Introduction to Fiscal Metering (Custody Transfer)

INTRODUCTION TO FISCAL MEASUREMENT

Mozaffar EtezadifarFall 2016

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Energykade.com

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Energykade.com [email protected]

Content


Content


Chapter 1

Fiscal Metering Fundamentals


1.1. What is fiscal metering?

• Fiscal metering is combination of regulations, laws, protocols, systems and devices which enables two parties to transfer and measure a valuable product from one side to another in a way that both sides agree on.


1.2. When do we need fiscal metering?

• When seller and buyer are dealing on huge amount of material OR expensive one, it is important to have precise measurement of amount transferred between two parties.

• Both seller and buyer should agree on the amount and the way it’s calculated, to have a deal.

• In Oil&Gas field, it’s both huge and expensive


1.3. How much value does it make?

• A very large custody transfer system can $6,000,000 worth of natural gas per day, or $2.2 Billion per year. If the measurement is off by 0.25%, that’s an error of $15,000 per day or $5.5 million per year in somebody’s favor.


1.4. What can be done using created value?

• We can build much better custody transfer systems, spending portion of that $5.5 million at first, And save a lot every year!

That’s the importance of having an accurate material transfer system


Chapter 2

Fiscal Metering Categories


• Fiscal measurement is a general word: measurement for money

• Fiscal measurement includes:1- Allocation2- Custody Transfer


2.1 Allocation

• Allocation is the numerical distribution of products between parties according to their equity share.

you share whatever you have, good or bad,

according to everyone’s share.


2.2. Custody Transfer

• Custody transfer is contract driven: that means that there is a contractual obligation between buyer and seller which may require adherence to accuracy, repeatability, linearity or uncertainty standards as defined by measurement standards such as API, GOST (Russian equivalent to API), etc.

• The terms custody transfer and fiscal metering are often interchanged. Custody transfer takes place any time fluids are passed from possession of one party to another.


2.3. Accuracy vs. Uncertainty and Validation

• All meters and metering systems are subject to uncertainty and it is a common mistake to mix accuracy and uncertainty as they are subtly different.

• Accuracy is matching the meter output to a known standard or reference and will include terms like bias, readability and precision, this can be considered the best estimate according to the scale of the measurement.

• Uncertainty is more related to repeatability and is an estimate of the limits where the true value is expected to lie for a given confidence level.

• Validation, before we can report any data, we should be able to make sure our obtained data is valid! It takes some equipment, observation, time and money but it totally worth it, because all these data is useless if they are not valid.


2.4. Maximum allowed uncertainty

• For every application there is a limit for whole metering system uncertainty:

Application Typical Uncertainty in mass flow rate measurement (%)

Liquid Gas

Custody Transfer 0.25 1

Allocation 0.5-5 2-5

Well Test 10 10Multi-Phase Metering 10-20 10-20


Chapter 3

Fiscal Metering Frame Work


• Custody transfer details is formed by:1. Industry Standards2. National Metrology Standards3. Contractual agreement between custody

transfer parties4. Government regulations and taxation


3.1. Industry Standards

Every industry has its own standards. Some of them may be initiated by dominant country in that industry at first and then they’d become wide spread all around the world. Like AGA which stands for American Gas Association but it’s widely used in other countries too. Also IGS stands for Iranian Gas Standards.


3.2. National Metrology Standards

Every country may have National Metrology organization or Standard organization which issues general and specific regulations for each industry. A project, should obey general regulations beside industry-specified ones.


3.3. Contractual agreement between custody transfer parties

When two parties go for a deal, they can both ask for special criteria in their mutual contract. Good contract should cover all the possible and required situations and data so it prevent disagreement in the middle of the deal. It can start with a tender announcement and end up in an official contract.


3.4. Government regulations and taxation

Some times governments ask their ministries or organizations to conform specific rules and policies. Also they can issue tax and financial rules as their favor which will affect a fiscal metering project.Good example is forcing tenders to be provided be national-made products.


Chapter 4

Custody Transfer


4.1. Why is Custody Transfer growing fast?

• Not only because of its widespread use for accounting purposes due to escalation in material values, but also because of its application in several other aspects of upstream and pipeline operation such as:– leak detection systems– batch operation (for liquids only)– loss/gain balanceAll of these applications constitute key elements for the operator who wants to maximize pipeline efficiency, and requires a very strict correlation with accurate and reliable flow measurement.


4.2. Where can it happen?• Gas custody transfer flow measurement can take place anywhere

along the process value chain from the wellhead to delivery or sale location. The dynamics of where these transactions are actually located can be influenced by a number of factors with the two primary ones being regulation and commercial arrangement.

• However for the lowest uncertainty in measurement, custody transfer generally takes place at stable, predictable single phase locations or physical discrete hand-over points (e.g. platform/production exit location, pipeline entry/exit, terminal entry etc.).

• These locations generally provide the favorable conditions that flow measurement devices can operate predictably and repeatability.


4.3. Custody transfer components:

• It’s not only about the flow meter, the whole system should be designed for fiscal metering:a) Multiple Meters/Meter runsb) Flow computers and data management systemc) Gas sampler and gas chromatograph d) Calibration system (Master Meter or prover)e) Valves, Piping and Flangesf) Pressure regulator or boostersg) Transmitters (TT, Pt, …)h) Gas filtrationi) Skidj) Validating (Operator control, After sales services, Training, Monitoring

system, …)


4.3. Custody transfer components:


4.4 Single Run and Multi-Run

• Single Run


4.4 Single Run and Multi-Run

• Multi-Run


4.5. Standards and codes:

As mentioned before, there are many codes and standards which should be considered during establishing and operating a fiscal metering station. Standards and codes like:

• AGA• ISO• IGS, OIML, API and …


4.5 Standards and codes:

4.5.1. AGA• AGA–Report No 3: Gas custody metering based on orifice metering.• AGA–Report No 7: Gas custody metering using turbine meters.• AGA–Report No 9: Gas custody metering using Ultrasonic flowmeters.• AGA–Report No11: Gas custody metering using Coriolis mass flowmeters.• AGA–Report No 8: Compressibility and Super

Hydrocarbon Gases. Transmission Measurement. • Report No 10: Speed of Sound in Natural Gas and related hydrocarbon gases.


4.5. Standards and codes:

4.5.2. ISO • ISO 12765: Measurement of Fluid Flow in Closed Conduits Methods using Transit

Time Ultrasonic Flowmeters. • ISO 10723: Natural gas – Performance evaluation for On line Analytical Systems.• ISO 5168: Measurement of Fluid Flow: Estimation of Uncertainty of Ultrasonic Flo

wmeters.• ISO 6569: Natural Gas – Rapid Analysis by Gas Chromatography.• ISO 6976: Natural Gas Calculation of Calorific Value, Density and Relative Density.• And …


4.5 Standards and codes:

4.5.3. IGS and OIML …• OIML DR 3: Draft Recommendations Gas meters (Combined revision of R6, R31 a

nd R32 Draft).• OIML_D11 General requirements for measuring instruments - Environmental

conditions• OIML_R137-1&2 Gas meters Part 1: Metrological and technical requirements

Part 2: Metrological controls and performance tests

• IGS-M-IN-104(1) Multi-Path Transit Time ultrasonic gas flowmeters• IGS-C-IN-105(0) Calibration Duration of Measuring Instruments (Flow ,Pressure

and Temperature)• IGS-M-CH-033(1) Specification for Iranian Natural Gas Quality


4.6. Affecting factors on accuracy

Reading and calculation factors Fluid and line factors

Flow computer setting and performance Distance from regulators ad control valves

TT and PT and Flow meter true reading Site headers and sizes

Calibration and its processes TT installation

Prover Meter Installation

Site condition

Fluid turbulence

conditioner

Piping


4.6.1. Reading and calculation factors

• 4.6.1.1. Flow computer setting and performanceAll the actual data come from transmitters to flow computer to be changed to standard data (At standard condition), so every flaw in your flow computer’s setting or calculation will show your system wrong even though they’re working great.You should be aware of gas components or signal ranges ( 4 to 20 mA signals from transmitters). Flow computer reporting system should be set as customer needs reports or logs otherwise data will be lost. There should be UPS for power outages to avoid data missing.



• 4.6.1.2. TT and PT and Flow meter true readingAll the transmitters including Flow, Temperature and pressure should send valid signals to flow computer. Their validity and accuracy depends on many factors but their main problems usually initiates from outdated or wrong-range calibration, bad cabling which affects data validity, bad physical installation or damaged parts.So their validity should be checked on site or be guaranteed by valid test certificates.



• 4.6.1.3. Calibration and its processesAll the devices should be calibrated for working range, further more, there should be periodic calibration for all of them to keep devices precise and accurate. Kind of calibration and its period should be determined by standards or professionals. Uncalibrated device may cause hidden error for whole system.



• 4.6.1.4. proverOn-site provers can help to make sure your whole system is working right. There are many kinds of one or Bi-deirectional provers. Not all of custody transfer stations have prover because of extra cost and space they need.


4.6.2. Fluid and line factors

• 4.6.2.1. Distance from control valve:Noise from control valves can interfere with an ultrasonic sensor’s measurement, so a good practice is to place valves downstream of meters (if possible), put as much distance as possible between valves and meters, and put some bends in the piping to reduce noise. “Noise trap” tees are very effective in reducing valve noise. In a similar fashion, Coriolis meters can be affected by vibration, so they need their own form of protection.



• 4.6.2.2. Site header and its sizeCost increases as the header size increases, but performance suffers if headers are undersized. Header sizing sounds like a very basic concept that every engineer should know, but we have seen a large number of incorrectly sized headers on legacy systems.Furthermore, sites with headers which have more than one flowmeter, can use one meter as Master meter (with higher accuracy). Also these kind of sites can shut down one line for maintenance and calibration which in total leads to higher accuracy of system.



• 4.6.2.3. TT installation The location of temperature sensors is critical for maximum accuracy. For gas, AGA 9 recommends the thermowell be installed between two and five diameters downstream of the flowmeter in a uni-directional system, and three diameters from the meter in a bidirectional installation.Inappropriate TT placing may cause unwanted turbulences which leads to lose of accuracy.



• 4.6.2.4. Meter installationFlow meter, as front face of metering site, should be installed according to its codes and standards to provide site owner with highest accuracy and performance of device. Factors like, adequate direct pipe line before and after meter place, aligned axis installation, pipe diameter increaser/decreaser, Gasket edge, and many other factors which should be consider for meter installation



• 4.6.2.5. Site ConditionHigh temperature or direct sunlight may cause damage or malfunction in whole system performance and accuracy. Also, ambient temperature and pressure are necessary values to know to set up calculations for flow meter or flow computer. Humidity can be affecting value on system performance too.



• 4.6.2.6. Fluid Turbulence To have measurement theories true and working and accuracy as desired, we need certain fluid velocity profile. Many factors may affect this velocity profile such as path that fluid goes through like 90° or U Turns before and after meter, vertical or horizontal path, size changers and many other factors which all in all will affect Reynolds number. Reynolds number describes fluid turbulence.



• 4.6.2.7. ConditionerConditioners or straighteners are parts that we use when our fluid has high turbulence and we want to shape its velocity profile as needed to have high accuracy. These parts have different kinds which may cost our system a little more but will affect the accuracy in a good way.



• 4.6.2.8. PipingAs mentioned in 2 previous items, we need symmetric and non turbulent flow to have true measurement. So every piping method (horizontal alignment, turns, sizes and…) may affect fluid Reynolds number and of course system accuracy. Piping method should be as close to standards and recommendations as possible to avoid this loss of accuracy.


Chapter 5

Modules as hardware, Monitoring system as software


5.1. necessity of a monitoring system and after sales services• What if you buy an expensive car and give it someone who doesn’t know how to

work with gears, and he only uses first gear?You need to know how to use your product to get maximum out of your expensive product!

• What if you invest a lot on buying an expensive car and you want to use that for a lifetime and suddenly some part of it breaks down and you can’t find any spare part for it?If you want to make sure your investment will work a long time for you, you should be provided with spares and service.

• What if it’s said that your expensive car burns very little amount fuel, but because its engine isn’t adjusted, it’s burning much more than ordinary cars?You should keep your product calibrated and adjusted at its best.

• And…


5.2. Monitoring system components

5.2.1. Trained Operator5.2.2. Online monitoring and observation system5.2.3. Periodic calibration



• 5.2.1. Trained OperatorEvery controlling or monitoring system needs trained operators who knows exactly how system works and what every signal means. With this, we can make sure that human flaws or system errors will be minimum which can make whole system a lot of profit (preventing losses) .All operators should be trained and updated on preset schedule.



• 5.2.2. Online monitoring and observation systemHowever an station may have its own local operator, but being watchable and controllable from distance make the whole system safer and more trustable. It can guaranty that there’s not any manipulation or missed data. Also using distance monitoring we can have remote backups of data.



• 5.2.3. Periodic calibrationEvery system need re-calibration, eventhough the system is fully calibrated at first. Not to care about calibration sessions, will lead to loosing accuracy in whole system because all devices will go out of calibration setting after a while. Some devices has standard periods of calibration but many others don’t. it should be checked with used standards.


5.3. After Sales Services

5.3.1. Spare parts5.3.2. Maintenance and guidance5.3.3. Training new operators5.3.4. Technology upgrade



• 5.3.1. Spare PartsIf you’ve spent a lot of money for your metering system, of course you don’t want to loose your whole system operation because of one simple part damage or malfunction.It’s not rational to halt 1,000,000 $ system’s correct operation for 5,000 $ part. So we should always consider necessary original spare parts for our system.



• 5.3.2. Maintenance and GuidanceIn case anything happens for metering system, it’s always heart warming to be sure a team can guide our engineers or operators to get over the problem or if it wasn’t solved their team can come and check the situation ASAP.



• 5.3.3. Training New OperatorsEvery company or project may loose their experienced operators or employees. To minimize its costs, there should be always a team to train new employees and operators for metering station to keep it safe, accurate and working.



• 5.3.4. Technology UpgradeGood metering station will work for many years and during these years new technologies and product may appear. Usually, vendor companies are most up to date companies about these changes, So they can offer their former customers about new solutions to be more efficient.


Chapter 6

Conclusion


Conclusion• Fiscal metering system is your cash register, invest on its

accuracy and validity. Investment on its accuracy and performance will pay off a lot more in long term.

• Fiscal metering system isn’t only your flow meter. look at it as a living system which needs maintenance, training, backup. All its parts should work together properly to provide us with good results.

• Paying for expensive and accurate metering system without sticking to training and solution upgrades is waste of money in midterm.

THANKS

Engineering

Introduction to Fiscal Metering (Custody Transfer)