Measurement Library

North Sea Flow Measurement Workshop Publications (2009)

New Challenges In Oil & Gas Measurement
Author(s): Douglas Griffin
Abstract/Introduction:
The topics covered in this short paper by no means represent an exhaustive list. However, some of the major oil and gas measurement issues arising from the development of the remaining reserves in the UK sector of the North Sea are presented from DECCs perspective. The purpose of this paper is to stimulate discussion in these areas at this years workshop, as well as to clarify DECCs position in one or two key areas.
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Document ID: BDAD2BF3

Calibration Errors Of Ultrasonic Meters In The Bernoulli Laboratory Due To Non-Isothermal Flow Conditions.
Author(s): Aernout Van Den Heuvel, Frans Doorman, Piet Van Den Herik, Arjan Stehouwer, Robert Kruithof,
Abstract/Introduction:
The Bernoulli laboratory (Westerbork) in the Netherlands, jointly operated by Gasunie, NMi and KEMA, holds a record of over 30 years in calibrating very large gas meters at high pressure with natural gas. NAM, a major producer of natural gas in the Netherlands, utilises a large number of ultrasonic meters. Elster-Instromet is a world wide operating manufacturer of multi-path ultrasonic meters. Gastransport Services is the national gas transporting company of the Netherlands, who is connected to the network of NAM via several delivery stations utilizing ultrasonic meters. Due to the results of five calibrations of 24-inch ultrasonic meters in the Bernoulli laboratory early 2008, a quality check procedure (number QC-11) was started by the Bernoulli laboratory. Four out of five ultrasonic meter showed strongly non-linear behaviour at low flow rates, with a maximum at about 560m3/h (approximately 2% of Qmax) with errors peaking as high as +2%. Taking into account, the demands set in ISO/FDIS 17089-1: 2009(E), all four meters would have been rejected had the standard had already been ratified. Together, the manufacturer, the user and the calibration facility decided to give high priority to quickly identify and resolve this problem. After excluding all straightforward errors, two possible causes remained on the short list: a disturbed flow profile at low flow rates, typically below 2 m/s, and meter problems. A series of experiments and improvements to the calibration facility were executed in the course of 2008: an additional temperature measurement at the bottom dozens of calibrations of one specific 24-inch ultrasonic meter, made available by the user (this meter was even calibrated in the up side down position) thermal lagging was improved and finally, in January 2009, the full measurement section was insulated. Applying full thermal lagging with 15C temperature difference between gas and ambient, temperature differences were largely reduced, as was the error of the ultrasonic meter at 800m3/h. Also the ultrasonic meter diagnostics showed a large improvement of the flow profile. Although the thermal lagging had insufficient heat transmission resistance, which prevented a 100% success, the experiment showed, without doubt, that non-isothermal flow conditions were the root cause of the calibration errors. Non-isothermal flow conditions have previously been addressed at the 2005 Flomeko conference 3, however, the discussion at that time concentrated on the temperature measurement error and the effect was characterised as stratification. In that paper, other effects of non-isothermal flow: non-axial velocity components and an asymmetric flow profile, were not recognised as a problem. The majority of gas meters calibrated in Bernoulli laboratory, turbine meters, are not sensitive to non-isothermal flow conditions. Ultrasonic meters however, measure velocity components and may be very sensitive to a combination of non-isothermal flow, depending on their path configuration. Clearly, the Q.Sonic-4C of Elster-Instromet is sensitive to these non-isothermal flow conditions present in Westerbork.
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Document ID: 7978C699

Field Experience Of Ultrasonic Flow Meter Use In CO2-Rich Applications
Author(s): Keith Harper John Lansing Toralf Dietz
Abstract/Introduction:
Ultrasonic gas flow meters have gained a wide acceptance in the field of natural gas exploration, transport, storage and distribution as well as in the process industry. There is one major segment, which could not be addressed so far with this technology - high attenuating gases like Carbon Dioxide. On the other hand exploration of less conventional natural gas sources will lead to more diverse operating conditions and compositions for natural gas measurement. One significant change compared to traditional sources is the increased level of CO2 in the gas. While standard applications deal with levels well below 5 mole percent, this amount may be as high as 20 mole percent, or even higher at some installations. Re-injection of CO2 into declining oilfields will require accurate and reliable flow measurement. Such applications contain up to 60% CO2 and require an accuracy level comparable to custody transfer for natural gas. While the flow measurement is currently being done primarily using Dp devices, such as orifice meters, it would be a significant improvement to use ultrasonic meters with their increased functionality, larger turn-down ratio reduced maintenance, and diagnostic capabilities. Applications such as CCS (Carbon capture and storage) with CO2 concentrations near 100% are even feasible today.
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Document ID: 12F938E0

Oiml R 137-1, The First Ultrasonic Meter To Be Tested To Accuracy Class 0.5?
Author(s): Skule Smrgrav Atle K. Abrahamsen
Abstract/Introduction:
Over the past 20, 10 and 5 years gas production world wide has been on an ever increasing rise. At the same time measurement of gas has been changing from the traditional turbine and orifice meters to the ultrasonic meters. Multi-path gas ultrasonic meters have by now become the preferred device for custody transfer measurement. The first step in an international acceptance of these state of the art technology based devices was probably the first edition of the AGA Report number 9 which was released in June 1998. This report was updated and the second edition was released in April 2007. The AGA Report No. 9 has since been used all over the world as the reference standard when ultrasonic meters have been specified for most allocation and custody transfer projects. In Europe there has been a working group in session for several years working on a corresponding ISO standard for Ultrasonic meters, and the ISO 17089 will hopefully be officially released in 2009. But, there is another standardization organ in Europe which released a gas meter recommendation in 2006 which is also applicable to ultrasonic meters - the OIML R 137-1. This creates a third standard which manufactures of gas ultrasonic meters may be asked to follow. Already a number of meters have been tested to the defined accuracy class 1 in OIML R 137-1, but FMC has now fully tested what we have been informed is the first multi-path gas ultrasonic meter to the accuracy class 0.5 together with the PTB of Germany. This paper will describe the key items of OIML R 137-1, point to the differences and similarities between OIML R 137-1 and AGA-9 and highlight certain limitations/shortcomings in OIML R 137- 1. The second part of the paper will describe the detailed tests required for accuracy class 0.5, show the results from multiple size meters tested and comment on how the industry and standardization committees can work even closer together to get even more applicable and relevant standards and test methods. The latter to achieve more repeatable, comparable and usable results across the industry, and across the different geographical areas of our shrinking planet.
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Document ID: 73265BDA

Ultrasonic Meter Condition Based Monitoring - A Fully Automated Solution
Author(s): George Kneisley John Lansing Toralf Dietz
Abstract/Introduction:
The customer requires a fiscal meter that measures with highest reliability within the required accuracy limits throughout the life time. Whenever this requirement isnt fulfilled due to changed process/flow conditions or changes to the meter, the user needs to be warned in real-time. To ensure such warning, the diagnosis parameters implemented into modern ultrasonic flow meter can be useful. Since the introduction of the global diagnosis concept major improvements in diagnosing a USM have been achieved. This requires a thorough understanding of the meters operation and also understanding what normal, and non-normal responses of all diagnostic parameters are in order to insure proper operation. The automated diagnostics will monitor, and alarm, on all important parameters such as Profile Factor, Symmetry, SNR, Turbulence, etc. These warnings are today an important factor for driving the condition based maintenance of the installation. Additionally, it is very important to have a long-term history of these diagnostics in order to properly determine if a meter is still operating accurately. Beside this features inherent to every ultrasonic flow meter with a multiple number of paths additional concepts to compare measurements directly exist. Two main concepts can be realised - permanent serial metering with two independent fiscal meters or with a combination of a fiscal and a check meter, introduced by TransCanada Pipeline (TCPL) several years ago. This concept involves using a single path USM downstream of the fiscal multipath meter. Papers have shown that single path USM meters are significantly affected by abnormal measurement conditions such as flow conditioner blockage, pipeline contamination from oil and mill scale, and any other change in operation that impacts accuracy. Since the single path meter has significantly more sensitivity, comparing the uncorrected readings of both meters provides a simple solution for determining if the fiscal meter is still operating accurately. If both are in agreement, then measurement must be OK. Should the two meters deviate, then more than likely there is some condition which might impact the accuracy of the fiscal meter. This paper will discuss the results and benefits in terms of reliability and economic impact of the TCPL-method installed in various field applications. Data will be presented on dirty vs. clean meters to show that the single path meter shifts significantly in a dirty environment while the 4-path custody meter is relatively insensitive to this.
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Document ID: 68FEFA34

Three Columns Gas Chromatograph Analysis Using Correlation Between Components Molecular Weight And Its Response Factor
Author(s): Anwar Sutan Charles Johnson Jason Laidlaw
Abstract/Introduction:
Gas Chromatographs (GCs) are delivered from factory with a multilevel calibration already programmed. While this is an effective method to handle the linearity of the detector, it requires many sets of gases at varying concentrations to obtain the multi level calibration parameters. On site when component parts of the GC are changed such as columns, diaphragm, detectors, etc. The GC may require a new set of multilevel calibration parameters. For a number of reasons this is not always practical to do on site or in the field. Other calibration issues on site can result in the systematic drift of the response factor. This sometimes cannot be detected by the GC automatically as the response factor shift can remain within the tolerance limit from the previous response factor set in the GC controller. Even with the wrong calibration result, the Gas Chromatograph still can give repeatable results, however the results will not be accurate and can increase the uncertainty of the measurement. The repeatability and reproducibility tests are good to prove that a GC is working within limits which are specified in ASTM D1945:1996 3 or GPA 2261:1995 5. However, due to the wide tolerance on some compounds these tests do not guarantee that the GC is working as intended. Using these tests does not ensure that each of the components goes through its intended column and further it does not confirm that all the valve timings are correct. A further analysis is required to check this functionality and this can be done by analyzing the response factor of each components. This paper describes a practical method that can be used to overcome these issues by looking at the correlation between components molecular weight and its response factor, and by looking at the historical response factor data for each component.
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Document ID: B59CF7F4

Validation Of The CFD Method For Determining The Measurement Error In Flare Gas Ultrasonic Meter Installations
Author(s): Jeff Gibson
Abstract/Introduction:
This paper discusses the results of an ongoing project assessing the effectiveness of using Computational Fluid Dynamics (CFD) modelling to predict the installation error on a singlepath flare gas ultrasonic flowmeter. The work is being funded through the National Measurement Offices (NMO) Engineering and Flow Programme (www.flowprogramme.co.uk) and will be detailed in TUV NEL report 2008/301 1. The CFD simulations were compared with experiments undertaken in TUV NELs National Standard Atmospheric Flow Measurement Facility. Tests were performed using a 1.5D-radius single bend placed at various pipe diameters (D) from the inlet flange of the meter. The experimental work was conducted using ultrasonic transducers supplied by GE Sensing. The transducers were installed in a specially-made 12- inch meter spool to allow the error to be assessed at the commonly used diametric and midradius positions. The meter was tested from 0.25 m/s to 30 m/s corresponding to a range of Reynolds numbers of 5,000 to 600,000, the Reynolds numbers at the lower end being such that the flow was likely to be in laminar-turbulent transition. Such flows are not uncommon in emergency flare systems during routine day-to-day flaring. The flow simulations were undertaken using the commercial CFD package FluentTM. The work described in this paper demonstrates the capabilities of the TUV NEL low-pressure test facility for determining the installation error in flare gas ultrasonic meters. In addition, CFD modelling has proved to be a very useful tool for determining the installation errors, also helping to interpret and rationalise the experimental data. A follow-up project is underway to further investigate the issues raised by the initial phase of work and this will be briefly discussed in this paper.
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Document ID: 57DE79F3

Nitrogen Subtraction On Reported CO2 Emission Using Ultrasonic Flare Gas Meter
Author(s): Kjell-Eivind Frysa Henning Ekerhovd Atle A. Johannessen
Abstract/Introduction:
The CO2 emission from flaring is typically measured by ultrasonic flare gas meters. In order to reduce the CO2 emissions, nitrogen purging is often utilized in situations of low flow in the flare. At such purging conditions, a significant amount of the gas flow in the flare is nitrogen. The CO2 emission data are to be reported to authorities. In order to get a realistic report of the CO2 emissions, the nitrogen purging should be subtracted from the total combustible gas flow. Ultrasonic flare gas meters measure primarily the flow velocity through the flow meter. From this, the volumetric flow rate at line conditions can be calculated using dimensions of the pipe, and by using measured pressure and temperature, the volumetric flow rate at a reference condition (for example 15 C and 1.01325 bar) can be calculated. Such flow meters also measure the velocity of sound. From this measured velocity of sound, in combination with pressure and temperature, the density of the flare gas is estimated, and also the mass flow rate can thus be found. In the models relating the velocity of sound to the density, there are underlying assumptions regarding the gas composition. Typically, the assumption is that the gas contains hydrocarbons, in addition to up to some few percents of inert gases like nitrogen and carbon dioxide. Through the measured velocity of sound there is also a potential for estimation of nitrogen molar fraction in cases where nitrogen purging is a significant part of the flow. In the present paper, tests of such an algorithm in real flow tests at StatoilHydros process plant at Kollsnes is reported.
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Document ID: C1C4B607

Comparison Of Multipath Ultrasonic Meter Calibration Data From Two Liquid Hydrocarbon Facilities And One Water Facility
Author(s): Gregor J Brown Terry Cousins Bobbie Griffith Donald R Augenstein
Abstract/Introduction:
The comparison exercise presented here started as a bilateral inter-laboratory comparison of the Cameron calibration facility at the Caldon Ultrasonics Technology Centre in Pittsburgh with the oil flow facilities of TUV NEL Ltd in Scotland. The primary driver for the intercomparison was to provide results of proficiency testing in support of the laboratorys ISO 17025 accreditation. NEL was selected as the second laboratory for a number of reasons, including their ability to cover an overlapping flow and Reynolds number range, the low uncertainty of their facilities and their position holders of the UK national standards. Most importantly, NEL also has ISO 17025 accreditation for their facilities and regularly participates in international intercomparison exercises, thus ensuring a high level of confidence in the validity of the comparison. The facilities at NEL are based on gravimetric (weighing) systems, traceable to the UKs primary mass standards. The Cameron calibration laboratory uses a volumetric prover, which is in turn calibrated using a traceable volumetric tank. Good comparison results produced by these two different methods would therefore also demonstrate that the results obtained are independent of the calibration method used. When designing the transfer package to be used at the two laboratories it became clear, as with any intercomparison, that the meters should be as immune as possible to installation effects. Also as it was necessary to transport the package across the Atlantic, it would need to be compact and robust. To meet these requirements, and bearing in mind that the Cameron calibration facility is used primarily for calibration of ultrasonic meters, the decision was made use the Caldon 280Ci eight path ultrasonic in the package. The transfer package was assembled in the Cameron lab and included two 280Ci flowmeters, with an upstream straight run and a perforated plate (CPA) flow conditioner. The 8-path configuration of the Caldon 280Ci usually negates the need for a flow conditioner, but in this case the CPA plate was included in the package as additional insurance against installation effects, as the requirement was to reduce any possible meter related differences to an absolute minimum. The package was calibrated at the Cameron laboratory against the ball prover and then transferred by ship to NEL where the oil intercomparison tests were completed. The opportunity was then taken to also perform a water calibration at NEL, which would add a further data set, against another independent calibration system, and with a fluid having differing properties.
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Document ID: 9B1E843D

High Viscosity Hydrocarbon Flow Measurement, A Challenge For Ultrasonic Flow Meters?
Author(s): Jankees Hogendoorn, Karsten Tawackolian, Peter Van Brakel, Jeroen Van Klooster And Jan Drenthen
Abstract/Introduction:
Ultrasonic flow meters for custody transfer application were introduced in the industry in 1996. Supported by a significant number of national and international approvals, ultrasonic measurement techniques have been adopted by oil and gas industries and frequently used for custody transfer measurement of hydrocarbon products worldwide. After the introduction of the API standard 5.8 Measurement of liquid hydrocarbons by ultrasonic flow meters using transit time technology in February 2005 the confidence of industries rose and resulted in higher acceptance of this technology for custody transfer crude oil applications. During the introduction of the first ultrasonic flow meters approved for custody transfer applications, manufacturers focussed on the generic applications where most of the applications were liquids with viscosities up to 140 cSt. Analysing the present crude oil exploration and production developments it is evident that highly viscous crude oils are being increasingly produced and make up a significant part of global crude oil production.
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Document ID: E4B355C4

A Multipath Ultrasonic Meter With Reducing Nozzle For Improved Performance In The LAMINAR/TURBULENT Transition Region
Author(s): Gregor J Brown Terry Cousins Donald R Augenstein Herbert Estrada
Abstract/Introduction:
With rising worldwide energy demands and depletion of existing conventional oil reserves the production of heavy oil is becoming increasingly common. The high viscosity of heavy oils presents measurement challenges for most types of flow meter. For example it limits the maximum flow of PD meters, reduces the turndown of turbine meters and can result in measurement errors in Coriolis meters. Ultrasonic meters can be used for measurement of high viscosity oils. However, in order to do so with high accuracy they have to cope with increased signal attenuation and changing velocity profiles through the transition from turbulent to laminar flow. This paper explains the technical challenges faced when using ultrasonic meters for high viscosity/low Reynolds number flows and shows how these conditions can adversely affect the performance of some designs of ultrasonic meter. Modelling using velocity profile data and analysis of meter diagnostic data is presented in order to illustrate the physical processes that are at work. Test data is presented to demonstrate the performance of conventional and improved ultrasonic meter designs. The improved ultrasonic meter design incorporates a reducing nozzle to flatten and stabilise the velocity profile in the transition region. The impact of this design feature on permanent pressure loss is also evaluated.
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Document ID: 025FACCE

Significantly Improved Capabilities Of DP Meter Diagnostic Methodologies
Author(s): Richard Steven
Abstract/Introduction:
Differential Pressure (DP) flow meters are a popular generic flow meter type. DP meters are simple, sturdy, reliable and inexpensive devices. Their principles of operation are easily understood. However, traditionally there has been no DP meter self diagnostic capabilities. In 2008 a generic DP meter self diagnostic methodology 1 was proposed. In this paper these DP meter diagnostic principles are reconfirmed and a simpler methodology is also explained. These two methods will be shown to operate in conjunction increasing the overall sensitivity of a DP meters diagnostic capability. These diagnostic methods work for all generic DP meter designs. However, in this paper they are proven with extensive experimental test results from orifice plate and cone DP meters. Finally, it is recognized that it can be beneficial to have real time diagnostics where the diagnostic results are shown to the operator in a very simple and easily understood format. DP Diagnostics proposes such a method.
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Document ID: DC62C01E

Cost Benefit Analyses In The Design Of Allocation Systems
Author(s): Phillip Stockton
Abstract/Introduction:
This paper considers issues pertaining to the costs of the implementation of measurement systems, e.g. to reduce uncertainty, against the benefits accrued by a reduction in exposure to loss of revenue in allocation systems. Statistical based techniques are presented to assess the risk of loss of revenue. In Section 2 these issues and methods are discussed and illustrated with simplified theoretical examples. The discussion is principally in terms of flow meters but the issues can equally be extended to any measurements used as inputs to allocation. Indeed in Section 3 the techniques are applied to data from a real system in which the cost savings accrued from a reduction in compositional sampling frequency were compared with the potential impacts on the allocation system.
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Document ID: AF4B49D6

Realistic Pipe Prover Volume Uncertainty
Author(s): Paul Martin
Abstract/Introduction:
Traceability for liquid turbine metering systems is generally achieved via a calibrated pipe prover volume used to verify the meter K-factor in situ. This paper demonstrates how incompatibility between an arbitrary tolerance set for the calibration of a pipe prover and the achievable uncertainty in measurement when determining the prover volume can lead to practices which may result in measurement bias. This paper presents a robust method of estimating the pipe prover volume uncertainty determined using the master meter/master pipe prover calibration method. The individual uncertainty components used in the estimate, and the method of combining them, are included along with a comparison of the gravimetric and volumetric calibration methods for determining the compact prover volume. The traceability chain relating to the calibration of the pipe prover and the importance of accreditation for measurements are also discussed. The paper concludes by examining the tolerances in place in the North Sea and how the practices which have evolved to meet the tolerances may compromise good metrology and lead to measurement bias.
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Document ID: 495A66FB

Inferential Chemometric Allocation
Author(s): Phillip Stockton
Abstract/Introduction:
What is Inferential Chemometric Allocation? Chemometrics is the science of extracting information from chemical systems by datadriven means. The chemical data used in this approach to allocation are the compositions of the feed and product streams in a commingled system. These are used to infer an allocation of the product stream between two or more contributing streams without measuring the flow of the feed streams. A simple example will illustrate the concept. Consider two streams: Field A and Field B, each of different compositions. The composition of each stream is known and remains constant. These streams are mixed together and the commingled products composition is measured as shown in Figure 1.
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Document ID: 66568637

A Portal To Create Transparency In Production And Fiscal Measurement Data
Author(s): Lex Scheers Oi-Mee Voon And Tjidde Boers
Abstract/Introduction:
The paper describes the development and implementation of a tool that will optimize work processes between the Metering Data Consumers (Reservoir Engineers, Production Technologists, Operators, Programmers, Metering Engineers, etc) and Metering Data Providers (Facility or Metering Engineers, Maintenance/Production Operators and Production Chemistry). The connecting link between the Metering Data Consumers and the Metering Data Providers is a web-based portal, called Metering Atlas. This portal collects data related to measurement equipment from the various software applications and data sources that are used in the oil and gas business. Examples of these software applications and data sources are an instrument and meter engineering master database, data historian, hydrocarbon oil and gas production administration system, laboratory information systems, financial, resource and work planning systems, etc. Although all these software applications are in principle independent and they all have their own workflow processes, their own data flow and their own custodian, it is obvious that combining the information from these independent software applications will results in valuable additional information regarding the status of a metering system. Combining all this information it is possible to judge the health status of a metering system, whether it can be trusted or distrusted. By having all this information available in an easy accessible web-based system, with easy navigation, similar to an atlas, also creates transparency of the companys metering system with the Metering Data Consumers and might initiate discussions regarding improvements (or relaxations) of requirements of metering facilities. Ultimately this will lead to an optimal focus on metering equipment and delivering production data of adequate quality.
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Document ID: A6CB2F24

Cone DP Meter Calibration Issues
Author(s): Casey Hodges, Charles Britton, William Johansen & Richard Steven
Abstract/Introduction:
Cone DP flow meters are becoming increasingly popular in the oil and gas industry. A cone DP meter is a member of the generic Differential Pressure (DP) meter family and operates according to the same physical principles as other DP meter types. ISO 5167 1 states the performance of orifice plate, nozzle, Venturi nozzle and Venturi DP meters across set geometry designs, over particular ranges of flow conditions. ISO 5167 covers these meters as they have a long history of research where the massed data sets are publicly available for scrutiny. However, ISO 5167 does not cover cone DP meters as the patent protection has only recently lapsed and no independent research has yet shown that cone DP meters of set geometries have repeatable and reproducible performances over given flow condition ranges. This paper reviews cone DP meter data from CEESI independent research, a CEESI wet gas Joint Industry Project and multiple third party1 tests. The cone DP meters discussed are produced by multiple manufacturers. Performance comparisons are made between nominally identical cone DP meters. The relative merits of calibrating cone DP meters with low Reynolds number water flows or high Reynolds numbers gas flows will be discussed. The pros and cons of cone DP meter periodic re-calibration is also discussed. The effect of damage changing the cone alignment will be considered. Finally, the prospect of cone DP meters being eligible for inclusion in ISO 5167 is discussed
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Document ID: 78CB3450

Recent Field Experiences Using Multiphase Meters For Fiscal Allocation
Author(s): Eirik bro Kare Kleppe Leif Jarle Vikshaland
Abstract/Introduction:
StatoilHydro has about 150 multiphase and wet gas meters in operations, with additional 70-80 multiphase and wet gas meters to be operative in near future. Most of the meters in operation today are used for production optimisation and production management. During the last years, several oil/wet gas fields operated by StatoilHydro have been developed by use of multiphase and wet gas meters for fiscal allocation purposes. The fields are developed as subsea productions system (SPS) where unprocessed multiphase flows are transported to process platforms through pipelines. In this paper the allocation metering installed on Kristin and sgard B in connection with the tie-in of the Tyrihans Field is presented. The ownership allocation between the Halten West Unit (Kristin) and Tyrihans Unit is based on multiphase metering of the Tyrihans flow line production, i.e two parallel topside multiphase meters installed onboard Kristin platform. Subsea multiphase meters are installed for the 11 subsea producing wells, 8 oil producers initially in 2009, one gas producer in 2015 and converting of two gas injectors to gas producers in 2023. The Tyrihans field started to produce in July 2009 and data from the multiphase meters and the test separator meters have been compared frequently in order to verify the topside multiphase meters. The contributions of the overall fiscal metering system uncertainties of the allocation metering for the Tyrihans production are identified, such as test separator metering, PVT compositions, gas lift measurements and multiphase meters. Field experiences with results from the multiphase meters used for fiscal allocation of the Tyrihans productions from the first months in operation are presented.
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Document ID: 2799AE15

Fluid Characterisation In A Subsea On-Line Multiphase Fluid Sampling And Analysis System
Author(s): E.M. Bruvik M.B. Holstad J. Spilde B.T. Hjertaker, S.H. Stavland, K-E. Frysa1, S.K. Meyer
Abstract/Introduction:
The trend in subsea petroleum production systems in offshore field developments points towards integrated production and processing facilities at the seabed along with more extensive use of multiphase transportation technology. The SOFA (Subsea On-line multiphase Fluid sampling and Analysis) system designed by Christian Michelsen Research in cooperation with the University of Bergen is an autonomous metering station for permanent installation subsea. The SOFA carries out fluid analysis subsea, and the current method of transfer of fluid samples to surface by a remote operated vehicle is avoided. A laboratory prototype for capturing multiphase fluid samples in a dedicated measurement chamber/sample container has been built and tested. This is equipped with ultrasound sensors, a dual modality densitometer (DMD) gamma-ray system, pressure and temperature sensors, which together with conductivity, permittivity or similar measurements will be used as a multi-modality system for fluid characterisation. This paper presents experimental results for fluid sampling and characterisation based on multimodality. The focus is on detection and monitoring of water salinity, water density and oil density. In addition, perspectives for operational use are discussed.
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Document ID: ADD72DBC

X-Ray Based Densitometer For Multiphase Flow Measurement
Author(s): Stein-Arild Tjugum, Romulus Mihalca
Abstract/Introduction:
Flow measurements by use of gamma-ray attenuation has been utilised in multiphase flow meters for many years. This represents a robust and reliable type of flow composition measurement1. The use of a radioactive isotope does however introduce some challenges. When using radioactive sources there is additional paper work to be done, the source has to be tracked through its life-time and after end of life-time of the instrument the source has to be disposed of in a safe way. The radiation hazard has to be handled during storage, transportation and installation. An X-ray based system will only be switched on after it has been installed and it does not represent any radiation hazard when switched off. Multiphase flow meters are installed worldwide and Roxar has experienced that in some parts of the world it is more difficult to install nucleonic gauges and there is a request for multiphase meters with no radioactive source. Most Roxar multiphase meters are equipped with a Cs-137 source for density measurement. For some years Roxar has also supplied non-gamma multiphase meters where the gamma-ray measurement is replaced with a patented algorithm that combines the information from the other flow measurements in the meter. The non-gamma meter does however have flow-range limitations and higher measurement uncertainty compared to the standard meter with gammaray source. The X-ray based flow meter is a new option without radioactive source that does not have these performance limitations. A prototype X-ray based flow densitometer has been developed in collaboration between Roxar (Norway) and PANalaytical (the Netherlands). The prototype meter has been successfully flow loop tested at Christian Michelsen Research (CMR) in Bergen and TUV NEL in Scotland. The flow testing includes both measurements on multiphase flow and on wet gas flow
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Document ID: 35E0A5CC

Successful Implementation And Use Of Multiphase Meters
Author(s): ystein Fossa Gordon Stobie Arnstein Wee
Abstract/Introduction:
Allocation of production using multiphase meters offers significant benefits in terms of both CAPEX and OPEX. For successful implementation, it is important to have thorough understanding of the application and identify the main issues which influence the performance of the multiphase meter. In order to find a workable solution, the need for metering functions, installation requirements and operation procedures must be addressed. In order to perform accurate measurement of oil, water and gas production the measurement principle needs to be able to cover a wide range of flow rates and combinations of oil water and gas. This is particularly important for slug flow applications where the flow may instantly change from multiphase to wetgas flow conditions and improper use or design of the meter may introduce significant measurement uncertainties. It is also important to understand the influence on the measurements related to uncertainty in PVT configuration data and how this can be dealt with in a practical and cost effective manner. An extensive operator driven development and qualification program has been performed by 10 oil companies in co-operation with MPM to develop a solution that can handle a wide range of operating conditions and be tolerant to significant uncertainties in the PVT configuration data. This paper presents the technical principles of the MPM meter, some multiphase metering challenges which needs to be overcome and the test results from a blind test of the meter at Ekofisk, a field located in the North Sea, operated by ConocoPhillips.
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Document ID: 04E1524F

An Improved Model For Venturi-Tube Overreading In Wet Gas
Author(s): Michael Reader-Harris, Emmelyn Graham
Abstract/Introduction:
Venturi tubes are commonly selected for the measurement of wet-gas flows. Reasons for this include their physical robustness to withstand erosion and the impact of liquid slugs at high velocities, familiarity with their use and the availability of standards for their use in dry-gas conditions. The presence of the liquid causes an increase in the measured differential pressure and results in the Venturi tube over-reading the actual amount of gas passing through the meter. This over-reading is usually corrected using available correlations derived from experimental data to determine the actual gas mass flowrate. This trend is observed in all differential-pressure meters. The flowrate of the liquid, which can be a combination of water and hydrocarbons, is normally determined by an external means such as from test separator data, tracer experiments or sampling etc. Information on the liquid flowrate and density is necessary to use the correlations. The correlations currently available for correcting the over-reading of Venturi tubes have been derived from a limited set of data and may only be suitable to cover restricted ranges of Venturi tube parameters, for example, a specific diameter ratio. Use of correlations outside the conditions used to define them can result in large errors in the calculation of the gas mass flowrate. This paper describes a new Chisholm/de Leeuw-type model for the over-reading, which covers a broader range of Venturi parameters such as diameter ratio and pipe diameter. The model also accounts for the behaviour of the over-reading with different liquids.
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Document ID: 21B45878

Measurement Of Water In A Wet Gas
Author(s): Arnstein Wee Lex Scheers
Abstract/Introduction:
Accurate measurement of liquids in a wetgas stream is a complex and challenging task. Acceptable performance in detection of extremely small liquid volumes requires a highly sensitive measurement system. Furthermore, measurement of water fractions is particularly important since it has a direct impact on scale, hydrate and corrosion management in long pipelines on the seabed. Water measurement is conversely, the most challenging one since water typically constitutes the smallest volume fraction. Water volume fractions may be as low as 0.001 % of the total volume in the pipe. In order to perform accurate measurement of water, the measurement principle must be repeatable over time and able to sense small variations in the water content. Furthermore, the measurement principle must be able to tolerate significant variations in the hydrocarbon PVT properties. Operationaly, regular measurement of PVT properties is both expensive and time consuming and low dependence on sampling is desirable for the overall success of the measurement system. The dominating configuration parameter for measurement of the phase that occupies the smallest volume fraction is the PVT properties of the dominating phase. Hence, in order to achieve reliable water measurements in wetgas, it is critical that the system be tolerant to changes in the gas PVT properties.
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Document ID: C7FEA0A5


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