Paper 1.4. EXPERIENCES WITH THE MASTER METERING PRINCIPLE AND ULTRASONIC FLOWMETERS AT OFFSHORE LOCATIONS (FPSO s) John Thorogood KROHNE Oil & Gas

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1 Paper 1.4 EXPERIENCES WITH THE MASTER METERING PRINCIPLE AND ULTRASONIC FLOWMETERS AT OFFSHORE LOCATIONS (FPSO s) John Thorogood KROHNE Oil & Gas

2 Experiences with the Master Metering Principle and Ultrasonic Flowmeters at Offshore Locations (FPSO s) John Thorogood, KROHNE Oil & Gas 1 INTRODUCTION This paper looks at the operating experiences when using multi path liquid ultrasonic meters for custody transfer duties offshore. The performance of the duty meters have been checked with a master meter, which has either been proved in situ or returned to a flow test laboratory. Results presented in this paper demonstrate the long term stability and high confidence in the measurement results. 2 FPSO s Mobile production units such as FPSO s (Floating Production, Storage and Offloading vessels) have become increasingly popular for offshore applications. FPSO s are mostly used for smaller oil fields and deepwater oils fields. South East Asia (e.g. Singapore and Korea) has become the centre for building new FPSO s and converting oil tankers. South East Asia is also one of the regions with the highest concentration of mobile offshore production units and many more will go into operation in the future. Limited space and weight are important restrictions set by end-users for flow metering systems on any offshore application and particularly for mobile offshore production units. Because of the limited accessibility to offshore locations for service and repair, high standards are set on the quality of flow metering systems. Flow meters should be highly reliable and require a minimum of maintenance. To save space, end users prefer not to install mechanical provers offshore. In addition, flow meters or provers should never block the line. Not surprisingly ultrasonic flowmeters have become increasingly popular for FPSO s and for offshore applications in general. The applications vary from fiscal metering to allocation metering, production metering, export metering, metering of crude oil and seawater after the separators, well water injection, offloading and shuttle tanker loading. The flowmeters, based on the transit time principle, have a rugged construction, a large dynamic range, are easy to install without filters, measure independent of product properties and require minimal maintenance as they have no internal moving parts. 2.1 Where Is The Custody Transfer Point? There are a number of different operating scenarios for fiscal authorities when it comes to the actual point of custody transfer point. Factors that can affect this point are: Terms of the contract between oil company and FPSO owner/operator Oil sales contract and actual point of sales Location of FPSO and territorial waters Custody transfer onboard the FPSO The occurs when the oil company usually contracts the FPSO to a fixed term contract for the vessel and operation of the production facility. Therefore the fiscal point is determined on the deck of the FPSO as the crude is produced into the storage tanks. Specifications for the metering and control system are well defined and the operation of the facility is strictly controlled and monitored. 1

3 Allocation metering upstream of final separation prior to the main fiscal systems can also occur. Discharge of the crude to shuttle tankers is still important but usually handled by single cargo transfer meters. Custody Transfer onboard of the FPSO Custody transfer during the discharge from FPSO to shuttle tanker In this case the field/s are produced with production and allocation metering taking place into the storage tanks of the FPSO. Following a period of production the crude is pumped from the FPSO s tanks through a fiscal metering system to a shuttle tanker. This occurs mostly when the oil company is selling the cargo directly from the FPSO and/or the shuttle tanker cargo is going to be off loaded in another country. Custody Transfer during Discharge to Shuttle Tanker Custody transfer at the shore discharge of shuttle tanker load In this case production /allocation metering and cargo discharge metering take place as the crude is transferred from the field via FPSO storage to the shuttle tanker. At the discharge point for the shuttle tanker the crude is measured in accordance with local authorities. 2

4 The crude can be either measured by an onboard metering system, receipt metering package or into shore tanks. This set up is usually adopted when the oil company is operating all stages and the oil doesn t leave territorial. Three Discharge options from the shuttle tanker to shore: Custody transfer on discharge from shuttle tanker 3 EXPERIENCE WITH UFM OFFSHORE The first liquid ultrasonic flowmeters for custody transfer have been in operation at various North Sea platforms for over 10 years. In the mean time ultrasonic flowmeters for fiscal metering have been installed at offshore locations including FPSO s loading shuttle tankers all over the world. In Brazil for example, one of the countries with the largest installed base of offshore mobile production units, more and more the complete production, allocation, fiscal and cargo loading measurement of crude oil relies on ultrasonic flowmeters. Virtually none of the offshore platforms or FPSO s has installed a permanent prover. In most 3

of the applications one multibeam ultrasonic flowmeter (the master meter) regularly or continuously checks another multibeam ultrasonic flowmeter(s) (the duty meters). 3.

5 of the applications one multibeam ultrasonic flowmeter (the master meter) regularly or continuously checks another multibeam ultrasonic flowmeter(s) (the duty meters). 3.1 The Fluminense PFSO The FPSO Fluminense was converted from one of the world s largest tankers. The FPSO is located in the Bijupira and Salema oilfields in the Campas Basin, offshore Brazil and some 250 km East of Rio de Janeiro. Initial production started in August 2003 with approx 20,000 barrels of oil per day from one of the 8 production wells already completed. Production has gradually increased to the maximum production rate of 80,000 bpd of relatively light crude oil and associated gas. The FPSO has a storage capacity of 1.2 million barrels Basic Master-Duty Configuration Basic Master-Duty Configuration of the Fluminense FPSO The offloading metering facility, shown in the above picture and schematics, consists of 2 off 24 5 path KROHNE ALTOSONIC V meters set up in a duty master meter configuration. This facility is designed to measure the crude oil discharge to the shuttle tankers at 5,500 cm/hr although the meters themselves can handle up to 10,000 cm/hr Original calibration of the Master meter The flowmeters were manufactured and tested on water prior to an original hydrocarbon calibration where the meters were tested against a large Bi-Directional prover (15 cm volume). The test results for the original; calibration are given below. Based on these multiproduct calibrations the meters have their meter factors loaded into their electronics. 4

6 Serial number : Diameter : 584.2mm/24" Verification 1 : SPSE Verification1[%] Error% flow [m3/h] Original Calibration at SPSE in July 2002 According to local regulatory authorities the master meter will need to be returned to the site of the original calibration. Initially this exercise had to be completed every year but due to previous projects and data from other recalibrations, the master meter from the Fluminense was returned for recalibration after three years of operation. The master meter was retested in the same location and the recalibration results are shown plotted against the initial calibration. You can see that there is very good correlation with the original data. Other factors that affect the actual results include the uncertainty of the flow laboratory/test facility. The meter was well within custody transfer uncertainties over the complete operating range of the flow meters 5

7 Serial number : Diameter : 584.2mm/24" Verification 1 : SPSE Verification 2 : SPSE Verification1[%] Verification2[%] Error% flow [m3/h] Recalibration versus original calibration at SPSE 3.2 Data from in-situ proving using Master Meter Normal operation for the metering facility is where the flow is passed through the duty meter only. This provides the FPSO operator with the lowest pressure drop and therefore the maximum volume throughput with the installed pumping capacity. Regular metering operation: Oil flows through the custody transfer ultrasonic duty meter. As we saw from the flow schematic the flow path can be set up to pass the flow through both meters when installed on site. In this configuration is possible to monitor the performance of the duty meter against the master meter. 6

8 During a batch unloading the flow configuration will be set up to evaluate the flow data from both the master and duty meters Inline proving. Oil flows through the Master meter and then through the duty meter. 3.3 Metering Consistency Data has been presented from shuttle tanker loadings from Ticket number 69 on 6th June 2005 to Ticket number 99 on 11th November You can see that the variation in the meter factor between the master and the duty meter has been almost constant at.044 %. 7

9 Data obtained on 6th June 05. Multiple proving tickets on individual batch Batch No. Proving Ticket Flow rate MF Batch No. Proving Ticket Flow rate MF Typical data taken during on shuttle tanker loading batch number 69 with multi proving cycles, proving ticket 213 to Further Advantages of the Chosen Master-Duty Configuration The chosen configuration has the additional advantage that in the unlikely event that someone damages duty meters, the Master Meter can be used as a Duty Meter until the Duty Meter is replace. It also allows the Master Meter to be removed for offsite calibration without interrupting the metering service. Failsafe operation: Oil flows through the Master Meter which if needed can act as a duty meter. 8

10 3.5 Conclusion on Fluminense FPSO Project This data and the recalibration of the master meter at the original flow laboratory after a three period has demonstrated a very stable meter performance and has given a high degree of confidence in the overall measurement system and the uncertainties of the crude oil offloading measurements. This methodology has been employed in many high capacity measurement systems using KROHNE Ultrasonic 5 path meters and where no mechanical proving device is feasible. More than 150 meters have been installed on FPSO s to date. 4 FIXED PLATFORM MASTER METER An operator in the North Sea has had two 5 path KROHNE Altometer liquid ultrasonic meters installed since Master-Duty Configuration for the Snorre / Vigdis to Gullfaks custody transfer metering These meters are installed in a duty master meter configuration with the master meter being proved in situ with a portable turbine meter/small volume prover calibration device. Initially the calibration device was brought to the platform every month for recalibrating the installed ultrasonic meters; since 1999 the meter are only calibrated every year. Data from 1999 to 2006 is attached. The meters are located on an offshore platform and measure crude oil from two different fields and with different ownerships, it is therefore essential that the measurement uncertainty is low and the ultrasonic meters provide long term accuracy with non maintenance requirements as the platform is unmanned. There has been no maintenance required on the ultrasonic meters since they were installed is 1997.Turbine meters working on the same fluid have to be removed and cleaned every week due to scale build up. The results show excellent stability over a long period of trouble free operation. The ultrasonic meter factor is within 0.02% for the last four years of recalibration. 9

11 4.1 Ultrasonic Meter Factor Stability The most important factor to the operator is long-term meter factor stability. As the graph shows, the meter factor of the installed meters shows an extremely high level of consistency. The trust in the meter that stems from such results enabled the operator to dispense with regular provings and regular maintenance, hitherto unknown with mechanical meters. Percentage meter factor variation versus time 5 CONCLUSION Multi path liquid ultrasonic meters have proved themselves to be ideally suited to provide long term low uncertainty measurements in hostile operating conditions and with minimal maintenance. The master meter concept for these devise has demonstrated that it is possible to achieve very precise measurements without the expenses and space requirements of a large fixed mechanical provers. The use of multi path liquid ultrasonic meters on FPSO/FSO and unmanned platforms has brought significant savings in both CAPEX and OPEX. 6 ACKNOWLEDGEMENTS The author would like to thank his colleagues and co-authors at KROHNE Altometer and KROHNE Oil & Gas who provided access to internal and external calibration reports, site surveys and commissioning reports to enable the data to be collected and presented in this paper. 10

KROHNE Oil & Gas Overview Liquid flowmetering systems Gas flowmetering systems Supervisory systems Flow computers Tank Management Systems Loading & Offloading systems Leak Detection Systems From the

12 KROHNE Oil & Gas Overview Liquid flowmetering systems Gas flowmetering systems Supervisory systems Flow computers Tank Management Systems Loading & Offloading systems Leak Detection Systems From the well head, through massive pipelines, onto tankers and into the terminals and refineries; the flow of oil and gas products needs to be measured accurately and reliably. That is the world of KROHNE Oil & Gas. In 2001, the leader in flow metering KROHNE in Duisburg, grouped together all its experts and established a specialist company at their main manufacturing site in the Netherlands. The company has grown continuously since then. The need for more space while retaining access to a qualified workforce brought KROHNE Oil & Gas to customdesigned premises in Breda. The dynamic growth continues with the workforce having grown to over 160 persons solely dedicated to the oil and gas industry. Through acquisitions and expansions KROHNE Oil & Gas now has 8 manufacturing facilities in the Netherlands, UK, India, Malaysia, USA, Brazil, South Africa headquarters in Breda servicing the world's oil industry through offices of the KROHNE group, in more than 60 countries worldwide. The scope of KROHNE Oil and Gas starts with custody transfer flowmetering for oil, gas and liquefied gas and continues through tank management, loading and offloading and leak detection and localisation systems. KROHNE 03/2007 All rights reserved KROHNE Oil & Gas Minervum ZG Breda The Netherlands Tel.: Fax.: info@krohne-oilandgas.com KROHNE Companies Australia Austria Belgium Brazil China CIS Czech Republic France Great Britain India Iran Italy Korea Malaysia Netherlands Nigeria Norway Poland Singapore South Africa Switzerland Spain Turkey Ukraine United Arab Emirates USA Representatives Algeria Argentina Cameroon Canada Chile Colombia Croatia Denmark Ecuador Egypt Finland Gabon Ghana Greece Hong Kong Hungary Indonesia Iran Ireland Israel Ivory Coast Japan Jordan Kuwait Latvia Libya Lithuania Malaysia Mauritius Mexico Morocco New Zealand Peru Portugal Romania Saudi Arabia Senegal Serbia Slovakia Slovenia Sweden Taiwan Thailand Tunisia Turkey Venezuela Vietnam Yugoslavia

BP Statistical Review of World Energy June 2017

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