experiences with the master metering...

Paper 1.4

EXPERIENCES WITH THE MASTER METERING PRINCIPLE AND ULTRASONIC FLOWMETERS

AT OFFSHORE LOCATIONS (FPSO’s)

John Thorogood KROHNE Oil & Gas

6th South East Asia Hydrocarbon Flow Measurement Workshop

7th – 9

th March 2007

1

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

2.1.1 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.


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th March 2007

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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

2.1.2 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

2.1.3 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.


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th March 2007

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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


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th March 2007

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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.

3.1.1 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.

3.1.2 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.


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th March 2007

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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

-0.50

-0.45

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0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200

flow [m3/h]

Error%

Verification1[%]Serial number : 1252691002

Diameter : 584.2mm/24"

Verification 1 : 04-07-2002 SPSE


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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.

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0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200

flow [m3/h]

Error%

Verification1[%]

Verification2[%]

Serial number : 1252691002Diameter : 584.2mm/24"Verification 1 : 04-07-2002 SPSE Verification 2 : 03-05-2006 SPSE


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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 2006. You can see that the variation in the

meter factor between the master and the duty meter has been almost constant at .044 %.


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Data obtained on 6th June 05. Multiple proving tickets on individual batch

BatchNo.

Proving Ticket Flow rate MF

BatchNo.

Proving Ticket Flow rate MF

69 213 5746.64 0.996262 69 218 5859.36 0.995348

69 214 5753.69 0.99642 69 218 5888.74 0.995376

69 214 5746.19 0.995713 69 218 5885.87 0.995144

69 214 5743.98 0.995682 69 218 5888.59 0.995525

69 214 5743.78 0.995965 69 218 5890.48 0.995766

69 214 5746.46 0.996339 69 219 5878.67 0.995248

69 215 5742.59 0.996153 69 219 5876.42 0.994958

69 215 5737.97 0.996235 69 219 5878.10 0.995472

69 215 5738.90 0.996255 69 219 5878.87 0.995361

69 215 5739.14 0.996276 69 219 5877.72 0.995441

69 215 5739.12 0.996269 69 220 5922.53 0.995202

69 215 5705.54 0.996538 69 220 5922.06 0.995106

69 216 5819.97 0.996177 69 220 5920.61 0.995105

69 216 5818.74 0.996162 69 220 5922.27 0.995593

69 216 5819.03 0.996525 69 220 5917.55 0.995206

69 216 5819.71 0.996363 69 221 5913.30 0.995377

69 216 5814.61 0.995880 69 221 5911.01 0.995336

69 217 5806.36 0.996289 69 221 5909.85 0.995296

69 217 5838.68 0.995754 69 221 2926.78 0.995938

69 217 5835.96 0.995687 69 221 2887.15 0.995830

69 217 5838.60 0.995781 69 221 2883.30 0.995371

69 217 5836.77 0.995531 69 221 2876.14 0.995636

69 221 2998.65 0.995946

Typical data taken during on shuttle tanker loading batch number 69 with multi proving cycles, proving ticket 213 to

221.

3.4 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.


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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 1997.

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.


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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.

Liquid flowmetering systems

Gas flowmetering systems

Supervisory systems

Flow computers

Tank Management Systems

Loading & Offloading systems

Leak Detection Systems

From the well head,through massivepipelines, onto tankersand into the terminalsand refineries; the flowof oil and gas productsneeds to be measuredaccurately and reliably.That is the world ofKROHNE Oil & Gas.

In 2001, the leader in flow metering KROHNE in Duisburg,grouped together all its experts and established a specialistcompany at their main manufacturing site in theNetherlands. The company has grown continuously sincethen. The need for more space while retaining access to aqualified workforce brought KROHNE Oil & Gas to custom-designed premises in Breda.

The dynamic growth continues with the workforce havinggrown to over 160 persons solely dedicated to the oil and gasindustry.

Through acquisitions and expansions KROHNE Oil & Gasnow has 8 manufacturing facilities in the Netherlands, UK,India, Malaysia, USA, Brazil, South Africa headquarters inBreda servicing the world's oil industry through offices of theKROHNE group, in more than 60 countries worldwide.

The scope of KROHNE Oil and Gas starts with custody trans-fer flowmetering for oil, gas and liquefied gas and continuesthrough tank management, loading and offloading and leakdetection and localisation systems.

KROHNE Oil & Gas Overview

KROHNE Oil & GasMinervum 74414817 ZG BredaThe Netherlands

Tel.: +31-76.71.2000Fax.: [email protected]

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