter of 0.005) this remains true. [CLICK] The right hand plot shows one data set with the lowest liquid loading (XLM = 0.005). This is also the data set which, when plotted on the NDB, has ALL three diagnostic points closest to the origin. In other words, for all data from the wet gas tests, this is the least dramatic effect we would see in the diagnostics due to liquid loading. [Whenever liquid is present, the DPt v DPppl point is the furthest from the origin and therefore furthest from the NDB of the three points associated with any given flow condition. The other two points in the third quadrant likewise also move away from the origin but the effect is not as visually obvious to the casual viewer as it is for the traditional DP and the PPL point in the first quadrant] All Petronas meter wet gas test data plotted on NDB Point closest to origin (XLM = , DR = 0.078, Frg = 2.7) VERY sensitive, even at very low liquid loadings

0.099 0.049 Same trend for all other DR and Frg data sets 0.020 XLM 0.010 0.005 As the liquid loading increases, the ‘DPt & DPppl’ point moves further away from the NDB. Same with other two points but not as noticeable Wet gas tests were performed at two different gas to liquid density ratios each at different velocities (or Gas Froude numbers) We see here a plot of the diagnostic results for the data set with DR = with Frg = 1.7 It is clear that as the liquid loading increases, the DPt v DPppl point moves further away from the NDB. [CLICK] Actually this is also true of the other two points but is not as dramatic a shift and is not so visibly noticeable. [CLICK] The same trends were seen for the other four pairs of DR and Frg. All data from density ratio (DR) 0.034, gas densimetric Froude number (Frg) 1.7

0.099 But NDB is dwarfed and too small for any practical use 0.049 0.020 XLM 0.010 0.005 Very sensitive to small change in liquid loading SO, this proves that the Prognosis NDB plot is very sensitive to a small change in liquid loading and hence it can be used as an indication of when liquid loading has changed and so when a new tracer sample is required. i.e., [CLICK] monitoring this traditional DP and the PPL point on the computer screen as it is updated with live data offers a real time check on the liquid loading of the wet gas flow But the method is not really practical [CLICK] and how do we know the point has moved ‘significantly enough’ to warrant a new spot check? Fortunately, the “Prognosis” software provides a solution, that is to “zero” the wet gas data plot.... I’ll give an example However, it is understood that such a method would require for the user to memorise and monitor the point co-ordinates. The NDB would be too small for any practical use in such a method of judging co-ordinate position with a wet gas flow. Only monitoring changes in the numerical co-ordinates would practically work. Also, the simple concept of ‘if anything is outside of the NDB, there is a problem, otherwise, the meter is operating correctly’ is not relevant with wet gas flow. Monitoring this point offers a real time check on the liquid loading of the wet gas flow

Zeroing of Prognosis Response to Wet Gas
Wet gas point, DR = 0.078, Frg = 2.7, XLM = 0.005 ‘zero’ If applying the diagnostics for the first time on wet gas, this is the kind of response we expect on the left. It is a classic over-reading pattern. If the liquid loading is uncertain, the operator will perform a spot check to determine liquid loading and correct the apparent gas mass flow. Once the liquid loading is recorded we can then ZERO the diagnostic results, that is apply a correction factor for the given wet gas flow condition [CLICK] The software provides a suggested ‘Z factor’ (the difference in the calibrated PLR and the actual PLR) which the user inputs, the software then mathematically corrects all diagnostic results The zeroing technique takes any wet gas plot and removes the effect of that particular wet gas flow condition therefore placing the points inside the NDB, making monitoring the points a lot more practical. Non zeroed wet gas point Zeroed wet gas point, Z = Z factor (Z = PLRact – PLRcal ) is used to remove the effect of the current wet gas condition

DR = and Frg = 2.7 Diagnostic response to liquid load increase( new XLM = 0.010) Previously ‘zeroed’ wet gas results (XLM = 0.005) XLM = 0.010, Z = XLM = 0.005, Z = This plot shows when the previously ‘zeroed’ wet gas results at the centre of the NDB (hollow points). A subsequent increase in liquid loading (from Xlm = to Xlm = 0.1) produces results which are plotted here as the solid points. In other words, if there is a subsequent change in liquid loading after the zeroing of the points the points move back outside of the NDB thereby indicating a change in liquid loading without the requirement for the operator to closely monitor the co-ordinates. ‘Zeroing’ means no need for operator to closely monitor co-ordinates. Can simply have an alarm when points move ‘outside the NDB’

Wet gas results (XLM = 0.010) ‘zeroed’ using Z = DR = and Frg = 2.7 Subsequent DECREASE in liquid loading (XLM = 0.005) Xlm = 0.01, Z = As before, once the new liquid loading is recorded (and the apparent gas flow is corrected) we can ‘zero’ the diagnostics. In this case we require Z = The solid points of this plot are the zeroed wet gas data for Xlm = The hollow points [CLICK] are the diagnostic response if the liquid loading then DECREASES (in this case returns to Xlm = 0.005) which in turn can be zeroed again The pattern of the points as they move outside of the NDB indicates if the liquid loading has increased or decreased. Hence we see that Prognosis gives a very clear response to either an increase or decrease in liquid loading. Xlm = 0.005, Z = The pattern of the points as they move outside of the NDB indicates if the liquid loading has increased or decreased

DP Transmitter Integrity Issues
Example: Wet Gas, Xlm = 0.05, Approximate measurement error +15% Apparent gas flow rate = 1.15 x Actual gas flow rate Wet gas DP = 1.32 x Dry gas DP ((1.15)^2 = 1.32 ) →Saturated DPs are common Traditionally NO WARNING SYSTEM for false DP readings Saturated DP → negative bias in flow rate prediction Increased PLR → too high liquid loading assumed (apparent flow rate ‘over-corrected’) As mentioned earlier, the integrity of DP measurements is a big problem when measuring wet gas. DP transmitters often become saturated or damaged and impulse lines can be blocked. When liquid flows with a gas flow the resulting traditional DP has an increased value compared to when the gas flows alone. For example, a Lockhart Martinelli parameter of 0.05 can give an over-reading of approximately 15%. This means that the apparent Venturi meter’s gas flow rate prediction is 1.15 times higher than the actual gas flow rate. In turn that means that the wet gas DP compared to the DP if the gas flowed alone is 1.15 squared. That is, the wet gas DP is 1.32 times higher than if the gas flowed alone. For this reason it is a common problem for wet gas flows to saturate the DP transmitters of a Venturi meter. Often users simply do not expect the DP’s to be as high as they are as, they are used to dry gas flow performance, or they under-predict the liquid loading at the design stage and the subsequent large liquid loading in service causes a higher over-reading than predicted. A saturated DP transmitter gives the flow computer an artificially low DP value, and therefore the flow rate prediction will have a negative bias. Also if we are purely monitoring liquid loading by a change in PLR the corresponding increase in PLR can falsely indicate that the liquid loading is higher than it is. (Therefore, an artificially low flow rate prediction may be ‘over-corrected’). [CLICK] Traditionally, there is no warning system to indicate to the operator that the system has a saturated DP transmitter and is therefore in error. Clearly there is the potential to cause significant gas flow rate prediction errors. Huge potential for mis-measurement

Saturated DP Transmitter Example
Solid points: Non-zeroed ‘wet gas’ data (XLM = 0.05) . Hollow points :same data but saturated traditional DP Actual DPt =135.5 bar Saturated DPt = bar Here is a diagnostic plot, solid points show a wet gas data point, hollow points is same data point but diagnostic response when the traditional DP is slightly saturated (in this case DPt = bar instead of actual DPt = bar). This will not be detected just by monitoring the NDB [CLICK] BUT Prognosis has the ability to detect errors in DP readings unlike any other traditional system Effect of saturated DPt is dwarfed by effect of wet gas on NDB BUT.... Prognosis has ability to detect this!

Saturated DP Transmitter Example
Any true DPs must agree with first law of thermodynamics! DPr + DPppl = DPt 91.8 bar bar = bar Compared to traditional DP of bar +8.9% Difference in measured and inferred traditional DP’s Any true DP’s created by any flow through the Venturi meter agree with this equation (DPt = DPr + DPppl). Prognosis calculates the ‘inferred DPt’ (i.e., DPr + DPppl) and compares this to the actual DPt produced from the transmitter. [CLICK] It can clearly be seen if these two values do not agree to within allowable uncertainties hence we know there is a problem with one of the transmitter readings. [Can give an example e.g., 91.8 bar bar = bar, compared to a traditional DP of bar gives +8.9% difference in measured and inferred DPt ] This simple but very effective check is never usually performed in industry Automatic check performed by Prognosis software (typically an alarm is raised if difference > 1%)

Saturated DP Transmitter Example: Dry Gas
Solid points: dry gas data Hollow Points: same data point but saturated DPt Error in any of the three DPs displays a distinct pattern on the NDB – Clear WHICH DP reading is in error Interestingly, if we are measuring dry gas the pattern of the diagnostic results on the NDB is enough to detect a false DP reading (see the plot) AND it is clear WHICH DP is in error (in this case the traditional DP as the DPr & DPppl point has not left the box). In fact, AS LONG AS ALL THREE DPs are being read from the field ANY false DP reading is clear and the pattern of the diagnostic points tells use WHICH DP transmitter is in error DRY OR WET GAS: AS LONG AS ALL THREE DPs are being read from the field the simple check of this sum will alert the operator is any DP reading is significantly incorrect. The traditional method of detecting a change in liquid loading would never detect a false DP transmitter reading DPr + DPppl = DPt Dry OR Wet gas: Prognosis makes a simple check of this sum and can detect any false DP reading

Summary During both dry gas calibration and wet gas testing, the Petronas meter was proven to be repeatable and to behave in line with accepted theory and published data Prognosis system performed as expected and identified simulated errors during the dry gas calibration During the wet gas testing the Prognosis system was shown to be VERY sensitive to liquid flow in gas flow So what have we learnt? DP Diagnostics supplied to Petronas a 6”, schedule 120, 0.7 beta ratio Venturi meter that has been dry and wet gas tested at CEESI. The gas calibration done in the CEESI air blow down facility produced constant diagnostic parameters and associated uncertainties. The Prognosis software developed by Swinton Technology was shown to operate as advertised for single phase gas flow problems, detecting all common errors simulated. The meter was proven to be repeatable during both dry gas calibration and wet gas testing: The meter was “fully” calibrated in single phase flow across the full Reynolds number range of the meters application. Wet gas flow testing was then carried out that showed the Venturi meters wet gas flow performance followed all known general wet gas flow trends for Venturi meters. Prognosis was originally developed for single phase applications - it was only as a consequence of Petronas questioning whether Prognosis could be used to identify an increase in the level of liquid in wet gas, to establish when tracer dilution testing was required, that it was considered for such applications. During the testing at CEESI it was proven that Prognosis could be used to identify when the level of liquid changed. The wet gas flow was clearly seen by the diagnostics. The diagnostics can monitor the health of the DP measurements during the wet gas flow. [repeat!]The diagnostics can also be used to clearly indicate when the liquid loading of the flow has changed.

Summary Zeroing of wet gas diagnostic results allows easy detection of change in liquid loading and pattern of results determines increase or decrease AS LONG AS THREE DPs ARE BEING READ Prognosis will also alert the user as soon as any of the DPs is in error due to saturation / damage / blocked impulse lines When measuring dry gas, Prognosis can identify WHICH DP is in error BUT above that, Prognosis is will alert the user as soon as any DP is in error!!!!!!!!!!!!!!!!!! When used with three independent transmitter readings, the diagnostic solution will detect when one of the DP transmitters is giving a false reading due to saturation, blocked impulse line, drifting etc. This is true in both dry gas and wet gas applications. Therefore Prognosis can be used to provide a number of benefits to operators of both dry gas and wet gas systems

Realisation Clear indication when liquid loading changes
Real time monitoring of system health PLUS - Simple yet powerful check on DP accuracy Real time monitoring of system health Clear indication when liquid loading changes PLUS - Simple yet powerful check on DP accuracy

Petronas Application of Prognosis System
PC running Prognosis Software Field Data I/O Overview of the site system setup Flow Computer Including additional DPs

Petronas Field Experience
Planned Installation Date July 2011 We had hoped to be able to share with you all today some real site data showing how the system is performing; however unfortunately it has not yet been installed – it is due for installation July 2011

Deverapalli Vijay, Petronas Carigali
Petronas view “Petronas are delighted to be pioneers of this new DP Meter diagnostic technology and can see huge benefits in measuring wet gas. Benefits above other methods of monitoring wet gas are clear as Prognosis can identify when there is a Saturated DP transmitter as opposed to a change in liquid loading hence reducing ‘false alarms’ which would otherwise wrongly predict a change in liquid loading.” Deverapalli Vijay, Petronas Carigali

Centrica Ensign Project
Prognosis for: 3 x 6” Venturi Meters 1 x 10” Venturi Meter Potential wet gas issues! Calibrations found all diagnostic parameters fit to Reynolds number with low uncertainties

Calibration results 6” meter no.1 6” meter no.2 Diagnostic Parameter Uncertainty (+/-) Cd = (1e-9)*R 0.65% Kr = (1e-9)*R 1.00% Kppl = (3.6e-9)*R PLR = (1.6e-9)*R 1.60% PRR = (1e-9)*R 0.50% RPR = 4.74-(6.2e-8)*R Diagnostic Parameter Uncertainty (+/-) Cd = (8e-10)*R 0.45% Kr = 1.09-(1e-9)*R 0.80% Kppl = (4e-9)*R PLR = (2e-9)*R 1.00% PRR = (1e-9)*R 0.90% RPR = 5.32-(6.3e-8)*R 1.10%

Meter no.1 using calibration results for meter no.2:

The Future? Proven on single phase applications to provide powerful diagnostic information for any DP meter Proven to provide a method of monitoring liquid loading changes on wet gas Venturi applications AND identify DP measurement errors Establish magnitude of DP measurement error based on given information and pattern of results

Thank You QUESTIONS? Well thank you very much.
Does anybody have any questions?

Prognosis and Venturi Meters (wet gas application)

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Prognosis and Venturi Meters (wet gas application)

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